Ultimately, you should go with whatever time you feel most comfortable with and can manage considering all factors. These include your natural body clock plus social, work, health and environmental conditions as well as training and competing priorities.
Morning exercise
- The AM often suits running, walking and cardio exercise, rather than heavy weight lifting.
- Make sure you warm up before doing anything strenuous, especially in the morning.
- Take it easy on the back for a few hours after rising. Don't hop out of bed and try for a deadlift personal best.
- Weight training in the morning on an empty stomach is not a good idea because blood glucose can be low. (Diabetics can sometimes have high blood sugar in the morning.)
- Taking some food or a shake about 30 minutes before training can help power you through the sessions and avoid training in a catabolic environment, which won’t help your muscle maintenance or enhancement.
Evening exercise
- Team sports and weight training may benefit from evening or PM workouts. However, this may not apply to everyone.
- Early evening gym sessions are popular with weight trainers.
- Training too late in the evening may not be ideal for nutritional recovery and sleep patterns.
- Some trainers find that doing cardio in the morning and weight training in the evening works well for them.
Sources
Atkinson G, Reilly T. Circadian variation in sports performance.
Sports Med. 1996 Apr;21(4):292-312. Review.
Winget CM, DeRoshia CW, Holley DC. Circadian rhythms and athletic performance. Med Sci Sports Exerc. 1985 Oct;17(5):498-516. Review.
Reilly T, Atkinson G, Gregson W, Drust B, Forsyth J, Edwards B, Waterhouse J. Some chronobiological considerations related to physical exercise. Clin Ter. 2006 May-Jun;157(3):249-64. Review.
Reilly T, Atkinson G, Edwards B, Waterhouse J, Farrelly K, Fairhurst E. Diurnal variation in temperature, mental and physical performance, and tasks specifically related to football (soccer).
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Bird SP, Tarpenning KM. Influence of circadian time structure on acute hormonal responses to a single bout of heavy-resistance exercise in weight-trained men. Chronobiol Int. 2004 Jan;21(1):131-46.
