For hamstring size, do both a heavy load, lower-rep range and a higher rep range.
.
1 – Heavy, Low Reps: Your hamstrings are primarily fast-twitch dominant. This may contribute to the massive hamstring development in sprint athletes. In the gym, this means you should incorporate heavy, explosive, and/or low-rep training.
.
2 – Lighter, Higher Reps: As with all muscles, a longer time under tension increases metabolic stress, a primary factor in muscle growth. Given you can create sufficient tension in a muscle, higher rep sets and a longer time under tension will help you grow any lagging muscle group, hamstrings included.
.
The Study: A study in the Journal of Strength and Conditioning Research makes a compelling argument for a mix-and-match approach. Japanese researchers had a group of male lifters do conventional hypertrophy training for six weeks before dividing them into two groups. Some did typical strength work – five sets of each exercise, using 90% of their 1RM. The others did the same thing, plus a final set of 25 to 35 reps using 40 to 50% of their 1RM. The second group made slightly better gains in size over the next four weeks. Not a huge surprise because, hey, a tack-on burnout set is hardly ever going to put your gains in the ground. But the big surprise is that the second group made bigger increases in strength as well.
.
This study suggests a compelling take-away message: Those light weight, high-rep sets following heavy weight, low-rep sets will make your hams stronger—and the stronger they get, the more effective high-rep training becomes.