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When Is the Best Time of the Day to Train…The Latest Research

April 7th, 2009 · No Comments

It’s 8:00 am and all the football players have arrived for pre-season max out in the bench press, squat, and power clean. Many of the players still look they are not completely awake and others just seemed stiff yet they are expected to max out! I never understood when I was a strength coach why they scheduled max out’s so early in the morning when the latest research suggests that maximal strength is best achieved in the afternoon1. In the July issue of the International Journal of Sports Medicine, researchers examined peak strength at four different times of the day (7-8 am, 12-1 pm, 5-6 pm, 10:30-11:30 pm) for two consecutive days.

The researchers reported that on the morning values were significantly lower when compared to the rest of the day. There are many variables which can affect a lifter’s ability to generate peak force; however none of the variables measured (sleep, stress level, normal circadian rhythms of the person (morning or night person) had a significant effect on the outcome. This study was similar to an earlier study which had subjects perform peak isometric strength parameters at 8-9 am, 1-2 pm, and 6-7 pm; peak strength was greatest between 6-7 pm. When they compared the percent increase from session to session, there was a 2.76% increase from the morning to afternoon session, but an 11.13% increase from the afternoon to the evening session5. Similar results were also reported in the Journal of Electromyography and Kinesiology where it was found that peak muscle strength was higher at 6 pm compared to 6 am4. The average increase in strength from morning to evening was 4.6%. Clearly this is not a psychological issue yet more of a physiological condition. This is not the first study to demonstrate this effect; at least two other studies have demonstrated peak strength to be higher at 6 pm than at 6 am2, 3. This means much like there are changes in GH/cortisol throughout the day; it appears there are also circadian rhythms in strength during the day with strength being higher in the afternoon/early evening.

Temperature and Muscle Strength
The circadian rhythm amplitude of muscle strength has been found to range from 3.9% for the biceps muscles to 10.6% for the back muscles. So why is muscle strength higher in the afternoon compared to morning sessions? There is one physiological variable that seems to correlate with the peak increases in strength which is body temperature. Body temperature is lowest in the morning and increases throughout the day. Muscular strength and body temperature appear to be associated by some authors6, 7. It is now recognized that torque and temperature vary during the day but fluctuations in torque cannot be entirely explained by change in temperature. Maximal performance is generally improved by the end of the afternoon, at the peak of the body temperature curve7, 8. Some studies have suggested that the simultaneous increases in both body temperature and muscular performance are causally related, and that the circadian rhythm of body temperature could be regarded as a passive warm-up effect9.

Raising Body Temperature May Enhance Strength
The change in body temperature seems to have a favorable effect on increasing strength. In a previous study conducted in a tropical environment, researchers failed to show any daytime variation in muscle performance. That suggests that the passive warm-up effect of the moderately warm and humid environment may have blunted the passive warm-up effect of time of day10. Researchers from France did a study in which they manipulated the temperature at various time of the day. The four following sessions were conducted in random order in the following conditions: morning/neutral, morning/moderately warm and humid, afternoon/neutral, and afternoon/moderately warm and humid. The results of the study suggests that muscle contractility was differently influenced by a moderately warm and humid exposure, depending on whether the tests were performed in the morning or in the afternoon, that is, depending on the initial level of body temperature. For example, in the morning, muscle contraction was significantly increased in moderately warm and humid conditions in comparison with neutral environment, whereas it did not vary in the late afternoon, which explains the lack of variation in maximal contractions in the moderately warm and humid conditions. This shows that muscle force was more sensitive to an external passive warm-up effect in the morning, when body temperatures are their lowest levels. Nevertheless, muscle force does not seem to be sensitive to an external passive warm-up effect in the afternoon, when body temperatures are their highest levels. In summary, the data showed that both a warm exposure and the diurnal increase in body temperature influence muscle contractility to increase muscle strength, but that the improvement in muscle contractility after these two passive warm-ups cannot be combined to improve force to a greater level. This suggests that a ceiling effect of the possible beneficial effects of passive warm-ups is reached with either the diurnal increase in body temperature or a moderately warm exposure.

Is it the Calcium, Blood Flow, or Hormones?
flex_wheeler_and_don_long_reps.jpgResearchers are not exactly sure as to how muscle temperature affects muscle strength but some interesting theories have been suggested. The increases in afternoon strength do not seem to be mediated by the nervous system, but most likely are mediated at the peripheral level (muscle itself) 14. One theory suggests greater Ca2 retention by the sarcoplasmic reticulum (Ca which causes muscle contraction is stored in the sarcoplasmic reticulum) decreases when the temperature drops12, 13. Another possibility to consider is that interleukin-6, tumor necrosis factor, and cortisol all have diurnal variations which are higher in the morning compared to the afternoon. Blood flow to muscle could also be a contributing factor.

British researchers looked at heart rate, core temperature, sternum skin temperature and forearm skin blood flow during exercise, and throughout a subsequent 30-minute recovery period in 12 males exercising at 70% VO2max at both 8.00 am and 6.00 pm. Comparisons were made of the changes of heart rate, temperature, and skin blood flow produced by the exercise at the two times of day. What the researchers found was that the increases in core and sternum temperatures during the afternoon exercise were significantly less than the morning, even though the workloads were not significantly different. Also, resting forearm skin blood flow (a measure of the ability of the body to lose excess heat) was higher in the afternoon exercise bout and the rate of change of blood flow as exercise was commenced was also higher.

What If you can only Train in the Morning?
If you can only train in the morning are you totally screwed? Most of the studies examining strength changes in the morning and afternoon have used participants whom normally train in the afternoon which cloud the results of the study. Previous research has documented that several weeks of repeated strength training performed in the morning hours may reduce the typical diurnal strength patterns by increasing maximum strength more in the morning than at other times of day17. This means that after several weeks of training in the morning, the body resets the nervous system to adapt to morning strength sessions. In fact, a previous study reported that traditional low-frequency strength training performed in the morning, but not in the afternoon, was found to attenuate the typical diurnal variation in maximum strength. However, the absolute increase in maximum strength was similar regardless of the time of day of training18. It seems that if you normally train in the afternoon, maxing out in the morning is going to lead to a reduction in peak strength but after several weeks of morning training the body adapts to morning training.

In conclusion, getting to the gym is the key point regardless of whether it’s in the morning or afternoon. It seems that there are circadian rhythms in strength during the day with peak strength peaking in the afternoon compared to the morning. Many studies have demonstrated that peak strength occurs is casually related with body core temperature. Muscle temperature can explain some but not all the variations in muscle strength throughout the day. If you have to train in the morning, you can also increase muscle strength by raising body temperature. You may want to bundle up and get a good sweat going before starting to workout. As reported in the study mentioned above, lifters were able to increase muscle strength in the morning when they trained in a warm/humid environment. Possibly by sitting in a sauna for 15 minutes before training or spending a little extra time warming up may be needed to increase body core temperature. If you have to max out at a certain time of the day, try to schedule an afternoon session which seems to be where peak strength hours occur. It also seems that by training in the morning for several weeks causes the body to adapt to morning training which can favor strength increases.

Key Points:

? Maximal strength is best achieved in the afternoon compared to the morning.
? Maximal strength has been casually correlated with body temperature which peaks in the afternoon which may have a “pre-warm” up effect on muscle which may enhance force production.
? Interleukin-6, tumor necrosis factor, and cortisol all have diurnal variations which are higher in the morning compared to the afternoon which may have a unfavorable training effect

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