By Dr. Changhyun Lim
As many of you know, lifting heavier weights is the most effective method for muscle hypertrophy. I completely agree with this. However, if you’re asking whether lifting heavy weights is the only way to induce muscle growth, my answer is clearly NO.
The practice of lifting heavier weights (70-80% of your 1 rep max or maximal effort) for muscle growth originally came from the bodybuilding community. Interestingly, this approach wasn’t based on scientific research at first, but rather on the undeniable visual proof — the massive muscle mass of bodybuilders. This was so persuasive that most exercise prescription textbooks have long recommended heavy weight lifting for hypertrophy. However, this can sometimes become a barrier to initiating exercise for the first or increase the risk of injury, especially for individuals who may be physically frail, ill, ageing, or simply uncomfortable lifting heavy weights.
Thankfully, research, including my own study, has shown that lifting lighter weights (30% 1RM) can result in similar muscle growth to higher weights, as long as the sets are performed to near failure [1-3]. In other words, whether you’re lifting heavy or light weights, muscle hypertrophy can be achieved as long as you push your muscles close to fatigue (you don’t need to reach complete failure but close to it).
So, how does this work? When you lift weights, your body recruits motor units — bundles of muscle fibres controlled by a nerve — to contract the muscle. As you continue lifting closer to fatigue, some motor units get tired, and your body has to recruit additional motor units to maintain the effort. Eventually, all available motor units (i.e., muscle fibres) are recruited [4], triggering the cellular and molecular mechanisms responsible for protein synthesis [5].
In line with this, my previous study demonstrated that lighter-weight resistance training effectively recruits type II fibres (those typically activated during higher-force contractions, such as with heavier weight lifting) [1]. This was evidenced by the increase in the cross-sectional area of both type I and II muscle fibres. Additionally, and surprisingly, lighter-weight training with higher repetitions (to reach near fatigue) showed significantly improved mitochondrial function ¾ an effect usually associated with aerobic exercise, not heavy-weight training.
This doesn’t mean there’s anything wrong with lifting heavy for muscle growth. However, it’s important to know that there are more choices available for muscle hypertrophy, such as lighter-weight training. The lighter-weight training can be safer, reduce barriers to participation, and offer similar results. Lastly, while more research is needed, lighter weight training may even provide the added bonus of improving aerobic adaptations while building muscle mass— essentially, “kill two birds with one stone.”
References
1. Lim C, Kim HJ, Morton RW, Harris R, Phillips SM, Jeong TS, et al. Resistance Exercise-induced Changes in Muscle Phenotype Are Load Dependent. Med Sci Sports Exerc. 2019;51:2578-85. doi:10.1249/MSS.0000000000002088
2. Carvalho L, Junior RM, Barreira J, Schoenfeld BJ, Orazem J, Barroso R. Muscle hypertrophy and strength gains after resistance training with different volume-matched loads: a systematic review and meta-analysis. Appl Physiol Nutr Metab. 2022;47:357-68. doi:10.1139/apnm-2021-0515
3. 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. J Strength Cond Res. 2017;31:3508-23. doi:10.1519/JSC.0000000000002200
4. Morton RW, Sonne MW, Farias Zuniga A, Mohammad IYZ, Jones A, McGlory C, et al. Muscle fibre activation is unaffected by load and repetition duration when resistance exercise is performed to task failure. J Physiol. 2019;597:4601-13. doi:10.1113/JP278056
5. Lim C, Nunes EA, Currier BS, McLeod JC, Thomas ACQ, Phillips SM. An Evidence-Based Narrative Review of Mechanisms of Resistance Exercise-Induced Human Skeletal Muscle Hypertrophy. Med Sci Sports Exerc. 2022;54:1546-59. doi:10.1249/MSS.0000000000002929