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Evening swims yield fastest Olympic times, study finds
Analysis of medal-winning swimmers across four Summer Games reveals a consistent performance peak around 5:12 pm local time. Researchers say the pattern reflects broader evidence that exercise outcomes vary by time of day.
Circadian rhythms shape athletic performance
The body's internal clock, or circadian rhythm, governs daily fluctuations in strength, endurance, and metabolism. A central pacemaker in the brain's hypothalamus synchronises peripheral clocks in muscle and fat tissue, adjusting to cues such as light, meals, and physical activity.
Juleen Zierath, an exercise physiologist at Sweden's Karolinska Institute, notes that these clocks can be recalibrated. "Exercise itself acts as a signal to the muscle clock," she says, suggesting that consistent training at specific hours may shift peak performance windows.
Morning vs. evening: health benefits diverge
Animal studies indicate morning exercise may enhance fat burning, while human trials show gender-specific effects. Women who trained in the morning reduced abdominal fat and blood pressure, whereas evening sessions improved muscular strength. Men, by contrast, saw greater fat breakdown and lower blood pressure from evening workouts.
"Exercise is beneficial at any hour," Zierath says, "but timing could fine-tune metabolic outcomes for conditions like diabetes and obesity."
Can athletes retrain their body clocks?
Preliminary research in mice suggests yes. Karyn Esser's team at the University of Florida found that morning endurance training shifted molecular clocks in muscle and lung tissue, advancing the rodents' performance peaks. After six weeks, both morning- and afternoon-trained mice achieved similar endurance levels, but morning trainees adapted faster.
"The clocks in our muscles pay attention to when we train," Esser says. While human data remain limited, the findings hint at potential strategies for shift workers, jet-lagged travellers, and elite athletes preparing for competitions at non-peak hours.
Practical takeaways for athletes and amateurs
Experts recommend consistency. "Train at the same time you'll compete," advises Zierath, emphasising that routine helps the body adapt. Chronotype-whether someone is a "morning lark" or "night owl"-also plays a role, with performance peaks varying by up to several hours between individuals.
Despite the nuances, researchers stress that any exercise is better than none. "The key is finding a time that works for you and sticking with it," Esser says. "Your body may just respond by giving you that extra edge."
