Top-Half Partial Reps Kept Testosterone Elevated Longer—But Does That Mean More Muscle?
UPLIFT IRON CLUBA September 12, 2026 study found that young men using the top half of Smith-machine squats and bench presses could handle substantially heavier 10-repetition loads, and their total testosterone remained elevated 15 minutes after training while it had returned to baseline after full-range sets. That sounds like a win for partial reps—until you separate an acute hormone response from long-term muscle growth. The experiment is interesting, but it does not show that shortened partials build more muscle.
Ten untrained men performed three sets of 10RM Smith-machine squats and bench presses using either full range of motion, the top half of the movement, or passive rest. Top-half partials allowed heavier loads and produced a longer-lasting testosterone elevation, while full-range work produced more lactate and a later cortisol increase. Those are acute physiological responses, not proof of superior hypertrophy. For most lifters, full-range training remains a strong default, with partials used strategically for overload, specificity or extra work.
- Top-half partials let the participants use much heavier 10RM loads.
- Testosterone stayed above baseline at 15 minutes after partial-ROM training, but acute hormone spikes do not equal future muscle gain.
- Full-range sets created a larger lactate response and a significant cortisol rise at 15 minutes.
- The study involved only ten untrained young men and measured one workout, not months of hypertrophy.
- Shortened partials should not be confused with lengthened partials, which are a different training method.
What the Researchers Actually Tested
The experiment used a crossover design, so each participant completed all three conditions one week apart. The ten men were about 24 years old and had no regular resistance-training experience. They performed back squats and bench presses on a Smith machine for three sets at their own 10-repetition maximum, with two minutes between sets.
The full-range squat descended until the thighs were parallel to the floor, while the full-range bench touched the chest. The partial condition used only the top half of each movement. That detail matters. These were shortened-position partials designed to avoid the mechanically difficult lower half of the lift—not the long-muscle-length partials that have become popular in hypertrophy discussions.
Blood samples were collected before training, immediately afterward and 15 minutes later. Researchers measured lactate, growth hormone, total testosterone and cortisol. They also tracked heart rate and perceived effort. In other words, this was a study of what happened around one training session, not a study that measured changes in muscle size.
The Biggest Practical Difference Was Load
Because the top-half reps skipped the weakest portions of the movements, participants could use far more weight. Their partial-ROM squat 10RM was about 43.3 kilograms heavier than their full-range 10RM, while their partial bench 10RM was about 16.1 kilograms heavier. That is not surprising: a shorter, mechanically favorable range usually lets you overload the strongest part of the lift.
This is where partial reps can be useful even without making exaggerated claims about hormones. A powerlifter may train a lockout because that specific range needs more strength. A bodybuilder may use a partial after full-range work to extend a set. A lifter returning from a limitation may temporarily use a tolerable range. The tool has value because it changes the mechanical task.
But heavier weight alone does not automatically mean more hypertrophy. The bar travels a shorter distance, total work may be lower, and the muscle is exposed to a different length profile. Range of motion, load, effort, exercise selection and progression all interact.
Why the Testosterone Result Sounds Bigger Than It Is
Total testosterone rose immediately after both full-range and partial-range training. Fifteen minutes later, the full-range condition had returned to baseline, while the partial condition was still significantly elevated—about 56.6 ng/dL above baseline. That is the headline-friendly result.
The mistake would be jumping from “testosterone stayed elevated longer” to “this workout builds more muscle.” Short-lived post-workout hormone changes are not the same thing as maintaining chronically higher testosterone, and this experiment did not measure muscle growth. Acute endocrine responses can tell researchers something about the stress of a session, but they are only one small piece of adaptation.
Growth hormone increased over time after both training conditions, with no significant difference between the ranges. The testosterone-to-cortisol ratio also did not show a meaningful condition effect. So the picture is more nuanced than a simple anabolic-hormone scoreboard.
Full Range Produced More Metabolic Stress
Full-range training produced the larger lactate response immediately after exercise: roughly 11.97 mmol/L versus 9.37 mmol/L in the partial condition. Cortisol also rose significantly at 15 minutes only after the full-range workout. Heart rate remained higher 15 minutes later after full-range work as well.
That does not make full range “catabolic” or partial range “anabolic.” Cortisol is a normal stress hormone, and lactate is a normal by-product of hard glycolytic work. A session that creates more metabolic disturbance is not automatically worse, just as a session that creates a bigger testosterone spike is not automatically better.
A cleaner interpretation is that the two ranges imposed different kinds of stress. Full range involved more displacement and a larger metabolic response; top-half partials let lifters move much heavier loads through less distance.
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SHOP THE COLLECTIONShortened Partials Are Not the Same as Lengthened Partials
This distinction is easy to lose in social-media arguments. The new study used the top half of the squat and bench press—the portion where the target muscles are generally shorter and the leverage is more favorable. By contrast, “lengthened partials” deliberately emphasize the stretched region of an exercise, such as the bottom of a curl or the deeper portion of some leg movements.
Evidence around long-muscle-length training has made lengthened partials an interesting hypertrophy tool, but that cannot simply be transferred to top-half reps. If two methods both have the word “partial” in the name, that does not mean they create the same stimulus.
For a general lifter, a useful hierarchy is simple: learn and progress stable full-range patterns first, then use partials for a reason. The reason might be overload, sport specificity, a targeted range, accommodating equipment, or extending a hard set. “The hormone spike looked better” is a much weaker reason.
What This Study Cannot Tell Us About Muscle Growth
The limitations are important. Only ten participants completed the experiment. They were young, untrained men. The exercises were Smith-machine squats and bench presses. The study tested one acute workout under each condition and measured blood markers for only a short period afterward.
There was no multiweek training block, no ultrasound or MRI measurement of muscle growth, and no direct test of whether one range produced more hypertrophy. The researchers also note that total mechanical work was not measured. Diet was partially standardized by asking participants to repeat their prior intake, but a detailed nutrition analysis was not performed.
Those limitations do not make the findings useless. They tell us exactly what the study is good for: showing that changing range of motion can substantially change load capacity and the immediate metabolic and hormonal profile of a workout in beginners. It is a physiology result, not a bodybuilding verdict.
How Lifters Can Use Partial Reps Without Overthinking Hormones
For most muscle-building programs, keep a full and repeatable range of motion as the foundation unless a specific exercise, injury history or goal gives you a reason to modify it. Progress load and reps over time, train close enough to failure to create a meaningful stimulus, and choose movements you can execute consistently.
Then add partials strategically. Top-half squats or presses can expose you to heavier loads. Bottom-half or lengthened-biased partials can emphasize a different muscle-length region. Partials after a full-range set can extend effort when technique remains controlled. The key is knowing which problem the partial is supposed to solve.
The new study adds an interesting detail: shortened partials can produce a different short-term endocrine profile even when perceived effort is similar. That is worth studying further. It is not a reason to replace full-range training with lockouts in pursuit of a 15-minute testosterone bump.
