Isometric strength training builds muscle, strengthens and stiffens tendons, and helps prevent injury—making it a powerful, low-skill tool for ultrarunners to train smarter.
By Molly Schmelzle, CTS Ultrarunning Coach
For a long time, runners acted like they were allergic to strength training. Thankfully, both research and running culture have embraced strength training as a positive and necessary activity. Once ultrarunners realized health and longevity are key factors for being a successful and lifelong athlete, they accepted various forms of resistance training as essential tools to achieve their goals.
Before you get exhausted at the thought of yet another exercise or activity to add to your busy schedule, it’s important to recognize you may already be doing some form of isometric exercises in your training routine. Or, you may just need to slightly shift your thinking about movement and musculoskeletal health to specifically address connective tissues (tendons, ligaments) as well as muscles.
The world of isometric strength training is expansive and nuanced. It has been around for decades and is a safe and effective way to drive strength and tissue adaptations (Barr & Smith, 2024; Natera 2025). It plays a role in everything from beginner strength programs to tendon rehabilitation, and advanced performance-based prescriptions for sport-specific athletes – including runners.
Isometrics aren’t flashy but their impacts on stability, strength, injury prevention, and tendon health are remarkable. Endurance athletes benefit from strength training but tend to gravitate to strength exercise that mimic sport-specific movement. Most ultrarunners adopt simplified strength programs focused on bilateral – some unilateral – and sagittal plane exercises with a concentric emphasis. Adding isometric exercises is a low-risk/high-reward situation. Smart isometric resistance training can enhance musculoskeletal adaptations for “faster and farther” benefits including helping runners stave off occasional tendinopathy.
The prototypical description of an isometric contraction is a static movement in which muscle length stays the same as it contracts. However, this is only partially accurate. It is more appropriately defined as a constant joint angle with a concurrent muscle contraction held under load (Dietz and Peterson 2012). Taking it a step further, as the joint angle stays the same, the muscle slowly shortens while the tendon slowly lengthens. In other words, the tendon creeps (Barr and Smith 2024: Natera 2025). The most common example of an isometric exercise is holding a wall sit or a low lunge position for 30 – 60 seconds.
To put isometrics into context we must compare them to concentric and eccentric contractions. An eccentric contraction is when the muscle produces force while lengthening and during concentric contraction the muscle produces force while shortening. Almost every real-world movement includes all three types of contractions. Think about squatting down to 90 degrees and then standing back up. Lowering is eccentric, rising is concentric. At the bottom of the squat there’s a moment: there’s a short isometric contraction after the eccentric contraction stops and before the concentric contraction begins. An isometric contraction therefore is the connection, the inflection point, between the eccentric and the concentric movements.
Explained differently, isometrics are when and how energy transfers through the musculoskeletal system. This is extremely important in running because of the stretch shortening cycle (SSC), a spring-like process whereby elastic energy is stored (in the loading phase of the stride) and then returned to increase the rate of force production during propulsive phase of the stride. Isometric exercises may look static, but they are more dynamic under the surface. This may be a reason why they can affect dynamic performance (Natera, 2025). Now you can think of an isometric as a quick hold at the bottom of an eccentric action.
There are two main types of isometric exercises:
One of the most important benefits of overcoming isometric training is that it has the highest activation level of all muscle movement – concentric or eccentric (Dietz and Peterson 2012). This means the total percentage of motor units involved with the muscle contraction is greater with an overcoming isometric, comparatively.
Overcoming isometrics activate the muscle-tendon unit and build greater tendon stiffness. Renowned physiologist and musculoskeletal researcher Dr. Keith Barr noted that during a fast isometric movement, more collagen cross-links are created, making the tendon stiffer (Barr and Smith, 2024). Why is this important? Within the musculoskeletal system, tendons store and release energy and stiffer tendons produce greater muscular force output and have an increased rate of force development (Lum and Barbosa 2019; Stone et al. 2004). This improves running economy. Furthermore, Lum and Barbosa (2019) found that force produced at the trained joint angles improved 10 degrees on either side of the contraction.
Improving running economy doesn’t always translate to improved performance but in this case, research specific to endurance runners found that isometric training increases tendon stiffness and corresponed to improved running performance (Kubo et al. 2017; Lum et al. 2023; Albracht and Arampatiz 2013). Further findings indicate that the force required to maintain a given speed was reduced, relative to the increased muscular strength after athletes assumed isometric protocols. Lum et al (2019) concluded that this led to a reduction in fatigue enabling runners to maintain a higher running speed for longer duration.
Because runners experience significant loading during regular run training, isometrics offer an opportunity to build muscle strength, postural control, tendon health, and joint stabilization without high impact forces. They are also easy to recover from and can be practiced year-round, independent of running periodization, especially leading up to competition. Isometric exercises are low impact and have decreased injury risk compared to other resistance training modalities which perfect for runners newer to strength training. However, smart holistic training would integrate isometric training in with both heavy lifting and plyometrics for more enhanced performance and health benefits.
Isometric strength exercises are often the first tool in the box to rehab tendinopathies. Specifically, isometrics are prescribed in rehab settings for improving tendon-muscle properties and promoting tendon collagen repair. Anyone who has ever suffered through tendinopathy knows that patience is fundamental, and that loading it is even more central to the return to play process. Isometrics are one of the first types of exercises prescribed to kickstart the loading and tendon rehab process. Loading a tendon with isometrics helps lay down collagen in the right direction of strain. Similarly, isometric exercises have been effective in reducing pain in athletes with patellar tendon or Achilles tendon pain (Lum and Barbosa 2019).
Isometric training is nuanced and versatile. Start simple and small. Various forms of planks and wall sits fall under the umbrella of isometric training. Try holding the bottom of squats, lunges, and bench presses for 3-5 seconds to increase the time under tension and intramuscular integrity before concentrically contracting your muscle back to the starting position. Longer positional holds like a low lunge isometric hold can be prescribed throughout a workout for stability, rehab, and injury prevention. Lastly, overcoming isometrics generally use rack systems with stop pins, but can be executed with walls, boxes, and towels that allow for a stop action against your body’s pull or push for maximum muscle recruitment.
1. Unloaded / Loaded Split Squat Isometric
3. Long Lever Hamstring-Calf Hold
4. Unloaded / Loaded Skater Squat Hold
5. Tricep Isometrics – partner
6. Spanish Squat Dynamic Hold
7. Standing Plantar Flex / Heel Raise Push
8. Isometric Mid-thigh Pull
References
Albracht, K., Arampatzis, A. (2013). Exercise-induced changes in triceps surae tendon stiffness and muscle strength affect running economy in humans. Eur J Appl Physiology 113(6) :1605-15.
Barr, K. and J. Smith. (2024) Podcast: Dr. Keith Barr on Tendon Health, Rehab and Elastic Power Performance Episode 156. https://www.just-fly-sports.com/podcast-156-keith-baar/
Dietz, C & B. Peterson (2012). Triphasic Training: A Systematic Approach to Elite Speed and Explosive Strength Performance.
Fletcher JR, Esau SP, MacIntosh BR. (2008). The effect of isometric training on muscle tendon unit stiffness of medial gastrocnemius and the economy of locomotion in highly-trained distance runners. Med Sci Sports Exercise; 40: S392.
Kubo, K., T. Ishigaki, T. Ikebukuro. (2017). Effects of plyometric and isometric training on muscle and tendon stiffness in vivo. Physiological Reports. First published: 11 August 2017 https://doi.org/10.14814/phy2.13374
Lum, D. and T.M. Barbosa. (2019). Brief Review: Effects of Isometric Strength Training on Strength and Dynamic Performance. Internation Journal of Sports Medicine; 40: 363-375.
Lum, D.; T.M. Barbosa; A.R. Aziz; and G. Balasekaran. (2023). Effects of Isometric Strength and Plyometric Training on Running Performance: A Randomized Controlled Study. Research Quarterly for Exercise and Sport. 94-1: 263-271.
Natera, Alex (2025). All isometric training is not the same: differences in the execution, prescription, and use of pushing and holding isometrics. https://www.sportsmith.co/articles/combining-plyometrics-and-isometric-training-to-improve-tendon-stiffness-and-performance/
Stone MH, Sands WA, Carlock J, Callan S, Dickie D, Daigle K, Cotton J, Smith SL, Hartman M. (2004) The importance of isometric maximum strength and peak rate of force development in sprint cycling. J Strength Cond Res; 18: 878–884
