Sooner or later, every serious exerciser learns that after a hard workout, they feel sleepy and need to go to sleep to recover. Older people may need even more sleep after intense exercise than younger people. A recent review of 37 studies recommends that competitive athletes and serious exercisers should consider napping 20 to 90 minutes every afternoon (Nat Sci Sleep, Jun 24, 2021;13:841-862). One study recommended that athletes training near their limits should try to nap 90 minutes (Sports Med, May 27, 2021), because increased quantity and quality of sleep helped athletes improve performance (Current Sports Medicine Reports, 2017;16(6),413–418).
• Basketball players who extended their sleep to 10 hours a night ran faster in half-court and full-court sprints, and improved shooting for both free throws and three-point shots by nine percent (Sleep, 2011;34(7):943–950).
• Swimmers who napped swam faster in races, improved their reaction times to diving off the blocks and turning times, and increased kick stroke rates (Inter J Sprts Med, 2019;40(8):535–543).
• Varsity tennis players improved the accuracy of their serves when they increased sleep duration by nine hours per week (Physiol Behav, Nov 1, 2015;151:541-4).
• A short afternoon nap improved endurance performance in runners who regularly slept less than seven hours a night (Eur J Sport Sci, Oct 2018;18(9):1177-1184).

How Does Sleep Help You Recover?
If you don’t get extra sleep when you do prolonged intense exercise, you don’t recover as quickly and are at increased risk for injuring yourself (J Pediatr Orthop, Mar 2014;34(2):129-33). Nobody knows why prolonged intense exercise makes a person sleep longer and deeper. We don’t even know whether sleep is necessary primarily for healing of your brain or your muscles or both (Front Physiol, 2014 Feb 3;5:24). It is most likely that you sleep longer and deeper to help damaged muscles heal from exercise. Athletes who suffered from sleep deprivation improved their athletic performances and had decreased muscular-oxidative damage after napping regularly after lunch (Int J Sports Physiol Perform, Feb 4, 2020;15(6):874-883).

The soreness and burning you feel during prolonged intense exercise is a sign that muscles are being damaged. A muscle is made up of thousands of muscle fibers just as a rope is made of many strands. Each muscle fiber consists of a series of blocks called sarcomeres that fit up against each other end-to-end, at junctions called Z-lines (diagram). The soreness that you feel with prolonged endurance exercise is caused by damage directly to the Z-lines. When this happens, the muscle can no longer contract with as much force. The muscle gets stronger when you cause damage at the Z-lines and then allow the damage to heal.

Damaged muscles heal faster while resting, and the best way to rest your muscles is to sleep. The damaged muscles start healing by a process called inflammation that turns on your immune system. The damaged muscles release two cytokines, called interleukin 6 and tumor necrosis factor alpha, that make you feel sleepy and prolong the time that you normally sleep. During sleep, your brain produces growth hormone that stimulates muscle and bone repair and growth.

Top Athletes Must Sleep for Recovery
Tour de France cyclists race for many hours day after day. They all know that the first thing to do after finishing a stage is to eat and drink copious amounts of foods and fluids to supply them with the nutrients necessary to help their muscles heal from the tremendous abuse, and then to lie down and try to sleep as much as they can before their next day’s race.

Athletes who have jobs that require manual labor cannot compete at their best in endurance sports. Top endurance athletes either have no other job or work in jobs that allow them to sit all day long. Just standing or walking can delay muscle recovery from hard training. When I was training for marathons I had frequent injuries, probably because my medical practice kept me walking from room to room to treat patients when I should have been lying in bed to allow my muscles to recover.

My Recommendations
You will not reach your full potential in an endurance sport unless you are able to sleep long hours and do not have a job that requires you to move about much of the day. Endurance training requires spending lots of time sleeping and resting your muscles. Nobody really knows exactly how sleep helps you, but it appears that the older you are, the more sleep you need to recover from the muscle damage of vigorous exercise.