New research says that if you do strength training and cardio workouts at certain times, you'll maximize fitness' sleep-enhancing effects

By Caitlin Carlson
December 10, 2014

Getting enough exercise and sleep is key to scoring a healthy body and mind (check out what happens to your body when you're sleep deprived). And fitness and zzz's compliment each other nicely: Sleep gives you energy to exercise and exercise helps you sleep sounder, per, well, countless studies. But, most of those studies have focused on cardio rather than resistance training-until recently.

To find out how the timing of strength workouts impacted sleep quality, Appalachian State University researchers had participants visit their lab for a 30-minute workout on three separate days at 7 a.m., 1 p.m., and 7 p.m. People wore sleep trackers to bed. The results: On the days they worked out, participants spent less time awake throughout the night compared to days when they didn't exercise. But here's where it gets interesting: People fell asleep in almost half the time if they did strength training at 7 a.m. rather than 1 p.m. or 7 p.m. "Resistance exercise increases resting heart rate leading to (temporarily) higher blood pressure-making it slightly tougher to fall asleep," says study author Scott Collier, Ph.D.

A strange twist: When researchers looked at the quality of sleep, they found subjects who lifted at night slept more soundly! "Resistance exercise has a thermal effect (it warms you up internally-like a warm bath before bed), which could explain why subjects slept sounder upon falling asleep," says Collier. So, while it may take you longer to fall asleep if you lift later in the day, this study suggests you'll sleep better.

Aerobic exercise, on the other hand, decreases resting heart rate, so doing it first thing in the a.m. is smart. (Try this cardio workout that's better than the treadmill) In fact, according to research previously done by Collier and his team, "7 a.m. is the best time to engage in aerobic exercise since it clears stress hormones earlier in the day which lends to a better night's sleep."

The bottom line: Exercise-resistance or cardio-is great whenever you do it. But if you're having trouble sleeping or want to switch things up, try doing cardio in the morning and weight training in the afternoon or early evening, Collier suggests.