How to Build Bigger Hamstrings: Train Both Functions
How to build bigger hamstrings: train both jobs — hip extension and knee flexion. Best hamstring exercises, rep ranges, and a leg curl vs RDL breakdown.
To build bigger hamstrings, you have to train both of their jobs: hip extension with hip-hinge movements like Romanian deadlifts, and knee flexion with leg curls. Most leg routines only hammer one of these — usually squats plus a token set of curls — which leaves half the muscle undertrained and a lot of size on the table.
Here's the anatomy, the exercises, and the rep ranges that actually grow the back of your thighs.
Hamstring anatomy and its two separate functions
The hamstrings (posterior thighs) are a group of three muscles: the biceps femoris (with a long and a short head), the semitendinosus, and the semimembranosus. Together they make up most of the mass on the back of your upper leg.
What makes them tricky to train is that they perform two distinct movements:
Hip extension — driving your thigh backward, like standing up out of a hinge or a deadlift lockout.
Knee flexion — bending your knee, like curling your heel toward your butt.
Most of the hamstrings cross both the hip and the knee, so they contribute to both actions. The important exception is the short head of the biceps femoris, which only crosses the knee — meaning it does knee flexion and nothing else. Train only hip hinges and that head barely gets stimulated.
This is the core reason a "build bigger hamstrings" program needs two categories of movement, not one. Train both functions and you cover the whole muscle group. Train only one and you cap your growth.
Hip-hinge movements for the long head and overall mass
Hip-hinge exercises are the foundation of any serious hamstring workout for mass. They load the hamstrings hard during hip extension and stretch the upper, two-joint portion of the muscle under heavy resistance — exactly the conditions that drive hypertrophy.
The best hamstring exercises in this category:
Romanian deadlift (RDL) — the gold standard. Push your hips back, keep a soft knee, and feel a deep stretch through the hamstrings before driving the hips forward.
Stiff-leg deadlift — similar to the RDL but starting from the floor each rep, for an even bigger range of motion.
Conventional and trap-bar deadlift — heavier and more systemic; great for overall posterior-chain strength, though they share load with the glutes and back.
Good mornings and 45-degree back extensions — excellent stretch-biased accessories that let you load the hamstrings without taxing your grip or lower back as much.
Form cues that matter: hinge at the hip rather than rounding the spine, keep the bar (or load) close to your legs, and chase the stretch at the bottom rather than how much you can lockout-squeeze at the top. The eccentric — lowering under control — is where most of the growth stimulus lives.
Knee-flexion (curl) work and why it isn't optional
If hinges were enough, everyone who deadlifts would have huge hamstrings. They don't, because hinges skip knee flexion almost entirely — and the short head of the biceps femoris never gets the message.
Leg curls fix that. They directly train knee flexion and bias the lower hamstrings near the knee, rounding out the muscle's shape and completeness. This is the half of the equation lifters most often neglect, and adding it is frequently the single fastest way to grow hamstrings that have stalled.
Your main curl options:
Seated leg curl — performed on a leg curl machine with your hips bent, which keeps the hamstrings in a more stretched position throughout the set. Research comparing seated and lying curls suggests the seated variation tends to produce greater growth, likely thanks to that lengthened position.
Lying leg curl — still effective and a great second curl variation for volume.
Nordic hamstring curl — a brutal bodyweight knee-flexion exercise with a huge eccentric component. Outstanding for both size and hamstring-strain resistance, though you'll likely need to assist the lowering at first.
You don't have to choose between seated and lying — rotating both across the week is a perfectly good way to accumulate knee-flexion volume.
Leg curl vs RDL: how to decide
The leg curl vs RDL question is the wrong frame — you need both because they train different functions. But for emphasis:
Hamstrings looking flat up near the glutes? Prioritize RDLs and hinges.
Hamstrings lacking thickness near the knee, or a visibly weak "lower hamstring"? Add curl volume.
The stretched position and eccentric control for growth
A recurring theme in modern hypertrophy research is that training a muscle at long (stretched) lengths tends to produce more growth than training it short. The hamstrings respond especially well to this.
Two practical takeaways:
Pick stretch-biased variations. The RDL's deep bottom position and the seated leg curl's hip-flexed setup both load the hamstrings while they're long. That's a feature, not a coincidence — lean into it.
Own the eccentric. Lower under control on every rep, take 2-3 seconds on the way down, and resist the urge to bounce. The Nordic curl is the extreme version of this principle, and it's one of the most effective hamstring builders precisely because it forces a slow, loaded lengthening.
Don't shorten your range to add weight. A controlled rep through a full stretch beats a heavier rep cut short every time.
Volume, rep ranges, and progression to build bigger hamstrings
Here's how to put it together when you want to grow hamstrings:
Weekly volume: about 10-20 hard sets, split across hinges and curls and spread over two-plus sessions. Start lower, add sets as recovery allows.
Rep ranges: heavier hinges sit nicely in the 5-10 range; curls and stretch-biased accessories do well at 8-15+, where you can really feel the target muscle. Both heavy and moderate loads grow the hamstrings, so use a mix.
Progression: apply progressive overload — add a little weight, a rep, or a set over time. The same RDL and curl weights you used three months ago won't keep building new tissue.
Recovery: the hamstrings handle a lot of stretch and eccentric load, so respect soreness early in a new program, prioritize sleep, and ramp volume gradually.
Tracking each lift's top sets is what turns this into actual growth. A training app like Styrki logs your hamstring exercises, tracks personal bests on your RDLs and curls, and adapts your plan as you recover and get stronger — so you can see overload happening instead of guessing.
Balancing quads and hamstrings for healthy, resilient legs
Bigger hamstrings aren't just an aesthetic goal — the hamstring-to-quad strength relationship matters for knee health and sprint performance. Many lifters are heavily quad-dominant because squats and leg presses crowd out direct posterior-chain work, and that imbalance is associated with a higher hamstring-strain risk.
Balancing your training — pairing your squats and presses with dedicated hip-hinge and knee-flexion work — builds legs that look complete from every angle and hold up under load. Strong, well-developed hamstrings stabilize the knee, support faster sprinting, and protect you from the pulls that sideline so many athletes.
Frequently asked questions
What is the single best exercise for bigger hamstrings? There isn't one — the hamstrings do two separate jobs, so you need at least two movements. A hip-hinge like the Romanian deadlift builds the upper hamstrings under stretch and trains hip extension, while a leg curl trains knee flexion and the short head of the biceps femoris, which hinges barely touch. If you can only pick two exercises, choose one of each: an RDL and a seated leg curl.
Leg curl vs RDL — which one should I prioritize? Do both, because they train different functions. The RDL trains hip extension and emphasizes the upper and mid hamstrings under a deep stretch; the leg curl trains knee flexion and the lower hamstrings plus the short head of the biceps femoris. If your hamstrings lag specifically near the knee, add volume to curls. If they're flat up near the glutes, prioritize hinges. Most lifters under-train curls, so adding 3-4 hard sets per week is usually the fastest fix.
How many sets per week do hamstrings need to grow? Roughly 10-20 hard sets per week works for most intermediate lifters, split across hip-hinge and knee-flexion movements and spread over two or more sessions. Start near the lower end, add a set or two per week when recovery allows, and only push toward 20 once 12-14 sets stop driving progress. Quality and a full stretch matter more than chasing a set count.
Why are my hamstrings not growing even though I squat and deadlift? Squats are quad-dominant and conventional deadlifts share load with the back and glutes, so neither fully overloads the hamstrings — and neither trains knee flexion at all. The short head of the biceps femoris only crosses the knee, so it gets almost nothing from hinging. Add direct leg curls and a stretch-focused hinge like the RDL, train them through a full range, and progress the load over time.
Start training both functions
Bigger hamstrings come from covering both jobs — hinge for hip extension, curl for knee flexion — and overloading them consistently. Start free on Styrki to plan your sessions, track every set, and watch your hamstring lifts climb.