Engaging in physical activities that elevate the heart rate is essential for maintaining physical and mental well-being. Regular exercise, whether light like walking or intense like uphill cycling or weight lifting, offers numerous benefits for both body and mind. Daily physical activity is crucial for preventing various diseases and health issues.

However, a recent study published in Medicine & Science in Sports & Exercise suggests that intense exercise sessions might reduce subsequent physical activity and lower body temperature, potentially leading to weight gain.

The Role of Circadian Rhythm and Stress Hormones

The study also examined the impact of circadian rhythm, the body's natural sleep-wake cycle, on physical activity. Researchers focused on the stress hormone corticosterone, which regulates circadian rhythm. This hormone, which peaks around waking time and is lowest at bedtime, influences both physical and mental activity levels.

Despite the numerous health benefits of exercise, its impact on weight loss can sometimes be less than expected. This could be due to a decrease in physical activity following exercise, although the exact mechanism is unclear. Researchers hypothesized that a single session of high-intensity exercise could disrupt the circadian rhythm, leading to decreased physical activity, lower heat production, and diminished weight loss effects.

High-Intensity Exercise and Weight Gain

To test this hypothesis, mice were divided into three groups: high-intensity exercise, moderate-intensity exercise, and rest. Researchers monitored their physical activity and core body temperature, indicators of heat production, before and after exercise. They found a disruption in the synchrony between physical activity and body temperature. Lower blood corticosterone levels during wake times were associated with reduced physical activity.

The findings indicate that a single session of high-intensity exercise can disrupt corticosterone’s circadian rhythm, leading to decreased physical activity, lower body temperature, and weight gain. This study highlights the need to consider not only the calories burned during exercise but also subsequent activity levels and circadian rhythm when designing exercise regimens for effective weight loss.

Expert Opinions

Lead researcher Takashi Matsui, PhD, from the Institute of Health and Sport Sciences at the University of Tsukuba in Japan, explained, "Our study found that while exercise is a powerful strategy for weight loss, a single session of high-intensity exercise that induces heavy sweating can significantly reduce subsequent physical activity and core body temperature, leading to weight gain, despite no changes in food intake."

Matsui added, "These phenomena are likely due to disruptions in the circadian rhythm of the stress hormone corticosterone and disturbances in the synchronization between physical activity and body temperature. It is important to consider not only the energy expenditure during exercise but also the subsequent activity levels and circadian rhythm when setting appropriate exercise intensity for effective weight loss."

Ryan Glatt, CP, senior brain health coach and director of the FitBrain Program at Pacific Neuroscience Institute in Santa Monica, CA, commented, "This animal study questions the benefits of vigorous exercise for weight loss, suggesting it might actually cause weight gain by reducing activity levels afterward and disrupting body temperature. The research shows that high-intensity workouts may have complex effects on metabolism that aren’t fully understood."

Mark A. Anton, MD, medical director at Slimz Weightloss, described the study as fascinating. "While vigorous exercise has its benefits, it can also lead to reduced activity levels outside of exercise sessions and potentially impact body temperature regulation. This can sometimes counteract weight loss efforts if not managed properly."

Beyond Exercise: Maintaining an Active Lifestyle

Matsui emphasized that the research "adds new evidence to the emerging theory that animals, including humans, tend to compensate for the energy expenditure of exercise by reducing energy use in other activities. Therefore, it is crucial to recognize the beneficial effects of maintaining an active lifestyle beyond just exercise."

Glatt agreed, stating, "Overall, this study suggests rethinking the focus on intense exercise, considering the potential benefits of more moderate and consistent activity for weight loss."

He also highlighted that these results are from animal studies and may not directly apply to humans. "For weight loss and weight management, I recommend a balanced approach that includes a mix of moderate-intensity aerobic exercises, such as brisk walking or cycling, combined with resistance training. This combination helps to burn calories, build muscle, and maintain a higher metabolic rate. It’s also crucial to incorporate rest and recovery to prevent burnout and ensure sustainable progress."

Matsui concluded, "To fully benefit from exercise, it is important to engage in moderate exercise that does not hinder overall daily activity and to perform this exercise regularly rather than sporadically. This approach would ensure that the benefits of exercise are sustained and do not inadvertently lead to weight gain."