While convenience ultimately prevails and you may be better off working out whenever your schedule allows, here are some things to consider.
The average person is about 25% hypoglycemic upon awakening. This could be good or bad. Good because the resultant insulin levels are low from a hypoglycemic state and you are more lipolytic naturally (favorable to burning fat) than any other time of day. Bad, because your core body temperature, your energy level (and quite possibly motivation) is low and your joints are stiff (especially if you are over 40).
Historically, there is a higher frequency of heart attacks in the morning than other times of the day. This is attributed to a combination of high testosterone and cortisol levels from fasting all night (typically 8 hrs) and the fact your body is at a low point having just come out of deep sleep. If you are a beginner or deconditioned, over 40, and have coronary risk factors, take extra caution if you intend to exercise strenuously in the morning. A proper warm-up and cool-down is vitally important as part of your early morning exercise session.
During the course of a day, your core body temperature, blood pressure, muscle temperature and heart rate fluctuates. Energy levels are influenced by everything from mood changes to the natural cycles in your body called the circadian rhythm. Your body is truly at its "physical best" for a workout in the latter part of the day.
Performing exercise in the middle of the day could prove to be beneficial as it may prevent the "biological sleepy time", by increasing the flow of epinephrine and norepinephrine, hormones that elicit an excitability response. Performing strength exercises during this time is optimal, as body and muscle temperature are at their highest. Joints and muscles are more flexible. Breathing is easier because the lungs' airways are more open.
In the end however, the best solution is to come up with a regular schedule and stick to it because regularity is far more important than being concerned with whether you workout in the morning or afternoon. Let us know if we can be of help at Azhar Therapy & Fitness.
