The stretch shortening cycle, or SSC, is a commonly used facet of exercise responsible for many of the observable phenomena in exercise. However, the degree to which it affects the efficiency of movement, especially between men and women, is not well understood. Investigators took a look into this topic in a recent article in the Journal of Strength and Conditioning Research.
SSC occurs when a muscle stores elastic energy as a muscle lengthens. This stored-up energy is then used when the muscle immediately shortens. SSC is so pervasive in exercise that we almost don’t notice it. For example, try kicking a soccer ball without drawing your leg back first. Not only is it hard to stop the natural lengthening of the kicking muscles just before the kick, but doing so also substantially reduces the power of your kick.
Although it is a pervasive phenomenon in exercise, the underlying mechanisms that govern SSC remain mysterious. For example, while we know SSC works for increasing power and efficiency, what we don’t understand very well is which mechanism gets spared when we improve SSC, and by how much. We also don’t have a good understanding of the differences in SSC between men and women.
In the newest study in this area, the researchers examined two different muscle actions – concentric and eccentric – and how they each affect the amount of work an athlete can perform. They also looked at both muscle actions combined. They used all three methods with a squat and a bench press on a group of men and women.
Everyone used the same relative weight of 85% of their one rep max. This weight was chosen because it heavily taxed the musculature and also allowed for enough repetitions to show significant differences between the muscle actions. Although the researchers tested eccentric and concentric versions of the exercises, they used 85% of the standard gym version of both lifts, which is the same as the combination of concentric and eccentric.
The researchers found that for both lifts and for both sexes, the eccentric-only test allowed for the most repetitions performed. The combined eccentric and concentric group had the second most reps, and concentric-only had the least reps performed. This result is interesting. Eccentric lifting allows for the heaviest weight, so that result was no surprise, but the fact that the combined lift yielded more reps than the concentric alone is intriguing.
Think about it: the combined lift is concentric, but with an added eccentric lift. According to the researchers, a concentric lift is seven times more costly from a metabolic standpoint than an eccentric one. So if we made up an energy scale, and an eccentric lift cost us one unit of energy on our scale, a concentric lift cost us seven units of energy. Combining the two would cost us eight units.
Here’s the unexpected part. According to these results, we can perform more reps with both muscle actions combined than with concentric alone. This is because SSC actually improves efficiency so much that not only does a combined lift cost us less than eight units of energy on our made-up scale, but it may actually cost us less than seven. Of course, metabolic cost isn’t the only issue here – otherwise we could do seven times more eccentric reps than concentric, which we can’t – but that’s still pretty cool stuff.
So there you have it. SSC is an efficiency booster, allowing for more work to be done with less energy. And by the way, the girls beat the boys on both eccentric reps and concentric reps.
1. Shawn Flanagan, et. al., “The Relationship between Muscle Action and Repetition Maximum on the Squat and Bench Press in Men and Women,” Journal of Strength and Conditioning Research, DOI: 10.1519/JSC.0000000000000337.
Photo courtesy of Becca Borawski Jenkins.