Velocity-based training with your phone camera

Velocity-based training (VBT) is a simple idea: the speed of the bar tells you how hard a set really is. When you're fresh, the first rep moves fast. As you tire, each rep slows down, and by the time you're one or two reps from failure the bar is crawling. Measure that slowdown and you get an honest read on effort, with no guessing.

Why bar speed beats feel

Most programs ask you to judge effort yourself, often as reps in reserve. That works, but people are notoriously bad at it, especially on sets of more than five reps or on lifts they're new to. Bar speed is a number you can't talk yourself out of. It also changes day to day with sleep and stress, so it doubles as a readiness check: if your warm-up sets are slower than usual, today isn't the day for a new best.

Velocity loss: the number that matters

Absolute speed varies between lifters and lifts, so the most useful measure is how much a set slows down from its fastest rep. Research on squats and bench presses (for example, González-Badillo and Sánchez-Medina's work on velocity loss) has found that velocity loss tracks closely with how many reps you have left. As a rough guide:

• Under 10% slower than your fastest rep: plenty left in the tank. Good for power and technique work.
• About 20% slower: a few reps left. A sensible stopping point for most strength sets.
• 30% or more slower: about one rep left. Ending the set here keeps most of the benefit and much less of the fatigue.

You don't need a sensor any more

VBT used to mean a clip-on sensor or a linear encoder on the bar, which most lifters never bought. Pose models that run on a phone have changed that. Prop the phone up side-on, and the camera can follow your joints through each rep, time the lifting part, and turn the distance moved into metres per second using your height for scale.

In Liftsmith this lives in Settings › Labs › Camera bar speed (Labs is part of Pro). While the camera counts your reps, it shows the last full rep's speed, and from the third rep it tells you roughly how many reps are left. At 30% velocity loss it says it's a good place to end the set, with one buzz. Video is read on the phone frame by frame and dropped; nothing is recorded or uploaded.

Tip: Add your height in Your stats so the camera can measure in m/s. Without it you still get the slowdown as a share of your fastest rep, which is the part that predicts reps left.

Lifts it works best on

• Back squatQuads, Glutes
• Goblet squatQuads, Glutes
• Barbell bench pressChest
• Standing overhead pressFront delts
• Romanian deadliftHamstrings, Glutes
• One-arm dumbbell rowLats, Upper back

Lifts with a clear up and down and joints the camera can see from the side give the cleanest numbers: squats, presses, rows and hinges. Holds and carries don't have reps to measure.

How to use it in your training

1. Set a stopping point. For strength, end most sets at 20 to 30% velocity loss instead of grinding to failure.
2. Watch your first rep. If it's clearly slower than usual at a weight you know, keep today's sets lighter.
3. Keep logging normally. The reps the camera counts fill in your set, so Log set stays one tap and your progression carries on.