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What's the Best Time to Work Out?

On any given day, you can find millions of people engaging in some sort of exercise or physical fitness regiment. Some exercise with hopes of losing weight, others to build muscle and others for a variety of other purposes. Based on your specific fitness goals, you may benefit from working out at different times to maximize the potential benefits of your workouts. There are several reputable sources that point to the fact that the purpose and availability of time for exercising determines the best time to work out.

Our bodies follow a 24-hour cycle called the circadian rhythm. Within the circadian rhythm lies the ultradian rhythm, which is a recurrent period that cycles within this 24-hour period. Such things as blood circulation, heart rate, thermoregulation, urination and appetite constantly change during this 24 hours period which can affect the quality and quantity of a workout.

Woman showing her abs with alarm clock after weight loss on blue background

For Athletic Performance

Research has demonstrated that the time of day has more of an effect on anaerobic exercises requiring muscular strength than it does for aerobic exercises requiring maximal cardiorespiratory capacity.

Muscular strength was found to increase during the latter part of the day as compared to the morning. Several factors may contribute to this effect, including but not limited to increased body temperature, availability of increased glucose stores, increased flexibility and increased contractility of muscles. 1 It was also noted that resistance to muscle injury was increased later during the day. Strength gains were documented to have increased between mid to late afternoons. These strength gains were contributed to many of the factors listed above, but mainly to the ingestion of food throughout the day, which results in the “topping off” of available stored energy (glucose).

On the other hand, research has shown that aerobic exercises are less affected by the time of day.  Testing found that heart rate, exhaustion nor maximal oxygen uptake differed from a morning or afternoon workout.

For Weight Loss

Research has shown that AM workouts help to produce the highly sought after slimming effect of exercise. In a 2010 Belgium study, several male subjects were placed into three groups. All groups were fed 30% more calories and 50% more fat per day for 6 weeks.2 The first group performed endurance exercise training for 4 days per week in a fasted state. The second group ingested carbohydrates before and during each training session. The third group didn’t train at all. Of course, body weight increased for the third group and second groups. However, the first group never realized any body weight increases. Since we tend to be in a fasted state in the morning, the best time to work out to lose weight is in the AM.

However, with all of this research, the general rule for the best time to exercise is to exercise when you have time to do so. Generally speaking, consistently exercising within a window of time that allows you to meet the American College of Sports Medicine’s (ACSM) standard of 150 minutes of moderate-intensity of exercise per week works best as a rule of thumb.3


  1. “Chronobiological Effects on Exercise.” ACSM CURRENT COMMENT (n.d.): n. pag. American College of Sports Medicine. Web. 13 Oct. 2015. <>.
  2. Van Proeven, K., K. Szlufcik, H. Nielens, K. Pelgrim, L. Deldicoue, and M. Hesselink. “Training in the Fasted State Improves Glucose Tolerance during Fat-rich Diet.” National Center for Biotechnology Information. U.S. National Library of Medicine, Nov. 2010. Web. 13 Oct. 2015. <>.
  3. “ACSM Issues New Recommendations on Quantity and Quality of Exercise.” ACSM | News Releases. N.p., n.d. Web. 13 Oct. 2015. <>.