The hamstrings cross two joints, so a curl and a hinge solve different problems. Use both ideas without treating squats as hamstring training.
Biceps femoris: long head — The outer hamstring, from the sitting bone down to the outside of the knee, where you can feel its tendon.
Biceps femoris: short head — Beneath the long head, starting on the thigh bone itself — so it crosses the knee only.
Semitendinosus — On the inner side, from the sitting bone to the shin, ending in the long cord you can feel behind the inside of the knee.
Semimembranosus — Broad and flat underneath the semitendinosus, following the same inner path.
Bends the knee
Standing, pull one heel toward your backside while your other hand resists it. The back of the thigh balls up and the tendons stand out on both sides behind the knee.
Extends the hip
Lie face down and lift one straight leg a few centimetres. The back of the thigh works with the knee never bending at all — the same muscles, doing a job at the other end.
Slows a straightening knee
Walk, and notice the moment just before each heel lands. The back of the thigh tightens to stop the shin swinging out ahead of you: the job that fast movement demands most, and where these muscles are most often hurt.
Frequently asked questions
Do squats train the hamstrings?
Barely, as a growth stimulus. They assist some squat patterns, but depth trials repeatedly find little hamstring growth even when the quadriceps and glutes respond well to the same training. The reason is anatomical: as the hip and knee both bend, the two-joint hamstrings lengthen at one end and shorten at the other. If the hamstrings are a target, they need a curl or a hinge of their own.
For hamstrings, should I do curls or hinges?
They are two joint actions of one muscle group, so the honest answer is one of each. A curl brings the heel toward the pelvis; a hinge sends the hips back and asks the hamstrings to help pull you upright. A six-week comparison of Romanian deadlift against Nordic training found similar changes in hamstring size and architecture,[2] which is a good argument that both movement families work — and none at all for treating either as a brand.
Does hip position change a leg curl?
Substantially. In a within-person trial, one leg trained seated curls with the hip flexed — hamstrings held longer — and the other trained the identical knee action lying face down. The seated leg grew more.[1] Covering a long position is worth doing, but do not read it as proof that every lengthened partial beats full range; a curl through a full range already passes through the long position.
Are Nordic curls only for athletes?
No, but the full version is genuinely hard, and falling from the knees is not a strong eccentric repetition. Use enough hand assistance that you can slow the last part of the descent, or use a slider curl, where shortening the slide shortens the lever. In the slider version, if the pelvis drops as the feet travel out, the exercise gets easier exactly where it should be getting harder.
One common mistake
• Choosing the hardest Nordic setup before being able to control the descent.
• Falling from the knees is not a strong eccentric repetition.
• Use substantial hand assistance or choose sliders.
• In hinges, the matching mistake is rounding farther after the hips have stopped moving just to lower the bag.
What's normal
A tight fullness down the back of the thigh, and — after the first sessions of curls especially — soreness a day or two later that this group is unusually prone to. A hard chair is where you notice it.
How sore is normal? →Stop if you notice
A sudden sharp or tearing pain at the back of the thigh, a pop, or strength that disappears at once, with bruising showing up over the following days. Sharp pain behind the knee or deep in the buttock, as opposed to a broad muscular pull.
These guides are general information, not medical advice. Stop for sharp or persistent pain, and consult a qualified professional before beginning any exercise program.