Plyometric mechanics and physiology

Plyometric exercises involve powerful movements that use a pre-stretch or countermovement, activating the stretch-shortening cycle (SSC). The goal is to increase power output by utilizing:

• The elastic properties of muscles and tendons
• The stretch reflex

Plyometric training enhances force and speed, both essential for athletic performance. Two models help explain its effectiveness:

Mechanical model of plyometric exercise

This model focuses on the storage and use of elastic energy within the series elastic component (SEC):

• A rapid eccentric stretch stores elastic energy in tendons.

• If a concentric contraction follows immediately, the energy is released and adds to the total force.

• If there’s a delay, the stored energy dissipates as heat and force is lost.

Key components:

• CC (Contractile component): Actin–myosin crossbridges that generate active force.
• SEC (Series elastic component): Stores and returns elastic energy, primarily through tendons.
• PEC (Parallel elastic component): Passive structures, such as connective tissue, that provide resistance when the muscle is stretched.

Neurophysiological model of plyometric exercise

This model explains plyometric power through the stretch reflex, which is triggered by:

• Muscle spindles, sensing the rate and magnitude of muscle stretch.

• Fast stretch = more spindle activation = greater reflexive muscle activity.

Potentiation is the enhanced force output caused by this reflex if the movement transitions quickly from stretch to contraction.

If the time between eccentric and concentric actions is too long, the reflex effect is lost.

Stretch-shortening cycle (SSC)

The SSC enhances force production by combining stored elastic energy (from the series elastic component) and reflex activation (via the stretch reflex). It consists of three phases:

Shorter amortization = greater force output. If it’s too long, the stored energy dissipates and the reflex response is lost.

Plyometric program design

Plyometric training follows similar principles to resistance training, with attention to:

• Mode (e.g., jumps in place, depth jumps, bounds)

• Intensity (affected by speed, height, body weight, contact type)

• Frequency (typically 1–3 sessions/week depending on experience and sport)

• Recovery (48–72 hours between sessions; 2–3 minutes between sets)

• Volume (measured in ground contacts)

• Program length (usually 6–10 weeks)

• Progression (start low, build intensity and volume gradually)

Warm-up and implementation

Warm-up should include dynamic, low-intensity movements. For example:

• Marching, jogging, skipping, footwork, and lunging

Steps to implement plyometric training:

1. Evaluate the athlete.

2. Establish sport-specific goals.

3. Assign program variables (intensity, volume, frequency).

4. Teach technique.

5. Progress the program safely.

Age considerations

• Adolescents can perform plyometrics if supervised and developmentally ready.

• Avoid depth and high-intensity jumps for young athletes with open growth plates.

• Emphasize landing mechanics to reduce injury risk (e.g., prevent valgus knee collapse).

Proper landing cues

• Knees aligned over toes.

• Shoulders over knees (center of gravity).

Masters athletes

When designing plyometric programs for masters athletes, consider:

• Lower volume and intensity

• Longer recovery between sessions (3–4 days)

• Avoiding depth jumps and single-leg drills if there’s a history of joint degeneration or surgery

• Prioritizing proper technique, feedback, and recovery

Integrating plyometrics with other training

Plyometric + resistance training:

• Combine lower body resistance with upper body plyos and vice versa

• Avoid high-intensity resistance and plyos on the same day unless using complex training (e.g., squat then jump)

Plyometric + aerobic training:

• Perform plyometrics before aerobic training to preserve power output

Sample schedule:

Safety considerations

To minimize injury risk:

• Use a structured warm-up and progression

• Monitor fatigue and soreness

• Teach proper jumping and landing technique (knees over toes, no valgus collapse)

Pre-training evaluation of the athlete

Key readiness factors include:

• Technique: Proper landing and jumping mechanics

• Strength: Lower body strength of 1.5x body weight recommended for depth jumps

• Balance: E.g., 30-sec single-leg hold or squat

• Body weight: >220 lbs should avoid depth jumps from >18 inches

Equipment and facility recommendations

• Landing surface: Grass, rubber mats, or suspended floors preferred

• Training area: Requires ~30m for bounding, 3–4m ceiling for depth jumps

• Boxes: Height 6–42", with nonslip top and solid construction

Depth jumping guidelines

• Recommended box height: 16–42" (40–107 cm)

• 220 lbs: Use 18" or less

• Avoid excessive box height which lengthens amortization and reduces stretch reflex efficiency