People train when it's convenient or when they feel like it, letting their life or emotions dictate when they hit the gym. However, changes in measures of muscular performance as well as hormone levels fluctuate throughout the day. Is it possible to choose a specific time where you have peak performance and hormone levels? Let's break down the science.
The Regulator of Life: Circadian Rhythms
A circadian rhythm is a 24-hour cycle controlling all the physiological processes of humans and animals. The functions of the circadian clock include organization of sleep/wake patterns, control of your hormones and metabolism, and even athletic performance.
The circadian system becomes responsive and adapts to environmental changes such as light/dark cycles, food intake, and exercise. The most relevant aspects for optimal training time are its effects on regulation of nervous system activity and hormonal production. By understanding these processes you may have a better idea of when to train and how the time of day may affect your results.
Both of these fluctuate throughout the day, peaking at certain times while being low at others. Here's a depiction of the typical fluctuations of biochemical and physiological events with a 24-hour period, known as a biorhythm:
As you can see, fluctuations throughout the day may have an impact on our performance levels and influence the hormonal concentrations around training. Although some data suggests that training in the early evening may provide the greatest force and muscle strength, it's not always as black and white as that.
Have you ever wondered why most sporting events are played in the afternoon, and why most world records are set in the mid-afternoon to evening? Studies in a variety of sports and activities – weightlifting, cycling, etc. – have shown measures of strength and power to be highest in the afternoon/evening compared to the morning. So, if you're an elite athlete trying to win a competition or set some records, this time of day may help.
Optimal body temperature for training normally occurs during this time, providing you optimal nerve conduction velocity, joint mobility and safety, metabolism, and muscular blood flow. Your core body temp is low at night, rises quickly upon awakening, and reaches a maximum in the evening. Keep in mind that activities requiring strength and power have been shown to be more affected by time of day than other forms of activities, such as endurance events.
The circadian rhythm also affects the fluctuations of your key hormones. The most important hormones related to training and body composition are testosterone, cortisol, and growth hormone. Testosterone is well known as a potent anabolic, muscle-building hormone. If we look at our testosterone levels throughout the day, in most cases, they're highest in the morning and will drop throughout the day.
However, this normal rhythm can be altered depending on your lifestyle, sleep, and daily activity. One important consideration is that testosterone levels normally increase after exercise, and the rise in testosterone after exercise appears to be more profound in the evening than it is in the morning.
Growth hormone (GH) is another muscle building hormone. Normally, the majority of GH is released in "pulses" when you sleep, with the largest pulses occurring before midnight and some smaller pulses in the early morning. As with testosterone, intense exercise acutely elevates growth hormone levels, providing spikes post-workout and altering our body's normal pattern at night.
In contrast, cortisol is a stress hormone with a bad reputation as it can cause muscle protein breakdown. While this is sometimes overplayed, cortisol does have some important roles. If cortisol is left elevated for some time it may have detrimental effects.
Our cortisol levels at rest follow a natural pattern, peaking in the morning and decreasing during the evening. Researchers have found the elevations of cortisol in response to exercise are lower in the early evening compared with the morning. In other words, if cortisol or other related factors such as recovery are an issue and you want to keep them under control, training in the morning may be best.
Theoretically, for maximal muscle growth, you'd want to have a high testosterone to cortisol ratio (muscle building vs. muscle breakdown). However, at this point in time the research is still controversial with regard to the relationship and effects of brief fluctuations in hormone concentrations on muscle growth.
So Is There Actually a Best Time to Train?
Only a few research studies have examined the relationship between training at different times and muscle growth. The most supportive evidence came from a 10-week training study where the subjects were assigned to either a morning (7-9 AM) or afternoon (5-7 PM) training group, both following the exact same training routine. Researchers found the afternoon group experienced a 3.5% increase in muscle size, versus 2.7% in the morning group.
So, while the trend is there, it failed to reach statistical significance. This may have been due to the timeframe (only 10 weeks, and muscle building is very slow) or amount of participants. Over 20, 30 or 40 weeks, these results may have been more noticeable, demonstrating a benefit for afternoon or evening training.
Lifestyle and Preference
Your preference is always an unappreciated yet vitally important aspect of diet or training. Far too often, people will make programming decisions based on what they believe to be "most optimal" at the cost of their own preference and lifestyle. For example, if training in the morning suits you better, is it best to disregard this and train in the evening for some form of hormonal and strength benefit?
The answer is no. Thinking logically, even if you were to get a 5% improvement in the evening, this would easily be countered by the fact you're probably less motivated and tired after work. You may also have less energy and will have decreased performance, which probably leads to you doing less total volume. Hey, you want to get home, right?
These variables, particularly intensity and volume (total sets, reps, and weight lifted), are proven to be the most important aspects of training for muscle growth. To maximize your progress, pick your training time on these two key variables. Train when you can perform best and have an uninterrupted workout and plenty of time for volume.
You can see the same issues with dieting. For example, a complex strategy, which may increase fat loss by 5%, will often be very difficult to sustain. The plan will be much harder to stick to, be less enjoyable, and cause you to quit or be less consistent. Consistency is the number one factor, so reducing your chances of achieving this for a small boost is a recipe for disaster, whether it's training or diet.
Pros vs. Average Joes
If you're a pro athlete who trains and competes for a career, training in the PM could give you that 1-2% boost that makes the difference between winning a race and placing tenth. However, a lot more research is needed to draw solid conclusions.
For most people, the optimal time to train is when it best suits your lifestyle and when you know you can go into the gym with focus, motivation, and energy. For some, this is in the morning before work when your mind is clear and you can give 100% to your workout. For others, it may be in the PM. It simply depends on your own preferences.
Even though it may seem that there's strong evidence for training in the mid-afternoon to evening to maximize performance and benefit from optimal hormone production, the evidence is far from conclusive. Ask yourself if it's really that important when you may end up leaving early, losing intensity and focus or, worst of all, not being consistent. Remember, consistency trumps "optimal" when it comes to training and nutrition.
- Shibata, S., & Tahara, Y. (2014). Circadian rhythm and exercise. The Journal of Physical Fitness and Sports Medicine, 3(1), 65-72.
- Hayes, L. D., Bickerstaff, G. F., & Baker, J. S. (2010). Interactions of cortisol, testosterone, and resistance training: influence of circadian rhythms.Chronobiology international, 27(4), 675-705.
- Atkinson, G. (1994). Effects of age on human circadian rhythms in physiological and performance measures (Doctoral dissertation, Liverpool John Moores University).
- Racinais, S., Perrey, S., Denis, R., & Bishop, D. (2010). Maximal power, but not fatigability, is greater during repeated sprints performed in the afternoon.Chronobiology international, 27(4), 855-864.
- Lericollais, R., Gauthier, A., Bessot, N., SesboŸŽ, B., & Davenne, D. (2009). Time-of-day effects on fatigue during a sustained anaerobic test in well-trained cyclists. Chronobiology international, 26(8), 1622-1635.
- Coldwells, A., Atkinson, G., & Reilly, T. (1994). Sources of variation in back and leg dynamometry. Ergonomics, 37(1), 79-86.
- Wyse, J. P., Mercer, T. H., & Gleeson, N. P. (1994). Time-of-day dependence of isokinetic leg strength and associated interday variability. British journal of sports medicine, 28(3), 167-170.
- Reilly, T., & Down, A. (1992). Investigation of circadian rhythms in anaerobic power and capacity of the legs. The Journal of sports medicine and physical fitness, 32(4), 343-347.
- Teo, W., McGuigan, M. R., & Newton, M. J. (2011). The effects of circadian rhythmicity of salivary cortisol and testosterone on maximal isometric force, maximal dynamic force, and power output. The Journal of Strength & Conditioning Research, 25(6), 1538-1545.
- Melhim, A. F. (1993). Investigation of circadian rhythms in peak power and mean power of female physical education students. International journal of sports medicine, 14(06), 303-306.
- Kelly, G. (2006). Body temperature variability (Part 1): a review of the history of body temperature and its variability due to site selection, biological rhythms, fitness, and aging. Alternative medicine review, 11(4), 278.
- Reilly, T., & Garrett, R. (1998). Investigation of diurnal variation in sustained exercise performance. Ergonomics, 41(8), 1085-1094.
- Dalton, B., McNaughton, L., & Davoren, B. (1997). Circadian rhythms have no effect on cycling performance. International journal of sports medicine,18(07), 538-542.
- GRISHAM, S. C. (1988). DIURNAL VARIATIONS IN RESPONSES TO EXERCISE OF ((MORNING TYPES AND ((EVENING TYPES. J Sports Med,28, 213-91.
- Reilly, T., & Garrett, R. (1995). Effects of time of day on self-paced performances of prolonged exercise. The Journal of sports medicine and physical fitness, 35(2), 99-102.
- West, D. W., & Phillips, S. M. (2010). Anabolic processes in human skeletal muscle: restoring the identities of growth hormone and testosterone. The Physician and sportsmedicine, 38(3), 97-104.
- Urban, R. J. (2011). Growth hormone and testosterone: anabolic effects on muscle. Hormone Research in Paediatrics, 76(Suppl. 1), 81-83.
- Kraemer, W. J., & Ratamess, N. A. (2005). Hormonal responses and adaptations to resistance exercise and training. Sports medicine, 35(4), 339-361.
- Brambilla, D. J., Matsumoto, A. M., Araujo, A. B., & McKinlay, J. B. (2009). The effect of diurnal variation on clinical measurement of serum testosterone and other sex hormone levels in men. The Journal of Clinical Endocrinology & Metabolism, 94(3), 907-913.
- Diver, M. J., Imtiaz, K. E., Ahmad, A. M., Vora, J. P., & Fraser, W. D. (2003). Diurnal rhythms of serum total, free and bioavailable testosterone and of SHBG in middle‐aged men compared with those in young men. Clinical endocrinology, 58(6), 710-717.
- Devi, S., Saxena, J., Rastogi, D., Goel, A., & Saha, S. (2014). Effect of short-term physical exercise on serum total testosterone levels in young adults.
- Zmuda, J. M., Thompson, P. D., & Winters, S. J. (1996). Exercise increases serum testosterone and sex hormone-binding globulin levels in older men.Metabolism, 45(8), 935-939.
- Deschenes, M. R., Bronson, L. L., Cadorette, M. P., Powers, J. E., & Weinlein, J. C. (2002). Aged men display blunted biorhythmic variation of muscle performance and physiological responses. Journal of Applied Physiology, 92(6), 2319-2325.
- Velloso, C. P. (2008). Regulation of muscle mass by growth hormone and IGF‐I. British journal of pharmacology, 154(3), 557-568.
- Weber, M. M. (2002). Effects of growth hormone on skeletal muscle.Hormone Research in Paediatrics, 58(Suppl. 3), 43-48.
- Davidson, J. R., Moldofsky, H., & Lue, F. A. (1991). Growth hormone and cortisol secretion in relation to sleep and wakefulness. Journal of Psychiatry and Neuroscience, 16(2), 96.
- Takahashi, Y., Kipnis, D. M., & Daughaday, W. H. (1968). Growth hormone secretion during sleep. Journal of Clinical Investigation, 47(9), 2079.
- Godfrey, R. J., Madgwick, Z., & Whyte, G. P. (2003). The exercise-induced growth hormone response in athletes. Sports Medicine, 33(8), 599-613.
- Goto, K. A. Z. U. S. H. I. G. E., Ishii, N. A. O. K. A. T. A., Kizuka, T. O. M. O. H. I. R. O., & Takamatsu, K. A. O. R. U. (2005). The impact of metabolic stress on hormonal responses and muscular adaptations. Med Sci Sports Exerc, 37(6), 955-63.
- Stokes, K. A., Sykes, D., Gilbert, K. L., Chen, J. W., & Frystyk, J. (2010). Brief, high intensity exercise alters serum ghrelin and growth hormone concentrations but not IGF-I, IGF-II or IGF-I bioactivity. Growth hormone & IGF research, 20(4), 289-294.
- Gore, D. C., Jahoor, F., Wolfe, R. R., & Herndon, D. N. (1993). Acute response of human muscle protein to catabolic hormones. Annals of surgery,218(5), 679.
- Simmons, P. S., Miles, J. M., Gerich, J. E., & Haymond, M. W. (1984). Increased proteolysis. An effect of increases in plasma cortisol within the physiologic range. Journal of Clinical Investigation, 73(2), 412.
- Peeters, G. M. E. E., Van Schoor, N. M., Van Rossum, E. F. C., Visser, M., & Lips, P. T. A. M. (2008). The relationship between cortisol, muscle mass and muscle strength in older persons and the role of genetic variations in the glucocorticoid receptor. Clinical endocrinology, 69(4), 673-682.
- Debono, M., Ghobadi, C., Rostami-Hodjegan, A., Huatan, H., Campbell, M. J., Newell-Price, J., ... & Ross, R. J. (2009). Modified-release hydrocortisone to provide circadian cortisol profiles. The Journal of Clinical Endocrinology & Metabolism, 94(5), 1548-1554.
- KRIEGER, D. T., ALLEN, W., RIZZO, F., & KRIEGER, H. P. (1971). Characterization of the normal temporal pattern of plasma corticosteroid levels. The Journal of Clinical Endocrinology & Metabolism, 32(2), 266-284.
- Weitzman, E. D., Fukushima, D., Nogeire, C., Roffwarg, H., Gallagher, T. F., & Hellman, L. (1971). Twenty-four hour pattern of the episodic secretion of cortisol in normal subjects. The Journal of Clinical Endocrinology & Metabolism, 33(1), 14-22.
- Kanaley, J. A., Weltman, J. Y., Pieper, K. S., Weltman, A., & Hartman, M. L. (2001). Cortisol and growth hormone responses to exercise at different times of Day 1. The Journal of Clinical Endocrinology & Metabolism, 86(6), 2881-2889.
- Hayes, L. D., Grace, F. M., Sculthorpe, N., Herbert, P., Ratcliffe, J. W., Kilduff, L. P., & Baker, J. S. (2013). The effects of a formal exercise training programme on salivary hormone concentrations and body composition in previously sedentary aging men. SpringerPlus, 2(1), 1.
- Schoenfeld, B. J. (2013). Postexercise hypertrophic adaptations: a reexamination of the hormone hypothesis and its applicability to resistance training program design. The Journal of Strength & Conditioning Research,27(6), 1720-1730.
- Sedliak, M., Finni, T., Cheng, S., Lind, M., & HŠkkinen, K. (2009). Effect of time-of-day-specific strength training on muscular hypertrophy in men. The Journal of Strength & Conditioning Research, 23(9), 2451-2457.