Biomechanical and Neurophysiological Factors in Exercise

Closed chain exercises involve compressive forces, whereas open chain exercises involve shearing forces.
Closed chain exercises require coordinated and sequential muscle activation patterns to control proper joint movement.
Closed chain exercises stimulate the proprioceptive system by proprioceptive feedback to initiate and control muscle activation patterns.

Percentage of body weight:
- Progress from partial to full weight-bearing.
- Add additional weight (weighted vest or belt, handheld or cuff weights, elastic resistance).
Base of support:
- Progress from wide to narrow.
- Progress from bilateral to unilateral.
- Progress from fixed on support surface to sliding on support surface.
Support surface:
- Progress from stable to unstable/moving.
- Progress from rigid to soft.
- Progress from ground level to increasing height.
Balance:
- Progress from with external support to no external support.
- Progress from eyes open to eyes closed.
Plane or direction of movement:
- Progress from uniplanar to multiplanar.
- Progress from anterior to posterior to diagonal.
- Progress from sagittal to frontal or transverse.

Plyometric training emphasizes the development of muscular power and coordination.
Plyometric exercises combine speed, strength, and functional activities.
Plyometric exercises are high-intensity, high-velocity exercises that aim to increase power (speed-strength).

Plyometric exercise refers to activities that enable muscles to reach maximal force in the shortest possible time.
Plyometric exercises involve a quick, powerful movement using a pre-stretch, or countermovement, that involves the stretch–shortening cycle (SSC).
The purpose of plyometric exercise is to increase the power of subsequent movements by using both the natural elastic components of muscle and tendon and the stretch reflex.

Mechanical model:
- Elastic energy is increased with a rapid stretch and then stored.
- When the movement is immediately followed by a concentric muscle action, the stored elastic energy is released, increasing the total force production.
- The series elastic component (SEC) acts as a spring and is lengthened, storing elastic energy.
Neurophysiological model:
- The stretch reflex is the body’s involuntary response to an external stimulus that stretches the muscles.
- Muscle spindles are proprioceptive organs that are sensitive to the rate and magnitude of a stretch.
- During plyometric exercises, the muscle spindles are stimulated by a rapid stretch, causing a reflexive muscle action.

Enhanced performance during functional activities emphasizes the ability of muscles to exert maximal force output in a minimal amount of time (rate of force production).
Quick, powerful movement involving an eccentric muscle action followed immediately by an explosive concentric contraction.
Provides the ability to train specific movement patterns in a biomechanically correct manner at a more functionally appropriate speed.

Plyometric exercises enhance the excitability, sensitivity, and reactivity of the neuromuscular system and increase the rate of force production (power), motor unit recruitment, firing frequency (rate coding), and motor unit synchronization.
All movement patterns that occur during functional activities involve a series of repetitive stretch-shortening cycles (eccentric and concentric contractions).

Exercises must be safe, done with supportive shoes, and performed on a proper training surface.
Progressive exercises with varying planes of motion, type of implements, and amplitude of movement.

Stabilization level: exercises involve little joint motion, designed to establish optimum landing mechanics, postural alignment, and reactive neuromuscular efficiency.
Strength level: exercises involve more dynamic eccentric and concentric movement through a full range of motion.
Power level: exercises involve the entire muscle action spectrum and contraction velocity spectrum during integrated functional movements, performed as fast and as explosively as possible.