Slow Repetitions: Why Power Drops, and Why Hypertrophy Is a Different Question

The key points in 30 seconds

• The experiment involved 13 competing para powerlifters performing single bench presses at 80% of 1RM.
• With a six-second eccentric phase, the subsequent concentric velocity and power were lower than with faster lowering.
• This is an acute result of a single repetition, not a study of long-term muscle growth, strength or injuries.
• Tempo should be chosen for the task: movement control and time under tension are not the same as maximal power in a repetition.

Where the argument about the "slow negative" comes from

In strength training it is commonly believed that slowly lowering the bar — the eccentric phase — makes an exercise "harder" and more useful for muscles. Some coaches recommend lowering the weight for three to six seconds, others demand the opposite: lower quickly and lift explosively. The argument often mixes different goals. For hypertrophy, for maximal strength and for power, tempo can mean different things, and there are few studies that compare all of this directly at once.

The new experiment answers a narrow question: what happens to the lift itself if the lowering before it lasted longer.

How the experiment was designed

Thirteen competing para powerlifters took part: eight women and five men from Brazil. This was a convenience sample, and no sample-size calculation was made in advance. In a single session the athletes performed the bench press under six conditions in random order: concentric-only movement, self-selected lowering without a pause, self-selected lowering with the competition pause on the chest, and controlled eccentric phases lasting 2, 4 and 6 seconds. The load was 80% of one-repetition maximum, taken from an official competition 2–10 days before the test. Each condition had two single repetitions, and velocity was determined from video recorded at 240 frames per second.

What came out

The conditions differed significantly in peak and mean velocity and in power. The highest values were seen with self-selected lowering without a pause — mean power about 315 W, mean velocity 0.39 m/s. The lowest were with the six-second eccentric phase: about 226 W and 0.28 m/s. The difference in mean power was roughly 89 W, or about 28%. Four-second lowering also reduced the result, while two-second lowering did not differ statistically from the faster variants. Differences between self-selected lowering with and without a pause, and comparisons with the purely concentric lift, were not significant.

This is biomechanically plausible: a long lowering phase increases fatigue before the lift begins, and the pause changes the contribution of the stretch–shortening cycle. But the authors did not measure neuromuscular variables or elastic energy, so this explanation remains a hypothesis.

Why this is not an answer about hypertrophy

Power is the rate of doing work in a specific repetition. Maximal strength is the ability to produce a large force. Hypertrophy is a long-term increase in muscle tissue. These outcomes are related but not interchangeable.

Comparing muscle growth requires weeks of training, comparable volume, proximity to failure and direct measurements of muscle tissue. The Santos study did not do this. A drop in power with a six-second lowering does not prove that slow repetitions are useless; it shows the cost of that tempo for the immediate concentric output at a given load.

How to read the power figures

Bench-press power is force multiplied by velocity. At the same load (here 80% of 1RM), lift velocity and power rise and fall together, so a drop in velocity of 0.1 m/s with six-second lowering means a noticeable loss in the "watts" the athlete can develop. Values such as 315 and 226 W should not be compared with other people's results: they were obtained by video analysis in a specific group of para athletes.

What the experiment does not show

It does not show what happens if an athlete trains with a slow tempo for months: whether muscle mass will grow or strength will change. It does not say how tempo affects the load on joints and tendons, does not compare men and women separately and does not test other percentages of 1RM. It is a precise answer to a narrow question — and that is exactly why it should not be stretched into general slogans such as "faster is always better" or "slower is always more useful".

Practical meaning

The authors advise avoiding deliberately prolonged eccentrics (four seconds or more) in maximal competition attempts while keeping the mandatory pause. If the goal is speed and power, an excessively slow lowering immediately before an explosive lift can get in the way. For learning technique, controlling position or a rehabilitation task, a slower tempo is sometimes appropriate. For hypertrophy, the whole training context matters, not a single tempo figure.

The result was obtained in experienced para athletes in a specialised competition bench press. It cannot be automatically transferred to squats, machines, beginners or programmes with sets of repetitions.

How convincing is the evidence

Repeated measurements in the same athletes are well suited to comparing acute conditions, and the random order of conditions reduces the influence of fatigue. But the sample is small, mixed by sex and type of impairment, the load was tested only at 80% of 1RM, the whole work fitted into one session, and the reliability of the video analysis was not formally assessed. The experiment did not track adaptation and says nothing about injury rates.

Sport in Luxembourg conclusion

Slow lowering can reduce the velocity and power of the next lift here and now. It does not follow that it impairs hypertrophy or is always harmful. Tempo is a programming tool, not a universal ranking of repetition quality.