Tissues, including muscle, adapt to the stress you place on them. The same is true of tendons. A tendon is a tough cord of fibrous tissue, comprised of collagen. It connects muscle to bone and allows for movement at a joint.
Tendons are stronger than muscles but not as flexible as ligaments, the tissue that connects bones to bones. Tendons enable you to straighten your arm, bend your knee, curl your fingers and toes, and rotate your wrists and ankles. Tendons act as pulleys for muscles to contract against. They are also some of the strongest tissues in your body. Despite this, they’re also prone to injury.
As mentioned, tendons, like muscles, adapt to the stress you place on them through training and the adaptation varies with the type of training that you do. The response of tendons to strength training differs from how they respond to plyometric exercises, where you generate force quickly.
How Tendons Respond to Plyometric Training
Plyometric training, also known as jump training, is a dynamic type of training that uses explosive movements to improve power, speed, and quickness. Plyometric training emphasizes the rapid stretching and contracting of muscles to increase the power output of a given muscle group. For example, athletic coaches use plyometric training to increase the vertical jump height of athletes and to improve speed and sprinting performance.
Plyometric exercises are also helpful for increasing jumping ability in sports like volleyball, basketball, soccer, football, and track & field events like the long jump and high jump. Plyometric training boosts the power output of muscles, so you can generate force quickly, but how does it affect your tendons?
Tendons Adapt Based on the Type of Exercise Training
The way tendons adapt depends on the type of training. For example, tendons respond differently to high-intensity strength training than they do plyometric or jump training. Heavy, slow resistance training where the muscle is under sustained tension, causes tendons to stiffen.
An advantage of increasing tendon stiffness is it allows for greater force transmission. When muscle fibers contract they pull on tendons, which transmits force to the bone. Stiffer tendons allow you to exert more force with less effort because they reduce energy losses related to muscle compliance (or “stretchiness”).
In other words, when you have a stiffer tendon, your muscles have less “give” than they would if they were unconstrained by tendons. So instead of losing some of the force as it travels through your muscles and into your bones, more of it will be available for force generation.
Plus, stiffer tendons provide more stability. Although tendons stiffen in response to strength training. training, research sheds doubt on whether they hypertrophy or enlarge the way muscles do.
Plyometric Stiffens Muscles More Than Tendons
Plyometric training also boosts tendon stiffness, although to a lesser degree than strength training. Plyometrics increase the stiffness of muscles more than they boost tendon stiffness. This leads to a higher ratio of muscle-to-tendon stiffness. So, strength training increases tendon stiffness more than muscle stiffness while plyometrics increases muscle stiffness more than tendon stiffness. Some studies also show plyometric training increases the cross-sectional area of tendons.
The relative increase in tendon stiffness relative to muscle stiffness suggests that strength training isn’t ideal for certain types of exercise, like running. However, plyometric training can be because it improves how the muscle and tendon interact during the stretch-shortening cycle of plyometrics. In response to plyometric training, tendons become better at storing and releasing energy during dynamic exercises. This enhances “recoil,” during running, jumping, and bounding, explaining some of the performance advantages plyometric training offers.
Does Plyometric Training Reduce the Risk of Tendon Injury?
You might also wonder whether plyometric training lowers the risk of tendon injury. Some of the most common tendon injuries are Achilles tendon ruptures, knee injuries, and ankle sprains. These injuries occur more frequently in sports like basketball, volleyball, soccer, and tennis because they involve running and jumping repeatedly over short distances. An Achilles tendon rupture can be a career-ending injury for an athlete.
Tendons have an amazing ability to stretch, but they can only do so much before they tear or rupture. When an injury occurs, blood vessels rupture, which causes bleeding and swelling within the tendon sheath. This is known as a tendon rupture and is one of the most severe types of tendon injury.
Tendon ruptures can occur in any of the body’s tendons, including those in the foot and ankle. A ruptured tendon usually requires surgical repair by a foot surgeon unless it is minor. Minor tendon injuries may respond to physical therapy and rest but the rehab can be prolonged.
Plyometric training can improve exercise performance for certain types of exercise. It also modestly increases tendon stiffness and may boost the cross-section size of a tendon, it’s less clear whether this translates into a lower risk of tendon injury. Doing plyometrics with poor technique could even make tendon injury more likely. Still, plyometric training is an important part of rehabilitation and reconditioning after tendon injury. Plyometric exercises help restore full function after tendon injury and are an important part of rehab.
The Bottom Line
Tendons respond differently to plyometric training than slow resistance training. The former boosts muscle stiffness more than tendon stiffness and enhances the performance of the muscle-tendon complex during plyometric movements jumping and sprinting. However, it’s not clear whether plyometric training reduces the risk of tendon injury, like tendon tears or ruptures though. It’s an area that still needs more research.
References:
- Proske U, Morgan DL. Tendon stiffness: methods of measurement and significance for the control of movement. A review. J Biomech. 1987;20(1):75-82. doi: 10.1016/0021-9290(87)90269-7. PMID: 3558432.
- Buchanan CI, Marsh RL. Effects of exercise on the biomechanical, biochemical and structural properties of tendons. Comp Biochem Physiol A Mol Integr Physiol. 2002 Dec;133(4):1101-7. doi: 10.1016/s1095-6433(02)00139-3. PMID: 12485694.
- Rinoldi C, Kijeńska-Gawrońska E, Khademhosseini A, Tamayol A, Swieszkowski W. Fibrous Systems as Potential Solutions for Tendon and Ligament Repair, Healing, and Regeneration. Adv Healthc Mater. 2021 Apr;10(7):e2001305. doi: 10.1002/adhm.202001305. Epub 2021 Feb 12. PMID: 33576158; PMCID: PMC8048718.
- Kubo K, Morimoto M, Komuro T, Yata H, Tsunoda N, Kanehisa H, Fukunaga T. Effects of plyometric and weight training on muscle-tendon complex and jump performance. Med Sci Sports Exerc. 2007 Oct;39(10):1801-10. doi: 10.1249/mss.0b013e31813e630a. PMID: 17909408.
- Milgrom Y, Milgrom C, Altaras T, Globus O, Zeltzer E, Finestone AS. Achilles tendons hypertrophy in response to high loading training. Foot Ankle Int. 2014 Dec;35(12):1303-8. doi: 10.1177/1071100714550651. Epub 2014 Sep 11. PMID: 25212862.
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