A stretch-shorten cycle (SSC) is an active stretch of a muscle followed by an immediate shortening of that same muscle.
In biomechanical terms, this is an eccentric contraction followed by a concentric contraction. In an eccentric contraction (lengthening contraction), the muscle elongates while under tension due to an opposing force greater than the muscle can generate. Rather than working to pull a joint in the direction of the muscle contraction, the muscle acts to decelerate the joint during the movement. A concentric contraction (shortening contraction) is a type of muscle contraction in which the muscles shorten while generating force.
There is a significant performance benefit associated with muscle contractions that take place during SSCs.
This stretch-shorten cycle occurs naturally in many sport activities, including running, jumping, and all other activities in which muscles are suddenly stretched by impact or other external forces, for example when a wind-up movement is performed before a throw.
SSC plays an important role in the generation of power in an efficient golf swing, especially during the transition phase, where the body segments are changing direction sequentially and stretching the muscles and connective tissue around the joints. In the transition phase, each body segment — the hips (pelvis), then the chest (thorax), then the lead arm, and finally the hands and club — change direction from backswing to downswing in a precisely timed sequence. Each segment changes direction while the next segment in the kinetic chain is still moving back, thus stretching the muscles in an eccentric contraction and augmenting the subsequent muscle (concentric) contraction forces in the downswing.
Most exercise scientists and coaches believe that greater performance in SSC movements is due to recovery of elastic energy and increased muscle activation due to the stretch reflex — energy from an external quick stretching force is temporarily stored in the muscles and tendons, and then released through elastic recoil.
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An overview of the golf swing kinematic sequence, including a detailed analysis of the Downswing phase in Golf Swing Sequence and Timing.
Golf Swing Sequence and Timing – The Transition, which describes how the stretch-shorten cycle is used to generate power in the golf swing transition phase.
Golf Lag and the Compound Pendulum, which describes how you can use physics to generate more speed, accuracy and consistency in your golf swing, with less effort and less strain on your body.
Golf Anatomy and Kinesiology, a collection of articles describing the roles of the muscles involved in the golf swing.
Ground reaction force (GRF), which describes how driving into the ground with your legs transfers power back up through your body.
Kinetic Chain, which describes how the different parts of your body act to transfer energy from the ground to the golf ball.
