How Accurate Are Activity Trackers? EE Data From Omron, Fitbit, Jawbone & Other Devices Reveals 10% Error & More

How Accurate Are Activity Trackers? EE Data From Omron, Fitbit, Jawbone & Other Devices Reveals 10% Error & More

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Even though the study doesn't provide a straight-forward answer to the question "Which is the best activity tracker?", it is still revealing.

I hope you don't rely on the data from your activity tracker as a basis to decide how much you can, should or may eat on a daily basis. Why? Well, the first and most important result of a recent study from the Human Performance Laboratory at the Ball State University is that "consumer-based PA [physical activity] monitors should be used cautiously for estimating EE [energy expenditure]" (Nelson. 2016) - and this goes for the data from all the devices that were tested by Nelson et al.: The BodyMedia FIT and the NikeFuel armband, the DirectLife monitor, the Omron HJ-720IT, the Fitbit One, the Fitbit Zip, the Fitbit Flex, the Jawbone UP24, the Basis B1 Band Monitor and the ActiGraph.

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In view of the fact that tracking your energy expenditure is only one of the functions activity trackers are supposed to fulfill and considering the fact that you probably use them only to see if you have gotten more or less active (I do at least hope that you don't use them to guide your appetite ;-), it is still worth to take a look at the detailed results of this recent study.

As you will have guessed, the study was designed to "examine the validity of EE estimates from a variety of consumer-based, physical activity monitors under free-living conditions" (Nelson. 2016). To this ends, sixty (26.4 ± 5.7 yr) healthy men (n = 30) and women (n = 30) wore eight different types of activity monitors simultaneously while completing a 69-min protocol.

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"The monitors included the BodyMedia FIT armband worn on the left arm, the DirectLife monitor around the neck, the Fitbit One, the Fitbit Zip, and the ActiGraph worn on the belt, as well as the Jawbone Up and Basis B1 Band monitor on the wrist.

The validity of the EE estimates from each monitor was evaluated relative to criterion values concurrently obtained from a portable metabolic system (i.e., Oxycon Mobile) [which is obviously in itself not 100% exact]. Differences from criterion measures were expressed as a mean absolute percent error and were evaluated using 95% equivalence testing" (Nelson. 2016).

A brief glance at Figure 2 reveals that the accuracy was surprisingly similar among the devices. To be more precise, the mean absolute percent error values (computed as the average absolute value of the group-level errors) were 9.3%, 10.1%, 10.4%, 12.2%, 12.6%, 12.8%, 13.0%, and 23.5% for the BodyMedia FIT, Fitbit Zip, Fitbit One, Jawbone Up, ActiGraph, DirectLife, NikeFuel Band, and Basis B1 Band, respectively (unfortunately, not all data appears to be fully reported in the manuscript version of the study I had access to, so don't ask me about missing data, please ;-).

What did the test protocol look like? Subjects took part in a structured activity protocol consisting of 11 activities (three sedentary, four household, and four ambulatory/exercise) chosen by researchers from a list of 21 activities ranging from lying around on the couch to treadmill jogging. Activities were counterbalanced so that sex and age categories had approximately equal participation in the activities. All subjects began by lying quietly on a bed for 10 min. All other activities were performed for 5 min each, in order of generally increasing intensity. All activities were performed at a self-selected intensity by the subject. Subjects chosen to perform the jogging activity had the option of participating in a brisk walk if unable to jog for 5 min.

As the scientists point out, of all tested devices, only "[t]he results from the equivalence testing showed that the estimates from the BodyMedia FIT, Fitbit Zip, and NikeFuel Band (90% confidence interval = 341.1-359.4) were within the 10% equivalence zone around the indirect calorimetry estimate. If you still insist on trying to match your energy intake "exactly" to your energy expenditure, you should plan for a 10% + X% difference from your actual energetic demands - after all, even the indirect calorimetry that was used as a yardstick to judge the accuracy of the devices is not 100% accurate.

Figure 1: Mean absolute percent error when estimating energy expenditure for selected devices (Nelson. 2016).

In that, it is also worth mentioning that the accuracy of the devices was activity and device dependent. The Fitbit One, for example, produces the least error for stair climbing. For the Jawbone UP24, however, the "activity" for which it predicts your energy expenditure best is sitting around.

Accordingly, you could argue that you'd have to wear a certain device for a certain activity, e.g. (a) the Fitbit One, when sitting around (13%), working in the household (27%), taking the stairs (11%), jogging (22%) or cycling (43%) [note: on absolute terms, the error of the Fitbit for being sedentary is still lower than with the device from Jawbone], and (b) the Jawbone UP24, when you're simply walking around... but let's be honest: Since even that wouldn't be 100% accurate, it would be dumb to buy multiple fitness / activity trackers, wouldn't it?

Figure 2: With the exception of data from cycling and housework, the step count data (this graph) is sign. more accurate than the EE data in Figure 1 | If you want to learn more about what activity trackers are good / not good for and what you can / should make of the results of the study at hand, listen to me discuss this study on Monday's installment Super HumanRadio | click here to download the complete podcast that also includes discussions of the links NSAIDs and satellite cells and BPC-157 for muscle and tendon repair!

With an error of 10% you will always lose or gain weight involuntarily: The idea that a tiny technical device on your arm or belt could exactly tell you how much energy you need is in itself hilarious. And that's not just because the study at hand shows that even the best devices are on average +/-10% off (remember: that's +/-10% off another rough estimate that's never 100% exact). If you were dumb enough to match your diet blindly to the data your activity tracker provides, you would thus never achieve reliable results.

With that being said, our body is no biological machine that works according to a set of several (complex) equations. Therefore, the whole idea of a "quantified self" - as awesome as it may seem for the average control freak - must be seen as a tool to hold yourself accountable; a qualitative or semi-quantitative tool in the sense of "oh, I have been roughly 20% less active this week than last week, maybe I should..."

If the previously described rationale is behind the way you use the data from your activity tracker, congratulations! If not, I have to warn you: The margin between "quantifying yourself" and suffering from obsessive-compulsive disorder (OCD) and/or using the devices to fuel your exercise addiction is narrower than you may think | Do you agree, disagree? Let's discuss. Leave a comment on Facebook!

References

• Nelson, Benjamin N; et al. "Validity of Consumer-Based Physical Activity Monitors for Specific Activity Types ED." Med Sci Sports Exerc (2016): Ahead of print.

Fit and Lean in 4 Min / Week: 1kg Fat Loss, +9% VO2Max, +13% Fat Oxidation - Men Lose Trunk, Women Leg Fat

Fit and Lean in 4 Min / Week: 1kg Fat Loss, +9% VO2Max, +13% Fat Oxidation - Men Lose Trunk, Women Leg Fat

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No excuse: You don't need an ex-pensive spinning bike for the workout.

This is not an article for the hardcore trainees among you... unless, obviously you are a trainer or have friends and family who fall into the same "I just wannabe fit and healthy" category as the subjects of a recent study by scientists from the Manchester Metropolitan University and the Cambridge University School of Clinical Medicine (Bagley. 2016),  24 men and 17 women with a mean age of 39 (±2) years, a normal weight (BMI 24.6 +/- 0.6) and average fitness levels.

In this group of "normal people", Bagley et al. aimed to examine the hypothesis that very short duration, very high-intensity sprinting exercise (on cycle ergometers) could not just improve their subjects fitness (as measured by VO2max), but also their ability to burn fat and to actually lose it.

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After baseline measurements on the DEXA scan (body fat and lean mass) and cycle ergometers (VO2max), the participants were told to do only one thing: A sprint-interval training (SIT) program on a standard cycle ergometer.

"The training consisted of a 2 min warm-up at a self-selected moderate intensity. This was followed by four bouts of 20 s ‘maximal effort’ sprints at a workload that was set at 175% of the workload attained in the VO2max test. Each of these intervals was separated by 2 min of very low intensity cycling (a workload of approximately 20% of that attained at VO2max). Thus, each training session lasted less than 10 min and only 80 s was completed at an inten sity that would be expected to improve physical fitness" (Bagley. 2016). 

The first training session for each participant, who were told to maintain their their usual dietary and exercise habits throughout the intervention, was fully supervised in the research laboratory. To ensure that the subjects would indeed do their three weekly workouts 80s-workouts, the participants were then provided with clear instructions on the use of the cycle ergometers and the training regimen.

But you said "fit in 4 minutes", now the subjects train for almost 10 minutes? Yes and no. They train for 20 minutes, but the actual "exercise", which is something I define as being significantly exerted is 80s per workout. With three workouts per week, that's 3x80s = 240s = 4 minutes! So, I don't want to hear complaints ;-)

The training work load was increased by 5% every 2 weeks. Gym staff were fully informed of the research and training protocols, they logged the training session and were available to offer advice to research participants if needed during training sessions. Participants maintained a training-log to record workloads during training sessions.

Figure 1: Maximal oxygen uptake and rates of fat oxidation measured during exercise in men and women before and after 12 weeks of SIT; all changes were stat. sign. p < 0.05 (Bagley. 2016).

As you can see in Figure 1, the effects these short, highly time-efficient, and absolutely manageable (everyone can workout at max intensity for 4x20s) had on the subjects' fitness were not just statistically significant, they were also practically relevant and, at least for VO2max, differed significantly for men and women.

But how did they lose weight without dieting? The secret is the proven lack of compensation for SIT sessions, which have been show to be as low as <50kcal/week - compared with endurance exercise where compensation is 10x higher, i.e. 500 kcal/week (Burgomaster. 2008). Still, the direct energy expenditure during the short SIT sessions cannot fully explain the fat loss. Therefore, Bageley et al. speculate that "[o]ther contributing factors might include an increase in post exercise energy expenditure [that's unlikely, learn why] or overall shift towards greater fatty acid oxidation during habitual activities throughout the day" (Bagley. 2016).

Overall, the increase in VO2max averages out at 9% - the reasons for the sex-differences is not clear. After all, the scientists point out that men have been shown to have higher gains in VO2max following conventional endurance exercise. The mixed results of previous studies into the effects of sprint interval training, however, are mixed and thus not necessarily contrary to the evidence from the study at hand. While Scalzo et al. (2014), for example, found that young women had similar gains in VO2max as young men, the results Allemeier et al. (1994) et al. presented in the Journal of Applied Physiology suggest that men don't see any increase in VO2max. What could be the reason? Well, this is what the scientists say:

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"A higher relative amount of lean mass in men compared to women, coupled with a higher relative body fat mass in women compared to men, may go some way in explaining the differences between men and women in maximal oxygen consumption. However, the supply of oxygen to the working skeletal muscles is thought to be a limiting factor in VO2max, so the higher VO2max response in women might point to higher adaptations of oxygen supply than those in men following SIT, but more focused studies examining cardiac output, blood volume, haematocrit and blood flow distribution are needed to clarify this finding.

Conversely, after regular endurance training, men had higher gains in VO2max compared with women. It is possible that the training volume (higher in endurance) and training intensity (higher in SIT) lead to disparate adaptations between men and women in the oxygen carrying capacity of blood (eg, total blood volume, haemoglobin or cardiac output) or local vasculature, but physiological mechanisms driving such responses are unclear" (Bagley. 2016).

No sex differences were observed for the measured health markers, namely glucose, insulin, HOMA, triglycerides, total cholesterol or LDL - only for HDL there was a significantly more pronounced increase in the female vs. male subjects. Eventually, the improvement of the total cholesterol to HDL ratio was yet similarly pronounced in both sexes (-16% in the men, -11% in the women).

Figure 2: Body composition before and after 12 weeks of SIT; * after the categories denotes p < 0.05 (Bagley. 2016).

The previously discussed changes were accompanied by a significant loss of total, leg and trunk fat, as well as significant increases in lean mass in both groups - with inter-sex-differences in total body mass, body fat %, leg fat, and lean mass. That's quite a result, if you take into account the total and actual exercise time the subjects had to invest.

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Bottom line: I am not sure how feasible this protocol would be for an obese person, but in the healthy normal-weight subjects in the study at hand, the 12x4 minutes of working out intensely made quite a change. Ok, you have to work out thrice a week, but 10 minutes on an exercise bike? That's something you could easily do every morning before showering or when you come home from work.

Ah, and before I forget to highlight that - even though the fat loss in the female subjects may have been smaller than in the male subjects, the women lost fat where many of them hate it the most: on their legs - not bad!? Comment!

References:

• Allemeier, CRAIG A., et al. "Effects of sprint cycle training on human skeletal muscle." Journal of Applied Physiology 77.5 (1994): 2385-2390.
• Bagley, Liam, et al. "Sex differences in the effects of 12 weeks sprint interval training on body fat mass and the rates of fatty acid oxidation and VO2max during exercise." BMJ Open Sport & Exercise Medicine 2.1 (2016): e000056.
• Burgomaster, Kirsten A., et al. "Similar metabolic adaptations during exercise after low volume sprint interval and traditional endurance training in humans." The Journal of physiology 586.1 (2008): 151-160.
• Scalzo, Rebecca L., et al. "Greater muscle protein synthesis and mitochondrial biogenesis in males compared with females during sprint interval training." The FASEB Journal 28.6 (2014): 2705-2714.

Nine Short Workouts (AM+PM) p. Week Yield Extra Strength, Size and Performance Gains Compared to Volume Matched 3-Day Split, All Differences are Non-Significant, Though

Nine Short Workouts (AM+PM) p. Week Yield Extra Strength, Size and Performance Gains Compared to Volume Matched 3-Day Split, All Differences are Non-Significant, Though

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15 min in the AM, 15 in the PM = Win? For many of you that may sound laughable, but according to a recent study from the University of Copenhagen it is at least as effective as three "mammoth" workouts-sessions per week.

What kind of trainee are you? Do you hit the gym thrice a week, spend two hours there and crawl out of the gymdoors totally exhausted? Yeah... Well that means you're not the fitness model guy, who trains twice a day for 15-20 minutes only and swears that this is the only way to do it?

After all these questions you're probably asking yourself if the answers you gave in your mind were good or bad for ya? Right? Well, eventually, both forms of training can be equally effective. If we take a closer look at the non-significant study outcomes in a recent paper by scientists from the University of Copenhagen (Kilen. 2015), though body composition and strength may in fact benefit more if you train more frequently - even if the total workout volume is the same.

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Workout volume? Yes, that's the number of sets and reps. So, let's say you do three 45-minute training sessions weekly, including 1 strength on Monday, 1 high intensity cardiovascular (HIIT) session on Wednesday, and 1 muscle endurance session on Thursday, then those 3x45 minutes + warm-up exercise are your total workout volume.

In case that's what you're doing on a regular basis, you're training just like those of the 21 study subjects (10 men, 11 women; 25 +/- 3 years) with some previous training experience who were randomly assigned to the "classical" training program in the previously mentioned study by Kilen, et al. (2015). If you're rather the fitness model type, you may recognize your own training in what the other subjects did, i.e. a "micro training" program with a total of nine 15-minute training sessions weekly that were divided equally between strength training, high-intensity cardiovascular training, and muscle endurance training and performed in the AM and PM from Monday to Friday (there was no PM training on Friday, though, and cardio and strength were rotated | see caption of Table 1).

Table 1: Description of the two different training regimen (Kilen. 2015) | *To minimize the potential negative effect of concurrent cardio + strength training, MI performed 2 days of strength (Mon and + Tue) and 1 day of cardio training (Wed) in odd weeks, and 1 day of strength (Mon) and 2 days of cardio training (Tue + Wed) in even weeks.

Unlike the training frequency and rest between workouts, the strength training, HIIT and muscular endurance training sessions, themselves, were identical in both groups:

• Strength training consisted of leg exercises (deadlifts, lunges, step-ups, and 1 leg squats), with 1–2 warm-up sets and 2–3 target sets of 8RM, and upper-body exercises (pullups, dips, weighted push-ups, and 1 arm rows), with 1–2 warm-up sets and 2–3 target sets of 5RM. For progression, the exercises were adjusted using extra loading (sandbags in 1-kg steps) if the subjects were able to accomplish more repetitions than prescribed. If the subjects were not able to perform the number of repetitions prescribed, they performed as many as they could in proper form and finished the set conducting only the eccentric phase of the exercise. 
• High-intensity cardiovascular training (HIIT) consisted of running for 2 and 4 minutes at an average speed of 15.1 and 14.5 km/h, respectively, which elicited ;90% maximal heart rate during exercise. Micro training performed two 4-minute run intervals in the morning with 3 minutes of rest in between and four 2-minute run intervals in the afternoon with 1 minute of rest in between. Classical training performed three 4-minute and six 2-minute run intervals in the same training session with the same rest as MI in between. The training volume was evaluated and the only significant difference was running distance during 2-minute and 4-minute intervals, where MI ran significantly further than CL in each interval. 
• Muscle endurance training consisted of three 5-minute exercise sessions involving 5 different exercises performed continuously for 30 seconds with 30-second rest periods. Micro training conducted 3 sessions; the first was “easy,” the second “hard,” and the third “very hard.” Classical training conducted 9 sessions in the same order, starting over with “easy” on the fourth and seventh sessions. The exercises were weighted lunges (with a 20-kg sandbag); push-ups; shuttle runs; abdominal exercises ([a] regular sit-ups from a supine position with knees bent at 908, fists in contact with the ears and the lumbar arch supported by a folded towel, and [b] diagonal sit-ups from a horizontal supine position, outstretched hand to opposite raised foot, alternating); and back exercises ([a] back extensions on an incline bench and [b] kettlebell swings in a standing position). 

As Kilen et al. point out, "[a]ll training sessions were supervised by scientific staff, and subject attendance" as well as "[h]eart rate [...] during high-intensity cardiovascular training and muscle endurance training for the last 5 weeks of the training intervention" (Kilen. 2015) were recorded.

Figure 1: Relative pre- vs. post changes in all measures performance markers (calculated based on Kilen. 2015).

After the 8-weeks on the respective training regiment, a comparison of the pre- vs. post-training data yielded the following results:

• Increases in shuttle run performance were observed in both group, albeit with a higher significance as far as the pre- vs. post-difference is concerned in the classical training (CL) vs. micro training (MI) group (MI: 1,373 +/- 133 m vs. 1,498 +/- 126 m, p < 0.05; CL: 1,074 6 213 m vs. 1,451 6 202 m, p , 0.001).
• Significant improvements in peak oxygen uptake (3,744 6 +/- 615 mL/min vs. 3,963 +/- 753 mL/min | p < 0.05), maximal voluntary isometric (MVC) force of the knee extensors (646 +/- 135 N vs. 659 +/- 209 N | p < 0.001), MVC of the finger flexors (408 +/- 109 N vs. 441 +/- 131 N, p < 0.05), and the maximal number of lunges performed in 2 minutes (65 +/- 3 vs. 73 +/- 2, p , 0.001), however, were seen only in the micro = high frequency training group.

The question you may be asking yourselves now is: Why does the headline say that there were no significant differences? Well, the lack of statistical significance of the improvements in the classical training group does not suffice for a statistically significant between difference to the micro training group. Statistical significant inter-group differences did not exist either before or after the study. The scientists conclusion that

"similar training adaptations can be obtained with short, frequent exercise sessions or longer, less frequent sessions where the total volume of weekly training performed is the same" (Kilen. 2015)

is thus absolutely correct. The fact that statistical significance for the aforementioned study outcomes was achieved in the micro, yet not in the classical training group does still suggest that the high(er) frequency training regimen may have an adaptive edge... albeit in terms of study outcomes not everyone will deem practically relevant.

Figure 2: Neither the in-group nor the inter-group changes in body composition did reach statistical significance (calculated base on Kilen. 2015). At least in my humble opinion, though, they are still interesting.

Speaking of what people will deem relevant: We haven't addressed the changes in body composition yet. Why's that? Well, if we go by statistical significance, there were none. If we go by %-ages, though, the increase in lean and decrease in fat mass in the micro training, as well as the opposite trends in the classical training group add to the non-significant evidence that it may make sense to train more frequent and that - when all is said and done - total volume may eventually not be the only thing that matters... I mean, if you look at the data in Figure 2 it would - in defiance of the statistical insignificance of the changes - still seem as if the previously mentioned fitness model was right: For him or her, for whom improves body composition are the primary goal, his / her frequent AM/PM training regimen does in fact appear to be the training model of choice | Comment!

References:

• Kilen, Anders, et al. "Adaptations to Short, Frequent Sessions of Endurance and Strength Training Are Similar to Longer, Less Frequent Exercise Sessions When the Total Volume Is the Same." The Journal of Strength & Conditioning Research 29 (2015): S46-S51.