Sleep Is a Training Variable

If you train four days a week, track your lifts, eat enough protein, and sleep six hours a night — you are leaving most of your adaptation on the table.

Sleep is when the body rebuilds. Growth hormone secretion peaks during slow-wave sleep. Testosterone is highest after a full night. Cortisol, which breaks muscle tissue down, is suppressed by adequate sleep and elevated by poor sleep. The biology is not complicated.

What the research says

Studies on sleep restriction consistently show the same things: reduced strength output, slower reaction time, impaired decision-making, and higher perceived effort for the same absolute load. One well-cited study found that cutting sleep from 8 hours to 6 hours for two weeks produced cognitive deficits equivalent to two full nights of total sleep deprivation — and subjects did not notice because the decline was gradual.

Practical implications for training

You cannot separate sleep from training. An athlete sleeping seven hours is a different athlete than the same person sleeping eight and a half. The programming, the nutrition, the supplements — none of it compensates.

Track it the same way you track lifts. I log sleep duration alongside training sessions. Patterns become visible. Bad sleep weeks correlate with stalled performance. This feedback loop is useful.

The pre-sleep window matters. A consistent wind-down routine — no screens, cooler room, same bedtime — produces more reliable sleep than any supplement. Magnesium glycinate is the one thing I have found to have a real effect on sleep quality, but it works on top of good habits, not instead of them.

The honest version

Most people know they should sleep more. What they lack is the conviction that sleep is as important as the session itself. It is. Treat it accordingly.