Matthew Walker on health: what the evidence says · JRE #1109
“The last week that you have hired your injury risk two people getting 9 hours fast is 5 hours was almost a 60% increase in probability of injury risk during the season.”
What the evidence says
Walker's claim traces to Milewski et al. (2014, Journal of Pediatric Orthopaedics), an observational survey of 112 adolescent middle/high school athletes (mean age 15). That study found athletes who slept under 8 hours per night were 1.7 times (a 70% increase, not 60%) more likely to have sustained an injury than those sleeping 8 or more hours, with a wide and only marginally significant confidence interval (95% CI 1.0-3.0, p=0.04). The study did not compare 5 hours to 9 hours of sleep specifically, and did not report a perfectly linear dose-response relationship; it used a single 8-hour threshold in a multivariate regression on a small, single-school sample. A larger body of subsequent research supports a link between shorter sleep and higher injury risk in athletes generally, but effect sizes reported across studies are more modest and heterogeneous than almost 60%, and the original small sample limits how precisely any single percentage can be stated. The claim's direction (less sleep, more injury risk) is consistent with the literature, but the specific figure and the description of a clean linear relationship overstate the certainty and generalizability of the underlying evidence.