C. BUZ SWANIK, PhD, ATC School of Physical Education West Virginia University KATHLEEN A. SWANIK, PhD, ATC School of Education University of Pittsburgh

T h e term "plyometrics" is commonly asso- This article will summarize the theoreti- ciated with high-intensity conditioning for ex- cal basis for using plyometric activities in plosive athletic competition. However, health lower extremity rehabilitation and will provide care professionals working with physically general models for their implementation. active populations have come to appreciate the benefits of integrating lower extremity plyometrics early in a rehabilitation protocol

Stratch-Sh~ratsnirrag Cycle

for musculoskeletal injuries. Numerous ex- The mechanism underlying all plyometric

involve pr eccentric t

To design

cs for the I( l w e i ex t ra

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and comple t activities.

ess.

For exercise proaresslon, moalrv the b intensity plyometri

xity of the

ercises for the lower extremity can be con- sidered plyometric if they involve pre- loading muscles with an eccentric contrac- tion, followed quickly by a concentric con- traction.

Plyometric acti- vities complement lower extremity reha- bilitation because they require anticipat- ing and reacting to joint loads through co-

activities contains three phases based on muscular contraction and is collectively termed the stretch-shortening cycle. The first is a "prestretch" or eccentric phase, which is defined by the forceful lengthening of a muscle being actively contracted. During this phase, joint loads are absorbed and stored in the elastic component of the tenomuscular unit. Several factors will influence the capac- ity of muscle to store elastic energy including the rate of stretch, magnitude of the load, muscle architecture, and joint position.

The second phase is defined by a brief period (amortization time) after eccentric loading wherein muscle length does not change. The amortization phase is critical to

ordinated muscular the stretch-shortening cycle because if this pe- contractions. Individual plyometric routines riod is prolonged, elastic energy will dissipate may b e developed to address specific and cannot be utilized for force production. muscles, joints, and functional movement The third phase is described by a concentric patterns for various athletic endeavors. How- (shortening) muscle contraction. The concen-

gressive exercise intensity can easily be modi- develop a potentially powerful muscular con- fied through a combination of repetition, load, traction (Wilt, 1975). Although the stretch- and complexity. shortening cycle maximizes muscle force

1999 Human Kinetics. ATT 4 3 ) . po. 16-22

1 6 1 MAY 1 9 9 9 ATHLETIC THERAPY TODAY

Photo B Exercises on a stool; tan use elastic tubing for resistance.

production, it also enhances the efficiency of move- ment, which is more desirable for lower extremity rehabilitation (Photo 1 ).

Physiological Wdagtatig~ls to PByomsratrEc Wgtivitioa

Supplementing a traditional rehabilitation protocol with plyometric activities may invoke adaptations that accelerate the athlete's return to full sports participa- tion. Long-term adaptations resulting from plyometric activities may include several of the neuromuscular characteristics needed to restore neuromuscular con- trol and dynamic joint stabilization. Muscular strength and power are the most recognized benefits of plyometrics. However, the underlying neuromuscular adaptations may be more desirable during lower ex- tremity rehabilitation. These adaptations include re- storing functional motor patterns, heightening muscle reflexes, and increasing proprioceptive awareness.

Functional Motor Patterns

Many sports emphasize explosive, well-coordinated lower extremity skills. These movements must be executed with precision but generate high joint loads in the lower extremity. Performing high velocity, bal-

listic activities requires planning movements and con- tracting muscles in anticipation of joint loads. Each time the brain initiates these motor patterns, the neu- ral pathways become more efficient at coordinating muscle recruitment.

During rehabilitation, the use of plyometrics will help generate or reestablish memories of complex and sport-specific functional movement patterns (Hutton & Atwater, 1992). Moreover, contracting muscles in preparation for eccentric loading promotes dynamic restraint and protects the lower extremity joints. With graduated intensity and repetition, the joint loads are increased while successful recruitment strategies are recalled to refine future movements. Therefore, plyometrics in rehabilitation promotes the efficiency of functional motor patterns and encour- ages dynamic joint stabilization.

Heightened Reflexes Reacting to unanticipated joint loads and movements is also critical for returning to sports participation. Reflexive muscle firing may be enhanced with plyometric activity due to adaptations in Golgi ten- don organs (GTOs) and the muscle spindle system.

Repetitive loads placed on the tenomuscular unit during plyometric training may desensitize GTOs to muscle tension (Hutton & Atwater, 1992). Thus the protective mechanism that normally inhibits muscu- lar contraction is reduced. This permits greater ec- centric loads, increasing the storage of elastic energy and heightening the reflexive muscle firing elicited from muscle spindles. These reflexes are superim- posed on the functional motor patterns to enhance muscle recruitment and dynamic restraint. Reestab- lishing these reflexes is an important component of rehabilitation if athletes are to protect themselves against recurring musculoskeletal injuries.

Proprioception

Athletes possess above average conscious apprecia- tion of joint motion and position. Many athletic events subject the lower extremity to plyometric types of activities. These activities may be partly responsible for enhanced proprioception when considering the effects of muscle contraction and chronic neural ad- aptations on proprioception. The sensitivity of muscle spindles, and thus proprioception, is heightened when

ATHLETIC THERAPY TODAY MAY 1999 1 17

C o N e E P Y s 1 . Perform exercises within the cardinal planes.

2. Use body weight as resistance.

3. Increase resistance by using elastic tubing; increase further by moving tubing distal.

4. Begin exercises in a pool to reduce joint loads; progress from pool to hard surface.

5. One to 2 sets of 10 reps is sufficient, 1 or 2 times a week; increase reps (20- 30) and sets (4 or 5).

EXERCISES 1 . Perform traditional open-chain exercises with weights; do not pause at end

of ROM but return immediately to starting position, then pause. Include hip, knee, or ankle ROM.

2. Exercises on a stool: Sit on a stool with wheels and move forward and back- ward or side to side. Add resistance through elastic tubing around the waist or weights to the stool. Progress to using only the involved leg (Photo 1) .

3. Slideboard: Perform hip flexion and quickly transition into extension while keeping feet on the slideboard (Photos 2a, 2b).

4. The Fitter can also be used as a plyometric activity as long as one does not pause between reps (Photo 3).

5. Stand-Squat-Stand: Squat and then immediately stand before resting; this activity can progress using just the involved leg and then onto uneven sur- faces.

6. Small hops: Go forward, backward, and side to side, progressing to single leg (Photos 4a, 4b).

i l~dpboard P X P ~

a and b). (ISPS, Photo 3 The "fitter." Photos !,a, hh (a) Small double and (b) slnqle leg hops.

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INTERMEDHATE LOWER EXTREMITY PLYOMETRECS GONCEPTS

1. Incorporate some plyometric activities outside the cardinal planes.

2. Begin to increase the speed of each exercise.

3. Perform 3 sets of 8-10 reps with each exercise, 2 or 3 times a week

EXERCISES 1 . Perform hops one at a time, progressing to repetitive hopping.

- Begin and end with knees in slight flexion.

- Use both feet, progressing to single-footed hop. - Increase the intensity by increasing jump height and adding resistance.

- Progress to an unstable platform (tramp or foam) (Photos 5a, 5b).

2. Hop-Lunge-Hop - Begin and end with feet together and knees in slight flexion. - Progress by hopping on a flat surface and lunging onto a box (Photos 6a,

6b). - Also include hop-lunge-lunge-hop sequences.

3. Slideboard exercises - Perform traditional slideboard activities.

- Progress by adding resistance, increasing the time, number of reps, or sets.

I

Hopping on e t tq .

uneven surfaces progressing from Phataa, 68, 63 Lunging to a box, al ternat~nq Iegs(a and b).

ATHLETIC THERAPY TODAY MAY 1999 1 19

ADVANCED LOWER EXTREMITY PLYOMETRICS

CONCEPTS 1. Involve complex movements.

2. Attempt to replicate functional, sport-specific activities.

3. Emphasize high eccentric loads. 4. Include quick changes in direction.

EXERCISES 1 . Hop off varying heights of boxes and immediately hop again with both feet.

- Progress to using just the involved extremity. - Hop onto different surfaces. - Include twists and hops in different directions (Photos 7a, 7b, 7c).

2. Semi-circle with elastic tubing

- Progress by using elastic tubing or include boxes of varying heights to jump over within the semi-circle (Photo 8).

3. Develop an obstacle course

- Include different heights and surfaces, with directions both in and out of the cardinal planes.

- Require quick changes in direction using single and double-leg activities.

- Progress by adding more tasks and restricting the time.

(a) Hop off varying heights of boxes using both feet; (b) progress to using just the involved extremity; (0 include I"%o". a Semi-circle w i th elastic tubing. irections. A weighted vest (an be added for resistance, as shown.

20 1 MAY 1999 ATHLETIC THERAPY TODAY

muscles are voluntarily contracted. The preparatory muscle contractions needed for plyometric activities serve to protect the joint but also increase sensory feedback to the central nervous system. This feed- back enhances the conscious appreciation of joint motion and position. Long-term adaptations that oc- cur in GTOs and muscle spindles may also improve proprioception. Long-term adaptations to the sensi- tivity of muscle spindles not only heighten reflexes but may also provide additional sensory information concerning joint position and motion (Lephart &

Kocher, 1993). The combined effect would be very beneficial dur-

ing rehabilitation because the athlete is able to protect against joint positions and motions where he or she is vulnerable to injury. Thanks to this proprioceptive feed- back, functional motor patterns that are successfully executed are reinforced. Although continued research is warranted, the proprioceptive benefits of plyometrics support its use in most stages of rehabilitation.

Safety It is imperative that safety remain a primary concern when using plyometrics in rehabilitation, even with highly skilled athletes. Although the heavy muscula- ture and mechanics for human locomotion make the lower extremity well suited for plyometrics, one should guard against proceding too quickly in rehabilitation.

Athletic trainers and therapists should first evalu- ate the setting where plyometrics are performed. Con- sidering the high-speed, functional nature of plyometric activities, the area should be clear of obstructions. If the exercises are performed while standing, the type of landing surface may be modified to provide more shock absorption. Instructions for the athlete begin with em- phasizing quality and technique rather than quantity.

The athletic trainer or therapist can describe and demonstrate the important phases of plyometric ac- tivities, but the emphasis must be on pain-free range of motion (ROM). The first phase should stress energy absorption by controlled lengthening of the muscles; the second phase is the short pause when the athlete changes direction; the third phase emphasizes a quick and forceful concentric contraction. The athletic trainer or therapist then acts as an objective observer to pro-

vide corrective feedback on technique. Several factors considered in the design and progression of the plyometric program can provide additional safety.

(onsiderations for Designing a Pjyom~tr ic Program

Goal setting is the first step in designing a program for rehabilitation. Ultimately the plyometric program will evolve and integrate into a conditioning regimen. Therefore the plyometric activities should adhere to a timeline for return to activity and mirror the athlete's functional progression.

To start, assess the athlete's muscle strength and history of physical activity. The level of strength will dictate a reasonable load he or she can manage while maintaining good technique. For example, light plyometric activity can be initiated shortly after strengthening exercises. At this stage, limb weight may be enough to elicit the desired neuromuscular response. If strength is insufficient or the load is too great, the motion will not appear controlled. The amoritization phase may be prolonged and the con- centric contraction will seem sluggish.

The history of physical activity or sports partici- pation is used to gauge motor coordination. This will help determine the complexity of the plyometric ex- ercises, such as single versus multiplanar movements. Again, a controlled motion is more desirable.

The plyometric component of rehabilitation should be initiated after a 5-minute period of active warm-up followed by stretching. Similarly, an active cooldown followed by ice will help minimize muscle and tendon soreness. Avoiding plyometrics at the end of the rehabilitation protocol will minimize fatigue and decrease the risk of injury. Sufficient time (usually a few seconds) should be allotted between individual repetitions to mentally rehearse the movement se- quence while the duration between sets is modified to emphasize power versus endurance elements of rehabilitation. Chu (1 984) recommends a worklrest ratio between 1 :5 and 1 : 10 to accentuate power.

Decreasing the rest period or including plyo- metrics into a circuit training routine will emphasize endurance. Initially, one exercise bout per week in re- habilitation is sufficient. Even aggressive plyometric conditioning is limited to twice a week. Soft tissue ac- commodation is the limiting factor for the frequency of plyometric activities, and clinicians should monitor

-

ATHLETIC THERAPY TODAY MAY 1999 1 21

the inflammatory response to training intensity. Con- sideration for the athlete's sport-specific tasks is also important and may help with exercise adherence. Once the goals and program framework are established, exercise progression can be addressed.

Exercise Progression

Plyometric programs become more advanced by in- creasing the intensity and level of difficulty. The level of intensity will depend greatly on the type of injury and its severity. Several methods used to regulate the intensity of plyometrics include the number of exer- cises, repetitions and sets, and the amount of eccen- tric loading (Chu, 1984). The total volume of plyometric activity in the rehabilitation program is determined by number of exercises (1 -4), repetitions (1 0-20), and sets (1 -3).

The athlete may attempt only 10 stretch-shorten- ing cycles at the beginning of the plyometrics pro- gram and continue until completing a high-intensity conditioning regimen designed to enhance perfor- mance. The amount of eccentric load will start with partial weight-bearing activities (pool exercises) or by performing active ROM exercises using only the weight of the limb for resistance. The load is increased by adding external weights, jumping from heights, or shifting to a single-leg stance. Caution should be ob- served when adding external weights to jumps be- cause the athlete's center of gravity will be altered, increasing the risk of injury.

The level of difficulty also contributes to exercise progression and includes increasing the speed and complexity of movements. Initially all exercises should be performed slowly and deliberately. The athletic trainer or therapist closely observes the speed of movement to make sure the quality of the stretch- shortening cycle does not suffer. Permitting the ath- lete to increase the speed will generate greater eccentric loads and a more vigorous reflexive re- sponse. Increasing the speed also demands more concentration and motor coordination. Therefore the speed movements may be a good indicator for pro- gressing the athlete to more complex exercises.

w ~ w s s The level of "diffimity is also"incre%sedbyy-using gross and fine motor movements (single vs. multiplanar). Initially the athlete should attempt only gross motor movements in the cardinal planes. As

these movements become familiar, multiplane actions can be initiated. By continuously refining the plyometric exercises, the athlete is able to progress to complex, functional types of activities.

Conclusions

Plyometrics are important for lower extremity reha- bilitation because athletes must anticipate and react to joint loads. Numerous exercises include the stretch- shortening cycle while simulating the demands on the lower extremity during athletic competition. All exercises that include preloading muscles with an ec- centric contraction, followed quickly by a concentric contraction, can facilitate adaptations to the stretch- shortening cycle. These neuromuscular adaptations may include restoring functional motor patterns, heightened reflexes, and improved pro-prioception.

Safety, a primary concern in rehabilitation, is pro- vided by carefully monitoring technique and exercise intensity. Designing a plyometric program should start with setting individual goals and assessing the athlete's level of strength and coordination. Exercise progres- sion for lower extremity plyometrics is accomplished by modifying the intensity (repetitions, external load, jump height) and complexity (single vs. multiplanar movements) of the activities. Implementing plyometrics into rehabilitation encourages neuromus- cular characteristics necessary for dynamic restraint and may accelerate the athlete's return to full partici- pation while minimizing the risk of reinjury. 81

Chu, D. (1 984). Plyometric exercise. National Strength and Conditioning AssociationJournal, 6(1), 56-62.

Hutton, R.S., & Atwater, S.W. (1992). Acute and chronic adaptations of muscle proprioceptors in response to increased use. Sports Medicine, 14, 406-421.

Lephart, S.M., & Kocher, M.S. (1993). The role of exercises in the preven- tion of shoulder disorders. In FA. Matsen, F.H. Fu, & R.J. Hawkins (Eds.), The shoulder: A balance of mobility and stability (pp. 597-6201, Rosemont, 1L: American Academy of Orthopaedic Surgeons.

Wilt, E (1 975). Plyometrics, what it is and how it works. Athletic Journal, 55(5), 76-90.

C. BuzSwanik is an assistant professor in the School of Physlcal Educa- tlon at West Vlrginja Un~verslty and serves as director of the graduate athletlc tralnlng curriculum at WVU

Kathleen A. Swanik is an ass~stant professor in the School of Educat~on at the Unlverslty of P~ttsburgh and serves as undergraduate athlet~c tram- Ing curr~culum d~rector and cllnical athletlc tra~ner at Pittsburgh

22 1 MAY 1999 ATHLETIC THERAPY TODAY