Training intensity is one of the most important variables that affects the physiological and performance adaptations to exercise. Different intensities of training can elicit different types of adaptations, such as aerobic endurance, anaerobic power, muscular strength, or fat loss. In this article, we will explore how a training intensity of 67 percent or less of the maximal heart rate (HRmax) or the heart rate reserve (HRR) is most closely related to which training adaptation.
Aerobic Endurance
Aerobic endurance is the ability to sustain a moderate to high intensity exercise for a prolonged period of time. Aerobic endurance depends on the efficiency of the cardiovascular system, the respiratory system, and the skeletal muscles to deliver and utilize oxygen for energy production. Aerobic endurance is also influenced by factors such as genetics, body composition, diet, and environmental conditions.
According to Physiopedia, aerobic endurance can be improved by training at an intensity of 50 to 85 percent of HRmax or 40 to 85 percent of HRR for at least 20 minutes, three times per week. However, for beginners or sedentary individuals, a lower intensity of 40 to 60 percent of HRmax or 30 to 45 percent of HRR may be sufficient to induce aerobic adaptations.
A study by Mezghani et al. compared the effects of three different intensities of combined endurance and strength training programs on physiological and muscular adaptations and insulin resistance in women with abdominal obesity. The study found that a moderate-intensity training group (G50), exercising brisk walking at 50 percent HRR, improved their aerobic endurance (measured by VO2max) by 10.5 percent after 12 weeks of training. The high-intensity training group (G75), exercising jogging at 75 percent HRR, improved their aerobic endurance by 13.9 percent, while the alternated-intensity training group (G50/75), exercising brisk-walking/jogging at 50–75 percent HRR, improved their aerobic endurance by 15.7 percent. These results suggest that a higher intensity of training may elicit greater aerobic adaptations than a lower intensity of training.
However, a higher intensity of training may also increase the risk of overtraining, injury, or illness, especially for untrained or obese individuals. Therefore, a lower intensity of training may be more suitable for beginners or those with health conditions that limit their exercise capacity. A lower intensity of training may also be more enjoyable and sustainable for some people, as it may cause less fatigue, discomfort, or boredom.
Fat Loss
Fat loss is another common goal of exercise training, especially for those who are overweight or obese. Fat loss depends on creating a negative energy balance, which means that the energy expenditure exceeds the energy intake. Exercise can increase the energy expenditure by increasing the metabolic rate during and after the exercise session. Exercise can also affect the energy intake by influencing the appetite and food choices.
According to Physiopedia, fat loss can be achieved by training at an intensity of 60 to 70 percent of HRmax or 50 to 60 percent of HRR for at least 30 minutes, four to five times per week. However, some studies have suggested that higher intensities of training may be more effective for fat loss than lower intensities of training.
A study by Mezghani et al. compared the effects of three different intensities of combined endurance and strength training programs on anthropometric variables, physiological and muscular adaptations, and insulin resistance in women with abdominal obesity. The study found that all three training groups reduced their body weight, body mass index (BMI), waist circumference, body fat percentage, and visceral fat area after 12 weeks of training. However, the high-intensity training group (G75) and the alternated-intensity training group (G50/75) achieved greater reductions in these variables than the moderate-intensity training group (G50). These results suggest that a higher intensity of training may elicit greater fat loss than a lower intensity of training.
However, as mentioned earlier, a higher intensity of training may also increase the risk of overtraining, injury, or illness, especially for untrained or obese individuals. Therefore, a lower intensity of training may be more appropriate for beginners or those with health conditions that limit their exercise capacity. A lower intensity of training may also be more enjoyable and sustainable for some people, as it may cause less fatigue, discomfort, or boredom.
Conclusion
In conclusion, a training intensity of 67 percent or less is most closely related to aerobic endurance and fat loss adaptations. However, these adaptations may vary depending on the individual’s fitness level, health status, and preferences. A higher intensity of training may elicit greater adaptations than a lower intensity of training, but it may also increase the risk of overtraining, injury, or illness. Therefore, it is important to consult a qualified professional before starting any exercise program and to monitor the intensity, duration, frequency, and recovery of the training sessions.
