Normally, a hard workout guarantees a good night’s rest, but there is a point when intense training can lead to diminishing returns, especially on nighttime sleep. In a small study published in Journal of Sports Sciences last fall, a team of exercise physiologists measured the effect an intensified fitness program had on the sleep of 13 highly-trained male cyclists. Researchers found that in just nine days of heavy training, cyclists saw a significant reduction in performance, sleep quality, and mood.
Sleep is one of training’s most important tools and getting enough of it—a recommended seven to nine hours per night—is essential for repairing and strengthening overtaxed muscles. When an athlete gets enough shuteye, blood supply increases to muscles and the pituitary gland releases natural growth hormone to facilitate muscle and bone growth, healing, and adaptation. Waking up refreshed means you’re likely rolling out of bed feeling stronger, faster, and ready to tackle another workout. Without a restful night’s cycles of REM and deep sleep, performance and mood wanes.
Few studies have looked into measuring the effect of the overtraining-sleepless connection and insight is sorely needed, says Sophie Killer, Ph.D., the study’s lead researcher and performance nutritionist with British Athletics at the English Institute of Sport. “Part of the reason there’s such a paucity of data is because it’s not easy to get approval to overtrain someone,” she says. “We had to find people willing to sign up because we really needed to push their boundaries and have them take a battering.”
In the study, Killer and her colleagues at the School of Sport, Exercise, and Health Sciences at Loughborough University, recruited 13 cyclists to complete two nine-day, intensified training periods in which they were given a diet of either moderate or high carbohydrate before, during, and after workouts. Researchers more than doubled the athletes’ baseline training volume and intensity, measuring their VO2, heart rate and power output stats as they trained. They also asked cyclists to keep a mood and diet diary, as well as wear an actigraphy watch to measure movements as they slept.
“We weren’t surprised that the athletes spent more time in bed at night during training,” Killer says. “But we found that despite the increased time in bed, they couldn’t get more sleep and actually got less than before.” The cyclists woke and moved more throughout the night, and logged less total time asleep.
You don’t have to train like a maniac to experience exercise-induced insomnia. Taking on a new fitness goal, such as going from the couch to half marathon training, could over-stress your muscles to the point of acute fatigue. Dubbed “overreaching,” the muscles are broken down during these cycles for a purposeful short-term decrease in performance to make them stronger.
But when athletes find themselves in a cycle of back-to-back racing or upping their mileage too quickly without giving their bodies adequate time to recover, the continual breakdown of muscles can lead to the more serious overtraining syndrome. With overtraining syndrome comes chronic fatigue, lingering muscle soreness, and even depression that can take months or years to recover from.
If a training program is making you feel irritable and low energy plus disrupting your sleep, it’s time to reevaluate your plan. Those symptoms are a first sign that you may need to take a couple of days off or decrease the volume and intensity of your workouts. Doing so might give you a better shot of reaching your fitness goals without sacrificing your body in the process. Killer suggests to practice “rest and recovery, eat decent meals packed with protein and iron, and even cross-training to reduce the mental fatigue that goes along with the grind.”