The human body and its musculature is an amazing machine. Without muscles, we as humans wouldn’t be able to perform basic movements or transfer our bodies from place to place. Muscles are the only voluntary organ of our body: they contract and relax when we decide. Pretty amazing, isn’t it? We would be totally immobile and live in a sad state of being unable to even hold our heads up without them.
Muscles get all the glory but don’t underestimate the importance of your tendons either. Tendons are tough connective tissue that connect your muscles to your bones. You can think of your tendons as a type of “mechanical bridge.” It carries the strength generated by muscle contractions to the bones. Tendons are also stiffer than muscles.
Eccentric and Concentric Contractions and Muscle Function
When you look at muscle function more closely, you can appreciate how elegantly they function. There are two types of muscle contractions: concentric and eccentric. A concentric muscle contraction is shortening of a muscle against resistance, while an eccentric contraction is where a muscle lengthens as it holds tension to oppose movement in the opposite direction. There’s also a third type of skeletal muscle contraction called an isometric contraction where the muscle doesn’t change length. Isometric movements include planks and wall sits where the muscles don’t change length; they hold tension at a fixed length.
If you’re confused about concentric and eccentric contractions, here’s a real-life illustration. An example of a concentric contraction is the “upward” phase of a biceps curl, where you lift the weight toward your shoulders. In contrast, the downward phase where you maintain tension as you lower the weight is the eccentric portion of a biceps curl. Isotonic exercises, those where the muscles change length, have a concentric and an eccentric phase.
The Stretch-Shortening Cycle
Now that you’re clear about concentric and eccentric contractions, what is the stretch-shortening cycle? The stretch-shortening cycle is a phenomenon where a muscle generates an eccentric contraction, pauses for a second, followed by a concentric contraction. The purpose of doing the eccentric movement is to make the following concentric contraction more forceful.
How does the stretch-shortening cycle make the concentration contraction that follows more forceful? During the eccentric contraction, the muscle stores energy, which is then released during the concentric phase. Some fitness experts liken the eccentric phase of the cycle to pushing down on a spring. When you press the spring down, it creates potential energy in your muscles that is released when you let it go, as happens during the concentric phase. The harder you compress the spring, the more energy it releases when you let up.
The task of storing this potential energy falls to the muscles and tendons and is referred to as elastic energy. Makes sense, doesn’t it? When you stretch a piece of elastic and let it go, it snaps back and releases the tension you created with the stretch.
An example of the stretch-shortening cycle at work is plyometrics. For example, when you do box jumps, you store energy in your muscles and tendons, the muscle stiffens during the pause between the eccentric and concentric phases, and the stiffened muscles and tendons release that energy during the concentric phase, or jump.
It’s important during the pause between the eccentric and concentric of the stretch and shortening phase for the muscle to stiffen. Otherwise, you won’t get the full performance enhancement that the stretch-shortening cycle provides.
The Stretch-Shortening Cycle and Plyometric Training
How much performance enhancement can you get? According to the National Strength and Conditioning Association, the stretch-shortening cycle can boost jump height by up to 20% relative to doing a standard static jump. The best way to get the benefits of the stretch-shortening cycle is through plyometric training since it uses the stretch-shortening cycle to enhance performance.
The Fitness Benefits of Stretch-Shortening Cycle
It’s clear that training that emphasizes the stretch-shortening cycle, like plyometrics, enhances performance with explosive movements, like box jumps, but it also improves performance with endurance-type sports too, like running. For example, research shows the ability to take advantage of the stretch-shortening cycle improves running economy, so a runner uses less energy when they run and can run longer before fatigue.
The Bottom Line
Training in a way that taps into the stretch-shortening cycle, like plyometrics, helps build power and explosive capabilities but it can also help if you do endurance exercise. So, include plyometrics in your routine, but don’t do it when you first start out. Work on building a baseline level of strength first. As mentioned, you need a certain degree of muscle stiffness between the eccentric and concentric phases to get the full performance-enhancing benefits.
You’ll be better at harnessing the power of the plyometrics if you build up strength first too. Studies show that people who have more muscle strength are better able to store elastic energy and release it during the stretch-shortening cycle. One of the best exercises for building up the strength you need to take advantage of this type of training is the squat. You should be able to squat around 1.5 times your body weight before attempting plyometric training to ensure you have adequate muscle and tendon stiffness.
Take advantage of the stretch-shortening cycle. They’re for anyone who wants to become faster, more powerful, or improve running economy. Make them part of your routine!
References:
- Padulo J, Laffaye G, Chamari K, Concu A. Concentric and eccentric: muscle contraction or exercise?. Sports Health. 2013;5(4):306. doi:10.1177/1941738113491386.
- Physiol., 03 May 2019 | https://doi.org/10.3389/fphys.2019.00536.
- “Stretch-Shortening Cycle – NSCA.” https://www.nsca.com/education/articles/kinetic-select/stretch-shortening-cycle/.
- “Stretch-Shortening Cycle – Science for Sport.” 23 Jan. 2016, https://www.scienceforsport.com/stretch-shortening-cycle/.
- “Why You Need to Understand the Stretch-Shortening Cycle ….” 09 Jun. 2014, https://www.stack.com/a/stretch-shortening-cycle.
- “Stretch-Shortening Cycle – NSCA.” https://www.nsca.com/education/articles/kinetic-select/stretch-shortening-cycle/.
- “Stretch-Shortening Cycle – Science for Sport.” 23 Jan. 2016, https://www.scienceforsport.com/stretch-shortening-cycle/.
- “(PDF) The Stretch-Shortening Cycle – ResearchGate.” https://www.researchgate.net/publication/276957535_The_Stretch-Shortening_Cycle.
- Hobara H, Kimura K, Omuro K, Gomi K. Muraoka T, Iso S, and Kanosue K. Determinants of difference in leg stiffness between endurance- and power-trained athletes. J Biomech 41: 506–514, 2008.
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