I got this from thefactsaboutfitness site, and thought it was interesting:
"The best time of day to hit the weights...
Everyone has their own theories and preferences about the "right" time of the day to exercise. Some people, such as 5-time Mr. Universe Bill Pearl, like to get up early and finish their workouts before dawn. Others prefer to exercise in the late afternoon or evening.
Measures of muscular performance (such as strength and power), as well as hormones (like testosterone, cortisol and growth hormone) have their own unique rhythm or timing pattern, where there are low points and high points over the course of the 24-hour day.
But, how much does it really matter? Should your workouts be timed to coincide with a certain hormonal profile, such as a high testosterone-cortisol ratio? Is the time of day you exercise all that important?
Performance
As a rule-of-thumb, most people seem to be strongest in the afternoon or evening. And most of the studies I've seen also show that muscle strength wanes in the morning and gradually improves until it peaks in the early evening.
One study, published in
Medicine and Science in Sports and Exercise, looked at the effect of time of day on muscular performance in a group of untrained men in their early twenties [1]
Each man performed a series of strength tests at 8:00am, 12.00pm, 4.00pm, and 8.00pm. The results show that muscle performance was greatest in the evening, but only during the exercises that involved faster movements.
Studies of older men show similar results. In one trial, ten older men with an average age of 76 performed a series of strength tests at 8.00am, 12.00pm, 4.00pm, and 8.00pm [2].
Similar to young men, the older guys were weaker in the morning than they were in the evening. Of 36 muscle function tests, performance was least impressive at 8.00am in 26 of the tests.
“Simply stated, in an aged system, the peaks and nadirs occur at the same times as they do in a younger system,“ say the researchers, “but these highs and lows are not as pronounced as those observed among the young.”
In other words, the extent to which performance differs between the morning and evening is not as pronounced in older as it is in younger men
Why was performance greater during the faster, rather than the slower movements?
One theory is that the activation of fast
twitch muscle fibers — which are called into action when force requirements are high — is preferentially enhanced at a higher body temperature, which tends to peak in the early evening
So, if your workouts involve a lot of strength- or power-based movements, the chances are you'll perform a little better in the evening than you will in the morning.
Hormones
Hormones such as testosterone (an "anabolic" hormone) and cortisol (a "catabolic" hormone) also vary during the day. Testosterone, for example, peaks in the morning and drops at the end of the day.
However, while resting testosterone levels reach a low point in the evening, the rise in testosterone after exercise appears to be greater in the
evening than it is in the
morning [2].
Resting levels of the hormone cortisol are also higher in the morning and lower in the evening. But the cortisol response to exercise is lower in the early evening (7.00pm) compared with the morning (7.00am) [5].
In other words, the testosterone-cortisol ratio (when testosterone levels are highest relative to cortisol levels) is higher in the early evening than it is in the morning. This, in theory at least, makes the evening the least "catabolic" time to train [4].
However, keep in mind that hormone levels are affected by your
habitual diet, as well as what you eat before and after exercise. And the effect that transient changes in hormone levels have on gains in muscle size and strength over several months is open to debate.
One study, presented at the 2005 National Strength and Conditioning Association's annual meeting in Las Vegas, looked at the effect of training in the morning or evening on muscle mass, body fat and strength.
A group of 16 men trained for 10 weeks either before 10.00am (AM group) or after 6.00pm (PM group). Workouts consisted of 45 minutes of weight training followed by 45 minutes of
cardiovascular exercise.
The PM group had a 3.2% increase in lean mass, compared with a 0.6% gain in the AM group. Body fat dropped by 4% in the PM group, while it actually increased by nearly 5% in the AM group. However, none of these changes was sufficient to reach statistical significance.
The problem here is that studies presented at conferences are often poorly controlled, and there's usually little or no information available about how the research was done.
This study, for example, was done at the University of Southern Mississippi. I'm guessing that the subjects who took part were also students at the university.
Based on my experience of students, a lot of them are still asleep at ten in the morning. Maybe the AM group didn't make much progress because most of the subjects skipped the workouts and stayed in bed. Perhaps they were all so tired that they just went thought the motions before sinking their face into a plate of pancakes for breakfast. In any case, it's hard to draw any meaningful conclusions about what these results mean for you and me.
Chronotype
Individual differences will also need to be taken into account when deciding on the "best" time of day to train. The Owl and Lark Questionnaire, for example, differentiates people according to their
chronotype. Owl individuals are said to be more "alert" during the evening while Lark individuals are more "alert" in the morning [6, 7].
It's possible that Owls will get better results from training in the evening, while Larks might make better progress if they train in the morning
Personally, I've trained at virtually every hour of the day, though I much prefer to get it done in the morning. Even though I know I'm slightly weaker at this time of day, the benefits of morning exercise (for me, anyway) far outweigh the downsides.
Firstly, the gym is quieter, so I don't have to wait around to use the equipment. Morning exercise also gives me more energy and brightens my mood for the rest of the day.
However, when I was studying at University (and working a full-time job at the same time) I would often train around midnight, simply because that was the only time I could fit it in.
The only time of day I actively avoid exercise is in the early afternoon, where I tend to suffer from a post-lunch "dip" in energy. Some studies also show that certain aspects of performance deteriorate at this time without a corresponding decrease in body temperature and even if no food is eaten at lunchtime [3].
If you want to get in shape and stay that way, exercise will need to be something you do most days of the week for the rest of your life. And there'll be times when you won't be able to match your circadian rhythms to your workout schedule, or set records every time you train.
Don't be discouraged. It's a lot more important to work hard and be consistent than to waste time and energy second-guessing whether you're training at the "right" or "wrong" time of day.
References
1. Deschenes, M.R., Kraemer, W.J., Bush, J.A., Doughty, T.A., Kim, D., Mullen, K.M., & Ramsey, K. (1998). Biorhythmic influences on functional capacity of human muscle and physiological responses.
Medicine and Science in Sports and Exercise,
30, 1399-1407
2. 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, 2319-2325
3. Atkinson, G., & Reilly, T. (1996). Circadian variation in sports performance.
Sports Medicine,
21, 292-312
4. Bird, S.P., & Tarpenning, K.M. (2004). Influence of circadian time structure on acute hormonal responses to a single bout of heavy-resistance exercise in weight-trained men.
Chronobiology International,
21, 131-146
5. 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.
Journal of Clinical Endocrinology and Metabolism,
86, 2881-2889
6. Bailey, S.L., & Heitkemper, M.M. (2001). Circadian rhythmicity of cortisol and body temperature: morningness-eveningness effects.
Chronobiology International,
18, 249-261
7. Merrow, M., Spoelstra, K., & Roenneberg, T. (2005). The circadian cycle: daily rhythms from behaviour to genes.
EMBO Reports,
6, 930-935"
So what is everyone's favorite time of the day to workout? I personally prefer to workout about 4 - 5 hours after I wake up, which varies in time from day to day.
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