Working out in the morning can boost energy for the rest of the day. An a.m. workout jump-starts metabolism in the same vein that eating breakfast does. The thermal effect of exercise (or activity) lasts at least four hours after a workout. That increases the total calorie expenditure throughout the day.
In the 8-12 hours prior waking, your body was in sleep mode and, depending on the quality of sleep, in a process of regeneration. A workout causes microscopic tears in the muscle fibers. Oxidation also takes place on the cellular level and energy stored in the muscle fibers are utilized. Sleep is the time for the body to repair damage. Antioxidants repair cellular damage. Food is digested and converted to glucose. In the morning, you're using a fresh, repaired and, in some instances, new body. During REM sleep, dreams are also a chance for the body to rehearse or even learn new motor skills — that clean and snatch is smoother and easier than it was during your last workout because you essentially had time to practice during your sleep.