What is an activity tracker?

An activity tracker is a wearable device that can track your workouts, monitor sleep habits, record your water intake, let you have competitions with friends, and even will remind you to get up and move around after you’ve been sedentary for a while.

Many studies have shown that consistently using a fitness tracker can help you increase your steps and movement throughout the day. Whether it is an Apple Watch, Fitbit, Garmin, Whoop, or any of the many other options, if you wear one then you have likely changed some aspect of your daily movement since you started wearing it. While these activity trackers offer us information and data points, how accurate is the information that we are receiving?

How does an activity tracker get information?

Activity trackers work by taking an individual’s information from sensors that track your everyday movement. This “movement” is then processed through multiple algorithms, varying from tracker to tracker, to provide you with information about your calories burned or your daily energy expenditure. To gather this information, infrared light penetrates the skin and looks for subtle changes in blood oxygenation, or more simply, the appearance of blood vessels (American Council on Exercise). While these activity trackers do a fantastic job at identifying movement, there is key information missing that is needed for the movement and expenditure to be accurate. Most activity trackers are currently unable to account for an individual’s muscle mass and also lack the complex technology to accurately detect respiratory rate and skin temperature (NASM).

Though some trackers are coming out with technology to improve this and offer these data points, it is still undetermined as to their accuracy. When evaluating a person’s Basal Metabolic Rate (BMR, or calories burned while resting), we must take all these factors into account. For most devices, all metrics are based solely on heart rate and movement. But these two factors alone are not a true indicator of total calorie expenditure.

We often assume that when your heart pumps faster you are creating a higher demand for oxygen and energy which leads to burning more calories. But, have you ever been excited, quickly jumped up from a chair, or even been blow-drying your hair and your activity tracker asked if you were starting a workout? These instances happen more often than not so let’s take a look at how different activities can lead to different energy expenditure and how that can translate into misconstrued calorie burning data.

Is caloric expenditure from cardio and resistance training the same?

Cardio and resistance training are both amazing forms of exercise. While both will lead to an increase in your overall calorie burn for the day, they vary in their long-term effects.

One of the benefits of consistent resistance training is an increase in your overall muscle mass. Studies have actually shown that the increased muscle mass from resistance training can lead to an increase in your metabolic rate by up to 7% which means an overall boost in your metabolism (American Council on Exercise). The immediate effect of resistance training is the training session itself, but the long-term effect is increased muscle mass which results in more burn over time. In fact, your resistance training session can actually lead to a higher rate of calories burned for up to 72 hours after the workout ends! This phenomenon is called Excess Post-Exercise Oxygen Consumption, or EPOC, and is more prevalent after difficult strength training workouts, HIIT, or any workout where your muscles are working hard to keep up. So whenever you are increasing the intensity of your workout and making your muscles work harder you are actually increasing your level of EPOC and therefore increasing your calories burned from that one workout even after you’re done.

When you train your cardiovascular system through sustained endurance activities such as running, biking, long walks, etc., you won’t be seeing the same long-term effects as you do with resistance training. The calorie burn you experience during cardio-type activities will end as soon as your workout ends and your heart rate returns to normal.

If you are doing any sort of resistance training such as strength training, HIIT workouts, CrossFit, work with resistance bands, etc. then you are burning more calories than your activity tracker is counting. True calorie burn is not determined by heart rate, but by the number of muscle cells that are activated to perform an activity. Unfortunately, activity trackers can’t make the distinction between muscle activation and heart rate. There are many other variables that can affect your heart rate as well such as blood pressure, your mood, if you are well-rested, your hydration levels, stress, and adrenaline. If any of these variables are off then your calorie burn according to your activity tracker will be off, too.

Should I base my Macrostax activity level on my activity tracker?

Since most activity trackers are unable to differentiate the caloric expenditure between activities, as well as the EPOC resulting from resistance-based activities, at Macrostax, we take an average of your week to determine the correct activity level for you. Though it can be tempting to underestimate your activity to alter your macros, this can have the opposite effect and cause the body to hold onto the weight. The Macrostax numbers are designed to get your body and metabolism fired up!