Application and Progression of Plyometric Training
Plyometric training is appropriate only in the later stage of rehabilitation of active individuals who must achieve a high level of physical performance in specific, high-demand activities.
Contraindications. Plyometrics should not be used if inflammation, pain, or significant joint instability is present.
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 to begin plyometric training usually include an 80% to 85% level of strength and 90% to 95% ROM.
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. Parameters of plyometric training are progressed as follows.
• 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. Emphasis should be placed on decreasing the reversal time 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. Increase the resistance applied but not enough to slow down the activity. Examples include use of a weighted vest, heavier Plyoballs (weighted balls), heavier grade elastic resistance, double-leg to single-leg jumping or hopping, or using higher height platforms. Intensity also involves progressing from simple to complex movements.
• Repetitions and frequency. Increase the number of repetitions of an activity so long as proper form (technique) is maintained; increase the number of plyometric exercises in a session; or increase the number of plyometric sessions in a week. A 48- to 72-hour recovery period is recommended.

PRECAUTIONS: As with other forms of high-intensity resistance training, special precautions must be followed to ensure patient safety. These precautions are listed below.

Isokinetic Regimens
It is well established that isokinetic training improves muscle performance. Its effectiveness in carryover to functional tasks is less clear. Studies support and refute that isokinetic training improves function. Ideally, when isokinetic training is implemented in a rehabilitation program, to have the most positive impact on function it should be performed at velocities that closely match or at least approach the expected velocities of movement of specific functional tasks. Because many functional movements occur at a variety of medium to fast speeds, isokinetic training is typically performed at medium and fast velocities.

Sample Plyometric Sequence for the Upper Extremities
• Warm-up activities
• Trunk exercises holding lightweight ball: rotation, side-bending, wood-chopping
• Upper extremity exercises in anatomical and diagonal planes of motion with light-grade elastic tubing
• Prone push-ups
• Throwing motions with a weighted ball to and from a partner: bilateral chest press; bilateral overhead throw; bilateral side throw
• ER/IR against elastic tubing (90/90 position of shoulder and elbow)
• Diagonal patterns against elastic resistance
• Unilateral throwing motions with weighted ball: baseball throw; side throws
• Additional exercises
• Trunk exercises holding weighted ball: abdominal curl-ups; back extension; sit-up and bilateral throw; long sitting throws
• Clap push-ups
• Prone push-ups from box to floor and back to box

Precautions for Plyometric Training
• If high-stress, shock-absorbing activities are not permissible, do not incorporate plyometric training into a patient’s rehabilitation program.
• If a decision is made to include plyometric activities in a rehabilitation program for children or elderly patients, select only beginning-level stretch-shortening drills against light resistance. Do not include high-impact, heavy-load activities—such as drop jumps or weighted jumps—that could place excessive stress on joints.
• Be sure the patient has adequate flexibility and strength before initiating plyometric exercises.
• Wear shoes that provide support for lower extremity plyometrics.
• Always warm-up prior to plyometric training with a series of active, dynamic trunk and extremity exercises.
• During jumping activities, emphasize learning techniques for a safe landing before progressing to rebounding.
• Progress repetitions of an exercise before increasing the level of resistance used or the height or length of jumps.
• For high-level athletes who progress to high-intensity plyometric drills, increase the rest intervals between sets and decrease the frequency of drills as the intensity of the drills increases.
• Allow adequate time for recovery with 48 to 72 hours between sessions of plyometric activities.
• Stop an exercise if a patient can no longer perform the plyometric activity with good form and landing technique because of fatigue.

Current isokinetic technology makes it possible to approximate training speeds to velocities of movement during some lower extremity functions, such as walking. In the upper extremities this is far less possible. Some functional movements in the upper extremities occur at exceedingly rapid velocities (e.g., more than 1000° per second for overhead throwing), which far exceed the capabilities of isokinetic dynamometers.
It is also widely accepted that isokinetic training is relatively speed-specific, with only limited transfer of training (physiological overflow causing improvements in muscle performance at speeds other than the training speed). Therefore, speed-specific isokinetic training, similar to the velocity of a specific functional task, is advocated.

Velocity Spectrum Rehabilitation
To deal with the problem of limited physiological overflow of training effects from one training velocity to another, a regimen called velocity spectrum rehabilitation (VSR) has been advocated. With this system of training, exercises are performed across a range of velocities.

NOTE: The guidelines for VSR that follow are for concentric isokinetic training. General guidelines for eccentric isokinetics are identified at the conclusion of this section.

Selection of training velocities. Typically, medium (60° or 90° to 180°/sec) and fast (180° to 360°/sec) angular velocities are selected. Although isokinetic units are designed for testing and training at velocities faster than 360° per second, the fastest velocities usually are not used for training. This is because the limb must accelerate to the very fast, preset speed before encountering resistance from the torque arm of the dynamometer. Hence, the contracting muscles are resisted through only a small portion of the ROM.
It has been suggested that the effects of isokinetic training (improvements in muscle strength, power, or endurance) carry over only 15° per second from the training velocity. Therefore, some VSR protocols use 30° per second increments for medium and fast velocity training. Of course, if a patient trains at medium and fast velocities (from 60° or 90° to 360°/sec) in one exercise session, this strategy necessitates nine different training velocities, giving rise to a time-consuming exercise session for one agonist/antagonist combination of muscle groups. A more common protocol is to use as few as three training velocities.

Repetitions, sets, and rest. A typical VSR protocol might have the patient perform one or two sets of 8 to 10 or as many as 20 repetitions of agonist/antagonist muscle groups (reciprocal training) at multiple velocities. For example, at medium velocities (between 90° and 180°/sec) training could occur at 90°, 120°, 150°, and 180° per second. A second series would then be performed at decreasing velocities: 180°, 150°, 120°, and 90° per second. Because many combinations of repetitions, sets, and different training velocities lead to improvement in muscle performance, the therapist has many options when designing a VSR program. A 15- to 20-second rest between sets and a 60-second rest between exercise velocities has been recommended. The recommended frequency for VSR is a maximum of three times per week.

Intensity. Submaximal effort is used for a brief warm-up period on the dynamometer. This is not a replacement for a more general form of upper or lower body warm-up exercises, such as cycling or upper-extremity ergometry. When training to improve endurance, exercises are carried out at a submaximal intensity (effort) but at a maximal intensity to improve strength or power.

During the early stages of isokinetic training, it is useful to begin with submaximal isokinetic exercise at intermediate and slow velocities so the patient gets the “feel” of the isokinetic equipment and at the same time protects the muscle. As the program progresses, maximum effort can be exerted at intermediate speeds. Slow-speed training is eliminated when the patient begins to exert maximum effort. During the advanced stage of rehabilitation, maximum-effort, fast-velocity training is emphasized, so long as exercises are pain-free. Additional aspects to a progression of isokinetic training regimens include short-arc to full-arc exercises (if necessary) and concentric to eccentric movements.

PRECAUTION: Maximum-effort, slow-velocity training is rarely indicated because of the excessive shear forces produced across joint surfaces.

Eccentric Isokinetic Training: Special Considerations
As isokinetic technology evolved over several decades, eccentric isokinetic training became possible, but few guidelines for eccentric isokinetic training and evidence of their efficacy are available. Guidelines developed to date are primarily based on clinical opinion or anecdotal evidence. Key differences in eccentric versus concentric isokinetic guidelines (intensity, repetitions, frequency, rest) are listed below. Several resources describe pathology-specific guidelines for eccentric isokinetic training based on clinical experience.

PRECAUTIONS: Eccentric isokinetic training is appropriate only during the final phase of a rehabilitation program to continue to challenge individual muscle groups when isolated deficits in strength and power persist. Because of the robotic nature of eccentric isokinetic training, medium rather than fast training velocities are considered safer. A sudden, rapid, motor-driven movement of the dynamometer’s torque arm against a limb could injure healing tissue.

Key Differences in Eccentric Versus Concentric Isokinetic Training
Eccentric isokinetic exercise is:
• Introduced only after maximal effort concentric isokinetic exercise can be performed without pain
• Implemented only after functional ROM has been restored
• Performed at slower velocities across a narrower velocity spectrum than concentric isokinetic exercise: usually between 60° and 120° per second for the general population and up to 180° per second for athletes
• Carried out at submaximal levels for a longer time frame to avoid extensive torque production and lessen the risk of DOMS
• Most commonly performed in a continuous concentric-eccentric pattern for a muscle group during training

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