If you want bigger, stronger hamstrings, which exercise is better, the stiff-leg deadlift (also known as the straight-leg deadlift) or the leg curl? Should you do one, the other or both?
The hamstrings are a group of muscles in the back of your thigh that flex the knee and extend the hip. You’ve got biceps femoris, semitendinosus, and semimembranosus.
Because the hamstrings cross two joints, it’s a muscle group you can train with exercises like the stiff-leg deadlift (which involves hip extension) and the leg curl (which involves knee flexion).
But which exercise works best? The stiff-leg deadlift or the leg curl?
Stiff-Leg Deadlift vs Leg Curl
To answer that question, researchers looked at muscle activity in the hamstrings during both the lying leg curl and stiff-leg deadlift [1 ].
A group of 10 resistance-trained men took part in the study. They performed both the stiff-legged deadlift and lying leg curl to muscular failure using a weight equating to their 8 repetition maximum for each exercise.
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Here’s how each exercise was done:
Lying Leg Curl
- The subject lay prone on the machine with legs extended.
- The lever arm was adjusted so that it rested just proximal to the heels.
- The subject flexed his knees until the pad stopped just short of contacting the buttocks.
- The pad was then returned to the start position.
- Subjects grasped an Olympic bar from a power rack with a pronated grip
- Hands were spaced slightly wider than shoulder width.
- The subject stepped out from the power rack and assumed a shoulder width stance.
- While maintaining a neutral spine and knees slightly flexed, the subject flexed forward at the hips until the torso was approximately parallel to the floor or as far as comfortably possible, then returned to the start position.
Muscle activity was recorded in four areas of the hamstrings:
- Upper lateral hamstrings
- Lower lateral hamstrings
- Upper medial hamstrings
- Lower medial hamstrings
Overall, the lying leg curl did hit the hamstrings harder than the stiff-leg deadlift, where the work is shared between the spinal erectors, glutes and hamstrings.
Specifically, the lying leg curl led to significantly greater activation of the lower lateral and lower medial hamstrings compared with the stiff-leg deadlift.
However, the stiff-leg deadlift still hit the hamstrings hard, particularly the upper medial hamstrings, where there was no significant difference in muscle activity compared to the lying leg curl.
Overall then, the lying leg curl did lead to more muscle activity in the hamstrings compared to the stiff-leg deadlift.
However, this doesn’t necessarily mean that the lying leg curl is better than the stiff-leg deadlift.
For one, the study used electromyography, or EMG for short, to chart electrical activity in the hamstrings during both exercises.
EMG can be useful for comparing biomechanically similar movements, such as lat pulldowns and pull-ups, or seated cable rows and barbell rows, to see how different exercises affect different muscle groups.
However, EMG doesn’t actually measure muscle growth, nor can it be relied on to predict hypertrophy after weeks and months of training .
In other words, short-term differences in muscle activation don’t necessarily translate into long-term differences in muscle size, and we can’t say for sure that the hamstrings would grow faster with leg curls than they would with the stiff-leg deadlift.
What’s more, other studies to compare a hip extension exercise (the Romanian deadlift) with the leg curl actually shows a greater level of muscle activity in the hamstrings with the former .
In summary, neither exercise is better than the other, they’re just different.
To isolate your hamstrings, go with the leg curl. To work the lower back and glutes as well as the hamstrings, choose a hip extension variant like the stiff-leg deadlift (or my personal preference, the Romanian deadlift).
If you want bigger, stronger hamstrings, a training program that involves both hip extension and knee flexion is the way to go.
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