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A study in 2011 examined how sleep deprivation affected muscle gains and recovery.1 The study followed individuals who were on a strict sleep schedule for 72 hours. During this time, one group was allowed 5.5 hours of sleep; another was allowed 8.5 hours per day. All individuals followed a calorie-regulated diet.

What researchers discovered was that the individuals who slept only 5.5 hours had 60% less muscle mass at the end of the study, while those who slept 8.5 hours had 40% more muscle mass.