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
- 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.
*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.
- 2008 Physical Activity Guidelines for Americans http://www.health.gov/paguidelines/pdf/paguide.pdf
- American College of Sports Medicine Roundtable on Exercise Guidelines for Cancer Survivors http://www.penncancer.org/pdf/palAmerican_College_of_Sports_Medicine_Roundtable_on_23.pdf
- Compendium of Physical Activities https://sites.google.com/site/compendiumofphysicalactivities/home
- Chemotherapy-Induced Anemia in Adults: Incidence and Treatment http://jnci.oxfordjournals.org/content/91/19/1616.full.pdf+html
- Anemia in Stage II and III Breast Cancer Patients Treated WIth Adjuvant Doxorubicin and Cyclophosphamide Chemotherapy http://theoncologist.alphamedpress.org/content/9/1/25.full.pdf+html
- Dog Ownership and Physical Activity: A Review of the Evidence https://www.naspspa.org/AcuCustom/Sitename/Documents/DocumentItem/16_christian_JPAH_20110283_750-759-ej.pdf
- Get a Dog and Start Walking http://www.medscape.com/viewarticle/780807
- Does Housework Count As Exercise? http://www.livescience.com/40523-housework-exercise-physical-activity.html