When it comes to cardio training, tracking calorie burn is relatively straightforward due to the consistent elevation of heart rates. However, strength training presents a more complex scenario, as it involves alternating periods of exertion and rest between sets.
During a set, your heart rate increases, leading to higher calorie expenditure. Conversely, during rest periods, your heart rate decreases, but you still burn more calories than at rest due to the phenomenon known as oxygen debt—where excess oxygen is consumed post-exercise. Additionally, your body continues to expend energy after your workout until it returns to a resting state. This complexity makes precise calculations challenging; the most accurate method involves using a gas analyzer, a specialized device worn during training that measures oxygen consumption and calculates calorie burn.
Nevertheless, research provides valuable insights into the energy expenditure associated with strength training.
Caloric Burn Estimates for Strength Training
A study examining calorie burn during strength training found that male participants averaged 5.6 kcal per minute, while female participants averaged 3.4 kcal per minute. This discrepancy is largely attributed to differences in body composition, as the average weight of the women was 62 kg compared to 90 kg for the men, who typically possess more muscle mass.
In another experiment, women burned approximately 155 calories during a full workout consisting of 10 exercises, each performed in three sets of 10 repetitions, with a minute of rest between sets. They also burned an additional 31 calories during recovery due to oxygen debt. The total workout duration was 45 minutes, reaffirming the average burn rate of 3.4 calories per minute for women.
Overall, during strength training, women typically burn around 3.4 kcal per minute, while men burn between 5 and 6 kcal per minute. The intensity of the workout—whether using heavy weights for fewer repetitions or lighter weights for more repetitions—does not significantly alter calorie expenditure, provided the exercises are performed to the point of muscle fatigue.
A study focused on different intensity levels of strength training revealed that young, trained men burned varying amounts of calories based on the intensity of their workouts. The study tested three regimens:
- Low Intensity: 2 sets of 15 reps at 60% of one-rep max (1RM).
- Medium Intensity: 3 sets of 10 reps at 75% of 1RM.
- High Intensity: 6 sets of 5 reps at 90% of 1RM.
Participants rested for 2 minutes between sets. The results indicated that high-intensity training resulted in approximately 610 kcal burned, medium intensity burned 360 kcal, and low intensity burned 283 kcal. However, these differences were primarily due to the duration of the sessions, with low-intensity training lasting 44 minutes, medium intensity 61 minutes, and high intensity 116 minutes.
Interestingly, during low-intensity strength training, men expended about 6.4 kcal/min, while medium intensity resulted in 5.9 kcal/min, and high intensity yielded 5.2 kcal/min. This suggests that higher repetitions with lighter weights can be more energy-consuming than fewer repetitions with heavier weights. However, if training durations were equalized, the difference in energy expenditure would be minimal—approximately 50 kcal.
It is worth noting that the study did not measure oxygen debt, which may influence post-exercise calorie burn. Some evidence suggests that heavy resistance training can lead to greater oxygen consumption and calorie burn at rest compared to moderate-intensity workouts, although this area requires further research.
Estimating Caloric Burn During Strength Training
To estimate the calories burned during strength training, one can multiply the workout duration by the average energy expenditure rates: 3.4 kcal/min for women and 5.6 kcal/min for men. However, it is essential to consider that these figures were derived from studies involving young individuals with low body fat percentages. Those with different body compositions may experience lower energy expenditure.
Several factors can influence energy expenditure during strength training:
- Rest Time Between Sets: Fixed rest periods of 60-120 seconds were used in studies. Extended rest due to distractions, such as socializing or using mobile devices, can significantly reduce calorie burn. Conversely, shorter rest periods can increase energy expenditure.
- Body Composition: Muscle tissue requires more energy than fat, so individuals with a higher muscle mass will burn more calories both at rest and during exercise.
- Fitness Level: As individuals become more accustomed to a workout, their bodies become more efficient, leading to reduced calorie burn over time.
While it is challenging to predict exact calorie expenditure based on variations in rest time or body composition, focusing on general values can provide a useful framework for estimating energy expenditure during strength training.
