The stretch shortening cycle (SSC) refers to the muscles ability to store and use elastic energy to create more powerful contractions. Most movements in exercise are isotonic muscle contractions.
This has two phases eccentric – lengthening under tension (storing elastic energy) and concentric – the muscle shortening or returning to its original state. When a muscle is stretched under tension rapidly it has a natural response to contract (resist the sudden change in length). This causes a greater force output because the muscle is using that stored elastic energy when contracting. Athletes use this technique to improve explosiveness, quickness and to exert more force when training. This is referred to as plyometric exercise.
A plyometric exercise called the box jump is an excellent example of the SSC. The hips and arms shoot back rapidly, quadriceps lengthen/hamstrings shorten, energy transfer begins, movement is reversed, hips snap forward, legs straighten, the quadriceps shorten/hamstrings lengthen, hips are fully extended, knees are flexed upward as the feet clear and land on the top of the box. The rapid loading of the hips and legs allow for a greater muscle contraction. The kettlebell two hand swing is another great example of a plyometric type exercise (very similar). The back swing (loading of the hips and legs) is rapid, and the upswing is equally explosive. The feet remain flat on the floor this time. Plyometrics and kettlebell exercises are used by power athletes and advanced fitness buffs who want superior conditioning. Novice and intermediate individuals can explore basic kettlebell and plyometric exercises as well.
The muscle contraction must be immediate or the elastic energy is lost in the form of heat. One factor affecting the SSC is the Golgi tendon organ located in the muscles tendon. Its responsibility is to detect excessive tension, pressure changes in the muscle and joints and protect them by promoting relaxation.
Regular flexibility training should be incorporated in any program (static, passive, and dynamic stretching). This will help maintain/improve joint health and function, lengthen muscle fibres, prevent injuries, and allow for more efficient athletic movements. In addition to plyometric training, this will promote even greater explosiveness and muscle power.