It’s a common question - and there’s no denying that when we bend over and touch our toes, we feel the hamstrings stretch. But does that automatically mean that performing that movement - as in a deadlift or “good mornings” - results in hamstring development?
The hamstring is a four-part muscle. Three of the four parts originate at the lower portion of the pelvis, on a boney area known as the “Ischial Tuberosity”. One small part of the hamstring originates on the surface of the Femur (thigh bone) - about three quarter of the way up.
The names of the four parts of the hamstrings are as follows:
1. Biceps Femoris long head
2. Biceps Femoris short head
The first one listed above is the largest of the four. It originates at the Ischial Tuberosity, which is on the medial (inner) side of the humerus, crosses over to the lateral (outer) side of the humerus, and attaches to the posterior / lateral area of head of the Fibula (one of the two lower leg bones), just below the knee joint.
The second one listed above originates on the upper portion of the Femur, but also attaches on the posterior / lateral area of the head of the Fibula.
The third and fourth muscles listed above both originate at the Ischial Tuberosity, and both attach on the back (posterior) side of the Tibia (at the “medial condoyle”) - the other lower leg bone.
The PRIMARY function of the hamstring (group) is knee flexion (to bend the knee). The hamstrings also assist in hip extension, which means they help push the femur backward. They also assist in rotation of the leg.
Here’s the crux of the argument: To what degree does the hamstring “assist” in hip extension? If the answer to that question is “a great deal”, then it would make sense to do straight-legged deadlifts for hamstring development. But if the answer to that question is “not very much”, then it might not make much sense - especially if that function gets worked in other ways already.
Another question worth asking is this: What constitutes a contracted hamstring?
Those are the two questions that will allow us to establish whether stiff-legged deadlifts are worth doing or not, in our quest for hamstring development.
Let’s use other bodyparts as a comparison, to see how things match up. The (long head of the) triceps muscle, like the hamstring, also crosses two joints. As such, it participates in two functions - elbow extension, and shoulder adduction (bringing the arm downward). But would we seriously consider doing pullovers as a triceps exercise? The answer is “no”, because there is a bigger, more powerful muscle (the Lats) who’s primary responsibility is to pull the arm down. Likewise, the Gluteus muscle is primarily charged with the task of hip extension, because it originates much higher on the pelvis, than does the hamstring. Therefore, hip flexion will always be more Glutes than hamstrings.
How about the biceps of the arm? It also crosses two joints - the elbow and the shoulder. This means that, although its primary function is to flex the elbow, it “assists” in shoulder abduction (moving the upper arm forward). Would we consider doing straight arm front raise as a biceps exercise? No. And - again - the reason is that there is a bigger, more well-positioned muscle who’s responsibility it is to do that: the front deltoid.
So the answer to the first question - “to what degree does the hamstring assist in hip extension?” - the answer is “not very much”, because the Glutes do the majority of the work. Yes, the hamstrings stretch when we bend forward, but could we build our triceps by doing a stretch without a contraction? Could we build any muscle, with a stretch only? Not likely.
A hamstring is not contracted until the knee is flexed - just like the biceps of the arm is not contracted until the arm is bent. While the biceps of the arm might assist in moving the upper arm forward (at the shoulder), it is not contracted until (and unless) the elbow is bent.
Can we make a muscle sore, with a weighted stretch? Yes - but that doesn’t necessarily result in muscle growth. Stiff-legged deadlifts DO work the hamstrings a little, of course. But the work is nominal, and has a “poor return on investment” - meaning that the amount of gain is not worth the amount of effort and the risk.
Risk? Yes - there are risks in doing any kind of deadlift. First of all, any kind of weighted stretch increases the chance of a muscle tear. Whether it’s heavy pectoral stretch with a pair of dumbbells, or a heavy preacher curl (at the bottom) - the riskiest part of the range of motion is always the stretch part.
In addition to the risk of a hamstring tear while doing stiff-legged deadlifts, there is certainly the risk of lower back injury. In most cases, if the upper body posture is perfect (spine arched throughout the movement), and the weight isn’t too heavy, the risk of lower back injury is relatively low. But if the spine is allowed to round at all, the risk of spinal injury goes way up. This is especially true if the person has already had lower back issues.
So when we compare the cost and reward - the investment of energy and the risk of injury, compared to a very small amount of possible gain - it seems clear that the wiser strategy would be doing only leg curls for hamstring development.
Incidentally, in my experience, I’ve gotten significantly better hamstring development by doing PRONE hamstring curls (lying on my stomach), as compared to doing them on the Seated Leg Curl Machine. Interesting - isn’t it? The Seated Leg Curl Machine clearly provides more hamstring stretch, because the body is half-way into a deadlift position when seated. Yet, despite the fact that it provides more stretch, it has resulted in LESS muscle growth than the prone leg curl - even though it doesn’t have as much stretch. I think it’s because the stretch limits the amount of weight one can use.
There is one other thing that is certainly worth mentioning - hamstrings participate in squats and leg presses, for the same reason they participate in deadlifts. All three of these movements involve hip extension. The only difference is that deadlifts involved hip extension with straight legs, and the other two involve hip extension with bent knees. So the hip extension function of the hamstrings is already being worked simply by doing squats and/or leg presses.
The bottom line is that it makes more sense to focus primarily on leg curls, with an emphasis on the prone version, rather than the seated version. I’ve been doing this for nearly 40 years; I’ve seen lots of people’s methods and results, and I’ve experimented with all sorts of exercises (including cable leg curls), and I’ve always gotten the best hamstring development (and seen the best development in others) with prone leg curls - period.