Most fit people can recover from a 60-minute endurance workout within a few hours, but it can take one to three full days for your muscles to mend after lifting, says study author Kenji Doma, Ph.D., exercise science researcher at James Cook University in Townsville, Australia. Earlier findings from his team show that during the repair process, your VO2 max is lower than normal.
If you regularly lift and then run on the same day or the next, you’ll never allow your body to fully recover, and thus you’ll be more likely to plateau, fatigue, and get injured, Doma says.
The bottom line:
You'd ideally run or cycle on one day and strength train the next once your muscles are back to full function. When doubling up, always do cardio first and weights at least six hours later, Doma says, and never on consecutive days.