Why Bodybuilders Use Higher Reps (It Has Nothing to Do With Muscle Growth)

Your muscles respond to tension, and they respond fast. Within the first few weeks of a new training program, you can see measurable strength improvements, not because you have built new tissue yet, but because your nervous system is learning to recruit more muscle fibers more efficiently. The muscle tissue itself starts adding size not long after that. The whole system adapts quickly, and that is what makes resistance training so effective.

But there is another structure involved that barely gets mentioned, and it adapts on a completely different timeline.

Tendons are the connective tissue that anchor your muscles to your bones, and they transfer every pound of force your muscles generate into actual movement. When you curl a barbell, your bicep contracts, and the tendon pulls on the bone. The tendon is not passive in that equation. It has to absorb load, store energy, and transmit force repeatedly across your entire training career, which means it needs to be stiff and resilient enough to handle whatever your muscles can produce.

The problem is that tendons do not adapt as fast as muscles do.

A 2010 study by Kubo and colleagues tracked changes in both muscle strength and tendon stiffness over a training program and found that muscle strength improvements showed up within about two months, but tendon stiffness did not change significantly until after that same two-month window. The muscle pulls harder before the tendon is ready to match it. That gap is not theoretical. It is a measurable, documented mismatch between two tissues that are supposed to work together.

Researchers call what happens next something called tendinopathy, which is a degradation of tendon tissue that occurs when the load being transferred through the tendon consistently exceeds what the tendon can handle without breakdown. It is not an acute snap or a one-time failure. It develops slowly, through accumulated overuse, and it tends to show up in the places where muscles are strongest relative to their tendons, which is exactly where heavy, progressive training targets.

A 2017 paper by Mersmann and colleagues put it directly: rapid muscle strength gains without corresponding tendon stiffness increases create elevated tendon strain and raise tendinopathy risk. The tendon is being asked to handle forces it has not yet been conditioned to manage.

Now here is where the rep range conversation actually starts.

A meta-analysis by Schoenfeld and colleagues looked at 21 studies comparing low-load training to high-load training and found that muscle hypertrophy was virtually identical between conditions as long as sets were pushed close to failure. A second network meta-analysis by Lopez and colleagues, covering 28 studies and 747 adults, confirmed the same thing: no meaningful difference in muscle growth between low, moderate, and high loads when training effort was matched. The rep range is not the driver of growth. Proximity to failure is.

So if your muscles grow the same way whether you are doing sets of 6 or sets of 15, the question of which rep range to choose becomes a question about something else entirely. It becomes a question about what you are doing to the structures your muscles are attached to.

Heavy loads generate more absolute force through the tendon on every single rep. Moderate loads generate less force per rep, which means the tendon is under less strain per repetition even when total training volume is matched. This is why a bodybuilder doing 3 sets of 15 at 60 percent of their max is building the same amount of muscle as someone doing 3 sets of 6 at 85 percent, but the tendon stress profile across those sets is not the same.

The injury data makes this visible in a way that is hard to ignore. A 2017 epidemiological review by Keogh and Winwood found that bodybuilders sustain roughly 0.24 to 1.0 injuries per 1,000 hours of training. Powerlifters, who train predominantly in low rep ranges with near-maximal loads, come in at 1.0 to 4.4 per 1,000 hours. Strongman athletes, who combine maximal loads with odd objects and less predictable mechanics, are at 4.5 to 6.1 per 1,000 hours. That is not a small difference. At the upper ends of those ranges, strongman athletes are getting hurt at more than 20 times the rate of bodybuilders.

Bodybuilders did not arrive at higher rep ranges because some researcher told them to. They arrived there through decades of trial and accumulated experience, and the injury data is the retrospective confirmation of what that culture figured out through practice.

The practical application of this follows a simple structure. Compound movements that move a lot of weight through a lot of range of motion, your squats and deadlifts and presses, can sit in that 6 to 10 rep range where the load is meaningful but not maximized. Accessory work that targets specific muscles with less systemic stress fits well in the 10 to 15 range. Anything that involves a joint under repeated strain or a structure that has historically been vulnerable for you, lateral raises, cable work, flyes, can be pushed further into the 15 to 25 range where load is light and cumulative tendon stress stays low. You push close to failure across all of it, because that is the actual signal your muscles respond to.

The insight underneath all of this is not that heavy training is bad. It is that the body is not one system. Your muscles and your tendons are running on different adaptation clocks, and when you treat them as though they are the same, you end up training your muscles beyond what your connective tissue is ready to support. The people who are still training hard at 60 and 70 are not the ones who lifted the heaviest in their 30s. They are the ones who understood that training is not a single event but a compounding process across decades, and that the bottleneck has almost never been muscle growth. It has always been staying healthy long enough to keep going.

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References

1. Schoenfeld BJ, Grgic J, Ogborn D, Krieger JW. Strength and hypertrophy adaptations between low- vs. high-load resistance training: a systematic review and meta-analysis. Journal of Strength and Conditioning Research. 2017;3112:3508-3523. Finding: From 21 studies, muscle hypertrophy was similar between low-load and high-load conditions. Source
2. Lopez P, Radaelli R, Taaffe DR, et al. Resistance training load effects on muscle hypertrophy and strength gain: systematic review and network meta-analysis. Medicine and Science in Sports and Exercise. 2021;536:1206-1216. Finding: No differences in muscle hypertrophy between low, moderate, and high loads when training to volitional failure 28 studies, 747 adults. Source
3. Kubo K, Ikebukuro T, Yata H, et al. Time course of changes in muscle and tendon properties during strength training and detraining. Journal of Strength and Conditioning Research. 2010;242:322-331. Finding: Muscle strength gains appeared within 2 months, but tendon stiffness did not change significantly until 2+ months. Source
4. Mersmann F, Bohm S, Arampatzis A. Imbalances in the development of muscle and tendon as risk factor for tendinopathies in youth athletes. Frontiers in Physiology. 2017;8:987. Finding: Rapid muscle strength gains without corresponding tendon stiffness increases create elevated tendon strain and tendinopathy risk. Source
5. Keogh JWL, Winwood PW. The epidemiology of injuries across the weight-training sports. Sports Medicine. 2017;473:479-501. Finding: Bodybuilding injury rate 0.24-1.0 per 1000 hours. Powerlifting 1.0-4.4 per 1000 hours. Strongman 4.5-6.1 per 1000 hours. Source

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