In contrast to cardiovascular training, where a consistently elevated heart rate facilitates the calculation of calories burned, strength training presents a more complex scenario due to the alternating periods of exertion and rest between sets.
During the execution of a set, an individual’s heart rate increases, followed by a decrease during rest periods. Nevertheless, even during these rest intervals, caloric expenditure remains elevated compared to resting levels, primarily due to the phenomenon of oxygen debt—an excess of oxygen consumed following intense physical activity.
Furthermore, energy expenditure continues post-exercise until the body returns to a state of homeostasis. This complexity renders precise calculations challenging; thus, the most accurate method for determining caloric burn involves the use of a gas analyzer—a specialized mask worn during training that measures oxygen consumption and calculates caloric expenditure.
However, existing research provides a general understanding of the energy expenditure associated with strength training.
Caloric Burn During Strength Training
In one study, researchers assessed the caloric expenditure of male and female participants during strength training. The subjects performed eight strength exercises, each consisting of one set of 15 repetitions, with weights selected to allow for exactly 15 repetitions.
The findings indicated that men expended an average of 5.6 kcal per minute during the exercises, while women expended 3.4 kcal per minute. This disparity is not unexpected, given that the average weight of the female participants was 62 kg, compared to 90 kg for the male participants, who possessed significantly greater muscle mass.
In another experiment, female participants burned approximately 155 calories during a complete workout consisting of 10 exercises, each performed in three sets of 10 repetitions with one minute of rest between sets. Additionally, they expended an extra 31 calories during the recovery phase due to oxygen debt. The total duration of the workout was 45 minutes, leading to a conclusion that the caloric burn was approximately 3.4 calories per minute. The average age of the female participants was 29 years, with an average weight of 59 kg.
Overall, during strength training, women typically burn around 3.4 kcal per minute, while men burn approximately 5 to 6 kcal per minute.
The intensity of the weights used—whether heavy with fewer repetitions or lighter with more repetitions—does not significantly affect caloric expenditure, provided that the exercises are performed until substantial muscle fatigue is achieved.
In a separate study, researchers aimed to quantify the energy expenditure associated with strength training at varying intensities. Young, trained men performed classic strength exercises, including bench presses, squats, and pull-ups, while a gas analyzer measured their caloric burn.
The study examined three training regimens:
- Low intensity: 2 sets of 15 repetitions at 60% of one-repetition maximum (1RM).
- Medium intensity: 3 sets of 10 repetitions at 75% of 1RM.
- High intensity: 6 sets of 5 repetitions at 90% of 1RM.
In all conditions, participants rested for 2 minutes between sets.
The results revealed that high-intensity strength training resulted in an average caloric burn of approximately 610 kcal, medium intensity burned 360 kcal, and low intensity burned 283 kcal. However, these differences were primarily attributable to the duration of the training sessions: low-intensity training lasted 44 minutes, medium intensity lasted 61 minutes, and high intensity lasted 116 minutes.
During low-intensity strength training, men expended approximately 6.4 kcal/min, while medium intensity resulted in 5.9 kcal/min, and high intensity yielded 5.2 kcal/min. Interestingly, a greater number of repetitions with lighter weights proved to be more energy-consuming than shorter sets with heavier weights. Nonetheless, had the training durations been equal, the difference in caloric expenditure would have been minimal—approximately 50 kcal.
It is important to note that the researchers did not measure oxygen debt in this study. Preliminary evidence suggests that individuals may consume more oxygen and burn additional calories at rest following heavy resistance training compared to moderate-intensity exercise; however, this area remains underexplored.
Estimating Caloric Burn During Strength Training
A rough estimate of caloric expenditure can be obtained by multiplying the duration of the workout by the average energy expenditure rates for women (3.4 kcal/min) and men (5.6 kcal/min).
It is essential to consider that the studies from which these figures were derived involved young individuals with low body fat percentages. Consequently, individuals with different body compositions may experience lower energy expenditure.
Caloric expenditure during training can vary based on several factors:
- Rest Periods Between Sets: In the studies, participants rested for a fixed duration of 60-120 seconds between sets and repetitions. Extended rest periods, such as those spent conversing or engaging with social media, may significantly reduce caloric burn. Conversely, minimizing rest intervals can enhance energy expenditure.
- Body Composition: Muscle tissue requires more energy than fat tissue, thus body composition directly influences caloric expenditure. Individuals with a higher muscle mass will utilize more energy both at rest and during exercise.
- Fitness Level: As individuals become more accustomed to a particular activity, their caloric burn tends to decrease. Initially, the body expends more energy to learn new skills, but over time, it adapts and performs movements more efficiently, resulting in reduced energy expenditure.
Predicting the exact caloric burn can be challenging, particularly if rest periods deviate from the standard 2 minutes or if an individual has a higher percentage of body fat and lower muscle mass. Therefore, it is advisable to rely on general estimates while acknowledging that individual energy expenditure may vary slightly from the stated values.
