The stretch-shortening cycle (SSC), sometimes referred to as reactive strength, is your ability to utilize elastic energy. Why is this important? For the simple reason that it allows us to produce more power (more on this later).
Any movement that has an eccentric (stretching) and a concentric (shortening) contraction of musculature, has the potential to utilize the SSC – jumping, squatting, sprinting, punching, throwing… Most athletic movements in other words.
Elastic components within the muscle and the tendon are stretched when the muscle is loaded (like a rubber band) and they are then released; thus, adding more power to the movement.
To utilize stored elastic energy in the muscle, one must change very briefly from an eccentric contraction to a concentric contraction. The phase between the eccentric and concentric contraction is called the amortization phase, and this is perhaps the most crucial of them all.
For instance, in a jump, the moment your feet touch the ground, and the eccentric portion is finished, the amortization phase has begun. This duration must be kept short. Generally, the shorter you can keep this duration, the more elastic energy you can produce. This ability will enhance the tendons of the muscle to produce maximal force in the shortest amount of time possible. If this transition is not done briefly, the elastic energy will dissipate as heat, and we have thereby nullified the benefits of the SSC.
Each sport will have appropriate exercises to address the SSC in a manner specific to the musculature and movements involved in the sport. For instance, a common training method for athletes in jumping events is Plyometrics, as this mainly emphasizes the SSC of lower body musculature. A boxer or thrower may additionally introduce SSC exercises that emphasize hip rotation as well (with rotational medicine ball throws for instance).
Regardless of which training method one chooses, the major key will be a very quick transition between eccentric to concentric. For instance, when it comes to Plyometric jumps, I like to instruct my athletes to think of themselves as a spring or a bouncing ball. Because when a bouncing ball is thrown on the ground, it doesn’t pause, it bounces again immediately.
Let’s compare three different jumping exercises to really grasp the importance of the SSC when it comes to the expression of power.
- Static Squat Jump (SJ)
- Counter-movement Jump (CMJ)
- Approach Jump (AJ)
Static Squat Jump (SJ):
In the SJ, we would produce the lowest power, and consequently, jump height. Reason being that the athlete starts from a static squatting position (most commonly 90° hip flexion and 90° knee flexion) and the athlete is not allowed to utilize a preparatory dip (eccentric); therefore, no elastic energy is involved.
Counter-movement Jump (CMJ)
In the CMJ, we will produce more power, when compared to the SJ. Because now the athlete is allowed to make a preparatory eccentric dip. This rapid eccentric dip will allow the athlete to utilize the elastic energy stored in the muscle.
Approach Jump (AJ)
In the one-step approach jump, the athlete will begin the jump by a determined step. This will give us an even faster and more forceful eccentric dip than the CMJ and consequently, we will produce more power and jump height.
Sources
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