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Should I Buy A Fitness Tracker?

fitness trackers

'Should I buy a fitness tracker?' I get asked this question a lot, and the answer really depends on what you want to achieve. Your GP may be encouraging you to increase your daily activity levels; or perhaps you're embarking on a new health kick and want to know how many calories you've burned today so that you can work out how much you're allowed for dinner?

Where it's a case of monitoring or increasing your daily activity levels, then a fitness tracker can be an effective tool. It can help draw attention to a point in the day where you're engaging in little or no activity and might be just what you're needing to help spur you into action and get you up on your feet. More excitingly though! your fitness tracker will show you how even modest levels of physical activity can add up to significantly influence your step-count and energy expenditure across the day. I'm talking things like walking to the corner store, riding your bike to work, opting for the stairs rather than the lift, and taking the dog for an extra lap of the block before bedtime.

For some unfathomable reason, we've got ourselves to this silly state of extremes where if we're not smashing out tempo runs or pumping iron in the gym, then it's just not worth bothering. It's not exactly sexy, and I guess that's half the problem, but simply by moving more, we can make significant reductions to the size our waistlines, improve our cardiovascular health and increase our longevity [1,2,3].

The national guidelines for physical activity have steadily evolved -or devolved depending on which way you look at it- over the years, from a specific set of exercise prescriptions, to simply increasing public awareness of the dangers of sedentary behaviour and encouraging us to get off our be-hinds [4,5,6]. On whether these recommendations are effectively translating into a marketable message, I have to admit I'm a little sceptical... They certainly don't seem to generate the same level of enthusiasm for physical activity as a topless Joe Wicks sweating it out over a HIIT session under the Californian sun (while he intermittently tugs at his waistband). So if fitness trackers can help reduce our all-or-nothing approach to exercise and help popularise daily activity, then, at risk of sounding really boring, I'm all for them.

If you're more interested in monitoring your energy expenditure, or calories out, then you might want to know a little more about the limitations of your device before you go letting it rule your health plan. To calculate your daily energy expenditure, your fitness tracker uses an algorithm, which is based on:

1.) Your heart rate. According to a recent study, most fitness trackers measure heart rate within 5% [7] - that's pretty good going;

2.) How many steps you take over course of the day. The type of motion sensor your particular fitness tracker has will affect the outcome, but studies suggest that most have this pretty down pat [8];

3.) A coefficient generated by a lab test to work out how many calories are burned for a given amount of time and effort. Depending of the methods used, the degree of error in this lab test can be as much as 45% [9]. Not so great;

4.) The information you give it; usually height, weight, age and gender. Sounds okay, but in reality you're much more than just a height, a weight, an age and a gender: What about all the other unique little factors that make up YOU..?

i.) Hormones. Energy expenditure is influenced by the thyroid hormone triiodothyronine (T3). Low plasma of levels of T3, or hypothyroidism, causes a reduced basal metabolic rate, and is often accompanied by weight gain; conversely, hyperthyroidism results in increased basal metabolic rate [10]. If you're a woman, then where you are in your menstrual cycle might also affect your energy expenditure. During the luteal phase, your body temperature goes up and energy expenditure can increase (and, as you might have noticed, so can energy intake) but it'll subsequently decrease as you move though the menstrual, follicular and ovulation phases [11]. Sleeping metabolic rate also decreases significantly in women as they transition from pre- to postmenopausal [12].

ii.) Brown adipose tissue. In addition to the better-known white adipose tissue, which specialises in lipid storage and undergoes pathological expansion during obesity, we're also equipped with brown adipose tissue (BAT). BAT functions to rapidly generate heat (thus expending large amounts of energy) and is especially abundant in newborns, but is also present to varying degrees in adults. Younger adults and people that live in a colder climates usually have larger stores of BAT, and consequently have higher rates of energy expenditure [13].

iii.) Epigenetics. The environment in which you exist has the potential to modify the expression of your genes; something called epigenetics. We're only just beginning to scratch the surface in terms of what we understand about the mechanisms that underly theses processes, but early studies in mice suggest that the metabolic environment can regulate the expression of a number of genes related to energy expenditure [14]. In other words, you might burn greater or fewer calories per day depending on the longer-term availability of energy.

iv.) Sleep. If you're not getting enough sleep, then chances are your energy expenditure might take a hit. Results of studies to date are controversial, mainly due to the wild variation between study groups and conditions and because of the difficulty in separating the simultaneous effects of increased appetite. However, those studies that have included longer follow-up periods suggest that sleep deprivation may lead to a reduced basal metabolic rate over time [15].

v.) Seasonal changes

You may have noticed that as the seasons move from summer into winter, you begin to feel more hungry and crave more stodgy, filling food? That's because at cooler air temperatures your sleeping metabolic rate increases [16].

vi.) The thermic effect of food. The thermic effect of food (TEF) is the energetic cost of digesting, absorbing and assimilating food. This includes the energy it takes to chew food, for enzymes to breakdown your food into molecules which can be absorbed into your bloodstream, and for transporters to shuttle these molecules across your intestinal walls, and it varies depending on the composition of your meal. With isocaloric amounts, it requires more energy to metabolise protein, than carbohydrate, than fat. Which means if you eat a meal that contains exactly the same number of calories but is made up predominantly of protein, you'll expend more energy just in digesting it than if your meal is predominantly made up of fats [17].

Phew! Hopefully you're still with me. It was a bit of a long-winded way of illustrating my point, but I wanted to show you that energy metabolism is much more complex than simply being a product of your height, weight, age and gender. I hope that you can now come to your own conclusion about how literally you're willing to take your fitness tracker's energy expenditure figures... but suffice to say I would absolutely never advocate using these values to determine how much you're allowed to eat for dinner.


References cited

[1] Ekblom, B., Vikström, M., de Faire, U., & Hellénius, M. L. (2014). The importance of non-exercise physical activity for cardiovascular health and longevity. British Journal of Sports Medicine, 48(3), 233-238.

[2] Myers, J., Prakash, M., Froelicher, V., Do, D., Partington, S., & Atwood, J. E. (2002). Exercise capacity and mortality among men referred for exercise testing. New England Journal of Medicine, 346(11), 793-801.

[3] Chan, C. B., Ryan, D. A., & Tudor-Locke, C. (2004). Health benefits of a pedometer-based physical activity intervention in sedentary workers. Preventive Medicine, 39(6), 1215-1222.

[4] UK Department of Health. (2004). At least five a week: Evidence on the impact of physical activity and its relationship to health. A report from the Chief Medical Officer.

[5] O’Donovan, G., Blazevich, A., Boreham, C., Cooper, A., Crank, H., Ekelund, U., … & Stamataki, M. (2010). The ABC of physical activity for health: A consensus statement from the British Association of Sport and Exercise Sciences. Journal of Sports Sciences, 28, 573-91.

[6] Department of Health, Physical Activity, Health Improvement and Protection. (2011). Start Active, Stay Active: A report on physical activity from the four home countries’ Chief Medical Officers.

[7] Shcherbina, A., Mattsson, C. M., Waggott, D., Salisbury, H., Christle, J. W., Hastie, T., ... & Ashley, E. A. (2017). Accuracy in wrist-worn, sensor-based measurements of heart rate and energy expenditure in a diverse cohort. Journal of Personalized Medicine, 7(2), 3.

[8] Evenson, K. R., Goto, M. M., & Furberg, R. D. (2015). Systematic review of the validity and reliability of consumer-wearable activity trackers. International Journal of Behavioral Nutrition and Physical Activity, 12(1), 159.

[9] Simonson, D. C., & DeFronzo, R. A. (1990) Indirect calorimetry: methodological and interpretative problems. American Journal of Physiology. 258(3 Pt 1) E399-412.

[10] Kim, B. (2008). Thyroid hormone as a determinant of energy expenditure and the basal metabolic rate. Thyroid, 18(2), 141-144.

[11] Davidsen, L., Vistisen, B., & Astrup, A. (2007). Impact of the menstrual cycle on determinants of energy balance: a putative role in weight loss attempts. International Journal of Obesity, 31(12), 1777-1785.

[12] Lovejoy, J. C., Champagne, C. M., De Jonge, L., Xie, H., & Smith, S. R. (2008). Increased visceral fat and decreased energy expenditure during the menopausal transition. International Journal of Obesity, 32(6), 949-958.

[13] Seale, P., & Lazar, M. A. (2009). Brown fat in humans: turning up the heat on obesity. Diabetes, 58(7), 1482-1484.

[14] Hino, S., Sakamoto, A., Nagaoka, K., Anan, K., Wang, Y., Mimasu, S., ... & Nakao, M. (2012). FAD-dependent lysine-specific demethylase-1 regulates cellular energy expenditure. Nature Communications, 3, 758.

[15] Jung, C. M., Melanson, E. L., Frydendall, E. J., Perreault, L., Eckel, R. H., & Wright, K. P. (2011). Energy expenditure during sleep, sleep deprivation and sleep following sleep deprivation in adult humans. The Journal of Physiology, 589(1), 235-244.

[16] Westerterp-Plantenga, M. S., van Marken Lichtenbelt, W. D., Strobbe, H., & Schrauwen, P. (2002). Energy metabolism in humans at a lowered ambient temperature. European journal of clinical nutrition, 56(4), 288.

[17] Hall, K. D., Heymsfield, S. B., Kemnitz, J. W., Klein, S., Schoeller, D. A., & Speakman, J. R. (2012). Energy balance and its components: implications for body weight regulation. The American Journal of Clinical Nutrition, 95(4), 989-994.


No calorie-counting, no dieting and no banned food items! If you're looking for a healthy, sustainable way to improve your fitness and nutrition then why not book a coaching consultation with me today to find out how I can help you achieve the results you need.

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