Does it Matter What time of Day You Train?

Background

To answer the question posed in the title of this post, it depends. Truthfully, the answer to most questions posed in the world of sports science is “it depends”. In brief, it truly doesn’t matter what time of day you choose to train, or when your athletes train if you are a coach, as whatever time works best for you to fit in your training as easily and efficiently as possible will always be best. However, if you are an athlete that has some flexibility in the time of day you choose to fit in your training session(s) and you want to maximize your sessions to the best of your ability, there are some important differences in your physiology that characterize morning versus evening times of day. Let’s discuss these differences next.

Time of Day: Morning versus Evening

Firstly, let’s define “morning” and “evening”. Most studies that investigate morning versus evening exercise use a time of day that falls within 7:00-10:00 am and soon after waking as a “morning” time of day and a time of day that falls between 4:00-8:00 pm as an “evening” time of day. Some studies will use an “afternoon” time that consists of a time of day a little earlier than 4:00 pm. For the purposes of this discussion herein, let’s define “morning” as any time between 7:00-10:00 am and soon after waking and afternoon/evening as any time after 12:00 pm and further away from waking.

It has long been documented in the strength and conditioning research literature that muscular strength and power performance as well as short-term anaerobic performance has a time-of-day effect, with better performance in the late afternoon or evening than the morning soon after waking (4-18). One of the primary contributors to this change in performance capacity throughout a 24-hour day is thought to be body temperature. Earlier in the morning and soon after waking, body temperature is near its lowest; however, body temperature reaches its natural peak in the afternoon (1,3). Body temperature matters quite a bit when it comes to athletic performance for a variety of reasons, most of which relate to improved nervous and muscular function when body temperature is higher. If you have ever gone on a run first thing in the morning on a cold winter day and compared it to a run on a mild spring afternoon, you might be acutely aware of what I am talking about here.

More recently, researchers have been looking at whether these time-of-day effects on performance are relevant to endurance athletes.

Effects of Time-of-Day on Endurance Performance

Kang and colleagues (2) just recently published a 2023 systematic review and meta-analysis (one of the highest forms of scientific evidence is a systematic review and meta-analysis) in which they aimed to answer the question of whether there is a time-of-day effect on cardiovascular exercise response and endurance performance. To answer their research question, they identified 31 published studies that, collectively, included 393 subjects (ages 18-38 years; 73% men; mostly healthy adults and some athletes with prior endurance experience) to include in the review. They then performed a meta-analysis to identify any time-of-day effects across various physiologic and performance outcomes (compared between morning [AM] and afternoon/evening [PM]).

The meta-analysis ultimately revealed the following key takeaways:

1. Higher resting oxygen intake (VO2) and heart rate (HR) in the PM compared to the AM

2. Higher HR at both submaximal and maximal endurance intensities in the PM compared to the AM

3. Greater endurance performance (as measured by time-to-exhaustion or total workload performed) in the PM compared to the AM

4. No significant metabolic differences during submaximal nor maximal endurance exercise (i.e., VO2, substrate utilization) in the PM compared to the AM

These findings are important for a variety of reasons. First, the differences in HR and overall performance are of note for researchers, coaches, and clinicians who might perform exercise testing with research subjects or athletes. Having an understanding that testing results might differ when comparing AM to PM performances is valuable information when deciding how and when to incorporate standardized testing in research settings or real-world settings. Second, this is important for athletes to understand as it might influence the timing of certain key training sessions. Let’s discuss this second point in more detail.

Choosing the “Best” Time to Train

From an athlete’s perspective, and even a coach’s perspective, knowing that endurance performance is potentially greater in the PM could influence the timing of key training sessions that include higher-intensity efforts. For example, if an athlete has the flexibility to choose between AM or PM sessions, performing intense training sessions later in the day could be advantageous as the total workload or output of the session during the intense efforts might be greater, thereby yielding a greater adaptive stimulus. This might not seem important when considering a single stand-alone training session, but stack together many weeks and months of PM training sessions in which the adaptive stimulus is slightly greater, and this could translate into greater long-term fitness improvements and race performances. At this point, that last statement is hypothetical as this sort of long-term research has not been done yet.

Despite the above, this is in no way an indication that performing an intense or key training session in the AM is somehow disadvantageous. It is simply a matter of suggesting that, if one has flexibility to do so and it works well for them, choosing to perform high-quality, intense training sessions at times of the day when performance might be marginally better could provide a greater return on their investment. Like I mentioned at the beginning of this write-up, performing training sessions when it is the most convenient and efficient for an athlete to do so will always be the optimal choice, regardless of the time-of-day (italicized for emphasis). Furthermore, research provides broad insights into what tends to work best for the average majority. There are always outliers, and some athletes might perform better in the AM when compared to the PM based on their individual psychology and physiology.

Conclusions

The evidence discussed herein suggests that there might be improved endurance performance in the PM compared to the AM. This can be very useful for many athletes and coaches looking to optimize the timing of key training sessions. Flexibility in having a choice in the time-of-day one trains is a prerequisite to take advantage of this potential performance benefit, in my opinion. Training that gets completed as smoothly and efficiently as possible will always be best, regardless of the time-of-day it was performed. If you are fortunate enough to have flexibility in deciding when to train and you enjoy training in the PM, then scheduling high-quality, intense training sessions later in the day might be a smart choice!

References:

1. Atkinson G, Reilly T. Circadian variation in sports performance. Sports Med 21: 292–312, 1996.

2. Kang J, Ratamess NA, Faigenbaum AD, Bush JA, Finnerty C, DiFiore M, Garcia A, Beller N. Time-of-Day Effects of Exercise on Cardiorespiratory Responses and Endurance Performance—A Systematic Review and Meta-Analysis. The Journal of Strength & Conditioning Research. 2022 May 9:10-519.

3. Waterhouse J, Drust B, Weinert D, et al. The circadian rhythm of core temperature: Origin and some implications for exercise performance. Chronobiol Int 22: 207–225, 2005.

4. Guette M, Gondin J, Martin A, Pérot C, Van Hoecke J. Plantar flexion torque as a function of time of day. International journal of sports medicine. 2005 Jun 2:171-7.

5. Sedliak M, Finni T, Cheng S, Haikarainen T, Häkkinen K. Diurnal variation in maximal and submaximal strength, power and neural activation of leg extensors in men: multiple sampling across two consecutive days. International journal of sports medicine. 2008 Mar;29(03):217-24.

6. Zbidi S, Zinoubi B, Vandewalle H, Driss T. Diurnal rhythm of muscular strength depends on temporal specificity of self-resistance training. The Journal of Strength & Conditioning Research. 2016 Mar 1;30(3):717-24.

7. Chtourou H, Zarrouk N, Chaouachi A, Dogui M, Behm DG, Chamari K, Hug F, Souissi N. Diurnal variation in Wingate-test performance and associated electromyographic parameters. Chronobiology international. 2011 Oct 1;28(8):706-13.

8. Souissi N, Bessot N, Chamari K, Gauthier A, Sesboüé B, Davenne D. Effect of time of day on aerobic contribution to the 30‐s Wingate test performance. Chronobiology international. 2007 Jan 1;24(4):739-48.

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10. Giacomoni M, Billaut F, Falgairette G. Effects of the time of day on repeated all-out cycle performance and short-term recovery patterns. International journal of sports medicine. 2006 Jun;27(06):468-74.

11. Hammouda O, Chtourou H, Chahed H, Ferchichi S, Kallel C, Miled A, Chamari K, Souissi N. Diurnal variations of plasma homocysteine, total antioxidant status, and biological markers of muscle injury during repeated sprint: effect on performance and muscle fatigue—a pilot study. Chronobiology international. 2011 Dec 1;28(10):958-67.

12. Hammouda O, Chtourou H, Chahed H, Ferchichi S, Kallel C, Miled A, Chamari K, Souissi N. Diurnal variations of plasma homocysteine, total antioxidant status, and biological markers of muscle injury during repeated sprint: effect on performance and muscle fatigue—a pilot study. Chronobiology international. 2011 Dec 1;28(10):958-67.

13. Racinais S. Different effects of heat exposure upon exercise performance in the morning and afternoon. Scandinavian journal of medicine & science in sports. 2010 Oct;20:80-9.

14. Racinais S, Hue O, Blonc S. Time-of-day effects on anaerobic muscular power in a moderately warm environment. Chronobiology international. 2004 Jan 1;21(3):485-95.

15. Zarrouk N, Chtourou H, Rebai H, Hammouda O, Souissi N, Dogui M, Hug F. Time of day effects on repeated sprint ability. International journal of sports medicine. 2012 Dec;33(12):975-80.

16. Chtourou H, Chaouachi A, Driss T, Dogui M, Behm DG, Chamari K, Souissi N. The effect of training at the same time of day and tapering period on the diurnal variation of short exercise performances. The Journal of Strength & Conditioning Research. 2012 Mar 1;26(3):697-708.

17. Chtourou H, Driss T, Souissi S, Gam A, Chaouachi A, Souissi N. The effect of strength training at the same time of the day on the diurnal fluctuations of muscular anaerobic performances. The Journal of Strength & Conditioning Research. 2012 Jan 1;26(1):217-25.

18. Gauthier A, Davenne D, Martin A, Cometti G, Hoecke JV. Diurnal rhythm of the muscular performance of elbow flexors during isometric contractions. Chronobiology international. 1996 Jan 1;13(2):135-46.

19. Martin A, Carpentier A, Guissard N, Van Hoecke J, Duchateau J. Effect of time of day on force variation in a human muscle. Muscle & nerve. 1999 Oct;22(10):1380-7.

20. Sedliak M, Finni T, Peltonen J, Häkkinen K. Effect of time-of-day-specific strength training on maximum strength and EMG activity of the leg extensors in men. Journal of sports sciences. 2008 Aug 1;26(10):1005-14.

Happy training and racing!

-Ryan Eckert, MS, CSCS

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