Is heart-rate an ideal measure of exercise intensity?

Aerobic exercises like jogging, biking, swimming or hiking are a fundamental way to maintain cardiovascular and overall health. The intensity of these exercises is important in determining how much time you should spend while training in order to reap its benefits.

During exercise, the heart beats faster to meet the demand for more blood and oxygen by the muscles of the body. The more intense the activity, the faster your heart will beat. Therefore, monitoring your heart rate during exercise can be an excellent way to monitor exercise intensity.

Exercise intensity is how hard your body works during physical activity. Your ideal exercise intensity is determined by your health, fitness goals as well as your current level of fitness.

This intensity is classified as low, moderate, or vigorous. For maximum health benefits, the goal is to work hard, but not too hard but the intensity can be measured using target heart rates, talk tests, or the exertion rating scale. 

According to Robert Ddamulira, a fitness instructor at Robbie Fitness, it may be challenging to measure exercise intensity because what is vigorous to one person may be moderate to another. 

He says, “Heart rate zone training provides an objective measure of intensity by breaking it down into various zones. However, it is not only exercise that affects your heart rate. Your beats per minute could be raised by a number of internal and external factors such as hot weather, stress or anxiety, caffeine intake, medication, hormone fluctuations, cigarette smoking.”

Heart rate zones are not a perfect measure of exercise intensity, but regularly getting your heart pumping is still important for fitness. 

Many fitness instructors and physiotherapists recommend a minimum of 150 minutes per week of moderate aerobic exercise, or 75 minutes per week of high-intensity exercise.

Heart rate and exercise intensity

Due to the increase of wearable heart rate technology, the use of the heart rate training zone to measure intensity has gained popularity. Naturally, as exercise intensity increases, so does heart rate. 

However, the gold standard for determining intensity of aerobic exercise is to measure the amount of oxygen consumed and carbon dioxide exhaled. This method is burdensome because it requires people to wear a breathing mask to capture respiratory gases. 

The American College of Sports Medicine outlines five heart rate zones based on a person’s predicted heart rate maximum. Zone 1, or very light intensity, equals less than 57percent of maximum heart rate; zone 2, or light intensity, is 57 to 63percent; zone 3, or moderate intensity, is 64 to 76 percent; zone 4, or vigorous intensity, is 77 to 95percent; and zone 5, or near-maximal intensity, is 96 to 100percent.

However, other organisations have their own measures of exercise intensity, with varying ranges and descriptions. Furthermore, companies that produce heart rate monitors also have higher thresholds for each zone. 

How the body responds to exercise is partly determined by exercise intensity. Zone 2 has received a lot of attention from the fitness community because of its possible benefits.

Performance coaches describe zone 2 as “light cardio,” where the intensity is low and the body relies mainly on fat to meet energy demands. Fats provide more energy compared to carbohydrates, but deliver it to cells more slowly.

Because fat is more abundant than carbohydrates in the body, the body responds to the cellular stress that exercise causes in muscle cells by burning fat.

The high-intensity interval training, on the other hand, involves exercising at a high intensity for short durations, like an all-out sprint or cycle for 30 seconds to a minute, followed by a period of low intensity activity. This should be repeated six to 10 times.

During this sort of high-intensity activity, the body primarily uses carbohydrates as a fuel source. During high-intensity exercise, the body preferentially uses carbohydrates because the energy demand is high and carbohydrates provide energy twice as fast as fats.

Some people who turn to exercise to lose fat may shun high-intensity training for zone 2, as it is considered the fat burning zone but this may be inaccurate.

Researchers have found that high-intensity interval training produces a similar increase in markers for mitochondria production when compared to longer, moderate aerobic training.

Studies have also shown that high-intensity exercisers build muscle and improve insulin resistance and cardiovascular health similar to moderate-intensity exercisers, and they made these gains faster. The main trade-off was discomfort during bouts of high-intensity exercise.