Most people’s idea of which muscles are small and which are large is based on their outward appearance. This is like trying to determine how many square feet an apartment has by only looking at it from the street.
My research team has compiled the data from all studies we could find that measured or estimated muscle volume in various muscles of the human body. These data are in untrained individuals to exclude confounding the measures by training experience. Obviously, more trained muscles would otherwise tend to be larger than lesser trained muscles. Many studies are done on corpses, as live human subjects are often reluctant to undergo dissection. The most relevant studies are Holzbauer et al. (2007), Lube et al. (2016), Garner & Pandy (2003), Wood et al. (1989), Veeger et al. (1991), Bassett et al. (1990), Winters & Stark (1988), An et al. (1981), Veegers et al. (1997) and Cutts et al. (1991). Most measurements agree well with each other.
The data paint a much different picture than you’d probably intuitively guess.
The quads are by far the biggest muscle group in the body, both in men and women. I’ve seen many claims that the glutes are the largest muscle group in the body, but in men the quads are about twice the size of the gluteus maximus. This means quad training likely has a disproportionately large effect on energy expenditure and any systemic factors.
The next biggest muscle group is a tie between the gluteus maximus and the calves. Yes, the calves are huge. However, this may be in part because the calves in untrained individuals are already relatively more developed than other muscles, as they’re used whenever you’re on your feet. So in trained individuals the calves probably won’t rank quite as high. Plus, when including the glute medius and minimus, the glutes are much bigger, so we can say the glutes are second largest and the calves come third.
Then we have the hamstrings, before we get to the upper body, which has far smaller muscle groups than the lower body. The huge size difference between the upper and lower body muscles may explain why lower body training is often perceived as more effortful.
The delts are the largest upper body muscle group. The biceps is by far the smallest. In between those, most muscles are roughly the same size, including the traps, pecs, triceps and lats.
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