According to WebMD, there is no single time of the day that is best for working out. A body's circadian rhythm, governed by the 24-hour rotation of the earth, influences a person's readiness to exercise. Choosing a time to work out is also influenced by family or work schedules.
Cedric Bryant, PhD, chief science officer with the American Council on Exercise in San Diego, states that research suggests exercising in the morning is most beneficial in establishing a consistent routine. The American Heart Association states that an individual should choose a time for working out based on location, type of physical activity and social setting. The important thing is to be consistent with regular exercise.