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. Anecdotally, 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, which is 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.
A study published 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.
- Robert W. Morton, Sara Y. Oikawa, Christopher G. Wavell, Nicole Mazara, Chris McGlory, Joe Quadrilatero, Brittany L. Baechler, Steven K. Baker, Stuart M. Phillips. Neither load nor systemic hormones determine resistance training-mediated hypertrophy or strength gains in resistance-trained young men. Journal of Applied Physiology, 2016; 121 (1): 129 DOI: 10.1152/japplphysiol.00154.2016