Chapter 23: Advanced Functional Training

Functional training involves developing and progressing exercise programs that improve a patient's muscle performance in order for the individual to regain his or her pre-injury level of function. For those individuals whose goal it is to return to high-level work, leisure, recreational, or athletic activities, rehabilitation must progress to meet the anticipated demands. The process requires that multiple steps be taken that utilize the individual's readiness to progress. For the therapist, it requires a continued process of decision-making that involves:

• A thorough knowledge of the anatomy, biomechanics, and function of the human body.

• An understanding of tissue healing, the effect of time on healing, and the response of tissues to imposed stresses.

• An understanding of neuromuscular responses to various forms of exercise.

• The ability to examine and evaluate the structural and functional impairments that restrict activity and full functional participation within the context of personal and societal expectations.

• Knowledge of diagnoses, surgical and therapeutic exercise interventions, special precautions, and each patient's potential for achieving the projected outcomes.

Rehabilitation begins as early as possible with specific muscle activation and training techniques designed to develop a balance in strength and timing of contractions between synergists and antagonists. Proximal stability is critical for coordinated functioning of the extremities, and therefore, exercises to develop stability and balance are incorporated early into the program as well.

As muscle strength, endurance, and control of the involved region improve (and other goals are met, such as increasing joint mobility and muscle flexibility), greater emphasis is placed on strengthening muscle groups in functional patterns, using both weight-bearing and nonweight-bearing exercises. Care is taken to ensure that stronger muscles do not dominate the pattern in preference to weaker, impaired muscles. As function improves, exercises become more activity specific.

Functional motor skills are composed of an array of movements carried out in various positions, at varying speeds, and for varying repetitions or durations of time. The cornerstone of a functionally relevant therapeutic exercise program is the inclusion of task-specific movements that are superimposed on sufficient stability, balance, and muscle strength, endurance, and power to meet the necessary, expected, and desired functional demands in a patient's life.

It is the purpose of this chapter to describe a variety of advanced exercises for functional training that involve the total body and may be appropriate for the final phase of rehabilitation. The chapter is divided into two sections. The first section focuses on advanced exercises for stability and balance and the second on advanced exercises for strength and power. The choice of exercises to be implemented and progressed is based on the desired outcome for the patient, so the motor skills needed for that outcome are the ones emphasized in the program.

Guidelines Revisited

Stability requires the ability to fixate a unit while external forces are imposed on it. The concept of proximal stability for controlled distal mobility can be applied not only to general postural stability but also to individual joints for effective and safe function.

Joint stability. Stability of each joint in the body is necessary for effective function. Examples of joint stability include the ability to maintain a scapular posture and glenohumeral joint alignment so the humeral muscles can safely coordinate movement of the upper extremity (see Chapter 17). It also includes coordinated segmental and global stability of the spine for postural alignment and safe body mechanics (see Chapters 14 and 16) and stability of the hips, knees, and ankles for control during functional weight-bearing activities (see Chapters 20 through 22). Because specific exercises for joint stability are described in detail in the respective chapters, the reader is referred to those chapters for study before progressing to the advanced exercises described in this chapter.

Postural stability and balance. For an individual to be able to execute functional activities, balance—or postural stability—is necessary to maintain the position of the body in equilibrium within the environment. These concepts are described in detail in Chapter 8. In addition, stability and balance exercises in upright postures that are appropriate early in a rehabilitation program are described in each of the lower extremity chapters. Parameters for progressing balance exercises are summarized in Table 23.1.

Advanced Stabilization and Balance Exercises

Sitting

Once the individual can sit on a firm, stable surface and maintain balance while reaching in all directions and under various loads, progress to sitting on an unstable surface. Suggestions include a foam cushion, rocker board, BOSU^®, or large gym ball.

Sitting and Reaching

Have the patient balance on an unstable surface and reach in various directions, first with one extremity, then with both. Add weights as the patient is able (Fig. 23.1).

Sitting with External Perturbations

While the patient maintains sitting balance on an unstable surface:

• Move the surface in various directions, first slowly, then more quickly.

• Pull on a length of elastic resistance held by the patient. Alter the speed and direction of pull.

• Toss a ball to the patient, requiring him or her to reach out in various directions and return the toss (Fig. 23.2).

• Increase the challenge by integrating a plyometric component into the balance activity, such as catching and tossing a weighted ball.

NOTE: Refer to the next section of this chapter for examples of plyometric exercises that also improve a patient's balance.

Kneeling

Kneeling activities can be performed in the half-kneeling (balancing on one knee with the other extremity forward and foot planted on the floor) or high-kneeling (tall-kneeling) positions and include reaching in various directions under loaded and unloaded conditions and responding to perturbations on stable and unstable surfaces.

Kneeling on a Stable Surface

• In the half-kneeling position, loop an exercise band under the forward foot and have the patient perform diagonal upper extremity patterns against the resistance (Fig. 23.3 A).

• While in a half-kneeling or high-kneeling position, have the patient reach and lift a weighted object from the floor with one or both hands, and then move the weighted object upward and outward in various patterns of motion and return (Fig. 23.3 B).

• While in a half-kneeling or high-kneeling position, toss a ball and have the patient reach outward to catch and then return it.

Kneeling on an Unstable Surface

• Have the patient kneel on a foam roller, balance board, BOSU^®, or partially deflated large therapy ball and perform arm motions in various directions; progress the activity by having the patient move the arms against resistance (weights or elastic resistance).

• While kneeling on an unstable surface, have the patient catch and return a ball. Progress by using a weighted ball (Fig. 23.4).

Bilateral Stance

Once the individual can stand upright and maintain balance while reaching in all directions and under various imposed loads (using free weights, pulley system, or elastic resistance), the patient is ready to progress to exercises that provide a greater challenge to stability and balance, first in bilateral stance and progressing to unilateral stance.

Bilateral Stance on a Stable Surface

• Begin with the patient standing with both feet on the floor, shoulder width apart, or in a stride position VIDEO 23.1 .

  • Toss a ball (unweighted or weighted) that requires the patient to reach outward, upward, or downward to catch and return it. Remind the patient to maintain a neutral spine and contract the abdominals when reaching upward to stabilize the spine or to rotate at the hips, not the spine, when reaching outward or downward.

  • Perform various arm motions against elastic resistance, with free weights, or while controlling a BodyBlade^®.

• Progress to balancing in tandem stance. Have the patient stand on a stable, narrow surface, such as a line on the floor or a balance beam. Apply quick alternating resistance against the patient's pelvis (Fig. 23.5), or apply quick pulling motions to elastic resistance held by the patient.

• Progress to tandem walking on a narrow but stable surface.

Bilateral Stance on an Unstable Surface

• While on a balance board or BOSU^®, have patient gain balance, then rock the feet forward and backward and side-to-side while attempting to control the motion and maintain balance VIDEO 23.2 . Instruct the patient to not let the edges of the board hit the floor.

• Have the patient stand on a foam half-roller (curved side down), a balance board, or BOSU^®; add the following perturbations as the patient is able.

  • Apply quick alternating resistance against the patient's pelvis.

  • Have the patient perform various arm motions against elastic resistance, with free weights (Fig. 23.6), or while controlling a BodyBlade^® (see Fig. 6.50).

  • Toss a ball (unweighted or weighted) back and forth to the patient (Fig. 23.7).

  • Have the patient perform partial squats (Fig. 23.8).

Unilateral Stance

Begin by having the patient practice standing in unilateral stance on a stable surface, progressing to an unstable surface and adding perturbations as described in the bilateral stance exercises.

Unilateral Stance on a Stable Surface

• Have the patient perform upper extremity diagonal patterns, unilaterally or bilaterally, using free weights or elastic bands (tubing) while balancing on one lower extremity (Fig. 23.9) VIDEO 23.3 . When using elastic resistance, change the angle of pull to vary the challenge and balance response.

• Have the patient, while balancing on one lower extremity, practice various lower extremity patterns that replicate functional activities. The following are suggestions.

  • Place a star pattern (such as four intersecting lines) on the floor. Have the patient place one foot on the center of the pattern and then touch the opposite foot on each of the lines of the pattern: directly forward, diagonally forward, sideways, diagonally backward (Fig. 23.10 A), straight backward, and crossed behind (Fig. 23.10 B). Then switch feet and repeat the pattern on the opposite side.

  • Perform an alternating PNF pattern such as D₁ flexion (flexion, adduction, and external rotation)/extension (extension, abduction, internal rotation) with one leg while holding a weight and flexing/extending the opposite elbow (Fig. 23.11).

  • Have the patient walk sideways, then progress to braiding or carioca motions using forward and backward cross-over steps. This requires alternating balance reactions from one lower extremity to the other.

  • Bend to one side while performing a partial squat to lift an object from a chair or the floor (Fig. 23.12).

  • Reach outward with arms while bending forward and extending one leg as in a "skater" position (Fig. 23.13 A). Increase the challenge by picking up a weight from the floor or by alternately moving the arms in a windmill manner (without or with weights in each hand) (Fig. 23.13 B).

Unilateral Stance on an Unstable Surface

• Have the patient stand on the round and then flat side of a BOSU^® or on a balance board or disc, and apply resistance against the patient's trunk or to upper extremity patterns using elastic resistance (Fig. 23.14).

• While balancing on an unstable surface, have the patient swing one leg forward and backward, first slowly, then with increasing speeds.

Moving and Planting Activities

Movement followed by a "plant" not only requires a coordinated movement but also a rapid balance response to keep from falling VIDEO 23.4 . These activities also prepare the individual for skills that involve rapid reversals of direction and agility drills.

Jump and "Freeze"

• Have the patient jump down from a platform or low step and hold the end position (Fig. 23.15 A). Progress to jumping up onto the platform.

• When the patient has learned one-legged balance and demonstrates control in the jump-and-freeze exercise, progress to having him or her hop down from a step and hold the end position then have the patient hop up onto the step and hold (Fig. 23.15 B).

Side Shuffle and "Freeze"

• Have the patient perform two to three side shuffles and hold the end position, then shuffle in the opposite direction and "freeze" (Fig. 23.16).

• Vary the pattern to include shuffling in various directions, such as moving diagonally forward then backward or in a curved pattern, freezing and then reversing the direction.

Run and "Freeze"

Have the patient run forward, sideways, and backwards and "freeze" when you call out "freeze" or blow a whistle.

Muscle strength and power are two critical elements for successful performance of many high-demand functional tasks and activities, such as moving heavy objects in the workplace and home or participating in selected sports. Muscle endurance also is necessary when performance involves tasks that must be repeated or sustained over time. Some functional activities involve slow, controlled, and sometimes repetitive movements, whereas others require bursts of movement or quick changes of direction. Therefore, an effective exercise program should address the areas of muscle performance associated with the unique qualities of each patient's physically demanding activities.

The remainder of this chapter focuses on exercises designed to improve muscle strength and/or power output—specifically, advanced strengthening exercises for the upper and lower extremities and plyometric exercises, which involve resisted movements performed at rapid speeds. All of the exercises described are built on a foundation of dynamic stability of proximal body regions (shoulder girdle, trunk, pelvic girdle), as well as balance. Conversely, a program of advanced strengthening exercises and plyometric training also imposes significant demands on a patient's balance and dynamic stability and, therefore, has been shown to improve these areas of physical function.⁸

Advanced Strengthening Exercises

As discussed in Chapter 6, progressive resistance is a necessary element of exercises designed to develop muscle strength, whereas increasing the duration of exercise (repetitions or time) is necessary to develop muscle endurance. The strengthening exercises in this section utilize functionally based and often total body movement patterns, such as pushing and pulling or lifting and lowering motions, against the resistance of body weight or external loads. They are implemented during the advanced phase of rehabilitation in preparation for returning to high-demand tasks and activities.

Many advanced strengthening exercises are carried out using weight machines designed to target specific muscle groups or by using a variety of set-ups with weight-pulley systems and isokinetic equipment. The exercises in this section, however, can be performed using simple but versatile resistance equipment, such as handheld weights or elastic bands or tubing. Other suggested exercises involve the use of equipment typically employed for cardiopulmonary training, such as a treadmill or stepping machine. Furthermore, some of the exercises described can be progressed by performing the exercises on unstable surfaces, using selected balance equipment to impose greater challenges.

Advanced Strengthening: Upper Extremities

The following exercises, performed in either weight-bearing or nonweight-bearing positions of the upper extremities, are designed to develop strength of selected upper extremity muscle groups. However, advanced upper extremity strengthening also requires activation of the trunk and lower extremity musculature. Therefore, before progressing to these exercises, be sure that the patient has developed sufficient scapular, shoulder girdle, and trunk stability and, for many of the exercises, sufficient balance in upright positions.

Exercises with a BodyBlade^®

• Patient position and procedure: While sitting or standing, have the patient hold the vibrating blade with one or both hands in a variety of shoulder positions with the elbow(s) extended or flexed (Figs. 23.17 A and B).

• Progression: Move the vibrating blade through a variety of anatomical and diagonal upper extremity patterns. Incorporate trunk rotation and weight shifting on the lower extremities for a total body exercise.

Upper Extremity Weight-Bearing Exercises Using Selected Equipment

• Hand-walking on a treadmill: While kneeling at the end of the treadmill, have the patient "walk" with his or her hands while bearing weight through the shoulders. The surface can be moving forward or backward.

• "Climbing" with hands on a stepping machine: While in a kneeling position and with each hand on a step of the unit, have the patient alternately push on each pedal to target scapular stabilizers and elbow extensors.

Pushing/Pulling and Lifting/Lowering Exercises

The following exercises involve various pushing and pulling or lifting and lowering motions. They are useful for developing upper extremity strength for functional tasks that require concentric and eccentric control of shoulder, elbow, and forearm musculature in combined movement patterns for moving objects of varying sizes and weights from one place to another. Depending on the size of the object, an exercise may be performed bilaterally or unilaterally. It is important to remind the patient to use proper body mechanics by maintaining a neutral spine and contracting the trunk stabilizing muscles during the task and by maintaining a stable base of support during each of these exercises.

• Pushing or pulling motions

  • Perform pushing and pulling motions against the resistance of an elastic band by moving the upper extremities in forward, backward, upward, and downward directions.

  • Using an upper extremity ergometer, perform pushing or pulling motions, "pedaling" against resistance in a forward or backward direction. Adjust the direction, speed, and arc of motion to replicate various functional tasks.

  • Reposition a heavy crate on a level surface by pulling (Fig. 23.18) or pushing (see Fig. 18.21) it from one place to another.

• Lifting or lowering motions

  • Lift a weighted crate from the surface of a table, hold it close to the body, and lower it to a different position on the table.

  • Lift and lower a heavy object to and/or from high and low surfaces (Fig. 23.19).

Seated Push-Ups on Unstable Surfaces

• Patient position and procedure: While in a long-sitting position on the floor with heels placed on a firm foam roller or BOSU^®, have the patient lift the hips from the floor by performing a seated push-up (Fig. 23.20 A) VIDEO 23.5 .

• Patient position and procedure: Have the patient sit on a firm foam roller, the flat side of a BOSU^®, or a balance board with legs on the floor and hands on the unstable surface at either side of the hips and lift the hips upward by performing a seated push-up (Fig. 23.20 B).

Prone Push-Ups in a Head-Down Position

Patient position and procedure: Once the patient can perform a prone push-up with hands and feet on the floor, progress to a prone push-up in a head-down position on an incline board, over a therapy ball, or on the floor with feet elevated on a platform to shift greater body weight to the upper extremities (Fig. 23.21).

Upper Extremity Step-Ups Combined with Prone Push-Ups

Patient position and procedure: Have the patient perform a prone push-up with both hands on the floor VIDEO 23.5 . While maintaining the push-up position, move one hand up onto and then off of a low platform (Fig. 23.22). Repeat the sequence, gradually increasing the number of repetitions. This exercise increases the weight-bearing force on the extremity that remains on the floor.

Prone Push-ups on Unstable Surfaces

• Patient position and procedure: Have the patient perform a series of push-ups with hands on the floor and knees on a foam roller (Fig. 23.23 A).

• Patient position and procedure: Have the patient perform a series of push-ups with hands on a foam roller or small ball and knees or feet on the floor (Fig. 23.23 B).

• Patient position and procedure: Have the patient perform a series of push-ups with hands on a balance board, BOSU^®, or small ball and knees on a foam roller (Fig. 23.23 C).

Ball "Walk-Out"

• Patient position and procedure: In a prone position with hands on the floor and lower extremities on a large therapy ball, have the patient "walk" forward and then backward on the hands while keeping the lower extremities in contact with the ball (Fig. 23.24) VIDEO 23.5 . To increase the challenge, perform a prone push-up before "walking" backward.

Plantar-Grade "Walking"

Plantar-grade walking with weight on hands and feet (also referred to as "bear-walking") places considerable weight through the upper extremities and can be used to develop strength of the musculature that stabilizes the scapulothoracic and glenohumeral joints.

• Patient position and procedure: Have the patient assume the plantar-grade position on hands and feet and "walk" forward.

• Progression: Perform plantar-grade "walking" against the resistance of an elastic cord harnessed around the pelvis and fixed to the wall or to a heavy piece of equipment.

Advanced Strengthening: Lower Extremities

The following exercises, some of which are progressions of exercises described in Chapters 20 through 22, are performed in functional movement patterns against progressive resistance and are implemented to develop advanced levels of strength of the lower extremities VIDEO 23.6 . Many of these exercises also improve dynamic stability of the trunk and balance.

Unilateral Supine Pelvic Bridges

Patient position and procedure: With one foot planted on the floor and the other extremity off the floor in either hip/knee flexion or hip flexion and knee extension, have the patient lift and lower the pelvis first against body weight and then while holding a weighted ball in both hands. Increase the challenge by planting the weight-bearing foot on an unstable surface, such as a BOSU^® or small balance disk (Fig. 23.25).

Supine Pelvic Bridges on an Elevated Surface

• Patient position and procedure: While on the floor in a long-sitting position with both feet on a chair, platform, or a large therapy ball and hands on the floor, have the patient extend the hips, lifting them from the floor (Fig. 23.26).

• Progression: Lift the hips from the floor with just one foot placed on the chair or platform and the other leg flexed toward the chest.

Supine Hamstring Curls on a Ball

• Patient position and procedure: While lying in the supine position on the floor, have the patient place both feet on a large therapy ball and roll it toward the hips by flexing the knees (Fig. 23.27) VIDEO 23.6 . In addition to strengthening the hamstrings, this exercise also challenges the trunk stabilizers.

• Progression: Have the patient perform the exercise unilaterally by lifting one foot off the ball and rolling the ball toward the hips with just one foot on the ball.

Hamstrings or Quadriceps Strengthening: Kneeling

• Patient position and procedure: Have the patient begin in a high-kneeling position on a padded surface for comfort.

• To strengthen the hamstrings: While manually stabilizing the patient's lower legs, have the patient lean forward from the vertical position as far as possible (Fig. 23.28 A), keeping the trunk erect and maintaining balance, and then return to the upright position by flexing the knees. In addition to strengthening the hamstrings eccentrically and concentrically in a closed-chain position, this exercise provides a significant challenge to the patient's balance.

• To strengthen the quadriceps: Have the patient lean backward as far as possible from the upright position without touching the buttocks to the heels and then return to the high-kneeling position. As the patient leans backward, the quadriceps contract eccentrically to control movement at the knees and then concentrically as the patient returns to the vertical position.

• Progression: Add a weight held close to the chest for additional resistance (Fig. 23.28 B).

Unilateral Wall Slides: Standing

• Patient position and procedure: While in unilateral stance with the back against a wall (but the weight-bearing foot several feet away from the wall), have the patient slide down the wall until the knee is flexed to 90° (Fig. 23.29), making sure the knee does not move into valgus or anterior to the toes. Hold the position, and then return to a standing position. This exercise strengthens the hip and knee extensors eccentrically and concentrically.

• Progression: Hold weights in both hands for additional resistance. Gradually increase the number of repetitions and/or the duration that the 90° position is held. Increase the challenge by placing a large therapy ball behind the back for these exercises.

Deep Squats

• Patient position and procedure: In bilateral stance with feet a comfortable distance apart, have the patient perform a deep squat by flexing the hips and knees (Fig. 23.30). Keep body weight distributed posteriorly through the heels, and be sure to keep the lower legs as vertical as possible to the floor so that the knees do not move anterior to the toes. Hold the deep squat position, and then return to the standing position. Have the patient hold both arms out in front of the body for balance or place one hand lightly on a countertop, if necessary.

• Progression: Perform repeated deep squats while holding weights or by combining squats with resisted upper extremity motions. This activity is beneficial for developing body mechanics in individuals who do heavy lifting in the work setting.

Variations of Lunges

• Deep forward lunge: While maintaining the trunk in an erect position, have the patient place one foot forward and perform a deep lunge, flexing the forward knee to a 90° position but keeping the lower leg vertical and the knee posterior to the toes (Fig. 23.31 A); then return to the standing position VIDEO 23.6 . Place one hand lightly on a stable surface (wall, countertop) for balance, if necessary.

  • As balance improves, have the patient perform deep forward lunges while holding a weighted ball away from the chest and performing trunk rotation.

  • Place the forward foot on an unstable surface, such as a balance disk, while performing the forward lunge exercise.

• Multidirectional lunges: Have the patient perform lunges diagonally forward, out to the side, diagonally backward, and then directly backward. This sequence is facilitated by placing four intersecting lines on the floor (in a star pattern or like spokes of a wheel) and having the patient keep one foot planted where the lines intersect. The patient steps out onto each line (Fig. 23.31 B) and returns to the upright position. Motion in the same direction can be repeated multiple times before progressing to the next line, or the patient can step out onto each line in succession.

• Lunges against added resistance: Increase the difficulty of the exercise by performing lunges against elastic resistance looped around the lower legs (Fig. 23.31 C) or holding weights or a weighted ball, wearing a weight belt, or holding a barbell on the shoulders. Controlling weights while performing lunges is beneficial for developing strength for individuals returning to work settings that require heavy lifting.

• Lunge-walking: Perform a series of lunges in various directions to move across the floor or to pick up objects of decreasing height (e.g., 16 to 4 in.) from various places on the floor.

• Lunge-jumps: Refer to the description and figure (see Fig. 23.63) in the next section on plyometric training.

Sitting Down and Standing Up from a Chair Against Elastic Resistance

• Patient position and procedure: Have the patient sit down against the resistance of an elastic band looped around the posterior aspect of the pelvis (Fig. 23.32 A).

• Patient position and procedure: Have the patient stand up against elastic resistance looped around the anterior aspect of the pelvis (Fig. 23.32 B).

Bilateral or Unilateral Heel-Lowering Over a Step

• Patient position and procedure: While standing with heels over the edge of a step or low platform, have the patient perform heel lowering and then a heel raise in bilateral stance. Place one hand lightly on a railing or a stable surface for balance. Heel lowering imposes eccentric loading of the gastrocnemius-soleus musculature against the resistance of body weight.

• Progression: Perform the same exercise while wearing a weight belt or vest or holding weights (Fig. 23.33), then progress to unilateral stance.

Band Walking

• Patient position and procedure: Have the patient walk forward (Fig. 23.34 A), sideward (Fig. 23.34 B), and backward against elastic resistance looped around the pelvis.

• Patient position and procedure: Have the patient walk forward against elastic resistance looped around the thighs for closed-chain strengthening of the external rotators (Fig. 23.35).

Pulling or Pushing a Heavy Object

• Patient position and procedure: With the arms positioned in a stable and comfortable position, have the patient use primarily lower extremity strength to pull (Fig. 23.36) or push a heavy object, such as a weighted sled or cart, across the floor. Select positions for pulling or pushing similar to the anticipated work-related tasks or sport activity. Be certain the patient uses proper body mechanics.

• Progression: Gradually increase the amount of weight moved from one place to another.

Resisted Running Start and Resisted Running

Patient position and procedure: While wearing a harness placed around the trunk and pelvis, have the patient move from the starting position typically assumed prior to a sprint and then run forward against the resistance of a heavy-grade elastic cord that is attached to the harness and affixed to the wall or a stationary surface (Fig. 23.37). As an alternative, the patient can perform backward running against resistance.

Plyometric Training: Stretch-Shortening Drills

Most pieces of equipment used for resistance training, such as free weights, weight machines or weight-pulley systems, are designed for developing advanced levels of strength but not power in that they provide substantial resistance but typically are used by performing slow, controlled movements. However, reactive bursts of force in functional movement patterns are often necessary if a patient is to return to high-demand occupational, recreational, or sport-related activities. A program of high-intensity, high-velocity exercises, known as plyometric training, not only improves muscle strength but also develops power output, quick neuromuscular reactions, and coordination.^4,11 This form of exercise also is recommended to improve athletic performance and reduce the risk of musculoskeletal injury.^4,6,9,17

Plyometric training typically is integrated into the advanced phase of rehabilitation as a mechanism to train the neuromuscular system to react quickly in order to prepare for activities that require rapid starting and stopping movements or quick changes of direction. This form of training is appropriate only for carefully selected patients who wish to return to high-demand functional activities and sports.

Definitions and Characteristics

Plyometric training,^4,11,14 also called stretch-shortening drills¹⁷ or stretch-strengthening drills,¹⁵ employs high-velocity eccentric to concentric muscle loading, reflexive reactions, and functional movement patterns. Plyometric training is defined as a system of high-velocity resistance training characterized by a rapid, resisted, eccentric (lengthening) contraction during which the muscle elongates, immediately followed by a rapid reversal of movement with a resisted concentric (shortening) contraction of the same muscle.^11,16,17 The rapid eccentric loading phase is the stretch cycle, and the concentric phase is the shortening cycle. The period of time between the stretch and shortening cycles is known as the amortization phase. It is important that the amortization phase be kept very brief by a rapid reversal of movements to capitalize on the increased tension in the muscle.

Body weight or an external form of loading, such as elastic bands or tubing or a weighted ball, are possible sources of resistance. An example of a stretch-shortening drill for the lower extremities against the resistance of body weight is represented in Figure 23.38. Additional examples of plyometric training for the upper and lower extremities are noted in Box 23.1.

Neurological and Biomechanical Influences

Plyometric training is thought to utilize the series-elastic properties of connective tissues and the stretch reflex of the neuromuscular unit. The spring-like properties of the series-elastic components of muscle-tendon units create elastic energy during the initial phase (the stretch cycle) as the muscle contracts eccentrically and lengthens while loaded. This energy is stored briefly and then retrieved for use during the concentric contraction (shortening cycle) that follows immediately. The storage and release of this elastic energy augments the force production of the concentric muscle contraction.^1,4,11,14

Furthermore, the stretch-shortening cycle is thought to stimulate the proprioceptors of muscles, tendons, ligaments, and joints; increase the excitability of the neuromuscular receptors; and improve the reactivity of the neuromuscular system. Therefore, the term reactive neuromuscular training also has been used to describe this approach to exercise. More specifically, the loaded, eccentric contraction (stretch cycle) is thought to prepare the contractile elements of the muscle for a concentric contraction (shortening cycle) by stimulation and activation of the monosynaptic stretch reflex.^4,5,14 Muscle spindles, the receptors that lie in parallel with muscle fibers, sense the length of a muscle and the velocity of stretch applied to a muscle and transmit this information to the CNS via afferent pathways. Impulses are then sent back to the muscle from the CNS, which reflexively facilitates activation of a shortening contraction of the stretched muscle (the shortening cycle).^3,10 Therefore, the more rapid the eccentric muscle contraction (the stretch), the more likely it is that the stretch reflex will be activated.

It has been suggested that the ability to use this stored elastic energy and neural facilitation is contingent on the velocity and magnitude of the stretch and the transition time between the stretch and shortening phases (the amortization phase).^4,11 During the amortization phase, the muscle must reverse its action, switching from deceleration to acceleration of the load. A decrease in the duration of the amortization phase theoretically increases the force output during the shortening cycle.^1,4,14,16

Effects of Plyometric Training

The evidence to support the effectiveness of plyometric training for developing muscle strength and power is substantial.¹¹ There is also evidence indicating that plyometric training is associated with an increase in a muscle's ability to resist stretch, which may enhance the muscle's dynamic restraint capabilities.¹ In addition, there is promising, but limited, evidence to suggest that plyometric training may enhance physical performance^2,9 and may decrease the incidence of lower extremity injury.^12,13

Application and Progression of Plyometric Exercises

Plyometric training is appropriate only in the advanced phases of rehabilitation for carefully selected, active individuals who must achieve a high level of physical performance in specific, high-demand activities.

CONTRAINDICATIONS: Plyometric activities should not be implemented in the presence of inflammation, pain, or significant joint instability.

Preparation for plyometrics. Prior to initiation of plyometric training, a patient should have an adequate base of muscle strength and endurance, as well as flexibility of the muscles to be exercised. Criteria that should be met to begin plyometric training usually include an 80% to 85% level of strength of the involved muscle groups (compared to the contralateral extremity) and 90% to 95% pain-free ROM of the moving joints.⁴ Sufficient strength and stability of proximal regions of the body (trunk and limb) for balance and postural control are necessary prerequisites as well. For example, scapulothoracic stability with the absence of scapular winging is necessary before engaging in a progression of advanced push-ups.

Specificity of training. A plyometric drill should be designed with specific functional activities in mind and should include movement patterns that replicate the desired activity.

Progression and parameters. When planning and implementing a plyometric training program, exercises should be sequenced from easy to difficult and progressed gradually. Box 23.2 summarizes a sequence of sample activities for upper extremity plyometric training.^2,4,14,16,17 Programs also should be individually designed to meet each patient's needs and goals. Note that prior to initiating each session of plyometric activities, a series of warm-up exercises should be performed in order to reduce the risk of injury to the contracting muscle groups.

The following parameters should be considered when progressing a plyometric program.

• Speed of drills. Drills should be performed rapidly but safely. The rate of stretch of the contracting muscle is more important than the length of the stretch.^11,14 Emphasis should be placed on decreasing the reversal time when transitioning from an eccentric to a concentric contraction (decreasing the amortization phase). This trains the muscle to generate tension in the shortest time possible. If a jumping activity is performed, for example, progression of the plyometric activity should center on reducing the time on the ground between each jump.

• Intensity. Resistance should be increased gradually so as not to slow down the activity. Methods for increasing external resistance include using a weight belt or vest, heavier weighted balls, or heavier grade elastic resistance; progressing from double-leg to single-leg activities; and increasing the height of platforms for jumping and hopping activities. Intensity also may be increased by progressing from simple to complex movements.

• Repetitions, frequency, and duration. The number of repetitions of an activity should be increased as long as proper form (technique) is maintained. The number of plyometric exercises in a single session also is increased gradually, working up to perhaps six different activities.² The optimal frequency of plyometric sessions is two sessions per week, which allows a 48- to 72-hour recovery period between sessions.^4,11,14 Maximum training benefits typically occur within an 8- to 10-week duration.¹¹

Precautions. Because of the emphasis on eccentric loading and rapid reversal to concentric muscle contractions, the potential for tissue damage is increased with plyometric activities. As with other forms of high-intensity resistance training, special precautions must be followed to ensure patient safety.^4,14 These precautions are listed in Box 23.3.

Plyometric Exercises: Upper Extremities

Plyometric exercises for the upper extremities can be performed in a variety of nonweight-bearing and weight-bearing positions, using anatomical motions that target a key muscle group or using combined movement patterns that involve multiple muscle groups throughout the entire upper extremity.^2,6,17 Many combined patterns used in plyometric activities incorporate trunk stability and balance into the movement sequence and often simulate desired functional motor skills that occur during work or recreational activities.

A variety of plyometric exercises for the upper extremities that could be incorporated into the final phase of rehabilitation as a component of advanced functional training are presented in this section.

Bilateral Diagonal Upper Extremity Movements

Patient position and procedure: While holding a weighted ball with both hands, have the patient perform diagonal patterns (D₁ or D₂) with a quick transition from the flexion to extension patterns. Incorporate trunk rotation into the movement patterns. These exercises also develop dynamic stability of the trunk rotators and lower extremities.

Bilateral Chest Press and Throw: Supine

Patient position and procedure: Supine with both hands reaching toward the ceiling. Have the patient catch a weighted ball dropped from above by the therapist (Fig. 23.39), control and lower it to the chest (eccentric phase), and then quickly throw it vertically back to the therapist. As the ball moves toward the chest, shoulder flexors and elbow extensors are loaded eccentrically.

Bilateral Chest Press and Throw: Standing

Patient position and procedure: While standing and with feet placed in a stride position for balance, have the patient catch a weighted ball with both hands, bringing it to the chest (eccentric phase) (Fig. 23.40), and then throw it back to the therapist or onto a rebounder (concentric phase).

Bilateral Overhead Catch and Throw

Patient position and procedure: While standing and with feet placed in a stride position for balance, have the patient use both hands to catch a weighted ball thrown over the head, controlling the momentum of the ball with shoulder and elbow musculature (eccentric phase), and then throw the ball back quickly to the therapist or onto a rebounder (concentric phase) (Fig. 23.41). This exercise targets the shoulder and elbow extensors.

Bilateral Horizontal Side Throw and Catch

Patient position and procedure: While standing with one side of the body about 10 feet away from a rebounder, have the patient hold a weighted ball in both hands with arms positioned across the chest and then throw the ball toward the rebounder by rotating the trunk and moving the arms across the chest in the transverse plane VIDEO 23.7 . The patient then catches the ball as it bounces back from the rebounder, controlling the momentum of the ball by allowing the arms to move back across the chest and rotating the trunk (eccentric phase). The patient then throws the ball back to the rebounder by reversing the movements of the arms and trunk (concentric phase) (Fig. 23.42). This exercise targets the horizontal abductors and adductors of the shoulder and trunk rotators. If a rebounder is not available, the exercise can be performed with a therapist or exercise partner.

Hand-to-Hand Overhead Catch and Throw

Patient position and procedure: While standing or kneeling with both upper extremities elevated to about 120° (aligned just anterior to the frontal plane of the trunk), elbows extended, and forearms supinated (palms facing upward), have the patient throw a bean bag or weighted ball over the head with one upper extremity and catch it with the opposite hand, controlling the weight of the ball with that shoulder (eccentric phase). Then throw the ball back to the other hand by abducting the shoulder (concentric phase). Repeat the sequence as if juggling the ball overhead (Fig. 23.43). This exercises targets the shoulder abductors.

Unilateral Plyometric Shoulder Exercises Using Elastic Resistance

Plyometric activities using elastic resistance can be set up to target individual or multiple muscle groups depending on the patient's position, the line of pull of the elastic, and which joints are moving during the exercise. Refer to Chapter 6 to review the principles of use of elastic resistance products. Setups for the shoulder rotators are described here.

• Patient position and procedure: To target the external rotators of the shoulder, have the patient stand facing a wall or door-frame and grasp one end of a length of elastic tubing or band attached to the wall at eye level. Begin with the shoulder and elbow in the 90/90 position (shoulder abducted 90° and in full external rotation and the elbow flexed 90°) (Fig. 23.44). Have the patient release the externally rotated position, controlling movement into internal rotation (eccentric phase), and then quickly reverse the motion by moving the shoulder into external rotation (concentric phase). The elastic should remain taut throughout the exercise.

• Patient position and procedure: To target the internal rotators of the shoulder, have the patient stand facing away from the doorframe or wall to which the elastic resistance is attached. Begin with tension on the elastic while the shoulder is in 90° abduction and full internal rotation, and control movement of the shoulder into external rotation (eccentric phase), then quickly return to internal rotation (concentric phase).

Bounce a Weighted Ball: Prone-Lying

Patient position and procedure: While lying prone on a table with the scapula retracted and the upper arm (humerus) supported on the table, position the shoulder in 90° abduction and external rotation and the elbow in 90° flexion. Have the patient bounce a weighted ball on the floor by internally rotating the shoulder; catch it, moving the shoulder back into external rotation under control (eccentric phase); and quickly bounce it again by internally rotating the shoulder (concentric phase) (Fig. 23.45). This exercise targets the shoulder internal rotators.

Unilateral Side Catch and Throw

These exercises target the internal rotators of shoulder.

• Patient position and procedure: While standing in the stride position and with the shoulder positioned in some degree of abduction (upper arm slightly away from the trunk), have the patient face the therapist, catch a weighted ball thrown to one side by the therapist, allowing the shoulder to externally rotate to control the momentum of the ball (eccentric phase) (Fig. 23.46 A), and return the ball using primarily shoulder internal rotation (concentric phase). If a rebounder is available, the patient can perform the exercise independently.

• Patient position and procedure: While standing in the stride position and with the shoulder abducted and externally rotated and the elbow flexed, have the patient catch and throw a weighted ball using shoulder rotation (a simulated baseball throw) (Fig. 23.46 B). Incorporate trunk rotation in the backward and forward motion of the shoulder. VIDEO 23.7

Unilateral Reverse Catch and Throw

This exercise primarily targets the external rotators of shoulder in the end-range.

Patient position and procedure: Have the patient assume a half-kneeling position, facing away from the therapist, with the involved shoulder abducted 90° and externally rotated, the elbow flexed to 90°, and the forearm pronated (palm facing therapist). Instruct the patient to look at the hand and catch a soft, lightweight object (ball or bean bag) thrown toward the hand by the therapist; control the momentum of the object by allowing the shoulder to move into internal rotation; and then quickly throw the object back to the therapist by externally rotating the shoulder (Figs. 23.47 A, B, and C).

Throw and Catch with Elbow Action

• Patient position and procedure: While in a standing position and with the arm positioned along the side of the trunk, have the patient throw a weighted ball into the air with one hand, using primarily elbow flexion; catch it, allowing the elbow to extend with control (eccentric phase); and then quickly throw it into the air again (concentric phase) (Fig. 23.48). This exercise targets the elbow flexors.

• Patient position and procedure: While standing and with one or both arms positioned overhead, have the patient catch a weighted ball and return it to the therapist or to a rebounder using primarily elbow action. This exercise targets the elbow extensors and can be done bilaterally or unilaterally.

Unilateral Throw and Catch with Wrist Action

Patient position and procedure: While seated, have the patient stabilize the elbow on the thigh in about 90° flexion, and with the forearm supinated, toss a weighted ball or bean bag into the air using primarily wrist flexion; catch it, allowing the wrist to extend under control (eccentric phases); and then quickly toss it into the air again (concentric phase) (Fig. 23.49). This exercise targets the wrist flexors.

Simulated Sport Activities

• Dribble a weighted ball or basketball against a wall (Fig. 23.50) or on the floor using either elbow or wrist actions. This activity targets either the elbow extensors or wrist flexors.

• Bounce a tennis ball or racquetball into the air or onto the floor (forearm supinated or pronated, respectively) with a short-handled racquet, progressing to a long-handled racquet. These activities emphasize the wrist flexors. In contrast, bouncing a ball into the air with the forearm pronated emphasizes the wrist extensors (Fig. 23.51).

• Swing a weighted golf club (Fig. 23.52) or baseball bat. The backward motion followed by a rapid reversal forward provides the plyometric stimulus.

Upper Extremity Weight-Bearing Movements on a Slide Board

Use of a slide board, such as a ProFitter^TM, provides an unstable, moving surface for performing movements of the shoulders that require quick changes of direction combined with weight bearing through the upper extremities.

• Patient position and procedure: Have the patient place both hands on a spring-loaded slide board while kneeling along one side of the equipment. Shift the arms side-to-side from the shoulders (Fig. 23.53), gradually increasing the speed of the shoulder movements and changes of direction.

• Patient position and procedure: Have the patient kneel at one end of the slide board and move the arms forward and backward from the shoulders.

• Progression: Perform the same movements while kneeling and bearing weight on one hand.

Push-Offs from a Wall

• Patient position and procedure: While the patient is standing several feet away from a wall (or countertop), gently push the patient directly forward toward the wall. Instruct the patient to catch himself/herself with equal weight on both hands, allowing the elbows to flex under control (eccentric phase) as the trunk moves toward the wall (Fig. 23.54 A). Then have the patient quickly push away from the wall with both hands (concentric phase) (Fig. 23.54 B), catch the patient as he/she falls backward, and then push the patient forward again to repeat the sequence.

• Alternative activity: Have the patient perform the sequence independently by falling forward to the wall and quickly pushing away.

• Progression: Have the patient use one hand to catch self and push away from the wall.

Side-to-Side Push-Offs from a Waist-Level Surface

Patient position and procedure: While standing and maintaining both feet approximately 3 feet away from a waist-height, stable surface (countertop, heavy table), have the patient fall forward and slightly to the right of midline and catch self with hands on the edge of the countertop or table; push off and shift arms and trunk to the left; catch self with both hands; and push off again, moving arms and trunk back to the right, past midline (Fig. 23.55) VIDEO 23.8 . This exercise alternately places greater weight on the right and then the left upper extremity.

Variations of Prone Push-Ups

• Clap push-ups: While on the floor, have the patient perform a forceful prone push-up from knees or feet; clap hands together; catch self with both hands, allowing elbows to flex (eccentric phase); and quickly perform another push-up (concentric phase) VIDEO 23.8 .

• Drop push-ups: Have the patient perform a prone push-up from knees or feet with hands on platforms positioned a shoulder width apart. Drop both hands and the chest to the floor, controlling the descent of the trunk (eccentric phase); quickly perform another push-up (concentric phase); and return both hands to the platforms (Figs. 23.56 A, B, and C).

Plyometric Exercises: Lower Extremities

Most plyometric exercises for the lower extremities are performed while standing and require eccentric and concentric control of the hip and knee extensors and ankle plantarflexors against body weight. These exercises require postural stability and balance because of the quick changes of direction involved. Plyometric activities can be progressed by adding an external load (a weighted belt, vest, or backpack) to augment body weight or by first performing the exercises in bilateral stance (jumping) and then in unilateral stance (hopping).

The following plyometric exercises are examples of lower extremity activities that can be incorporated into the final phase of rehabilitation in preparation for functional activities ranging from community ambulation to high-intensity sports.

Kicking a Ball

These exercises involve rapid eccentric and concentric open-chain contractions of hip musculature. Be sure the patient is wearing shoes during kicking activities.

• Patient position and procedure: While standing and facing an exercise partner, have the patient swing one lower extremity backward into hip extension (eccentric phase), then quickly swing the same extremity forward into hip flexion (concentric phase) and kick a ball to the partner with the anterior aspect of the foot. This activity targets the hip flexors and knee extensors.

• Patient position and procedure: While standing with one shoulder positioned toward an exercise partner, have the patient stand on the leg closer to the partner, swing the opposite hip into abduction, and then quickly adduct the hip to kick the ball back to the partner using the medial aspect of the foot (as in a soccer kick). This exercise targets the hip adductors.

Sit-to-Stand from a Ball

• Patient position and procedure: While in sitting, have the patient bounce on a therapy ball (stabilized by the therapist), come to a partial standing position, and then sit back down on the ball and quickly come to a partial standing position again (Fig. 23.57). Progress the exercise by eventually coming to a full standing position. This activity requires contraction of the hip and knee extensors against the resistance of body weight. To be effective, rapid reversals must occur between the lowering (eccentric) and standing-up (concentric) phases.

Bilateral Heel Raises on a Mini-Trampoline

Patient position and procedure: In bilateral stance, have the patient bounce on a mini-trampoline by performing repeated heel raises and lowering. This activity targets the gastrocnemius-soleus muscle groups.

Side-to-Side Shuffle

Patient position and procedure: Have the patient take several quick side steps to the right and then back to the left, and repeat. This exercise requires rapid contractions of the hip abductors and adductors against body weight during each change of direction.

Side-to-Side Movements on a Slide Board

Patient position and procedure: While standing on a slide board, such as a Pro-Fitter^®, have the patient shift body weight side-to-side (Fig. 23.58), gradually increasing the speed of the directional changes as skill and coordination improve.

Squat Jumps

Patient position and procedure: Have the patient move quickly from a standing position into a squat position (eccentric phase) (Fig. 23.59 A), quickly transition to a vertical jump (concentric phase) (Fig. 23.59 B), return to the squat position, and then perform another vertical jump VIDEO 23.9 . When landing and moving into the squat position, be sure the patient keeps the lower legs aligned as close to vertical as possible.

Bounding

• Patient position and procedure: Have the patient start with the feet positioned shoulder width apart, and take multiple jumps forward in a straight line across the floor (Fig. 23.60).

• Progressions: Increase the speed at which the activity is performed, and then increase the distance of each jump. When able, have the patient perform forward hopping across the floor.

Four-Quadrant Jumps or Hops

• Patient position and procedure: Using two lines on the floor intersecting at right angles as a guide, have the patient jump forward, backward, side-to-side, and diagonally from one quadrant to another, using quick directional changes (Fig. 23.61) VIDEO 23.9 .

Tuck Jumps

• Patient position and procedure: Have the patient begin in standing position, quickly lower the body into a squat position (eccentric phase), perform a tuck jump as high as possible, bringing the knees toward the chest (Fig. 23.62), and then land in proper alignment and return to the squat position to initiate the next tuck jump.

• Progression: Perform a series of side-to-side tuck jumps over a barrier.

Lunge Jumps

• Patient position and procedure: Have the patient begin in a symmetrical standing position, jump vertically, and land in a forward lunge position (eccentric phase); then quickly jump vertically (concentric phase) and again land in a forward lunge position VIDEO 23.9 . Perform multiple repetitions by landing with the same foot forward each time.

• Alternative activity—Scissor-lunge jumps: Perform a sequence of lunge-jumps, alternately bringing the right and then left foot forward, as in a scissoring motion (Fig. 23.63 A, B, and C).

• Progression: Increase the challenge by performing lunge-jumps while wearing a weighted vest or holding weights in both hands.

Zigzag Forward Jumping or Hopping

Patient position and procedure: Have the patient jump or hop across the floor in a zigzag pattern marked on the floor (Fig. 23.64). Progress by increasing the speed of jumping or hopping and the distance between jumps or hops.

Hopping Over Objects

Patient position and procedure: Have the patient hop over objects of various sizes placed on the floor like an obstacle course (Fig. 23.65) VIDEO 23.9 .

Single Platform Jumping or Hopping

Patient position and procedure: Have the patient jump and progress to hopping onto and off of a single, low platform in forward (Fig. 23.66), backward, and lateral directions, being certain to use proper landing technique. To progress, first increase the speed and repetitions of the jumping or hopping activity, then increase the height of the platform.

Multiple Platform Jumping or Hopping

Patient position and procedure: Have the patient jump (or hop) in a forward direction off of a platform to the floor and then jump forward again onto another platform (see Fig. 23.18 A, B, and C). Progress by performing the sequence more rapidly or by increasing the height of the platforms.

Critical Thinking Questions

1. Review the principles of balance training described in Chapter 8. Describe how each of the advanced balance activities presented in this chapter (Chapter 23) can be used to enhance the static, dynamic, anticipatory, or reactive aspects of balance.

2. Develop a sequence of balance activities in the standing position from least to most difficult, using progressively more challenging movements and equipment.

3. Identify the benefits, as well as the risks, of performing a program of plyometric exercises (stretch-shortening drills).

4. Analyze the plyometric training activities listed in Box 23.1, and determine in which muscle groups training-induced gains in strength and power would occur and what functional tasks each of the activities could enhance.

5. Develop a plyometric sequence for the lower extremities and trunk progressing from simple to more difficult (similar to the sequence for the upper extremities described in Box 23.3).

Laboratory Activities

1. Practice the sequence of balance activities in the standing position that you developed to answer Critical Thinking Question #2. Take turns with a laboratory partner role-playing the therapist and the patient. If you are the therapist, use proper safety precautions, critically analyze how your patient performs each balance task, and give your patient feedback to facilitate learning correct alignment and technique.

2. Perform and analyze a variety of plyometric exercises for the upper or lower extremities, and identify which muscle groups are loaded eccentrically or concentrically during the two phases of each activity.

   • Catch and throw a weighted ball with both hands (or one hand) while assuming supine, prone, and upright positions.

   • While kneeling and with hands placed on a slide board and elbows extended, move the arms forward and backward or side-to-side.

   • While standing a few feet from a wall, fall forward, catching yourself with both hands, and then push off the wall to return to a standing position.

   • In the prone position, perform bilateral drop push-ups to and from two low platforms.

   • While standing on a mini-trampoline, bounce your heels off and on the surface using only ankle motion.

   • Jump off of and back onto a low platform—forward, backward, and side-to-side.

Case Studies

Case Study #1

You have been following a 21-year-old female college volleyball player, who underwent an arthroscopic ACL reconstruction of the left knee 4 months ago. She now has full, pain-free ROM of the knee and 80% to 85% strength of left knee and hip musculature compared with the sound right lower extremity. Arthrometer measurements indicate that A-P stability of the operated knee is comparable to the sound side. However, her performance on a single step-down test reveals continued evidence of abnormal alignment of the operated lower extremity (excessive hip adduction, and internal rotation, knee valgus, and foot pronation). She has been given approval by her surgeon to return to intercollegiate play by 6 months postoperatively, following completion of an advanced training program individualized to her needs and goals.

• Develop an 8-week training program of advanced strengthening, balance, and plyometric drills for this patient. Identify specific exercises that would be included in each training session and how the exercises will be progressed over the 8-week period.

• In addition to exercises to enhance stability, control, and strength of the lower extremity, identify exercises that should be included to improve her upper extremity function.

Case Study #2

You have been working with a 35-year-old "weekend warrior" who was diagnosed with chronic tennis elbow. His symptoms are now under control, and he wants to return to competitive play at the local tennis club. Develop a training program of advanced strengthening and plyometric drills for this individual. Identify each exercise and its progression in terms of repetitions, resistance, control, and precautions. Include both upper and lower extremity drills and progressions that include total body-coordinated effort.

Additional Case Studies

For additional study, review the following case studies from previous chapters and modify your exercise interventions to include advanced drills based on the information you studied in this chapter.

1. Case study #4 in Chapter 17

2. Case study #2 and #3 in Chapter 20

3. Case study #2, #3, and #4 Chapter 22