A Review of an ACSM study:
Validity of Consumer-Based Physical Activity Monitors for Specific Activity Types
Arguably one of the most iconic new-age health and fitness devices is the physical activity monitors (PA) which can range from the expensive Apple watch, mid-grade Fit bit, to the cheapo dollar store monitors. All of which can perform a variety of important features such as sleep monitoring, step counting, heart rate monitoring, along with an even faster connection to peripheral devices. Of all the devices, almost all of them count caloric expenditure or energy expenditure (EE) to be more precise. However, in the implementation of these calculations there can be pitfalls in both diet and weight loss goals.
In a 2016 study conducted by the American College of Sports Medicine (ACSM), thirty participants were selected to perform sedentary activities followed by, stretching movements, and four preset household exercises. The study concluded that in a sedentary state, which means laying in bed for 10 min and relaxed, all PA EE predictions were within 8% of the actual caloric estimate. A person with a TDEE total daily energy expenditure of 2000 Kal would wear the PA and find that by the end of the day the PA would predict an EE of +/- 160 Kal. Which in terms of weight loss is not a significant determinant; however, there is a significant overestimation of EE when it comes to exercise between 16% – 40%. In terms of actual numbers, a person completing a workout where they burned 500 Kal in reality burned between 420 Kal from a more accurate PA or 200 Kal from a less accurate device reading the same caloric expenditure. Thinking best case scenario with all PA in the study were 160 Kal off from sedentary EE then having the most accurate PA for exercise off by 80 Kal from a 500 Kal workout daily would be off 240 Kal of the total daily energy expenditure. For those looking to lose 0.5lbs of body fat a week, this best-case scenario would completely end the caloric deficit needed to facilitate that weight loss. With that knowledge, one can infer the significant hindrances to weight management with an even less accurate PA.
These devices are useful in understanding exertion and progress in exercises rather than implementing more calories in a diet to compensate for exercise. A great way to use the device is by showing progression in perceived exertion. If a workout felt like an 8/10 and burned 500 Kal then a few weeks later the workout felt closer to a 6/10 but the energy expenditure was the same there can be some inference to an increased cardiovascular or muscular endurance. To support weight loss goals, one should look at exercises as an addition to weight loss rather than an “exercise to eat” mentality.
For more information and validity please review the full study: