• Introduction
  • The basics of the stretch-shortening cycle
  • A deeper look into stretch-shortening cycle mechanics
  • Exercises that utilize the stretch-shortening cycle
  • Final thoughts
  • Sources
  • Amortization phase: the transition phase between the concentric and eccentric muscle contraction.
  • Concentric muscle movement: muscle contracts and shortens to produce movement.
  • Cross-bridge: the attachment of myosin and actin within the muscle cell to produce a contraction.
  • Golgi tendon organ: located in the tendons, a mechanism that prevents producing too much tension on muscle or joint.
  • Eccentric muscle contraction: muscle lengthens while contracting.
  • Motor unit: a motor neuron and all muscle fibers innervated by it.
  • Muscle spindles: sense how fast and how much the length of a muscle is lengthened or shortened.
  • Proprioceptors: sensory receptors that measure changes in the length, tension and joint angles.
  • Rate coding: the frequency with which the muscle fibers are stimulated by their motor neuron.

Introduction

Stretch-shortening cycle (SSC) is a muscle action where an active muscle stretch is immediately followed by an active muscle shortening. This phenomenon also produces far more force than a regular contraction. One example of this is a countermovement jump which produces more force than a squat jump.

The theory behind stretch-shortening cycle is that your muscles and tendons are able to store elastic energy in the pre-stretch phase of the movement. This potential is then released when the muscle is shortened. In a way, it makes your muscles and tendons act like a stretched rubber band or a spring. Thus, generating more powerful movements.

The stretch-shortening cycle is not limited to a specific muscle group or activity. In fact, it provides efficiency in nearly all activities and everyday functions that humans do. Walking, running, jumping, and changing directions are all good examples of our natural ability to use the stretch-shortening cycle. 

This post explains the basics of the stretch-shortening cycle, and why it is such an essential part of athletic performance. 

The basics of the stretch-shortening cycle

The stretch-shortening cycle is a muscle action comprised of three phases; the eccentric phase, the amortization phase, and the concentric phase.

  • Eccentric phase: The muscle lengthening phase of a movement, also known as a pre-stretch phase. For example, the lengthening of the quadriceps muscles during the lowering phase of a squat.
  • Amortization phase: Also known as time to rebound. It is the transition period between eccentric and concentric contraction, where the tendon is loaded. For example, the short motionless moment between the lowering and lifting phases of a squat. 
  • Concentric phase: Unleashing the stored energy by contracting the muscles lengthened in the eccentric phase. For example, extending the legs during the lifting phase of a squat. 

The body can only produce additional power when the amortization period is relatively short (a few hundredths of a second). This time allows the elastic component and the stretch reflex to store additional force to the relative strength of the muscle. When the stretched muscle returns to its natural state, it recoils with significant force. The more force is applied to the tendon, the more force it generates as it rebounds (rate of loading). 

Although tendons have elastic properties, they cannot voluntarily contract. Therefore it is up to the muscles to contract during the eccentric and amortization phases and load the tendon. As the tendon lengthens and stores elastic energy, it can be released during the concentric phase. This can produce far more force than movements that do not utilize the pre-stretch phase. 

Share this post

The Stretch-Shortening Cycle

Occurs when a muscle is actively stretched before contractingCan be improved via plyometric trainingEssential for athletic performanceIncreases force productionUtilizes elastic energy

A deeper look into stretch-shortening cycle mechanics

The exact underlying mechanisms of the stretch-shortening cycle are still somewhat unclear. The aforementioned storage and utilization of elastic energy is the most widely considered reason for improved force production. However, it is likely to work in tandem with stretch reflexes and the active state (muscle activity) of the muscles.

Proprioceptors (muscle spindles, Golgi tendon organs, mechanoreceptors located in joint capsules and ligaments) are sensory receptors that measure changes in the length, tension and joint angles. When a muscle is rapidly stretched, muscle spindles send a reflex signal to the spinal cord. This causes a muscle contraction to prevent injuries caused by overstretching. This is thought to increase recruitment of more motor units or/and increase rate coding (the frequency with which the muscle fibers are stimulated by their motor neuron). 

Golgi tendon organs are located near where tendons and muscles intersect. They sense changes in tension in the tendon. When the tension on the tendon becomes too great, Golgi tendon organs send a reflex response to inhibit muscle contraction and excite muscle contraction of the opposite side of the joint (agonist). Because Golgi tendon organs are stretch-reflex inhibitors, they can reduce muscle stiffness during intense exercises. Plyometric training has proven to increase muscle stiffness and pre-activation, making it a valuable training tool to increase power. 

The active state of muscles refer to the force production phase before concentric movement. During the stretch-shortening cycle, the longer eccentric and amortization phase allow for more cross-bridges (attachment of actin and myosin filaments to produce contraction) to be formed. Thus, producing more force during the concentric phase. This results in the performance enhancements associated with the stretch-shortening cycle. 

Exercises that utilize the stretch-shortening cycle

The stretch-shortening cycle is used in all dynamic movements. However, plyometric training is designed for maximal effort of the stretch-shortening cycle. More importantly, it specifically focuses on training the time between eccentric and concentric phases.

Plyometric training refers to explosive movements such jumps and bounds to minimize the amortization phase of a given movement. Thus, enhancing the ability of muscle to generate power. Consistent plyometric training has proven to improve the way elastic components (muscle membranes and tendons) and muscle contractile units (muscle fibers) work together. It also improves the reactive ability of your neuromuscular system, allowing you to recruit more motor units at a faster rate. This leads to performance enhancements in situations that require explosive muscle contractions.

Plyometric training is considered a very advanced training method due to how strenuous it is for muscles and joints. However, it is also considered one of the most effective training methods to increase power and explosiveness. Plyometrics has even been called the link between strength and speed training.

Stretch-shortening cycle produces more force - but its mechanics are still relatively unknown.

Final thoughts

Whatever the underlying mechanism is for the stretch-shortening cycle, it’s performance enhancements are well established. In fact, it has proven to produce anywhere from 10-50% more force than a concentric movement depending on the muscle group.

We also know the best way to improve the utilization and force production of the stretch-shortening cycle is via plyometric training. There is a reason why it is the method of choice for most elite-level athletes regardless of their sport. So, why not take your performance to the next level? 

What did you learn about the stretch-shortening cycle? Let us know in the comments.

Sources

  • Aeles J, Vanwanseele B. Do Stretch-Shortening Cycles Really Occur in the Medial Gastrocnemius? A Detailed Bilateral Analysis of the Muscle-Tendon Interaction During Jumping. Front Physiol. 2019 Dec 13;10:1504. doi: 10.3389/fphys.2019.01504. PMID: 31920709; PMCID: PMC6923193.
  • Bobbert MF, Gerritsen KG, Litjens MC, Van Soest AJ. Why is countermovement jump height greater than squat jump height? Med Sci Sports Exerc. 1996 Nov;28(11):1402-12. doi: 10.1097/00005768-199611000-00009. PMID: 8933491.
  • Davies G, Riemann BL, Manske R. CURRENT CONCEPTS OF PLYOMETRIC EXERCISE. Int J Sports Phys Ther. 2015 Nov;10(6):760-86. PMID: 26618058; PMCID: PMC4637913.
  • Enoka RM, Duchateau J. Rate Coding and the Control of Muscle Force. Cold Spring Harb Perspect Med. 2017 Oct 3;7(10):a029702. doi: 10.1101/cshperspect.a029702. PMID: 28348173; PMCID: PMC5629984.
  • Komi PV. Stretch-shortening cycle: a powerful model to study normal and fatigued muscle. J Biomech. 2000 Oct;33(10):1197-206. doi: 10.1016/s0021-9290(00)00064-6. PMID: 10899328.
  • Komi, P.V. (2003). Strength and power in sport. Volume III of the Encyclopaedia of Sports Medicine - An IOC Medical Commission Publication. Chapter 10 The Stretch-Shortening Cycle, p. 184-202. https://www.researchgate.net/profile/Vladimir-Zatsiorsky/publication/227559959_Biomechanics_of_Strength_and_Strength_Training/links/5fbd851c299bf104cf74720e/Biomechanics-of-Strength-and-Strength-Training.pdf#page=200
  • Malisoux L, Francaux M, Nielens H, Theisen D. Stretch-shortening cycle exercises: an effective training paradigm to enhance power output of human single muscle fibers. J Appl Physiol (1985). 2006 Mar;100(3):771-9. doi: 10.1152/japplphysiol.01027.2005. Epub 2005 Dec 1. PMID: 16322375.
  • Seiberl W, Hahn D, Power GA, Fletcher JR, Siebert T. Editorial: The Stretch-Shortening Cycle of Active Muscle and Muscle-Tendon Complex: What, Why and How It Increases Muscle Performance? Front Physiol. 2021 May 20;12:693141. doi: 10.3389/fphys.2021.693141. PMID: 34093246; PMCID: PMC8173190.
  • Tomalka A, Weidner S, Hahn D, Seiberl W, Siebert T. Cross-Bridges and Sarcomeric Non-cross-bridge Structures Contribute to Increased Work in Stretch-Shortening Cycles. Front Physiol. 2020 Jul 28;11:921. doi: 10.3389/fphys.2020.00921. PMID: 32848862; PMCID: PMC7399218.
  • Wilson JM, Flanagan EP. The role of elastic energy in activities with high force and power requirements: a brief review. J Strength Cond Res. 2008 Sep;22(5):1705-15. doi: 10.1519/JSC.0b013e31817ae4a7. PMID: 18714212.
  • Wilson GJ, Murphy AJ, Pryor JF. Musculotendinous stiffness: its relationship to eccentric, isometric, and concentric performance. J Appl Physiol (1985). 1994 Jun;76(6):2714-9. doi: 10.1152/jappl.1994.76.6.2714. PMID: 7928905.

Join our growing list of subscribers!

Stay informed about the latest in sports science and physical performance. Subscribe to our mailing list for the latest updates, posts, products and much more.

    Stretch-Shortening Cycle