Gwyther et al. 2022, Sleep interventions for performance, mood and sleep in athletes: systematic review and meta-analysis

This meta-analysis of 27 studies (617 athletes; 16 controlled, 11 uncontrolled designs) examined sleep hygiene, assisted sleep, and sleep extension interventions. Sleep interventions showed a consistent positive direction for subjective sleep quality, mood and performance outcomes, but the 11 uncontrolled trials — including the widely cited Stanford basketball extension study — could not isolate intervention effects from practice effects or expectation, rendering their effect-size estimates unreliable. Evidence moderate.