How much did your set slow down?

Velocity loss is the percentage drop in speed from a reference rep, commonly the fastest rep in the set, to a later rep. It answers a narrow question: how much slower was this rep?

For example, if your fastest rep was 0.60 m/s and a later rep was 0.45 m/s, the later rep was 25% slower. The load may not have changed, but the way you moved it did. These are example numbers, not suggested target speeds.

How to calculate velocity loss

Subtract the current rep’s speed from the fastest rep’s speed, divide by the fastest rep’s speed, and multiply by 100.

Velocity loss (%) = (fastest − current) ÷ fastest × 100

For the example above: (0.60 − 0.45) ÷ 0.60 × 100 = 25%.

Use the same velocity metric for both reps. Mixing one rep’s peak speed with another rep’s average speed doesn’t produce a useful comparison. The bar speed guide explains the difference.

The calculator below uses the fastest rep as the reference. If your device uses the first rep or another reference, its displayed percentage may differ.

What the slowdown tells you

When effort and technique stay consistent, the drop in speed can help describe the fatigue building during a set. Sánchez-Medina and González-Badillo studied velocity loss alongside mechanical and metabolic responses in bench press and squat protocols, supporting its use as a fatigue indicator in those conditions. Read the study.

It isn’t a direct measurement of how many reps you have left. The same loss percentage can mean different things at different loads or on different exercises. A change in technique or a deliberately slower rep can also change the number without answering the question you’re interested in.

Keep your own notes about effort. Speed and how the set felt are two pieces of information you can compare.

Is there a percentage where you should stop?

Some velocity-based programs end a set when speed has fallen by a chosen percentage. That threshold is part of the program, not a universal rule built into the measurement.

An eight-week trial in 22 men compared squat training with 20% and 40% velocity-loss limits. Both groups improved strength similarly; the lower-loss group completed fewer reps, while the higher-loss group gained more size in some muscles. Read the trial.

That doesn’t mean a 20% limit is right for your next set. The goal, exercise, lifter, and total amount of training all matter. A number selected for a study shouldn’t quietly become a prescription for everyone reading about it.

Check the reference rep first

The whole percentage hangs on your fastest rep, so it’s worth a glance. If that rep was unusual, say a bounce out of the bottom, a cut-short rep, or a different grip, every later rep will look like it lost more speed than it really did.

When a percentage seems off, look back at the individual reps and see whether one of them doesn’t belong. A fair reference makes for a fair number.

The arithmetic is simple. Getting a comparison that means something takes a consistent measurement. Our introduction to velocity-based training puts that measurement in the context of an ordinary training log.

Let the app do the math

You don’t need to work any of this out between sets. The Strive puck measures the speed of every rep, and the Strive app shows how much each set slowed down. Every rep’s speed is saved with the set, so if one rep looks out of place you can see it right there.

The app also uses that slowdown to suggest the weight for your next set. It’s a suggestion, not an order: you can change it, and how the set felt still counts.