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CRI Research Review: Training for Muscle Strength vs. Size

Strength training, also known as resistance training, has countless benefits.  The primary outcomes of resistance training are increases in strength and size of the muscles we are targeting.  There are countless recommendations and guidelines for suggested schemes of the number of repetitions and sets for a strength exercise depending on the goals of your training.  For example, the ACSM recommends that low rep ranges (3-5) are the best for increasing muscle size, also known as hypertrophy.  However, a recently published paper out of McMaster University challenges this widely accepted claim (Mitchell et al. 2012).

The researchers sought to examine changes in quadriceps size and strength while using a leg extension machine.  They looked at three different groups: one performing three sets working with a light weight (30% of maximum), one performing three sets working with a heavy weight (80% of maximum), and one performing only one set at a heavy weight (80% of maximum).  All the groups exercised three times per week over a period of ten weeks.  The similarity between all groups: they had to work until complete failure – the point where the exerciser could not physically perform another repetition.  As you can imagine, the 30% group was able to perform many more repetitions than the 80% groups, but they all worked at the same intensity, meaning they had ‘maxed out.’

The findings were fascinating in that they found no difference in size increases between all three groups at the end of the ten weeks.  So, it appears that lifting a heavy weight or a lighter weight doesn’t matter for increasing muscle size, as long as you lift until failure.  The caveat: the researchers demonstrated that the groups that worked at a heavier load were stronger at the end of the study when compared to the low-weight group.  These results suggest that training for size should be done with the thought of working until muscle failure, while training for strength should be focused on training at higher workloads.  Of course, it seems that the best results would be from increasing both weight and intensity!

This information might be helpful in structuring a strength training program based on your personal goals.  Don’t forget that everyone’s body will respond differently to exercise, so keep that in mind when training yourself and especially when training others!

Cory Hofmann, M.S.

Research Project Manager
Cybex Research Institute


Mitchell CJ et al. (2012) Resistance exercise load does not determine training-mediated hypertrophic gains in young men. J Appl Physiol 113(1):71-7.


Cybex is a provider and manufacturer of premium commercial fitness equipment. Content featured in the Cybex Fitness Blog is meant to inspire healthy living and wellness and should not be taken as medical advice. For medical advice please consult a doctor.