By Gabe Mirkin, M.D.
Every athlete who trains for competition in sports that require endurance learns sooner or later that after exercising long and hard, you fell sleepy and have to go to sleep to recover, and older people may need even more sleep (JAMA. 1997; 227: 32-37). If you don’t get lots of extra sleep when you do prolonged intense exercise, you don’t recover and are at high risk for injuring yourself.
Nobody really knows why prolonged intense exercise makes a person sleep longer and deeper. In fact, we don’t even know whether sleep is necessary primarily for healing of your brain or 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.
The soreness and burning you feel during prolonged intense exercise is a sign that muscles are damaged. Scientists know exactly where a muscle is damaged. Each muscle is made up of thousands of muscle fibers like a rope is made of many threads. Each muscle fiber is made up of a series of blocks called sarcomeres that fit up against each other end-to-end, at a junction called the Z-line. The soreness that you feel with prolonged endurance exercise is caused by damage directly to the Z-line. When this happens, the muscle contracts with less force.
Damaged muscles start healing by a process called inflammation that turns on your immunity, and muscles heal faster by resting. The best way to rest your muscles is to sleep. During sleep, your brain produces large amounts of growth hormone that stimulates muscle and bone growth and repair.
We know that prolonged and intense exercise damages muscles. That’s why your muscles always feel sore 8 to 24 hours after you exercise intensely. Damaged muscles seem to know that you have to rest them for healing to occur. They release two cytokines, called interleukin 6 and tumor necrosis factor alpha, that make you feel sleepy and prolong the time that you normally sleep.
No athlete with a job that requires manual labor has ever been able to compete at his best in endurance sports. Today all top endurance athletes either have no other job or work in jobs that require them to sit all day long. Just walking can delay muscle recovery from hard training
Tour de France bicycle racers have to race for many hours day after day. They all know that the first thing they do after finishing each days’ stage is 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 they have had racing that day. Then they lie down and try to sleep as much as they can before their next race on the next day.
When I was training for marathons, I was always injured, primarily because I had to walk from room to room to treat patients when I should have allowed my muscles to recover by lying in bed.
The average, college athlete gets 6.5–7.2 h sleep each night (J. Sci. Med. Sport. 2014;18). Increasing a college athletes sleep duration to 8 or more hours per night improves performance in many different sports (Sleep. 2011 Jul 1; 34(7): 943–950).
Several studies show that 4 to 24 weeks of regular prolonged exercise helps insomniacs fall asleep more quickly (Sleep Med. 2011;12(10):1018-27 and Sleep Med. 2010;11(9):934-40).
However nobody really knows how or why prolonged exercise makes you so tired. The most likely explanation is that damaged muscles heal faster with rest and you move your muscles less when you are asleep.
You cannot reach your full potential in endurance sports 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.
Gabe Mirkin, M.D., is a sports medicine doctor and fitness guru. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin has run more than 40 marathons and is now a serious tandem bike rider with his wife, Diana, often doing 30-60 miles in an outing. His website is http://drmirkin.com/.