Strength Training Versus Endurance Training
Muscle recovery time for aerobic exercises like running or cycling is different than for lifting weight or other anaerobic exercises. You may not need to schedule a “recovery day” after an easy ride, run, or session on the elliptical. However, if you are doing a more strenuous aerobic workout, a recovery day may be warranted.
After weight lifting, muscle groups may need to rest for longer, possibly up to 48-72 hours before the next workout. This is one reason why many people who lift weights focus on single segments of the body during each session. After a lower body day, the upper body is still fresh and can be worked out sooner.
Regardless of whether you switch between exercises or upper and lower body workouts, you still need to take an official rest day. On this day, the only activities allowed are gentle ones such as walking or yoga. This will help you keep your free testosterone to cortisol ratio higher, and prevent overtraining.
Remember, muscle recovery is only part of recovery. You also need to let your mind and hormones recover!