Why warming up works

Coaches have told athletes to warm up for a century, but the reasons are more interesting than the habit.

A warm-up does three measurable things. First, it raises the temperature of your muscles by one or two degrees. Warmer muscle fibres contract and relax faster, which means more force with less effort. Second, it increases blood flow, so oxygen arrives where it is needed instead of being requested in a hurry. Third, it wakes up the nervous system: the connection between the brain and the muscles becomes faster and more accurate.

That third point explains something students notice. The first few repetitions of any movement feel awkward, and the counter sometimes misses them. This is not the software being unfair. Your early repetitions really are less controlled, and a camera that measures angles will show it.

A good warm-up for a thirty-second session is short. Twenty seconds of marching on the spot, ten arm circles in each direction, and five slow half-squats are enough. Nothing should be held still for a long time before training; long stretching belongs at the end, not the beginning.

The evidence on injury is more modest than people claim. Warming up reduces some injuries in some sports, but it does not make you injury-proof, and the studies disagree about how much it helps. What is clear is performance: almost every study finds that the same body does more work after a warm-up than before one.