There is a multitude of positive reasons as to why we should all do regular exercise. For many, the main reasons are to either lose weight or to maintain a healthy weight. To chart how productive a particular exercise session was, we tend to measure how many calories were expended during that session. While this is a benchmark, is it really the be-all and end-all of how productive a particular exercise session is?

At the end of the day, it is imperative to remember that exercise is a boon for overall health regardless of whether you lose weight. A review published in October 2021 in iScience suggests that while increased exercise doesn’t typically lead to long-term weight loss, improved cardiorespiratory fitness is associated with better health outcomes and a lower risk of premature death, regardless of weight.

How accurate are the measurements that show up on the gym equipment? Here are 6 factors that affect calorie loss, some of which may not be within our control.

  1. Biological Sex

Men tend to burn more calories at rest and during exercise than women because men tend to be larger than women, and they have more muscle mass than women of the same age and weight. Males burn up to 5 to 10 percent more calories than females at rest, and this percentage usually increases with exercise.

And while women can certainly add muscle mass through strength training, physiological differences mean that women will generally never be as lean as men because women are genetically predisposed to lay down more fat to support hormone production and childbearing.

The American Council on Exercise (ACE) has said that men need at least 2 to 5 percent body fat to support health, while women need a minimum of 10 to 13 percent. But these minimum numbers may not be sufficient. While there’s no official recommendation for optimal body fat percentage, the most cited study on the topic states that a healthy range for adults younger than age 40 is 8 to 20 percent for men and 21 to 33 percent for women. That said, the relationship between health and body fat is complex and not perfectly understood.

Instead of fretting about how your biological sex affects your calorie burn, focus on the things you can control. The bottom line is that both men and women should focus on building muscle and improving cardiovascular health with a well-balanced cardio and strength-training program.

2. Muscle Mass

We have touched on this above and as a general rule of thumb, the more muscle mass one has, the more calories one tends to burn both at rest and during times of exercise. One pound of muscle burns about five calories per day while a pound of fat burns about two calories per day.

While exercising, having more muscle mass will increase your total calorie burn, because your body needs to produce more energy to support the increased rate at which your muscles are contracting. As such, to increase your calorie burn, consider stepping up your strength training to build more muscles. Evidence has indicated that lifting weights burns more fat than just cardiovascular exercise. Given that muscle tissues also burn more calories at rest, it will yield more promising long-term results. It might therefore be worthwhile to speak to a qualified personal trainer to get a workout regime that comprises both strength training and cardiovascular exercises.

3. Body Weight

Calories are a measure of energy, so the more you weigh, the more energy it takes to move your body. Bearing this in mind, the more one weighs, the more energy one will burn while exercising because they will have to expend greater energy to move their bodies.

People with larger bodies also tend to have larger internal organs (such as the heart, liver, kidneys, and lungs), which is a significant factor in how many calories are burned both during exercise and at rest, because these organs and their processes require energy. 

This is one of many reasons that weight loss is so complicated — your body burns fewer calories as your weight decreases, which can lead to a weight loss plateau or even regaining weight. That said, it may not be the only reason. A previous review explains that weight loss can trigger other physiological adaptations as well, including the body’s tendency to burn stored fat for energy, a process called fat oxidation; greater hunger, due to higher levels of the hormone ghrelin; and less satiety, as levels of the hormone leptin dip.

If you are looking to lose weight and have hit a plateau, consider working with a registered dietitian who specialises in weight loss and can help you meet your goal in a healthy and sustainable way.

4. How Fit You Are

As your body adapts to training, you will burn fewer calories with the same workouts. That is why a newbie might burn significantly more calories than someone who has been doing the same workout for years. This is why changing your workout routine can increase your fitness level and potentially enhance your calorie burn if that is your goal.

It is important to remember that being fitter is a good thing. It means your body is more efficient and healthier. This is yet another reason not to get fixated by just the number of calories burnt during exercise.

5. Age

As we age, we will lose muscle mass. A review published in July 2017 in Ageing Research Reviews explains that this muscle loss is due to the body becoming more resistant to hormones that promote protein synthesis which is key to muscle maintenance. This loss of muscle mass lowers the metabolic rate — the speed at which you burn calories — at rest and during exercise.

study on human metabolism, published in the August 2021 issue of Science, made headlines for its findings that metabolic rate may not decline throughout adulthood, but rather that it plateaus between the ages of 20 and 60 then begins its decline. In the study, the authors measured the energy expenditure of 6,421 men and women between 8 days old and 95 years old using the doubly labeled water technique, the gold standard for this kind of measurement.

It is not possible currently to perfectly quantify metabolism. Aging is accompanied by multiple changes in human physiology — not all of which may have been adjusted for.

The good news is that while you cannot stop your body from aging, you can preserve or even increase your muscle mass through regular strength training. As touched on above, strength training can help you increase your resting metabolic rate, which will help with calorie burn over time.

6. Intensity

Two people doing the same workout may well be burning a different number of calories because they may not be exercising at the same intensity levels. Someone exercising at a high intensity can burn twice as many calories in the same amount of time as someone exercising at a low intensity. And just because you are covering the same distance as someone else, or going through the same motions, doesn’t mean that the two of you are working out at the same intensity.

The bottom line is that you should try not to fret too much about things that are out of your control. Exercise has countless benefits beyond just burning calories, so the most important thing is to find types of movement that are enjoyable and feel sustainable. The type of exercise that is better for a person ultimately depends on that person’s goals and capabilities.

*This article does not replace professional medical / nutritional advice.

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