Science Says This Is the Absolute Best Time of Day to Work Out

While it depends on a couple key factors, most people will experience peak athletic performance during this period of the day.

At this very second, trillions of clocks inside your body are ticking away.

Their job is to keep track of time and optimize your body to stay in sync with a 24-hour day/night cycle. These internal clocks help dictate your circadian rhythms, which are defined as "physical, mental and behavioral changes that follow a daily cycle." Ever wonder why you get sleepy at the same time every night? Or hungriest during the same periods every day? That's your circadian rhythms at work. But it's not just about sleeping and eating—your internal clocks can also determine when you're most ready to train. Every athlete knows the thrill of totally crushing a workout, only because they've also experienced the drag of training while they're at less than their best. Here's what you need to know about the relationship between circadian rhythms and athletic performance.

Michael Smolensky, co-founder of the Memorial-Hermann Chronobiology Center and an adjunct professor of biomedical engineering at the University of Texas, once told the Wall Street Journal that physical performance "is usually best, and the risk of injury least, from about 3 p.m. to 6 p.m."

Why would that be? For one, that's when most people's body temperature will naturally peak during the day. The authors of a 2010 study published in the Scandinavian Journal of Medicine & Science in Sports write that in a neutral environment, body temperature follows "a sinusoidal variation with an acrophase in the late afternoon, close to 18:00 hours (6 p.m.)." That means that the body's natural temperature is typically highest at about 6 p.m. How does that relate to athletic performance?

In general, warmer muscles perform better. Cold muscles contract less readily and can have a lower range of motion. That means they have to work significantly harder to perform athletic tasks. Warm muscles, on the other hand, are more efficient and explosive. The authors of a 2011 study published in the Journal of Sports Science & Medicine write that "functions such as resting levels of sensorimotor, perceptual and cognitive performance and several neuromuscular, behavioral, cardiovascular and metabolic variables have been found to occur in the early evening, in line with peak body temperature rhythm."

The authors of a 2007 study published in the journal Chronobiology International found that body temperature in young male association soccer players was, on average, 1.8 degrees fahrenheit higher at 4 p.m. than it was at 8 a.m. Those authors also looked at various performance metrics for the players at different times during the day. Participants were tested at 8 a.m., noon, 4 p.m., 6 p.m. and 8 p.m. on different days in a counterbalanced manner. Metrics tested included dribbling time, chip test performance, flexibility, spinal hyper-extension, juggling performance, self-rated alertness and grip strength.

"Results indicate football players perform at an optimum between 16:00 (4 p.m.) and 20:00 (8 p.m.) when not only football-specific skills but also measure of physical performance are at their peak," the authors concluded.

A 2002 study also found that participants had higher peak torques and peak anaerobic powers in the evening (between 5 p.m. and 6 p.m.) than they did in the morning (between 7 a.m. and 8 a.m.) prior to undergoing a 6-week course of regular training. A 2012 study found that young soccer players performed better in the Yo-Yo test and Wingate tests at 5 p.m. than they did at 7 a.m.

There are other factors at play in this phenomenon beyond body temperature. For example, a 2008 study found that lung function peaks between 4 and 5 p.m., performing 17.6% better than when it's at its lowest (which was around noon). So our bodies do seem to naturally peak for high performance in the late afternoon/early evening. If you're forced to follow a random training schedule, you can generally expect better performance during this period.

But if you're someone who regularly works out in the morning—either by choice or by necessity—don't feel the need to suddenly flip your life around. A 2012 study found that "regular training in the morning hours may increase the lower morning performances to the same or even higher level as their normal diurnal peak typically observed in the late afternoon…adaptations to training are greater at the time of day at which training is regularly performed than at other times."

What does that mean? For one, training at a regular time appears to be the most important factor of all. So if you regularly train at 7 a.m., eventually your body will tune into this and you should receive greater training adaptations then you would with randomly scheduled workouts. Do regular workouts at, say, 5 p.m. still offer bigger benefits than regular workouts at 7 a.m.? Possibly, as the authors do note "regular training in the evening hours may increase the morning-evening difference by a greater increase of performance in the late afternoon," but it seems that sticking to a consistent training time is the most important factor involved.

Furthermore, your chronotype matters. Chronotype is defined as "a person's natural inclination with regard to the times of day when they prefer to sleep or when they are most alert or energetic." So yes, being an "early bird" or a "night owl" is very real and rooted in circadian science. The majority of the population falls somewhere between the two and thus should expect peak athletic performance in the late afternoon/early evening in a neutral environment. But morning types (M-types) have been found to perform best in the morning, due to their unique circadian rhythms. A 2017 systemic review published in the journal Sports Medicine found that "M-types perceived less effort when performing a submaximal physical task in the morning than did N-types (neither a morning or evening type, the majority of the population) and E-types (evening types). In addition, M-types generally showed better athletic performances, as measured by race times, in the morning than did N-types and E-types."  Want to know what chronotype you are? The New York Times created a great questionnaire for exactly that purpose.

It's important to remember that something like the timing of your workout should always take a backseat to a smartly designed program and a consistent training regimen. Those are the two most important aspects to becoming a better athlete, while these other factors are simply opportunities for marginal gains. With that in mind, humans with a "neither" chronotype—who make up the majority of the population—do seem to experience peak athletic performance during the late afternoon/early evening in a neutral environment. However, regularly training at a different time can help close this natural gap. Additionally, if your chronotype is that of a morning person, you can expect to naturally perform your best athletically in the mornings.

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