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The Latest Evidence Proving Resistance Training is Essential for Athletes

BY Phil White

Endurance workouts don't expose your athletes to sufficient stimuli to get it all done. Let's review why resistance training is essential, share the latest evidence and suggest ways that you can help bulletproof your athletes by building strength work into their regular programming.

The go-to treatment for acute injuries has typically been the RICE protocol (rest, ice, compression and elevation). At the same time, chronic issues like runner’s knee, plantar fasciitis and Achilles tendonitis are often attributed to overtraining, which coaches believe can be remedied by reducing volume and intensity.

However, there’s a red thread woven through both issues: if bones and connective tissues aren’t subjected to high loads often enough, they will be more susceptible to acute and chronic injury. Simply put, endurance workouts don’t expose your athletes to sufficient stimuli to get the job done. Let’s review why resistance training is essential, share the latest evidence and suggest ways that you can help bulletproof your athletes by building strength work into their regular programming.

Building Stronger, Denser Bones

Your athletes might think that muscles are the only things that get developed through resistance training, but decades of scientific inquiry show that is simply not true. Exposure to the high acute loads typical of weight training, plyometrics, and other types of work that require moving load and bodyweight also changes the structure of connective tissues (which we’ll examine shortly) and bones.

During the late 19th century, German anatomist and surgeon Julius Wolff tested the hypothesis that placing a mechanical load on bones changed their function, structure and density. In 1892, he concluded that this was indeed the case, creating what has since been known as Wolff’s Law.

Oxford Reference summarized it like this: “Wolff (1836–1902) proposed that changes in the form and function of bones or changes in function alone, are followed by changes in the internal structure and shape of the bone in accordance with mathematical laws.”[1] This indicates that when a bone is exposed to sufficient external load, it begins to function better and look different externally, and then its internal composition starts to change too. Subsequent comparisons have shown that you can look at two bones that initially appear identical on the outside, but when they’re cut into, the cross-section of the healthy one exposed to greater loads is much denser — and therefore, more resilient.

In a paper published in Joint Replacement Technology, a research duo wrote, “Bone is in a constant state of flux. This remodeling process allows bone to react to its environment and stressors. According to Wolff’s law, bone is formed and strengthens along the lines of mechanical stress. The result is that bone devoid of stress, atrophies (like most tissues in the body).”[2] The second part of this statement explains why some of your athletes might be dealing with stress fractures.

Yes, running and many other weight-bearing endurance work provide stress that promotes particular adaptations in bones, but the acute load is not high enough to prompt most of the positive changes in bone structure that Wolff observed. So when an athlete’s chronic load (aka the combination of volume, intensity, density and collision) on ill-prepared bones is high enough, the skeletal system breaks down. The remedy to the problem is frequent resistance training.

Improving the Durability of Connective Tissues

The mechanical loading that regular resistance training provides doesn’t merely increase bones’ resilience, quality and density but also prompts positive changes in ligaments, tendons, fascia, cartilage, and other connective tissues. When athletes think about the benefits of their gym sessions, they usually think of their muscles becoming leaner or bigger and getting stronger and faster. These are valid points, but what they cannot see and most don’t even know is that the structures that support every part of their body will also benefit from resistance training.

Ligaments are a good example. A comprehensive review published by the National Strength and Conditioning Association via NSCA Coach stated that, “While the complete eradication of sports injuries is impossible, existing research clearly shows that the risk of ACL injury may be reduced when athletes are exposed to, and engage in, neuromuscular training programs.”[3] This is because, like bones, ligaments such as the ACL and – as we’ll see later in this article – tendons respond to the mechanical loading that resistance training provides by getting thicker, stronger, and more robust. This applied force makes an athlete less likely to get injured.

It’s worth noting that it takes tendons, ligaments and other connective tissues longer to change and adapt to the stimuli provided by resistance training than the more visible alterations that occur in muscles. The same is true of the increases in bone density and strength that result from mechanical loading, per Wolff’s Law. However, if your athletes are patient and consistent, they will create a more durable musculoskeletal system that enables them to spend less time sidelined with acute and chronic injuries.

Taming Achilles Tendonitis and Runner’s Knee

In the previous section, we examined how resistance training builds stronger tendons. Now let’s look at how it can also make meaningful changes to tendons. Two of the most common chronic issues among your training groups are likely Achilles tendonitis and patellar tendinopathy (aka runner’s knee). Both can be anything from an annoying irritant to a debilitating condition that keeps an athlete sidelined from training and competition. While resting and icing might provide some temporary relief, and mobility exercises can help feed slack into overly tightened tissues surrounding the ankle/foot complex and knee, neither issue is likely to clear up unless the tendons are strengthened and increase their load capacity.

A team of researchers from the Health and Medical Sciences department at the University of Copenhagen compared two groups of participants who had been suffering from Achilles tendonitis for at least three months. The first group performed eccentric training (abbreviated as ECC) movements. At the same time, the second did heavy, slow resistance (HSR) lifts that featured both concentric and eccentric components (i.e., contracting and lengthening muscles under load). “The results of this study show that both traditional ECC and HSR yield positive, equally good, lasting clinical results in patients with Achilles tendinopathy,” the co-authors wrote, noting improvements in tendon pain during activity, tendon swelling, tendon neovascularization, and treatment satisfaction.[4]

Some of the same exercise scientists examined the impact of heavy, slow resistance training on subjects suffering from patellar tendinopathy. Publishing their results in The American Journal of Sports Medicine, they concluded that after 12 weeks, “Heavy, slow resistance training improved the clinical outcome of patellar tendinopathy, and these improvements were associated with normalization of fibril morphology, most likely due to a production of new fibrils.”[5] In other words, the participants had less pain and more significant function after the intervention because the weight training prompted their patellar tendons to grow thicker and more durable.

Implementing Resistance Training with Your Athletes

So now that we’ve established how resistance training safeguards your clients against acute bone, ligament, and tendon injuries and can help them overcome chronic issues like Achilles tendonitis and runner’s knee, which exercises and modalities should they use? The Danish research team’s results show that eccentric variations of strength training exercises, in which athletes slowly lower the weight, are effective. These should typically be performed with lighter loads than for exercises that require evenly-paced concentric and eccentric contraction phases, as your athletes could get excessively sore due to increased time under tension. So, for example, if you had someone do a goblet squat taking five or more seconds to lower themself into the bottom position (which is exaggerating the eccentric load), you could use 50 to 65% of the weight that they’d utilize in a regularly-paced goblet squat.

In the NSCA Coach paper, the authors recommend “developing robust movement patterns in simple athletic tasks such as jumping and landing, squatting and lunging.” Power-centric movements like plyometrics are best performed at the start of a workout, as output will decline if done after strength- or endurance-focused exercises. Alternatively, your athletes can pair a slower movement, like a squat or deadlift, with a faster one, like box jumps. Adding two to three resistance training sessions into your clients’ weekly routine will help them improve strength, power, and muscular endurance and bulletproof their bones, ligaments, and tendons.


[1] Oxford Reference, “Wolff’s Law,”
Retrieved from https://www.oxfordreference.com/view/10.1093/oi/authority.20110803124341929.

[2] M Burke and S Goodman, “Failure Mechanisms in Joint Replacement,” Joint Replacement Technology, 2008,
Retrieved from https://www.sciencedirect.com/science/article/pii/B9781845692452500123.

[3] Rhodri Lloyd et al, “Reducing the Risk of ACL Injuries in American Football Players— Early Investment for Long-Term Gains,” NSCA Coach, March 2019,

[4] Rikke Beyer et al, “Heavy Slow Resistance Versus Eccentric Training as Treatment for Achilles Tendinopathy: A Randomized Controlled Trial,” The American Journal of Sports Medicine, July 2015,
Retrieved from https://pubmed.ncbi.nlm.nih.gov/26018970.

[5] Mads Kongsgaard et al, “Fibril Morphology and Tendon Mechanical Properties in Patellar Tendinopathy: Effects of Heavy Slow Resistance Training,” The American Journal of Sports Medicine, February 12, 2010,
Retrieved from https://journals.sagepub.com/doi/10.1177/0363546509350915.

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About Phil White
Phil White is an Emmy-nominated writer and the co-author of The 17 Hour Fast with Dr. Frank Merritt, Waterman 2.0 with Kelly Starrettand Unplugged with Andy Galpin and Brian Mackenzie. Learn more at www.philwhitebooks.com and follow Phil on Instagram @philwhitebooks.

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