Which Comes First, Cardio or Weights_ - Alex Hutchinson [29]
At what time of day am I strongest and fastest?
One of the hottest controversies leading up to the Beijing Olympics in 2008 was the decision to switch swimming and gymnastics finals from their traditional evening slots to early morning, so that they could be broadcast live in the United States. To understand why many athletes were outraged, imagine trying to run a mile all-out or bench-press your maximum weight—at 3 a.m. It’s a safe assumption that your performance wouldn’t measure up to your usual midafternoon abilities. These fluctuations, related to patterns of sleep and waking, are easy to understand, but they’re only part of the story. Your body contains an internal clock governed by a region of the brain called the hypothalamus, which regulates temperature, hormone secretion, sleep, and feeding cycles with a period of roughly 24 hours. As a result, your body experiences subtle changes throughout the day—even while you’re wide awake—that influence your physical capabilities.
Researchers in France and Tunisia performed careful studies of the hourly variation in a 30-second all-out cycling bout called the Wingate test. They found that peak and total power hit a maximum at about 6 p.m., with values between 8 and 11 percent higher than the low point at 6 a.m. Other studies have made similar findings about tests of back muscles, arm muscles, vertical and broad jumping, and anaerobic power, with the peaks always within a few hours of 6 p.m. Tests of sports as varied as running, swimming, football, badminton, and tennis have yielded similar findings.
Spanish researchers were able to shift the peak performance time of elite sprinters forward or back by two hours simply by adjusting sleep-wake and meal times by two hours. But it’s not clear whether performance was related to total time awake, or whether the change in meal and sleep times succeeded in changing the timing of the body clock itself, leading to other changes in the body’s chemistry.
Many researchers believe that body temperature, which increases by about 1.8°F (1°C) over the course of the day, could be the key factor. Increased core temperature could lead to looser muscles, faster metabolic reactions in the body, and faster transmission of nerve signals. A 2010 study by researchers in Guadeloupe found no difference in a series of jumps, squats, and cycle sprints performed either between 7 and 9 a.m. or between 5 and 7 p.m. The reason for the difference compared to studies in colder climates, they suggested, could be that the consistently warm and humid climate in Guadeloupe provided a “passive warm-up” that made the slight circadian increase in body temperature irrelevant.
These findings may be slightly worrying if you’re preparing for a competition that takes place at an unusual time, like a 10K or marathon that starts at 7 a.m. Fortunately, several studies have suggested that training has time-specific benefits. A 1989 University of Georgia study, for example, found that cyclists who trained early in the morning experienced greater improvements in their oxygen use at threshold pace when they were tested in the morning; another group that trained in the evening had larger improvements in evening testing sessions. A Finnish study in 2007 found similar results for strength training and also found that early-morning workouts changed how levels of the stress hormone cortisol fluctuated throughout the day, enhancing early-morning performance. So if you want to be at your best at 7 a.m., make sure to do some training at that time.
Despite all this evidence, the best time to work out is generally still whatever time fits best into your daily schedule, since factors like sleep, stress, and fatigue will outweigh the slight boost offered by circadian rhythms. You should also make allowances for individual differences: most of these studies were performed on volunteers with “typical” sleep