- The stretch-shortening cycle is an active stretch of eccentric contraction of a muscle or muscle group and accompanying tendons (fascial interconnective tissues) followed by an immediate shortening or concentric contraction of the same muscle or muscle group and accompanying fascial tissues.
- In this process of rapid stretch and eccentric contraction, the muscles and accompanying tendons (fascial interconnective tissues) experience an increase in their elastic energy. This stored elastic energy is released resulting in an increase in force production when the eccentric contraction is followed by an immediate concentric contraction.
- It is the process that defines many plyometric moves such as the squat jump, squat tuck jump, drop jump and bounds and all strokes in tennis particularly the tennis serve.
- The stretch-shortening cycle has three phases. It includes a descent or eccentric lengthening phase, an amortization or transition phase and an ascent or concentric shortening phase. More force production is generated when there is less time in the transition or amortization phase (or an immediate transition from the eccentric to concentric phases).
- The stretch-shortening cycle is a product of stretch reflex. The muscle motor neurons and spindles respond to a quick and dynamic stretch with an involuntary concentric contraction or stretch reflex.
- Tennis strokes involve a coordinated kinetic transfer of energy utilizing whole body facial lines in a sequential chain from one body segment to another beginning with a countermovement stretching and eccentric contraction followed by a forceful shortening or concentric contraction.
- The active stretch and muscle pretension/stiffness (or loading sequence) in the first phase of the stretch-shortening cycle causes deformation/elongation of the tendons resulting in the storage of elastic energy. This elastic energy is then released in the shortening or ascent phase of the stretch-shortening cycle to generate propulsive force, angular and linear momentum and ultimately racquet head speed. The process mimics the coiling and uncoiling of a tightly wound and then released spring.
- To maximize this propulsive rotational force, look to minimize the time in the transition/amortization phase of the stretch-shortening cycle. The coiling countermovement should be slow and deliberate to build a reservoir of elastic energy. The pause or lag in the transitional amortization phase should be quick and the final concentric contraction should be explosive. To apply numbers, the timing should follow a 4-1-2 or 3-1-2 count. Look also to maintain a lively, loose arm and soft hands to allow the racquet head to accelerate through the strike zone and generate “pop” at the point of contact. The dynamic pre-stretch or coil is followed by a proximal initiation in the path of the desired direction letting the hitting lever (arm) and hand follow in sequence like an elastic pendulum. The process mimics a whipping (lag and snap) action. Negatively, a tight arm and grip on the racquet leads to deceleration and dissipation of force.
- The process requires strength but relies more heavily on fascial elasticity and pliability. Using fascial elastic recoil lessons the demands for huge muscle effort in loading and push-off. This makes movement and stroke production less strenuous and demanding on fuel consumption and more fluid and effortless. The goal is synchronized, coordinated, fluid, balanced and effortless movement utilizing pliability and the elasticity of the fascial system.
- Training to enhance the benefits of the stretch shortening cycle and your ability to store and utilize elastic energy should begin with an eccentric-focused, extended time under tension program with the goal of improving your ability to absorb force, pliability training to improve muscle and tissue suppleness and resiliency and proprioception training to improve balance, body awareness and overall biomotor abilities. The next step is to add oscillation training (fast, short range of motion pulsing repetitions) and plyometrics (maximum force and speed efforts) to your program to develop speed and power (and your ability to better utilize elastic energy to transmit force). Training in general should be compound, multi-joint based and target multiple anatomical planes of motion, movement patterns, and fascia lines.
Stretch-Shortening Cycle and Fascial Elasticity
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Ten Things Tennis 