exercise physiology - stretch-shortening cycle

_____ of SSC training (ie. plyometrics) has been shown to reduce this GTO inhibitory effect (disinhibition) and increase muscular pre-activity and muscle-tendon stiffness

3-4 months

Stage 3: Short response jumps

begins the true plyometric training where the SSC is used to enhance subsequent concentric performance - jumps with minimal GCT while maintaining effective landing mechanics and body control - progress from low amplitude to greater amplitude jumps and the utilization of single-leg activities

Stage 1: Jump to Box

develops basic jumping and landing abilities in a controlled environment (minimize landing forces - not as much time for gravity to act)

If changes in muscle spindles and golgi tendon organs did not alter the level of EMG amplitudes after training, what can explain the increase in SSC activity power output?

training modified the reflex control of the golgi tendon organ during the eccentric loading phase, optimizing stiffening during the "Stretch" phase of the SSC

Active state

- Period of time in which force can be developed during the eccentric and amortization phases of the SSC (ex. countermovement action of a CMJ) before any concentric contraction occurs - Greater loading (amount and time available) during eccentric and amortization phases = more cross-bridge formation = enhanced power output (within limits) - Suggests that the active state is largest contributor to the performance enhancing effects of the SSC, as it allows for a greater build-up of force prior to concentric shortening

What is the best way to enhance an athletes use of SSC?

- Plyometrics (jumping, hopping, throwing and bounding-based exercises) in combination with multiple training modalities (ie. power/ballistic training), preceded by strength training to reduce the risk of injury and increase the quality and quantity of type II fibers - The exercises should enhance rate of force development specifically within the first 0.20 seconds of force production - assists in development of active state

How do athletes develop a better SSC capacity?

- Stronger, power-based athletes have a better ability to store elastic energy via augmented stiffness - In aerobic long-distance running, higher SSC abilities have also been shown to enhance running economy - suggesting that athletes with a better SSC capacity can conserve more energy whilst running

Storage of elastic energy

- Tendons cannot be voluntarily contracted and can only remain in a state of tension. Therefore, the muscle must contract and stiffen in the pre-activity stage and remain stiff during the eccentric and amortization phases. Because the muscle is stiff and wont stretch, the isometric forces are transmitted to the tendon causing it to lengthen which in turn results in the development of stored elastic energy for the concentric phase - During the concentric or positive acceleration phase, the tendon recoils back to its original shape releasing the stored energy. The muscle is also actively engaged through concentric contraction providing additional propulsive force to the SSC and greater performance. - Elastic energy storage in tendons have a half-life of ~0.85 seconds and by 1.00 seconds, the benefits diminished by 55% - amortization phase should be as rapid as possible

Neurophysiological model

- When a muscle is forcefully lengthened, the muscle spindles engage a stretch reflex by increasing recruitment of motor units and/ or an increasing the rate coding effect to prevent over-lengthening and limit the possibility of injury - leads to an increase in concentric force and power output, o But if the movement is slow (>0.85s) the stretch reflex is turned off - The GTO's role is to inhibit the excitation of muscle spindles when the forceful lengthening of the tendon becomes too large, relieving the stiffness in the muscle and shutting it off (inhibitory stretch reflex) - inhibitors the extensor muscle and stimulate the flexor muscle

What are the benefits of SSC actions?

- the pre-stretch action increases the load applied and the rate of loading during the countermovement (loading the spring) which can increase jump height - athletes shown to jump 2-4cm higher in CMJ as compared to SJ - leads to an enhanced concentric contraction (propulsive force) - efficient usage of SSC allows for a reduction in metabolic cost of movement

Stretch-shortening cycle (SSC)

1. Initial eccentric phase or pre-stretch (countermovement) 2. Isometric transition period (amortization phase) 3. Explosive concentric contraction Ex. natural parts of movements such as running or walking (limb changing direction) or the windup movement in throwing

What are the 3 primary mechanisms proposed to explain the SSC phenomenon?

1. Storage of elastic energy 2. Neurophysiological model 3. Active state

Determinants of plyometric intensity

1. The speed of movement, the greater the speed the greater the intensity 2. The points of contact, with single-leg drills being more intense than double-leg drills 3. The amplitude of movement, with greater amplitudes ground contact forces and hence increasing intensity 4. The athlete's weight (or additional load), with the greater weight leading to higher intensities

Is the effect of SSC greatest in limbs moving the fastest or slowest?

Fastest - the shorter the time, the bigger the SSCs are and the more efficient you are as less energy is lost

Stage 2: Jump and Stick

Further develops landing technique and allows the athlete to adapt to high landing forces (eccentric loads) through learned GTO inhibition - can involve low-amplitude movements but can increase by moving to single-leg landings

Why is a progressive system of plyometric exercises important when training an untrained individual?

Have to develop the two basic plyometric "skills" (jumping and landing) first because failure to do so will limit athletic development and expose the athlete to greater injury potentials

What is the primary site for the storage of elastic energy (EE) during SSC movements?

Tendon - when it is stretched, there is a build up of stored energy, which when released causes it to rapidly contract back to its original shape *Note: small amount of elastic energy stored in Titin (molecular spring which is responsible for the passive elasticity of muscle)

What are the two proprioceptors which are used to send information to the CNS about changes in length, tension and joint angles during movements? Where are they located?

o Muscle spindles - within the muscle body o Golgi tendon organs - within the tendons

The amount of stored EE (strain or potential energy) in a tendon is proportional to....

the applied force and induced deformation (ie. the amount of force used to stretch the muscle should be equivalent to the amount of force produced in order to return it to its pre-stretched state)