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Fifteen per cent. That’s how much one of the calf muscles grew in eight weeks in a group of young women who only ever trained the bottom half of a calf raise. A second group, doing the same exercise through a full range, managed less than seven.
For decades the rule has always been simple. Full range on every rep to get the most out of your training. Half reps were for people loading the leg press with too many plates and moving it a few centimetres. Now a growing pile of research suggests the bottom half of a lift, where the muscle is stretched, may actually be just as beneficial when it comes to building muscle.
So should your clients start cutting their reps in half? Well no, not quite…it depends.
Every muscle has a range it works through. When a muscle is near its longest, it’s stretched under load. When it’s near its shortest, it’s squeezed tight. Think of the bottom of a squat for the quads and glutes, or the bottom of a biceps curl with the arm straight. Those are long muscle lengths. The top of a leg extension, with the knee locked out and the quads fully contracted, is a short muscle length.
A “lengthened partial” is a rep that only covers the stretched half of that range. You lower the weight all the way down, then come back up only partway, and repeat. A “shortened partial” is the opposite, working only the top half where the muscle is tight.
There’s a second way to train a muscle long, and it has nothing to do with half reps. You can pick exercises that place the muscle in a more stretched position from the start. Raising the arm overhead stretches the long head of the triceps. A seated leg curl where you’re sitting upright, with the hips bent, stretches the hamstrings more than lying face down does. Same joint movement, different starting length.
If you’ve read our piece on stretching for strength and hypertrophy, this is a close relative. The difference here is that the muscle is working against a load through a range of movement, rather than holding a stretch.
Researchers have a few ideas about why the stretched position might be a stronger growth signal. The muscle produces a lot of tension at long lengths, partly from the contracting fibres and partly from the passive pull of connective tissue being stretched. There’s also some evidence that training at long lengths adds sarcomeres, the tiny contractile units that sit end to end along a muscle fibre, which makes the fibres longer as well as thicker. These explanations are still being tested, so treat them as likely rather than settled.
One of the trials that put lengthened partials in the spotlight came out of Brazil. Forty-five untrained women were split into a control group and four leg extension groups (Pedrosa et al., 2022). One trained the full range. One trained only the first half, with the knee bent and the quads long. One trained only the second half, near lockout. The fourth alternated between the two halves from session to session.
The group training the bent-knee half showed greater relative growth in several regions of the thigh than the full range and lockout groups. The lockout group did little better than the controls in some of the regions measured.
But there was a second result that gets less attention. Strength gains followed the range that was trained. The bent-knee group got strongest in the bent-knee position, the lockout group got strongest near lockout, and the group that alternated between the two did as well as anyone across every range tested. That pattern turns up again and again in this research, and it follows the rule of specificity to a T.
The second landmark study came from Japan and looked at exercise choice rather than partial reps. Twenty healthy adults trained one leg on a seated leg curl and the other on a lying leg curl for 12 weeks (Maeo et al., 2021). Both legs did five sets of ten reps at 70 per cent of their one-rep max, twice a week.
The hamstrings cross the hip as well as the knee. Sitting upright bends the hip and pre-stretches them, so the seated curl works the muscles at a longer length throughout.
MRI scans showed the whole hamstring group grew by 14 per cent on the seated side and 9 per cent on the lying side. The difference came from the muscles that cross both joints. The short head of biceps femoris, which only crosses the knee and so isn’t stretched any further by sitting, grew by about the same amount on both legs.
So, where sitting changed the muscle’s length, the growth changed. Where it didn’t, the growth didn’t.
The same research group then ran a similar experiment on the arms. Twenty-one adults did cable triceps extensions for 12 weeks, one arm with the elbow overhead and the other with the arm by the side, as in a standard pushdown (Maeo et al., 2023).
The long head of the triceps attaches above the shoulder, so lifting the arm overhead stretches it. After 12 weeks the whole triceps had grown by about 20 per cent in the overhead arm and about 14 per cent in the pushdown arm. The long head showed the biggest gap, at roughly 29 per cent against 20 per cent.
Here’s the part we really like. The overhead arm was lifting 34 to 39 per cent less weight than the pushdown arm throughout the study, and still grew more. Strength improved by a similar amount in both arms on their own exercise. Lighter loads with more growth is an appealing combination for a client with grumbly elbows.
The calf study behind our opening number is one of the neatest examples of a lengthened partial in action. Forty-two young women trained calf raises on a leg press machine three times a week for eight weeks, doing three sets of 15 to 20 reps (Kassiano et al., 2023).
One group worked the full range, from a deep stretch at the ankle to a full rise onto the toes. One group only worked the bottom half, from the deep stretch up to a flat foot. The third only worked the top half.
The medial gastrocnemius, the inner calf muscle, grew by 15.2 per cent in the bottom-half group, 6.7 per cent in the full range group and 3.4 per cent in the top-half group. For the outer calf the bottom-half group again grew most, although the difference against full range wasn’t statistically significant.
Anyone who has watched clients bounce through calf raises off the edge of a step will recognise the lesson. The stretch at the bottom is the part most people rush.
Small studies with eye-catching percentages are good indicators, but need checking against larger ones, and one of the largest in this area was published in 2025. It was co-led by British researchers James Steele and James Fisher from Solent University in Southampton, working with a US strength training provider (Gschneidner et al., 2025).
The trial was pre-registered, meaning the methods and analysis were fixed before any data were collected, and it ran across 15 sites. Just under 300 adults were randomised to train for 12 weeks with either full range or lengthened partial reps. The researchers measured muscle size in the upper arm and thigh, along with strength on the chest press, leg press and pulldown.
The result was close to a dead heat. The difference between the two approaches was small enough that the authors described them as practically equivalent for muscle size. Lengthened partials didn’t beat full range, and full range didn’t beat lengthened partials.
That’s an important counterweight. It suggests that, across a normal mix of exercises and in ordinary people, the full range already trains the stretched position well, so cutting off the top half adds little. It also suggests that cutting off the top half costs little, which is useful in its own right.
A second UK trial, from researchers at Ulster University and Manchester Metropolitan University, added another angle (McMahon et al., 2026). Forty-five adults were randomised to eight weeks of leg extensions in one of four ways. One group trained the top half of the range at 80 per cent of their max. One trained the bottom, stretched half at only 55 per cent. One trained the full range at 80 per cent. The last group didn’t train.
The lengthened partial group gained as much thigh muscle thickness as the full range group, despite using a much lighter weight. Both beat the top-half group at some of the measurement sites. The lengthened partial group also showed bigger increases in fascicle length, the length of the bundles of muscle fibres, which fits with the idea that stretched training makes fibres longer.
For us, there’s a bit of an appeal here. A client who can’t or shouldn’t handle heavy loads may be able to get a similar growth stimulus from a moderate weight worked through the stretched range.
There are some limits we need to think about before anyone rewrites a new programme. Most of these trials ran for eight to 12 weeks. That’s long enough to see early growth, but it tells us little about what happens over a year or a training career.
Most participants were young, healthy adults, and several of the studies used untrained people. Beginners grow from almost anything, which makes differences between methods harder to read. There’s very little data on older adults, people with joint conditions or clients carrying an injury.
Sample sizes were small. Studies of 20 to 45 people can produce big percentages that shrink when a bigger trial comes along, and the large 2025 trial is a good example of that happening.
Measurement is another catch. Most studies used ultrasound or MRI at a few points along the muscle. Growth can vary from one region to another, so a method that wins at one site may draw level at another.
Strength stays specific. People tend to get strongest in the range they train. A client who only ever does lengthened partials on the squat will get strong within that range and may stay weaker near lockout, which is a problem if they need to stand up from a low chair or lift a heavy box onto a shelf.
Finally, the effects are modest. All together, the evidence suggests that long-length training is at least as good as full range for building muscle and sometimes a little better for some muscles. It doesn’t suggest that full range reps are a waste of time.
For most clients, the easiest win has nothing to do with partial reps. It’s choosing exercises where the hardest part of the lift happens with the muscle stretched, and making sure the client actually reaches that position under control.
A quick way to judge an exercise is to ask where it feels heaviest. On a cable pushdown, the effort peaks as the arm straightens, with the triceps short. On an overhead extension, it peaks with the elbow bent and the long head stretched. On a preacher curl, the bottom of the rep is the hardest part. On a standing curl with a dumbbell, the bottom is the easiest.
| Muscle group | Long-length exercise choice | Coaching point |
|---|---|---|
| Hamstrings | Seated leg curl, Romanian deadlift | Sit tall on the curl so the hips stay bent. On the RDL, push the hips back until the hamstrings are stretched and stop before the lower back rounds |
| Quadriceps | Deep squat, Bulgarian split squat, leg extension from a fully bent knee | Use the depth the client can control. Let the front knee travel forward over the toes on split squats so the quads reach a long position |
| Glutes | Deep split squat, RDL, low step-up | The glutes are longest with the hip deeply bent, so depth and a slight forward lean help more than hip thrust lockouts |
| Triceps | Overhead cable or dumbbell extension | Keep the elbows pointing up and lower the weight behind the head until the triceps are well stretched. Expect to use lighter weights than on a pushdown |
| Biceps | Incline dumbbell curl, preacher curl | Let the arm hang behind the body on the incline. Lower fully but stop short of locking the elbow hard under load |
| Calves | Standing calf raise with a pause at the bottom | Pause for one to two seconds in the deep stretch with no bounce. Drive up from a still position |
| Chest | Dumbbell press or fly with a deep, controlled bottom position | Lower until the chest is stretched but the shoulder stays comfortable. Shoulder history decides the depth |
Lengthened partials can be used in two main ways. The first is to do the whole set as partials, lowering fully and coming up only halfway. This is what the large 2025 trial tested, and it seemed to work about as well as full range.
The second, and probably the more practical option for most clients, is to tag partials onto the end of a normal set. The client does full range reps until they’re close to failure, then keeps going with a few short reps in the stretched half of the movement. Three to six extra reps is plenty.
This works well on machines and cables, where the load is stable and easy to control. Leg extensions, seated leg curls, cable overhead extensions and calf raises are all good candidates. It works less well on free-weight lifts where fatigue can drag technique down, such as a heavy barbell squat or deadlift.
Keep the partials slow and controlled. The aim is time under load in the stretched position. A partial that turns into a bounce out of the bottom loses the point and adds joint stress.
Treat it as one tool among several. A couple of exercises with lengthened partials at the end of a session is a sensible starting point. There’s no need to convert a whole programme.
Some clients get on with this approach better than others.
Clients who feel pain or discomfort in the shortened position are good candidates. Some people find the top of a leg extension pinches the front of the knee, or that the lockout of a pushdown irritates the elbow. Working the stretched half can let them keep training the muscle while avoiding the uncomfortable part of the range, as long as the stretched position itself is comfortable.
Clients who can’t or shouldn’t lift heavy loads may also benefit. The overhead triceps study and the British leg extension trial both found good growth with lighter weights when the muscle was trained long.
Intermediate gym-goers whose progress has stalled often like the variety. A fresh way to train a familiar exercise can renew interest, and interest keeps people turning up.
Physique-focused clients who want to bring up a lagging muscle group, such as the calves or the long head of the triceps, have the most direct reason to try it. That’s where the evidence has shown the best results.
Beginners should always work on perfecting the full range first. Learning to control a squat, a hinge or a press through its whole range builds the control and confidence that underpin everything else. Partials come later, once that foundation is in place.
Hypermobile clients need extra thought. If a client can move well past a typical range at a joint, loading the end of that range repeatedly isn’t wise. For these clients, a controlled range that stops short of their maximum is often the better choice, and strength at mid-range positions is usually more useful.
Joint issues are a whole other story. A client with shoulder impingement symptoms may not tolerate a deep dumbbell fly or an overhead triceps extension. A client with a knee problem may struggle at deep knee flexion. The stretched position isn’t automatically the safe one, and the right range is the one the client can load without symptoms.
Expect more muscle soreness at first. Training a muscle hard at long lengths tends to cause more soreness in the early sessions, especially with a lot of slow lowering. Start with fewer sets and build up.
Finally, remember that strength stays specific. If a client needs to be strong through the whole range for daily life or sport, they need to train through the whole range at least some of the time.
Many of us find our clients either miss or rush the bottom of a rep and grind hard at the top, chasing the squeeze. The research on long muscle lengths suggests that habit may be the wrong way round. The stretched position looks like a strong growth signal, and at the very least it deserves as much of the client’s attention as the top of range.
That doesn’t mean throwing out full range training. The largest trial so far found lengthened partials and full range reps roughly equal, which tells us full range already covers the stretched position well when it’s done properly. The simplest changes are often the best ones. Swap a lying leg curl for a seated one. Put a triceps exercise overhead. Pause at the bottom of the calf raise. Control the descent and lean into the stretch.
Lengthened partials then become one more option, useful for a stalled client, a sore joint at lockout or a lagging muscle. When used properly and alongside full range work, they can be a simple, low-cost addition to a programme.
Gschneidner, D., Carlson, L., Steele, J. and Fisher, J.P. (2025). The effects of lengthened-partial range of motion resistance training of the limbs on arm and thigh muscle area: A multi-site randomised trial. Journal of Sports Sciences, 43(23), pp.2963-2976. Click here to review the full research article.
Kassiano, W., Costa, B., Kunevaliki, G., Soares, D., Zacarias, G., Manske, I., Takaki, Y., Ruggiero, M.F., Stavinski, N., Francsuel, J. et al. (2023). Greater gastrocnemius muscle hypertrophy after partial range of motion training performed at long muscle lengths. Journal of Strength and Conditioning Research, 37(9), pp.1746-1753. Click here to review the full research article.
Maeo, S., Huang, M., Wu, Y., Sakurai, H., Kusagawa, Y., Sugiyama, T., Kanehisa, H. and Isaka, T. (2021). Greater hamstrings muscle hypertrophy but similar damage protection after training at long versus short muscle lengths. Medicine and Science in Sports and Exercise, 53(4), pp.825-837. Click here to review the full research article.
Maeo, S., Wu, Y., Huang, M., Sakurai, H., Kusagawa, Y., Sugiyama, T., Kanehisa, H. and Isaka, T. (2023). Triceps brachii hypertrophy is substantially greater after elbow extension training performed in the overhead versus neutral arm position. European Journal of Sport Science, 23(7), pp.1240-1250. Click here to review the full research article.
McMahon, G., Morse, C., Burden, A., Winwood, K. and Onambele-Pearson, G. (2026). Moderate intensity resistance training with partial range-of-motion at long muscle lengths elicits similar hypertrophy and architectural adaptations as high intensity resistance training using full range-of-motion. Journal of Strength and Conditioning Research, online ahead of print. Click here to review the full research article.
Pedrosa, G.F., Lima, F.V., Schoenfeld, B.J., Lacerda, L.T., Simões, M.G., Pereira, M.R., Diniz, R.C.R. and Chagas, M.H. (2022). Partial range of motion training elicits favorable improvements in muscular adaptations when carried out at long muscle lengths. European Journal of Sport Science, 22(8), pp.1250-1260. Click here to review the full research article.
Knowing where a muscle is stretched, and choosing the exercise that loads it there, is the knowledge that sets the best coaches apart. It draws on anatomy, biomechanics and programme design, and it applies to almost every client who walks into a gym, from first-timers to competitive athletes. The more confident you are with that detail, the better your programmes become.
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