Your Squat Is Getting Stronger. Your Hamstrings Might Not Be Growing.
UPLIFT IRON CLUBWhy a Bigger Squat Does Not Automatically Mean Bigger Hamstrings
There is nothing wrong with chasing a better squat. It is one of the most useful ways to train your legs, improve coordination under load and build a foundation for heavier work. The mistake is assuming that every muscle near your hips and thighs must be growing equally because the bar is getting heavier. The hamstrings sit on the back of the thigh, yet the squat is not necessarily their best growth assignment. An exercise can recruit a muscle without giving it the kind of sustained challenge that drives much hypertrophy.
Most hamstring muscles cross two joints: the hip and the knee. During a squat, the hip extends as you stand, but the knee extends too. Those joint movements can partly offset changes in hamstring length. Meanwhile, the quadriceps are heavily challenged by knee extension and the glutes contribute strongly at the hip. The result is an excellent lower-body compound lift that does not distribute the same growth stimulus to every part of the thigh.
Consider a controlled 10-week trial involving 17 men who trained full or half squats twice each week. Magnetic-resonance measurements showed meaningful growth in knee-extensor muscles in both groups, while total hamstring volume did not change significantly. Squat strength improved, and deeper training produced larger glute and adductor changes. That is not proof that squats never stimulate a hamstring, and a small study cannot represent every training program. It is evidence that a squat personal record and a hamstring-size increase are different claims.
Before adding exercises, audit what you already do. A leg day made from back squats, leg presses, split squats and leg extensions can be brutally difficult while remaining mostly knee-extension dominant. You may have genuinely earned stronger quads and glutes without giving knee flexion its own work. If hamstring development matters to you, the question is not whether squats count as leg training; it is whether your routine includes movements that deliberately challenge the hamstrings.
Keep your squat, especially if you enjoy it or need it for a sport. Just stop using the squat number as your only posterior-thigh progress report. A strong leg program is not a contest to see which single exercise can pretend to do everything.
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Seated Leg Curls Put the Hamstrings in a Different Position
If you have a seated leg curl machine available, it is more than a convenient finisher. A curl makes knee flexion the task: you bend your knees against a load while your hips and torso are supported. Unlike a squat, the movement does not depend on your quads driving a loaded bar upward. That isolation makes it easier to assess whether the backs of your thighs are doing useful work, instead of letting stronger neighboring muscles handle most of the challenge.
The seated posture also changes the starting length of several hamstring muscles. Because the hip is flexed, those muscles begin relatively lengthened compared with the same curl performed lying face down. In one 12-week trial, 20 adults trained one leg on a seated machine and the other on a prone machine. Both legs grew, but average whole-hamstring muscle volume increased by roughly 14% seated versus 9% prone. The difference was clearer in the hamstring muscles that span both joints than in the single-joint portion.
Those numbers are not promises. The trial used a particular population, training prescription and pair of machines; no one is entitled to a 14% gain just for choosing a seat. It also did not compare curls directly with squats, so avoid treating the separate studies as if they were a three-way tournament. What the comparison does provide is a useful reason to consider the seated version when your primary interest is hamstring size.
Set the machine carefully. Align your knees with the pivot as closely as the design allows, place the lower roller comfortably above your heels and secure the thigh pad without pinching. Keep your hips on the seat and use a range you can control. Lower the weight without dropping the stack or sliding yourself forward to shorten the movement. Two deliberate sets of 10–15 repetitions, leaving around two good repetitions in reserve, can be a sensible starting dose if curls are missing from your program.
If your gym has several seated machines, do not compare the stack numbers as though each one uses identical leverage. Choose a comfortable setup, record your performance on that machine, and work to improve the same movement over time. A slightly smaller displayed number with cleaner repetitions can be more informative than a sloppy personal record.
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Lying Leg Curls Still Earn Their Spot on Leg Day
The seated-versus-prone comparison has an obvious temptation: declare lying leg curls obsolete and march toward the only machine crowned by a percentage. That is an overreaction. The prone condition in that study still produced substantial hamstring growth. It trained knee flexion directly, challenged the muscles with measurable resistance and improved with repetition. A useful movement does not become useless when another movement outperforms it in one experiment.
In a lying leg curl, your torso rests against the machine and you bend your knees to raise the padded lever. Your hips are usually closer to an extended position than in a seated curl. That shortens the two-joint hamstrings at their hip end, which helps explain why identical knee motion need not produce identical muscle-length demands. The machine's resistance profile, adjustment positions and your actual range of motion matter too. A well-fitted prone machine may be a much better option than a seated machine that forces an uncomfortable position.
To set up, place your knees near the end of the bench and align the machine pivot with your knee joint according to its instructions. Rest the ankle roller low on the lower leg rather than painfully against the heel. Keep your pelvis stable against the pad. Curl smoothly, pause briefly if you can hold the position without shifting, and return through a controlled range. If your hips lift dramatically every repetition, the weight is probably writing checks your hamstrings cannot cash.
For most recreational lifters, consistency outranks equipment snobbery. If the lying machine is available and the seated machine always has a queue, use it. If both feel good, you can prioritize the seated version for a block and use prone curls as extra work or an alternate variation. You do not need both versions in the same session just to collect exercises.
Do pay attention to the limitation of your routine. A curl is excellent at knee flexion, but it is not the same as a loaded hip hinge. Pairing one curl with a movement such as a Romanian deadlift gives your posterior chain a broader set of tasks. The point is not to create a shrine to leg machines; it is to cover the movement you otherwise skip.
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Romanian Deadlifts Train the Hip-Hinge Job That Curls Cannot
Leg curls solve the knee-flexion gap, but that is only one part of posterior-chain training. A Romanian deadlift, or RDL, asks you to move at the hips while resisting the bar's pull on your body. Your knees remain softly bent and relatively stable as you push your hips backward. That puts the hamstrings under substantial tension while they assist hip extension. Glutes and spinal stabilizers also participate, so this is a demanding compound exercise rather than an isolated curl.
The distinction matters because the hamstrings are not one simple rope. Three major hamstring muscles act at both the hip and knee, while the short head of the biceps femoris acts at the knee only. A curl directly loads knee bending. A hinge challenges the hip-extending role of the muscles that cross the hip. Each exercise may emphasize different regions and functions, and neither should be advertised as a magic switch that activates every fiber equally.
For a basic RDL, stand tall holding a barbell or dumbbells in front of your thighs. Take a small knee bend and keep it nearly unchanged. Brace your torso, push your hips back and let the load travel close to your legs. Stop when your hip motion and hamstring tolerance run out, not when a social-media coach's bar reaches a particular centimeter mark. Rise by driving the hips forward to stand tall, without leaning backward at the top.
The familiar failure mode is turning the hinge into a strange half-squat, with knees drifting forward and the torso staying too upright. Another is rounding the lower back to steal extra range after the hips stop moving. Start lighter, move slowly enough to own the path, and increase load only while your position remains repeatable. Straps can help when grip fails before the target muscles, but they do not substitute for control.
If your week already contains heavy conventional deadlifts, consider their recovery cost before adding several hard RDL sets. Two or three focused sets of six to ten on a different day can be a reasonable example, not a universal prescription. Pair the hinge with a curl rather than piling every variation into the same workout. Train the movement, recover, repeat: that recipe is considerably less glamorous than an exercise carousel, and usually more practical.
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Build Two Balanced Leg Days, Even Without Curl Machines
There is no law requiring a separate hamstring day, an expensive machine or a dozen exercises. What matters is giving the muscle direct, challenging work that fits around the rest of your training. If your current program has no curls, resist the urge to bolt four new movements onto the end of a long session. Start with one knee-flexion pattern and, if you do not already have one, one hip hinge. Keep your squat work because it still does an excellent job for other goals.
Here is a practical two-session example for someone who already lifts regularly and wants to fill an obvious gap. Day A: squat for three working sets of five to eight, seated or prone leg curl for two sets of ten to fifteen, then your usual calf or trunk work. Day B, several days later: Romanian deadlift for two or three sets of six to ten, a split squat or leg press for two sets of eight to twelve, and an optional easy curl set if recovery is good. Keep the last couple of reps technically clean. Adjust total volume when you already train legs hard elsewhere.
No curl machine? A floor hamstring slider can cover knee flexion with socks on a suitable smooth surface or sliders under the heels. Lie on your back, raise the hips into a bridge and slowly extend your knees while controlling the slide, then pull your heels back. Shorten the range or lower the hips if the movement is too demanding. Use a surface that will not slip unpredictably, and stop if the setup is unstable.
A Nordic curl is another option, but it is far tougher than its simple appearance suggests. Kneel on padding with your ankles held by a secure device or capable partner. Keep your torso and hips in line as you lean forward, controlling the descent as far as you can. Use your hands or an assistance band to reduce the load; full unassisted repetitions are not an entry requirement. Begin with a very small dose, because hard eccentric work can create unusual soreness when it is new.
Whether you choose a machine, slider or Nordic progression, the rule is the same: one reliable movement you can repeat beats five clever movements you cannot recover from. Neither a slider nor a Nordic is guaranteed to duplicate the precise loading curve of a seated machine, so judge them by consistent technique and progress rather than pretending they are identical.
Track the Hamstrings Directly Instead of Guessing From Soreness
A squat personal record is easy to celebrate. Hamstring development is more awkward to assess because there is no single dramatic number that covers knee flexion, hip extension, strength and muscle size. The solution is not to stare at your legs after every session hoping for visual proof. It is to track the movements you deliberately selected for them and compare like with like over enough weeks for the numbers to mean something.
For your next two weeks, record each curl and hinge: machine or equipment used, load, completed repetitions, number of working sets and a rough repetitions-in-reserve estimate. Add a note about range of motion and whether the pelvis stayed stable. A curl that goes from 30 to 35 kilograms is only a clear gain if the seat settings, lever arm, motion and technique are reasonably comparable. On an RDL, look for a stronger and more controlled hip hinge, not merely a lower bar position achieved by losing spinal control.
In week one, choose weights that leave roughly two good repetitions available at the end of each working set. In week two, try to add one clean repetition within the same range or a small amount of weight if you have reached the top of that range. Neither change is mandatory every workout. A flat day after poor sleep, sport practice or a difficult deadlift session is information, not evidence that the entire plan has failed.
Use soreness carefully. The first Nordic or new curl variation can make the backs of your legs tender even if the session was modest. That soreness does not measure the quality of the hypertrophy stimulus and should not be deliberately chased. Look instead at repeated performance, tolerable recovery, comfortable joint positions and whether you can train again without repeatedly carrying heavy fatigue.
Longer-term size changes take patience, consistent nutrition and training that gradually becomes more capable. Photos or thigh measurements can add context when taken under the same conditions, but small changes are easy to confuse with lighting, water or measurement error. The most useful lesson is simple: keep squats for what they do well, give the hamstrings a curl and a hinge, and let their own performance tell you whether the missing work is finally being done.
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