Capacity Discrepancy happens when athletes transition to running from non-weight-bearing sports like cycling. This article shows how strength and mobility training can help prevent injuries and support healthy development.
By Molly Schmelzle, CTS Expert Coach
Capacity Discrepancy can occur when endurance athletes from other sports, especially non weight-bearing sports like cycling and swimming, take up running. Their aerobic fitness is very good, but their bodies’ structures can’t keep up with the mechanical loading when they try training with the volume and intensity they’re accustomed to from other disciplines. Similarly, seasoned ultrarunners may encounter the same discrepancy if they dramatically increase volume and/or intensity or return from a hiatus. And aging runners or runners who only run may be at greater risk for capacity discrepancy.
Ideally, you want to address the body’s capacity to absorb load in a constructive and mindful manner by respecting the biology of the musculoskeletal system and the physiology of the cardiovascular system.
Just because an athlete is fit doesn’t mean they have the tissue strength or inherent resiliency – herein tissue capacity – to withstand the high force demands of running. The panoply of musculoskeletal tissue needs to be built concurrently with a thoughtful running practice and a variety of strength training modalities – not just miles and speed on repeat.
Surely, you know a runner with a strong aerobic engine who is always sidelined with muscle strains, tendonitis, fasciitis, or even stress fractures. Running can be hard on the body compared to other endurance activities. Many runners think running builds a strong body and that running more improves tissue tolerance. Just as volume is great to a point, specificity is also great to a point. Physical Therapist and Biomechanical Specialist Jay Dicharry writes, “Running may indeed develop a bomber cardiovascular system and supreme fitness, but it does fall short on building strong body parts” (2024). Demands are high in running and ultrarunning. Ground reaction forces can range from 1.8 to 2.6 times body weight (Michaud 2021). The mechanical fatigue of running can be far greater than other endurance sports and further compounded by speed, surface, terrain, and footwear.
At a high level, we understand that the human body’s structural design should align with functional demands (Weibel et al. 1991). Exercise Physiologist Dr. Stephen Seiler summarizes this concept of symmorphosis as an elegant connection between the adaptations at the cardiovascular level and the adaptations at the peripheral level. No system in the body is over-developed because adaptation to exercise demands will hit all steps of function and structure. The result is a natural symmetry that progresses as part of the endurance training process. However, changes in activities or training modalities can lead to asymmetry that disrupts this symmorphosis. The body’s structural elements must match the aerobic development process. To accomplish that, we must account for the unique loading demands and healing requirements of tissues (muscles, tendons, bone, fascia, and ligaments), all of which adapt and recovery at different rates.
Athletes must develop adequate capacity – the ability to handle load through movement, exercise, and/or postural positions – within body tissues. This means tissues must be loaded intelligently so they can adapt. When loading increases in a reasonable and planned manner, the tissue will grow stronger to resist that load. In the oft-witnessed examples above, problems arise when an athlete’s musculoskeletal system is either under-developed or under-prepared. Importantly, there may also be underlying biomechanical issues occurring such as overstriding, poor hip mobility, and weak calf muscles that can’t keep pace with the mechanical loading of running.
Capacity discrepancy is a multifactorial issue and must be viewed through the lenses of tissue type, nutrition, age, recovery, sleep, and injury history. Dicharry also importantly notes, that running itself stops short of developing the ability to produce the force needed for speed and running economy, and as strength naturally declines with age, endurance training alone won’t be sufficient to develop all the skills you need to run. No runner wants to hear this, but continuing to run without adding other exercises will unfortunately lead to a loss of athleticism.
Strength and mobility training are fundamental to tissue health and enabling musculoskeletal development to stay on pace with aerobic development. As mentioned above the spectrum of tissues – muscles, bones, tendons – respond, recover, and adapt to loads differently. Therefore, loading strategies should include plyometric and isometric exercises alongside with work targeting pure strength gains. Routinely performing multi-joint compound exercises with weight is a great way to load to the musculoskeletal system. For a great article with focused information on strength training for ultra-runners, read this from my colleague Sarah Scozzaro:
Mobility training is a hot topic in the fitness sphere because it inspires movement and helps maintain joint range of motion. Like so many things, mobility diminishes if you don’t use it or you’re not challenging yourself. Our joints should be inherently strong, flexible, and extensible around joint articulations. Incorporating basic joint mobilizations into a strength practice builds stronger biomechanics and more resilient joint mobilizers and stabilizers.
Holistic strength training should incorporate plyometric and isometric exercises – two great ways to achieve tissue-specific adaptations. Plyometrics involve skips, jumps, bounds, and hops with rapid reactive ground contact. The heart of plyometric work trains the stretch-shortening cycle (SSC), which is a spring-like process whereby elastic energy is stored and then returned to produce more force and to move faster. At a base level, plyometrics enhance muscle-tendon efficiency, tendon stiffness, and motor control.
Isometric exercises can reduce injury risk by increasing time-under-tension and the mind-muscle connection. During isometric exercises, muscles contract while muscle length and joint angles remain constant, generating intramuscular force and tension at the tendon muscle junction. Time-under-tension increases strength, reduces fatigue, and promotes joint and muscle stability. Common isometrics are plank variations and wall sits.
Foot health is crucial for increasing the integrity of the musculoskeletal system. Feet are our foundation. They need to be strong and engaged to stabilize our core and manage the extreme mechanical loading of running. The human foot has 26 bones, 33 joints, and over 100 muscles, tendons, and ligaments (Naboso 2021). How can you improve the strength and integrity of your feet? Spend more time barefoot, albeit conservatively. This isn’t a recommendation to run barefoot or a move back to minimally padded shoes, but walking around your house and yard barefoot more often is a good place to start.
It may be helpful to add more hiking and/or walking with a weighted vest to add load to the musculoskeletal system. This is important, because you’re using loaded walking to increase musculoskeletal load, not to stress your aerobic system. This is why we don’t recommend running with packs heavier than what you’ll carry in an ultramarathon; we don’t want to increase to the already-high impact forces from running. If you don’t like loaded walking/hiking, adding in weekly hill running workout will not only elicit a strength response, but will also keenly reduce overall mechanical loading on the body compared to running on terrain with little topography.
Cross training comes with a unique benefit of simply offloading from running to better absorb adaptations and to steer clear from doing too much volume. Sports like swimming and cycling lack direct mechanical loading, but they do provide multiple arrows in the quiver – aerobic maintenance, skills training, recourse for burnout, and athleticism.
Foot Health
Calf Strength
Hip Mobility
Plyometrics
Isometrics
On a running plan implementation level, it is important to have a gradually progressive training schedule. A good rule of thumb is to not do too much too fast and to balance volume, speed, frequency, and vertical accumulation. It may be wise to hire a professional coach to get started especially if you are new to ultrarunning or coming back from a previous injury.
Molly approaches coaching with a fit-for-life and hit-the-ground-running mentality, encouraging athletes to feel healthy and strong for event performance as well as quality of life and longevity.
In addition to the CTS Coaching College, Molly is a UESCA-Certified Ultrarunning Coach, Certified Strength and Conditioning Specialist (CSCS) with the National Strength and Conditioning Association, and holds a master’s degree from Humboldt State University. A Division 1 soccer player in college, Molly competed in cycling, triathlon, and running before focusing on trail and ultrarunning. With post-graduate specializations in strength training, biomechanics and pain-free movement, she helps athletes build resilience and durability for life as well as running events.
References:
Dicharry, J. 2024. Running Rewired: Reinvent your run for stability, strength, and speed 2nd Ed. Velo Press.
Dietz, C & B. Peterson 2012. Triphasic Training: A Systematic Approach to Elite Speed and Explosive Strength Performance.
Fast Talk Laboratories. Are your interval workouts effective? – with Dr. Stephen Seiler. Episode 267.
Michaud, Tom. 2021. Injury-Free Running 2nd Ed. Lotus / North Atlantic Books.
Naboso (2021) Three Steps to a Strong Foot to Core Connection. https://www.naboso.com/blogs/the-barefoot-advantage/three-steps-to-a-strong-foot-to-core-connection.
Weibel, E.R., R. Taylor, & H. Hoppeler. The concept of symmorphosis: A testable hypothesis of structure-function relationship. Proc. Natl. Acad. Sci. Vol 88. 1991 pp 10357-10361
