Sleeping badly injures you more than training too much

When someone gets injured running, the conversation always goes to the same places: how many kilometres, which shoes, what surface. Almost never to how much they slept the week before.

What has been measured

A meta-analysis of nine studies covering just over a thousand athletes found that sleeping little is associated with more injuries: roughly a third more risk. And in the work that looks at specific durations, the cut-off appears near seven hours, provided the shortfall lasts a couple of weeks. One bad night on its own doesn’t count.

Why it happens

There are two routes, and both matter. Tissue repair — muscle, tendon, bone — happens mostly while you sleep. And separately, sleeping little worsens attention and motor control: you land worse, you react later to a kerb, your form falls apart sooner when fatigue arrives.

What the studies don’t say

Time to be honest. These are observational studies: they see that people who sleep less get injured more, they don’t prove one causes the other. Something behind both — stress, shift work, training too much — could explain each of them. And nearly all of it is done on young team-sport athletes, not on people taking up running at forty.

Even so, the advice has no side effects and costs nothing, which is more than can be said for almost everything else.

What to do tomorrow

• If you’re sleeping under seven hours this week, that’s your training problem, not the mileage.
• One bad night changes nothing. Two bad weeks do.
• If you slept terribly and today was a hard session, swap it for an easy one. You lose nothing.
• And the other way round: if you feel clumsy and heavy for no reason, check how you’ve been sleeping before you change the plan.