Table of Contents
The human heart beats from birth to the end of life, but its pace changes according to need. When we sleep, it beats slowly, and during intense exercise, it races to meet the energy needs of the working muscles. However, the energy that the heart pumps through the blood has to come from somewhere. Whether the energy used is from fats, carbohydrates or protein depends on the intensity and duration of the exercise. Can proper exercise be used to get the heart pumping just right to burn fat and lose weight? That’s what you’ll find out in this article.
How is energy stored in the body?
The energy used by every cell in the body is transferred and used in the form of adenosine triphosphate (ATP). ATP in the body functions as the fuel that powers all molecular “motors”. ATP is essential for vital processes and is also a source of energy for muscle contraction. However, we receive energy not in the form of ATP, but in the form of food, from which our cells can produce ATP. What if we have more energy than we need? We store it for a challenging day.
Often, it is the adipose tissue that is referred to as an energy reserve for challenging days. But the truth is that the body has several ways to store energy.
In addition to adipose tissue, where energy-rich fats are stored, we also store excess energy in our muscles. Muscles contain not only water and glycogen, but also their own fat stores. Glycogen is a storage “reservoir” of carbohydrates, made up of a large number of glucose molecules that can be released when needed and used to make ATP. Some glycogen is also found in the liver. In times of prolonged energy deficiency, cells can also reach for proteins from which they can make energy. However, these represent the last resort.
Whether we primarily use energy stored in fat, glycogen or protein during sport depends on the intensity of the physical activity we perform. We can determine intensity by heart rate.
You might be interested in these products:
What is heart rate?
Heart rate is nothing but the number of heartbeats per minute. The heart pumps blood throughout the body constantly, and the frequency of these beats varies depending on the body’s actual need. The blood that the heart pumps throughout the body delivers both oxygen and nutrients while carrying away waste substances and CO2.
A great indicator of cardiovascular health is the resting heart rate (RHR). The lower the RHR, the healthier the heart. On average, RHR is around 70 beats per minute, but 60-100 beats per minute is considered a healthy range. Peak endurance athletes can have an RHR of 35 – 40 beats per minute due to long-term training and adaptation. [1]
Heart rate variability (HRV) is also related to heart rate. Variability refers to the difference in time between heartbeats. Nowadays, smart watches and rings can also measure it. We can use it to determine the activity of the autonomic nervous system, to measure our stress level or our level of recovery and readiness for further activities.
We can also track intensity in other ways
Heart rate is also related to the so-called VO2 max, which represents the maximum oxygen consumption per minute. The more oxygen we can use, the higher this value is. At the same time, the higher the VO2 max, the lower our resting heart rate. Based on VO2 max and heart rate, we can categorise physical activity by intensity [2]:
| Zone | VO2 (% of max) | HR (% of max) |
|---|---|---|
| 1 | 55 – 65 | 60 – 72 |
| 2 | 66 – 80 | 72 – 82 |
| 3 | 81 – 87 | 82 – 87 |
| 4 | 88 – 93 | 88 – 92 |
| 5 | 94 – 100 | 93 – 100 |
HR max, the maximum heart rate, can be calculated easily:
211 – 0.64 x age = HR max
For the most accurate determination of HR max, but also VO2 max, testing in a laboratory is the most appropriate way to accurately determine maximum heart rate and oxygen consumption.
Is exercising in a specific zone the most effective for weight loss?
The human body has ATP available in the muscles for a few seconds of intense physical activity (e.g. sprinting). When they are depleted, they have to reach into their reserves and replenish the ATP. The fastest source is the recycling of ADP to ATP by creatine. Creatine can meet the energy needs at high intensity for about 10 seconds. However, if physical activity persists, it is necessary to reach into the stores. Depending on the intensity, we will burn more fat or glycogen.
The longer and more strenuous the activity, the more the body will use protein. An example would be marathons, where not only electrolytes and carbohydrates need to be replenished, but also essential amino acids (high-quality protein). Thus, in some zones we will burn more fat, in others the body will reach for glycogen stores or, to a lesser extent, protein It should be added that normal workouts hardly consume protein [3].
Thus, the body uses different fuels from different reservoirs of energy in different proportions. The largest reservoir is fat, the smaller reservoir is glycogen, and the last rescue is the energy in protein. Although the body uses all the reservoirs, it depends on the intensity of the activity from which it will draw the most. With increasing intensity, we use more and more carbohydrates (glycogen) and less fat.
From person to person, the use of fat stores varies. It depends on whether it is a trained person or a person who is sedentary most of the time. If you are overweight and in poor physical condition, fat burning occurs much sooner [4].
As a rule, we mobilise most of our fat stores during moderate-intensity aerobic physical activity. In other words, the body burns the most fat during activity in the upper limit of zone 1 and zone 2 (~70% HR max). However, it is still true that fat is not the only source of energy and glycogen in the muscles is also consumed in large amounts. Much of the fat also comes from muscle stores, not just adipose tissue. At higher intensities, glycogen burning predominates, and in extreme cases, such as ultramarathons, protein burning also takes place at a higher rate [3].
How to exercise effectively for weight loss?
Burning fat, however, does not mean that we will also lose fat. Burning a certain amount of calories in a short period of time also doesn’t mean that all of those calories will come from fat stores alone. In order to get rid of fat and lose weight, we need to burn more energy than we take in.
In the long run, it doesn’t matter that we spend hours on the treadmill and the smart watch tells us we’ve burned hundreds of calories in the aerobic (fat-burning) zone. If we are not in a calorie deficit and we take in more calories than the body will use, we will not lose weight. So, ultimately, it doesn’t matter if the energy comes from fat or glycogen. Without a calorie deficit, we will constantly replenish these stores. It doesn’t matter which zone we exercise in, the important thing is to burn more energy than we take in.
What’s more important than heart rate monitoring?
Monitoring heart rate during aerobic exercise is important for improving fitness. If our goal is to lose weight, we can, in practice, ignore heart rate. A guaranteed recipe for weight loss is a calorie deficit combined with plenty of protein in a quality diet and strength training.
In a calorie deficit without exercise, we run the risk that the body will also start to lose muscle mass, which is extremely important for health and longevity. We also risk developing ‘thin obesity‘, which is characterised by a healthy BMI but a higher proportion of adipose tissue and less muscle.
Enough protein in your diet will ensure that your muscles have something to grow and recover from after more demanding workouts. However, in the recovery process, we should not forget about quality sleep, which will also help us overeat less and maintain good eating habits.
Conclusion
Heart rate can tell us a lot about the state of our physical condition. We can use it to set the right training plan and improve our cardiovascular health, in particular. In terms of weight loss, it is true that with moderate-intensity aerobic training (e.g. walking uphill), we burn mainly fat tissue reserves. However, if we do not maintain a calorie deficit, these stores are constantly replenished.
Therefore, the most important thing in terms of weight loss is to stay in a calorie deficit and not to forget about a good diet, sleep and strength training. Any movement is better than no movement, and if your goal is weight loss, you need to focus on calorie intake and not exercise intensity zone.
[1] Quer G, Gouda P, Galarnyk M, Topol EJ, Steinhubl SR (2020) Inter- and intraindividual variability in daily resting heart rate and its associations with age, sex, sleep, BMI, and time of year: Retrospective, longitudinal cohort study of 92,457 adults – https://doi.org/10.1371/journal.pone.0227709
[2] Seiler, Stephen. (2010). What is Best Practice for Training Intensity and Duration Distribution in Endurance Athletes? - doi:10.1123/ijspp.5.3.276
[3] Hargreaves, M., Spriet, L.L. Skeletal muscle energy metabolism during exercise. – https://doi.org/10.1038/s42255-020-0251-4
[4] Scharhag-Rosenberger, F et al. “Effects of one year aerobic endurance training on resting metabolic rate and exercise fat oxidation in previously untrained men and women. Metabolic endurance training adaptations.” doi:10.1055/s-0030-1249621
Add a comment