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The Effects of Exercise on Metabolism

For many years, the effects of exercise on metabolism has been studied. It has been proven that exercise and physical activity in general is a significant factor that can affect the body’s metabolism.

Metabolism includes all things that the body does in order to turn food into energy and keep yourself going throughout the day. It must be noted that not all metabolism is equal. It is different from person to person. This is because there are different factors that affect metabolism and they differ from each person based on their genetic makeup and lifestyle. These factors include the (1) Resting Metabolic Rate which is considered as the amount of calories burned just to keep you alive, with all your bodily systems ticking over. This factor accounts for the largest portion, about 60-75%, of total daily energy expenditure; the (2) Thermic Effect of Feeding the extra energy burned during and after eating anything. This effect is due to the work involved in absorbing food, digestive enzymes getting busy, increased blood flow, and so on. This takes up approximately 10% of the daily energy expenditure; and (3) Physical activity that uses up calories. These activities include daily exercise, as well as the normal or casual movement such as fidgeting of hands and the likes. Physical activity generally constitutes between 15 and 30% of daily energy expenditure. These three factors form the total daily energy expenditure which is the number of calories you burn in a 24-hour period

Exercise may indeed increase the usage of calories due to the need to fuel extra activity at the time. Hence, research has mainly focused on how far is the impact of exercise in the calorie-burning mechanisms and what are the effects of specific exercises such as aerobic and non aerobic exercises on the level of metabolism. With that, this article will give you a background and explanation on the effects of exercise on the level of metabolism.

What is Basal metabolic rate?

The Basal Metabolic Rate (BMR) refers to the amount of energy your body requires in order to maintain homeostasis. Because lean mass needs a lot of energy to maintain, your BMR is greatly dependent on your total lean mass, most specifically your muscle mass. Hence, anything that reduces lean mass will also directly reduce your BMR.

Because your BMR accounts for a significant factor in your total energy consumption, it is important to preserve or even increase your lean muscle mass by following an exercise program, especially when you are trying to lose weight. This means that you must combine exercise, specifically weight-bearing and resistance exercises in order to enhance your muscle mass gain, with changes towards healthier eating patterns rather than focusing on dietary changes alone as eating too little kilojoules encourages the body to decrease the metabolism in order to conserve energy. Moreover, maintaining lean muscle mass also aids in decreasing the risk of injury when training, and exercise increases your daily energy expenditure.

It must be noted that an average man has a BMR of approximately 7,100 kJ per day, while an average woman has a BMR of approximately 5,900 kJ per day. Energy expenditure is continuous, however the rate varies throughout the day. Lastly, it is good to note that the rate of energy expenditure is frequently lowest in the early morning.

Effects of Exercise on Metabolism

(Image lifted from: https://www.bfitday.com)

The Basal Metabolic Rate (BMR) refers to the amount of energy your body requires in order to maintain homeostasis. Because lean mass needs a lot of energy to maintain, your BMR is greatly dependent on your total lean mass, most specifically your muscle mass. Hence, anything that reduces lean mass will also directly reduce your BMR.

Out of all the factors noted above that affect metabolism, energy used during exercise is the only form of energy expenditure that you have any control over. Hence, if you are aiming to regulate your metabolism in order to gain or lose weight, you must utilize physical activity in order to be able to do so. The muscles of the body may burn through as much as 3,000 kJ per hour during strenuous or vigorous physical activity. At rest, the energy expenditure of the muscles makes up only approximately more or less 20% of total energy expenditure, but it may increase 50-fold or more during strenuous exercise. It must be noted however that estimating the specific amount of energy spent during exercise is difficult because there the true value for each person will differ due to several factors including the weight, age, health and the intensity with which each exercise routine is being performed.

However, in order to give you a rough estimate on the levels of calories you can burn when you exercise, a study conducted by Ainsworth et al. (2011) shows the estimated number of calories burned while doing various exercises for one hour. The study provides you with an idea of the relative calorie burn of various activities for a person who weighs 160 pounds or 73 kilograms.

(Image lifted from: https://www.mayoclinic.com)

With the figure above, you can have an idea how normal activities of daily life such as walking or running can have an impact on your caloric usage, which in turn increases your metabolic rate.

Moreover, the Harvard Health Publishing of Harvard Medical School has published in 2018 the calories burned in 30 minutes for people of three different weights when doing different activities in the gym.

(Image lifted from: https://www.ealth.harvard.edu)

Thus, with both of these figures, it proves that even specific calorie expenditures vary widely depending on the exercise, intensity level and individual characteristics such as weight, physical activity has indeed a significant impact on your total energy expenditure, and thus your metabolism.

Mechanism On How Exercise Impact Metabolism

As shown above, exercise does boost total daily energy expenditure. With that, it is important to understand that there are a number of potential mechanisms on how exercise is able to do this:

1. Increased hormonal activity

Several studies have proven that when you do endurance exercise, there is an associated increase in the blood levels and production of adrenaline and noradrenaline. This increase is directly proportional to the increase in the resting metabolic rate. These hormones are regulated by the nerves known as sympathetic nerves that are situated within muscles. Research has studied this sympathetic nerves in muscles and its role in metabolism. Findings have shown that exercise stimulates nerve activity and increases the production of the said hormones. Both adrenaline and noradrenaline tend in turn in order to stimulate various metabolic processes which have the net effect of raising Resting Metabolic Rate. It must also be noted that other hormones also play a role in this increase. There is some evidence that exercise leads to higher blood levels of thyroid hormone, which in turn steps up general metabolic activity.

2. Increased protein resynthesis

There are studies that suggest that altered protein metabolism is one of the mechanisms why there is increased metabolic rate following exercise. Recent research findings show that exercise increases protein breakdown. You must remember that protein synthesis would need to be stepped up following exercise in order to keep protein status constant. Moreover, findings show that exercise causes an increase in the levels of enzymes that are responsible in the production of new proteins. With that, this may be one of the reasons why there is increased metabolic rate during exercise. However, further studies must still be conducted in order to establish the direct experimental evidence confirming a direct link between increased protein turnover and metabolic rate.

3. Increased flux in energy

Two individuals can both be in a state of energy balance, but the number of calories vary due to several factors including the weight, age, health and the intensity with which each exercise routine is being performed. Studies have given significant importance in the concept of energy flux. This basically means that a high energy-flux state exists when the increase in calories burned due to an exercise program is coupled to an increased intake in calories. A study conducted by Goran et al. wherein they look at young mae volunteers whose activity levels and calorie intakes were strictly controlled over a 10-day period showed that there was a significant increase in the Resting Metabolic Rate, especially those volunteers who were in energy balance at a level of high energy flux. Thus, this study was able to conclude that increases in the Resting Metabolic Rate may occur following endurance exercise training if dietary intake is partnered in order to match the increased caloric expenditure of the exercise.

4. Activity leads to even more activity

Other than the direct effects of exercise on metabolism as listed above, studies have found out that exercising on a regular basis promotes general physical activity throughout the day. Many studies have surveyed people and found out that the fitter they are, the more energy they have in order to do physical activity in their daily lives. They are also more likely to perform many daily tasks with extra interest compared to those who do not exercise. To be more specific, a study showed that young men who do endurance training have a significant increase in their total daily energy expenditure after nine weeks. Furthermore, these men had an increased energy expenditure linked to increased general physical activity.

Recommendation for Adults

(Image lifted from: https://www.food.unl.edu)

As stated above, the only thing you have control over your metabolism is through regulating your physical activity. With that, in order to impact your metabolic rate as an adult, your health and wellbeing depend on you being physically active and reducing your sedentary behaviour. With today’s busy life, it is easy to put exercise at the bottom of a long to-do list, however you can plan physical activity in short bursts that fit around your life.

The guidelines recommend the following physical activity for general adults are the following:

  • Start doing any physical activity. If you are one of those who do not currently workout, start with a small amount of exercise and build it up slowly to the recommended level. You can spread your exercise throughout the day if you do not have the time. You must note that you must be active on most days of the week. If you can be active every single day, that is even better.
  • Try to accumulate 150 to 300 minutes of moderate intensity physical activity, or 75 to 150 minutes of vigorous intensity physical activity every week. You can also do an equivalent combination of the two levels of activity every week.
  • Do muscle strengthening activity on at least two days each week.
  • Minimize the amount of time you spend with sedentary activities such as sitting down or generally doing nothing. Observe yourself and remove these bad habits for you.
  • In conclusion, exercise does have a significant effect on metabolic rate. The levels of the calories you burn, and thus the impact on the total daily energy expenditure, vary per activity you do and the intensity on how you perform it. However, it must be noted that physical activity is the only factor you can control in order to regulate your metabolism. Hence, you must increase your physical activity by doing exercise and reduce your sedentary lifestyle in order to live a healthier life. With that, if you are new to exercise or are coming back from a long period of inactivity, you must first consult with your fitness instructor or health provider in order to do sme pre-exercise screening in order to help make sure that your exercise program is effective and brings benefits for your metabolism and your general health as well.

    References:
    1. Better Health Channel. 2018. Metabolism. Retrieved from: https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/metabolism. Retrieved 14 August 2020.
    2. Galgani J, Ravussin E. Energy metabolism, fuel selection and body weight regulation. Int J Obes (Lond). 2008;32 Suppl 7(Suppl 7):S109-S119. doi:10.1038/ijo.2008.246
    3. Goran MI, Calles-Escandon J, Poehlman ET, O’Connell M, Danforth E Jr. Effects of increased energy intake and/or physical activity on energy expenditure in young healthy men. J Appl Physiol (1985). 1994;77(1):366-372. doi:10.1152/jappl.1994.77.1.366
    4. Hamilton, A. Peak Endurance Sport. 2019. Metabolic Rate And Exercise. Retrieved from: https://www.peakendurancesport.com/endurance-injuries-and-health/endurance-health-and-lifestyle/metabolic-rate-exercise/#:~:text=But%20emerging%20evidence%20suggests%20that,a%20higher%20resting%20metabolic%20rate. Retrieved on 14 August 2020.
    5. Hargreaves, M., Spriet, L.L. Skeletal muscle energy metabolism during exercise. Nat Metab (2020). https://doi.org/10.1038/s42255-020-0251-4
    6. Harvard Health Publishing. Harvard Medical School. 2018. Calories burned in 30 minutes for people of three different weights. Retrieved from: https://www.health.harvard.edu/diet-and-weight-loss/calories-burned-in-30-minutes-of-leisure-and-routine-activities. Retrieved on 14 August 2020.
    7. Mayoclinic.org. 2019. Exercise for weight loss: Calories burned in 1 hour. Retrieved from: https://www.mayoclinic.org/healthy-lifestyle/weight-loss/in-depth/exercise/art-20050999. Retrieved on 14 August 2020.
    8. Pandey A, Swift DL, McGuire DK, et al. Metabolic Effects of Exercise Training Among Fitness-Nonresponsive Patients With Type 2 Diabetes: The HART-D Study. Diabetes Care. 2015;38(8):1494-1501. doi:10.2337/dc14-2378

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