The belief that more weight built more muscle than more repetitions did is being given a second consideration–at least in older men.
Researchers studied 2 groups of 6 young men (avg age 24) and 2 groups of 6 older men (avg age 70) who followed one of two exercise programs. Half of the young and half of the older participants performed knee extensions using 3 sets of 14 repetitions then 6 sets of 14 repetitions at lower weight while the other half performed the same exercise using 3 sets of 8 repetitions then 6 sets of 8 repetitions at a higher weight. The total muscle exertion was the same regardless of the number of sets and reps because when the weight was lower, the volume (sets and reps) was higher and vice versa. Biopsies were taken of the participants’ leg muscles to look for the amount of protein synthesis (which occurs when muscle is being repaired and rebuilt after a work-out). In the two groups of young men, the amount of muscle growth was not significantly increased when higher repetions or sets were involved, i.e. the higher weight played more of a role than the number of sets/reps. This was not the case for the older men. For those two groups, increasing the number of reps had a greater effect on protein synthesis even when the weight was low. From a safety standpoint, it is often recommended that older people benefit from lower weight and higher reps but now it may also be the case for muscle growth as well.
To your health!
Kumar, V. , Atherton, P., et al. (2012). Muscle Protein Synthetic Responses to Exercise: Effects of Age, Volume, and Intensity, J. Gerontol. A Biol. Sci. Med. Sci. DOI: 1093/gerona/gls141