The seated leg curl grew the hamstrings more than the lying (prone) curl: in 20 healthy adults who trained one leg each way for 12 weeks (5 × 10 at 70% 1RM, twice a week), whole-hamstrings volume rose 14% on the seated leg against 9% on the prone leg, and both trained legs were then about equally protected from the damage of a hard eccentric bout

Maeo and colleagues asked whether training the hamstrings at a longer length, by curling with the hip flexed (seated) rather than extended (prone), grows them more, and whether either version better protects against damage from a later eccentric-only bout. The two-joint hamstrings are lengthened more when seated.

Twenty healthy adults trained one leg on a seated leg curl and the other on a prone leg curl at 70% of 1RM, 5 sets of 10, twice a week for 12 weeks, with hamstring volume measured by MRI before and after.

Whole-hamstrings volume grew 14% on the seated leg and 9% on the prone leg; each two-joint hamstring muscle grew more seated (8-24% against 4-19%), while the one single-joint muscle grew alike (10% against 9%). Afterwards, 19 of them and 12 untrained controls did eccentric-only leg curls at 90% of 1RM.

The control legs showed much larger rises in MRI T2 and losses of 1RM than either trained leg, and the seated- and prone-trained legs did not differ at any time point. The authors conclude that seated curls build hamstring size more effectively, suggesting that long muscle lengths favour hypertrophy, while both versions reduce susceptibility to damage similarly.