Slow Eccentric Squats Showed the Most Quad Growth. Fast Reps Showed the Biggest Early-Force Gain
How fast should you lower a squat?
The usual answer is frustratingly vague: control the weight. A study first published online May 13 and now appearing in the October issue of the Journal of Strength and Conditioning Research suggests the best descent speed may depend on your goal.
The slow-eccentric group showed the largest measured quadriceps gain. The fast-eccentric group showed the largest early-force gain and significantly greater jump-height improvement than the slow group.
That is not a prescription to lower 100 percent of your max for five seconds.
Short answer:In 24 untrained men, five-second eccentric squats showed the largest measured quadriceps gain; rapid eccentrics showed the largest early-force improvement and better jump gains. With roughly eight men per group and specialized eccentric-only work, the study does not establish a universal squat tempo.
What the Squat Study Tested
The eight-week study assigned 24 untrained college-age men to slow eccentric squats, fast eccentric squats designed around jump mechanics, or weighted countermovement jumps. They trained three times per week.
The slow group performed five-second descents using a load equal to its back-squat one-repetition maximum. The fast-eccentric group descended rapidly with 50 percent of its one-repetition maximum. The slow and fast squat conditions were isolated-eccentric protocols: the lowering phase was the intervention, not a conventional set of complete down-and-up squats.
The slow group's quadriceps measure rose 10.7 percent versus a 0.3-percent decrease to a 2.5-percent increase in the other groups, although reported pairwise p values ranged from below .05 to below .10.
The fast-eccentric group improved quadriceps rate of force development during the first 25 milliseconds by 104.7 percent. Its jump height increased 9.6 percent, compared with 0.9 percent in the slow group. All three groups improved strength, with gains ranging from 9.8 to 23 percent.
Why Slow and Fast Reps Produced Different Results
The result fits the principle of training specificity.
A slow eccentric with a heavy load exposes the quadriceps to high force for a long lowering phase. That may create a strong growth stimulus, particularly in beginners.
A rapid eccentric asks the neuromuscular system to absorb and decelerate force quickly. That braking phase more closely resembles the descent before a countermovement jump, although the training repetitions themselves were eccentric-only.
The study does not prove that tempo was the only difference. The groups also used different loads and exercises. "Slow versus fast" is the clean headline, but the actual comparison bundled velocity, loading, and movement demands together.
This Does Not Make Slow Reps Universally Better for Growth
The broader literature is much less dramatic. A recent systematic review and meta-analysis of 14 studies found broadly similar hypertrophy with faster and slower repetition tempos. The estimated between-condition difference was trivial, although the certainty of estimates varied across analyses.
That review examined more conventional resistance training. The squat experiment used unusually heavy eccentric-only work, so its 10.7-percent result should not be applied to every normal back squat.
For most lifters chasing muscle, a controlled lowering phase that preserves position and range of motion is enough. Progressively add repetitions, load, or productive weekly work. You do not need to turn every descent into a five-second grind.
If power is the goal, include movements performed with high intent and appropriate loads—jumps, throws, Olympic-lift variations, or speed-focused squats—while stopping before fatigue turns fast work slow.
Do Not Copy the 100-Percent-of-Back-Squat-1RM Protocol Alone
Lowering a one-repetition maximum for repeated five-second eccentrics is not an ordinary tempo prescription. Eccentric-only training can use loads that are difficult or impossible to lift concentrically, which means the setup, spotters, safeties, and load-return process matter.
This was a controlled research protocol, not a do-it-yourself template. A recreational lifter should not take the headline as permission to load a barbell to his conventional back-squat 1RM and improvise the rest.
The study was also small, with approximately eight novice men per group, and it had no nontraining control. It lasted eight weeks, did not include trained lifters or women, and cannot tell us whether the differences persist over a longer program.
The Bottom Line
The slow, very-heavy eccentric group showed the largest measured muscle-size gain. The fast-eccentric group showed the largest early-force gain and significantly better jump gains than the slow protocol.
The useful lesson is not that one tempo is best. It is that tempo can serve a goal. Control heavy hypertrophy work well enough to keep tension and technique. Move power work with intent. Save eccentric-only protocols loaded to a conventional back-squat 1RM for environments equipped to perform them safely.
This article is for educational purposes only and is not medical advice. Eccentric-only squats loaded to a conventional back-squat 1RM require an appropriate rack, safety setup, trained assistance, and qualified supervision. Men's Fitness did not participate in the study, and no commercial entity paid for or influenced this coverage.
This story was originally published by Men's Fitness on Oct 26, 2026, where it first appeared in the Training section. Add Men's Fitness as a Preferred Source by clicking here.
