Effects of high-intensity exercise on metabolism

Friday, July 5, 2024

Conventional wisdom has long touted high intensity exercise as an effective way to burn calories and facilitate weight loss. However, a new study is challenging this widely-held belief, suggesting that pushing yourself too hard may actually have the opposite effect. 

Lead researcher Takashi Matsui, PhD, from the Institute of Health and Sport Sciences at the University of Tsukuba in Japan, explained the key findings of the study published in Medicine & Science in Sports & Exercise, to Medical News Today. He said, “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. Interestingly, this weight gain occurs despite no changes in food intake.”

This counterintuitive conclusion runs contrary to mainstream fitness advice. Dr Jagadish J Hiremath, medical director at AASRA Hospitals, says, “Contrary to popular belief, high-intensity exercise (HIE) can, under certain circumstances, contribute to an increase in body weight. This unexpected outcome is attributed to the complex interplay of hormones within the body, particularly cortisol, the stress hormone.”

HIE can disrupt the body’s natural sleep-wake cycle, he adds, known as the circadian rhythm, and trigger a surge in cortisol levels. Elevated cortisol not only amplifies appetite but also saps motivation for further physical activity. This vicious cycle leads to increased calorie consumption, often exceeding the calories burned during exercise, ultimately tipping the scales towards weight gain. 

Effects of high-intensity exercise on metabolism

According to Dr Hiremath, “High-intensity exercise puts the body’s metabolism through a series of peaks and valleys. Initially, it ignites a metabolic fire, accelerating calorie expenditure. However, the surge in cortisol that accompanies HIE acts as a double-edged sword.”

Not all high-intensity workouts are created equal. (Source: Getty Images/Thinkstock)

While it initially fuels the metabolic furnace, it also triggers intense cravings, particularly for high-calorie, unhealthy foods. Succumbing to these cravings can negate the calorie deficit achieved through exercise, potentially leading to weight gain.

When it becomes counterproductive

Dr Hiremath stresses, “Not all high-intensity workouts are created equal. Those that are excessively long, frequent, or intense can be detrimental to weight management goals.” 

Advertisement

For instance, engaging in daily high-intensity interval training (HIIT) sessions without adequate rest or pushing the body beyond its limits can disrupt hormonal balance, he says. “This disruption leads to a cascade of negative effects, including elevated stress levels, increased appetite, and a heightened risk of weight gain.”

Mastering high-intensity exercise for optimal results

The potential link between HIE and weight gain “doesn’t mean this form of exercise should be avoided altogether,” says Dr Hiremath. Rather, it stresses the importance of a balanced and strategic approach

Here’s how to optimise your high-intensity workouts for sustainable weight management:

Incorporate Variety: Intersperse high-intensity workouts with lower-intensity activities like yoga or brisk walking. This allows your body to recover and prevents overtraining.

Advertisement

Prioritise Nutrition: Be mindful of post-workout hunger and resist the urge to overindulge. Focus on consuming nutrient-dense foods that nourish and replenish your body.

Diversify Your Routine: Avoid monotony by incorporating a variety of exercises into your routine. This not only prevents boredom but also challenges different muscle groups and prevents plateaus.

Listen to Your Body: Pay close attention to your body’s signals. If you’re feeling excessively fatigued, experiencing persistent soreness, or struggling with constant hunger, it’s a sign to dial back the intensity or frequency of your workouts.