The trouble with activity trackers … or not.

A recent study (1) found that a high level of cardiorespiratory fitness (CRF) was associated with an increased risk for localized prostate cancer.  The reasons for this are unknown.  The researchers speculate that perhaps this group was more likely to undergo preventative screening or detection.  However, higher CRF still showed a 32% decreased risk of cancer specific death for lung, colorectal, or prostate cancers; or 68% decreased risk of death from cardiovascular disease (CVD).  Note: some cancer treatments can be toxic to the heart.

From: Midlife Cardiorespiratory Fitness, Incident Cancer, and Survival After Cancer in Men:  The Cooper Center Longitudinal Study.

Lakoski, S.G., et al. JAMA Oncol. 2015;1(2):231-237

Figure Legend: Cardiorespiratory Fitness (CRF) and Risk of Incident Lung, Colorectal, and Prostate Cancer.  The low CRF group is the referent group relative to moderate and high fitness.  The error bars for moderate and high fitness represent the 95% confidence limits.  Adjusted for age, examination year, body mass index, smoking, total cholesterol level, systolic blood pressure, diabetes mellitus, and fasting glucose level.

The authors distinguish CRF from physical activity (I believe research data for both could be provided by valid and reliable activity trackers):

“Cardiorespiratory fitness is also highly reproducible and objectively assessed via incremental exercise tolerance testing compared with physical activity, which is largely determined by self-report questionnaires [and/or activity trackers?].  A prior study demonstrated that CRF is be a more potent marker of mortality than physical activity.  As such, given the current study findings and prior evidence, we contend that measurement of CRF should be used more frequently in the cancer prevention setting.”

I agree.  Furthermore, I would like to see physical activity, CRF, or aerobic capacity assessed when the cancer diagnosis process begins.  How beneficial would it be to tie fitness to an actual biopsy tissue specimen?  It’s interesting that CRF in the Cooper Clinic Longitudinal Study was assessed by the duration of performance achieved on a maximal treadmill test (2).  Then, based on subjects’ performance time, maximal oxygen uptake (VO2max) and maximal METs achieved were estimated, not measured.  If estimates can be used to assess CRF then it’s possible that some activity trackers could also be used.  Granted, screening patients before a CRF test is recommended, but some activity tracking data may already provide an adequate assessment of CRF.  A few devices already assess VO2max using heart rate, and with acceptable errors (for field measurements) in the 6-7% range (11, 12).  Stratifying data from activity trackers may be an important part of sorting its value: data for showing a training effect requires good accuracy; less accurate data is probably acceptable to assess CRF; and, data for tracking physical activity volume (MET-hours per week, etc.) can perhaps be the least precise of these – particularly since current population research using questionnaires tends to overestimate actual physical activity (13).

In discussing limitations of their study the authors mention something I believe may be significant for exercise-oncology research, and which I think validated activity trackers may be able to provide data for:

“CRF was assessed years prior to a diagnosis of lung, colorectal, or prostate cancer or death in men diagnosed as having cancer.  Thus, it is not known how changes in CRF and related behaviors, such as physical activity from the initial preventive health care to cancer diagnosis as well as changes in CRF and physical activity after diagnosis, may have had an impact on these current findings.”

I believe that exercise during the time from cancer diagnosis until first treatment will be found to have a positive impact on cancer treatments, treatment side effects, and on survival.  Sophisticated activity trackers that also estimate VO2max, or measure heart rate variability (HRV), which is related to CVD, have the potential to provide data in and around the diagnosis/treatment time period.  Furthermore, they can provide data across more cancer types by doing it in a more cost-effective manner than mailing out questionnaires or doing a CRF test on every cancer patient.  One overlooked benefit of activity trackers is that consumers subsidize the data.

Some useable physical activity data already exists in activity tracking databases but sits there underutilized.  Most physical activity data needs standard medical codes to improve its interoperability.  Other data could be retooled by correcting METs, which could provide more accurate estimates of energy expenditure (4, 5, 6, 7, 8), population specific intensity levels (9, 10), and might influence adherence to exercise training programs.  Regarding METs, an issue for some researchers is that the ‘standard’ MET (3.5 ml oxygen/kg/min) was based on the measurements derived from one 70 kilogram, 40-year-old man (5), and then applied to survey research.  Conversely, some activity trackers use ‘standard’ MET values from the Compendium of Physical Activities, which are intended for survey research, to estimate the energy expenditure and exercise intensity for an individual, which the Compendium advises is not its intended purpose.

Besides valid data, another issue activity trackers face is how should data be displayed or reported within an Electronic Health Record (EHR)?  Doctors are already over-worked and many complain about the burden of EHRs, adding physical activity data to their workload and expecting them to do something proactive with it (without reimbursement too) is not going to happen.  Make physical activity data easy for doctors to accommodate: summarize activity tracker data into an indicator of ‘compliance‘ or ‘non-compliance‘ with recommended physical activity guidelines, and provide that to an EHR.  For research, and for the more inquisitive and less time constrained physician, the underlying data supporting a compliance indicator could be accessible via EHR patient portals (e.g. EPIC’s MyChart).

Finally, a new study (3) found the ActiGraph GT3X+ accelerometer not to be very accurate at low and moderate intensity levels.  Of the few validation studies done on accelerometer based activity trackers, some were validated against the Actigraph as the criterion measure.  However, this study itself also missed an opportunity for better measurement when they estimated Resting Metabolic Rate (RMR) using the Schofield equations rather than measuring it with the Oxycon Mobile system they had – RMR is essentially what 1 MET is.  The study’s authors do disclose that they have receive funding support from Bodymedia, which Jawbone recently bought.

There is more to be sorted out in the consumer fitness/activity tracking eco-space.  I think devices and apps that produce valid and reliable data can make an impact in exercise-oncology research, particularly in the time periods surrounding diagnosis and treatment.

1. Lakoski, S.G., et al.  Midlife Cardiorespiratory Fitness, Incident Cancer, and Survival After Cancer in Men The Cooper Center Longitudinal Study.  JAMA Oncol. 2015;1(2):231-237. doi:10.1001/jamaoncol.2015.0226

2. Pollock ML, Bohannon RL, Cooper KH, et al.  A comparative analysis of four protocols for maximal treadmill stress testing. Am Heart J. 1976; 92(1):39-46.

3. Kim, Y., Welk G.J. Criterion Validity of Competing Accelerometry-based Activity Monitoring Devices. Med. Sci. Sports Exerc. 2015 Apr 23. [Epub ahead of print]

4. McMurray, R.G., et al.  Examining Variations of Resting Metabolic Rate of Adults: A Public Health Perspective. Med. Sci. Sports Exerc., Vol. 46, No. 7, pp. 1352–1358, 2014.

5. Byrne, N., et al. Metabolic equivalent: one size does not fit all. J Appl Physiol 99: 1112–1119, 2005.

6.  Kozey, S., et al.  Errors in MET Estimates of Physical Activities Using 3.5 ml·kg–1·min–1 as the Baseline Oxygen Consumption. Journal of Physical Activity and Health, 2010, 7, 508-516.

7. Wilms, B., et al.  Correction factors for the calculation of metabolic equivalents (MET) in overweight to extremely obese subjects.  International Journal of Obesity (2014) 38, 1383–1387.

8.  Hall, K., et al.  Activity-Related Energy Expenditure in Older Adults: A Call for More Research. Med Sci Sports Exerc 2014 Dec;46(12):2335-40.

9. Blair, C.K., et al.  Light-Intensity Activity Attenuates Functional Decline in Older Cancer Survivors. Med Sci Sports Exerc 2014 Jul;46(7):1375-83.

10. Herzig, K-H, et al.  Light physical activity determined by a motion sensor decreases insulin resistance, improves lipid homeostasis and reduces visceral fat in high-risk subjects: PreDiabEx study RCT..International Journal of Obesity (2014), 1–8

11. Montgomery, P.G., et al. VALIDATION OF HEART RATE MONITORBASED PREDICTIONS OF OXYGEN UPTAKE AND ENERGY EXPENDITURE. Journal of Strength and Conditioning Research 23(5)/1489–1495.

12. Lebouf, SF., et al. Earbud-based sensor for the assessment of energy expenditure, HR, and VO2max. Med Sci Sports Exerc 2014;46(5):1046-52.

13.  A systematic review of reliability and objective criterion-related validity of physical activity questionnaires. International Journal of Behavioral Nutrition and Physical Activity 2012, 9:103 pgs 1-55.

What is exercise for cancer patients? It’s all relative.


In the US most adults do not get the recommended 150 minutes of moderate intensity or 90 minutes of vigorous intensity physical activity per week.  Nothing new about this, however, maybe it doesn’t accurately describe what is physical activity for cancer patients, particularly those in the midst of treatment.  I argue that many cancer patients may be meeting the recommended guidelines but they just don’t know it.

There is a measure in exercise physiology called maximum aerobic capacity, which is recorded as maximum oxygen uptake, or VO2max for short (maximum volume of oxygen).  Elite endurance athletes have values above 80 (it’s recorded as millilitres of oxygen per kilogram of body weight per minute: [ml/kg/min]).  However, in many of the exercise and cancer studies I read, I often see average maximum oxygen uptake for cancer patients below 20.  What does this mean and how does it relate to cancer patients meeting the physical activity guidelines?

Bear with me as I first translate VO2max into something easier to understand.  I noticed one study where the cancer subjects had an average VO2max of 17.5 ml of oxygen/kg/min, this is a convenient number that converts into something we can relate to.  An intermediate conversion is needed to something called a *MET, 1 ‘standard MET’ equals 3.5 ml of oxygen/kg/min, so a 17.5 VO2max = 5 METS.  A 5 MET activity is walking at 4mph, one mile in 15 minutes (4 laps around a high school track).

So there we have it, our cancer subjects have a maximum aerobic capacity to walk 4mph.  However, this doesn’t mean that they can actually walk the entire mile in 15 minutes, none the less, they should not feel inferior about it because an elite endurance athlete can’t go 15 minutes at their maximum aerobic capacity either.  What?  You see, maximum oxygen capacity can only be maintained for about 3-5 minutes regardless of who you are – cancer patient or elite endurance athlete.

For our cancer subjects, just one of those laps around that high school track at a speed of 4mph will take 3 minutes and 45 seconds.  It is an interesting comparison then that the track & field world record for one mile is 3 minutes and 43 seconds (all four laps around that high school track).  However, I guarantee you that the guy who set that world record could not have done another lap at his record pace – he was at his maximal oxygen capacity (actually a little above it as he sprinted the last part of the race, but he didn’t use any more oxygen to do that extra effort).  So it would be no surprise if our cancer subjects also became exhausted after 3:45 of walking only one lap at their maximal oxygen capacity.  This is just like the world record holder who is exhausted after running for 3:43 at his maximum oxygen capacity.  What then can cancer patients do to get 150 or 90 minutes of exercise in a week?  They can slow down.

If our 5 MET capacity cancer subjects slow down to 60% of their maximum, which is considered to be moderate intensity, they will be at 3 METs, and this intensity they will be able to sustain for longer than 5 minutes.  The relative part of all this is that they can achieved 3 METs by walking a dog!  Yep, according to the 2011 Compendium of Physical Activities, if our cancer subjects do this they are doing moderate intensity physical activity.  Below are some other 3 MET activities from the Compendium:

  • walking 2.5mph (a mile in 24 minutes rather than in 15 minutes), if our subjects were to walk 5 laps around that high school track 5 days a week then they would meet the physical activity guidelines.  Or if you are an in-patient, walk the oncology ward halls before breakfast, before lunch, and before dinner – break it up into three 10 minute segments.
  • home activities – implied walking, putting away household items
  • child care, standing (e.g., dressing, bathing, grooming, feeding, etc.)
  • home repair/maintenance
  • some lawn and garden activities
  • some occupations, work tasks, and work walking
  • bowling (an often maligned recreational activity)
  • mini golf, driving range
  • horseshoes
  • shuffleboard
  • Pilates, tai chi, Qi gong
  • How many more activities become moderate intensity if an ‘adjusted’ or ‘measured MET’ is used rather than a ‘standard MET’?

Considering household and caregiving activities, some cancer patients may be getting close to meeting the physical activity guidelines just by maintaining a near normal work schedule or by puttering around their home while recovering between cycles of chemotherapy.  There was a recent study that was critical of counting household activities as physical activity.  This may be true for healthy adults, however, for cancer patients, some adjustments have to be taken into account.

One important consideration is that some chemotherapies can cause anemia.  Other things too can affect our cancer subjects, some of them are mentioned in a previous blog: Mt. Everest and Cancer.  So, during treatment, rather than our subjects having a maximum aerobic capacity of 5 METS, it may be lower than that.  This means that if they want to sustain their physical activity beyond 5 minutes, their normal 60% intensity will now be at a slower pace, and this brings in  even more Compendium activities.  If they don’t slow down, they will find their normal pace is now more fatiguing and that they have to rest a little longer between activities.  Unfortunately, and mistakenly, this causes many cancer patients to think they are too tired to ‘exercise’, so they nap a lot.  Their old 60% pace is now a 70% or 80% intensity (vigorous), which is ok to do but they will need to walk for shorter periods of time and to rest a little longer.

I recently read an online post by a cancer patient who mentioned becoming fatigued from just walking across a room.  I hope we can now understand that this could actually be viewed as part of a ‘workout’.  The key may be for that patient to start treating a walk across the room as exercise and to mentally incorporate it into a modified ‘workout’ routine.  This is not unlike how that world record miler might workout – he may do an effort at a specific intensity, recover, then repeat this pattern a number of times on a training day.  For our subjects, walking across a room, up some stairs, down a hall, getting tired, resting for a bit, and then repeating this pattern, could be considered a type of workout called interval training.  It may not be at the same pace as the world record miler but the relative intensity can be the same, cancer patients and clinicians just might not realize that it is.

Keep moving!


*MET    Metabolic equivalent: one size does not fit all. Byrne, N.M., et al. J Appl Physiol 99: 1112–1119, 2005.  Examining Variations of Resting Metabolic Rate of Adults: A Public Health Perspective. McMurray, R.G., et al. Med. Sci. Sports Exerc., Vol. 46, No. 7, pp. 1352–1358, 2014.  The standard oxygen consumption value equivalent to one metabolic equivalent (3.5 ml/min/kg) is not appropriate for elderly people. M. Kwan, J. Woo and T. Kwok. International Journal of Food Sciences and Nutrition, Volume 55, Number 3 (May 2004) 179 /182.  Activity-Related Energy Expenditure in Older Adults:A Call for More Research. Hall, K.S., et al. Med Sci Sports Exerc. 2014 Dec;46(12):2335-40.  Errors in MET Estimates of Physical Activities Using 3.5 ml·kg–1·min–1 as the Baseline Oxygen Consumption. Kozey, S., et al. Journal of Physical Activity and Health, 2010, 7, 508-516.