Timing is everything, especially when it comes to working out.
If you exercise at the right time on your body's internal clock, it will fill you with energy, not fatigue. To figure out whether your body responds best to morning or evening exercise, keep a workout diary. For a few weeks, take careful notes about the time of your workouts and how you feel before, during and after them. Also note whether your workout patterns make it difficult to fall asleep at night, or make you want to nap during the day. Once you've tested your routine at various times of the day, check your notes and determine your ideal fitness schedule.