Consider this scenario: An overweight person starts working out and correcting his/her diet routines. This person witnesses a significant change in body weight over a couple of weeks which motivates him/her to work out more with exponential energy. Over the course of weight loss though the individual might perform physical activity routines for the stipulated time period with the same zest and keep an eye on diet too weight loss changes don’t happen as expected. There is a downslide in the weight loss levels and this is not reversed until the individual works out more or changes his/her course of workout. Our bodies seem to adjust to repeated physical exertion and energy demands by burning fewer (where our expectations would have been for more) calories through the day despite the same exertion and efforts taken. This brings us to the question whether there is an upper limit for human endurance and energy expenditure. A new study conducted during a 20-week running race across United States focused on an individual’s maximum endurance in different occasion such as running across the country, participating in the Tour de France or when pregnant.
To most of us, more time and efforts we contribute towards exercising and physical activity greater is our calorie expenditure and weight loss. Even a 2012 study on modern hunter-gatherers found that these people burned the same number of calories as those doing desk jobs despite being in motion through the day. That’s because their body has found a way to reduce daily energy expenditure even during movement which also helped them in other ways-for example, when their calorie expenditure decreased their need for more food through hunting also decreased. Another study in 2015 included some of the researchers involved in the 2012 study and these individuals monitored a group of six racers’ metabolism. This research group noted the daily calories burned by this group of athletes who ran six marathons a week for five months as part of an event called Race Across USA, a 3000-mile race from California to Washington D.C. The research team also focused on other activities that proved to be a test for human endurance including 100-mile trail races and pregnancy. What started as a high energy expenditure turned out to flatten and plunge at 2.5 times their basal metabolic rate for the rest of the event. Also, the maximum energy expenditure found among endurance athletes is only slightly higher than metabolic rates sustained by women during pregnancy.
The alterations in the athlete’s energy expenditure was revealed-while the runners burned around 6,200 calories of energy a day during the first week of the marathon 20 weeks later, they were losing 600 fewer calories every day despite running at the same pace and for the same duration with little loss in body weight. Also, at the end of the event these athletes expended only 2.5 times their resting metabolic rates daily very much lesser than 3.5 times their resting metabolic rates that happened during the start of the event. When the research group looked into past studies relating to energy expenditure in any event lasting for more than 12 hours it was found that the participant’s energy expenditure increased significantly and in course of time decreased until it reached a deadlock of 2.5 times their everyday resting metabolic rate. Analyzing the cause behind the limit to human endurance researchers found that it got to do something with the digestive process and the body’s ability to process food and absorb nutrients and calories to fuel all of the body’s processes. Also, maybe the same mechanism that reduces energy expenditure over time might also slow metabolic responses over weeks and months when an athlete starts preparing for marathons. This might also be the reason why some people who train for marathons gain weight. If you are into sports and would like expert help in planning your diet routine and daily activity schedule please get in touch with our expert dietitians and nutritionists at www.firsteatright.com.
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Dietitian & Nutritionist Dr. Nafeesa Imteyaz.