Travis’ Note: Today’s guest post comes from our friend and colleague Dr Ashlee McGuire. The study that Ashlee discusses in this post can be found here. More details on Ashlee and her work can be found at the bottom of this post.
I am sure that most people have heard that some physical activity is better than none and that any increase in physical activity is associated with health benefits. However, when considering a change in physical activity habits to improve health, many people still think that longer bouts of structured exercise (i.e., 30 minutes of moderate to vigorous physical activity on a treadmill) are the only way to gain meaningful improvements.
Unfortunately, this is an overwhelming amount of daily physical activity for someone who typically accumulates none outside of their activities of daily living and as a consequence, this person either a) attempts to engage in a structured physical activity program 5 days per week for a short period before giving up because it is too difficult or b) decides to continue living an inactive lifestyle without attempting to change.
This is a very disheartening and unfortunately common situation.
Thus, I was interested in exploring the association of cardiorespiratory fitness (CRF) with incidental physical activity – non-purposeful physical activity that is accumulated through activities of daily living and is generally low intensity (it is easy) and/or sporadic (it lasts less than 10 minutes in duration). CRF was chosen as the health outcome of choice for 2 main reasons: 1) moderate to high levels of CRF are associated with a significant reduction in morbidity and mortality, and 2) current recommendations suggest that to improve CRF physical activity must be at least moderate intensity and must be accumulated in sustained bouts of at least 10 consecutive minutes.
To examine this issue we investigated a sample of 135 abdominally obese, inactive men and women who had completed a maximal treadmill test to exhaustion to determine CRF and had worn an accelerometer (which objectively measures physical activity) for one week. First, incidental physical activity was quantified in average minutes per day using the accelerometer data. Then, to determine whether the intensity of incidental physical activity was important, it was further broken down into average minutes of light physical activity (e.g., preparing food, strolling through a park) and sporadic moderate physical activity (e.g., higher intensity activities that last less than 10 minutes in duration such as a quick sprint to stop your baby from ingesting a non-edible item or running a block to catch the bus).
What did we find?
Incidental physical activity was a significant predictor of CRF however it only explained a very small amount of variance in the regression model. This suggested that the total volume of incidental physical activity doesn’t have a huge role in determining CRF. However, when incidental physical activity was broken down into light and sporadic moderate physical activity, we found that light physical activity was not associated with CRF, whereas sporadic moderate physical activity was a significant predictor (explaining 20% of the variance in the regression model) and remained so after consideration for gender and body mass index. This suggests that, contrary to current recommendations, physical activity does not need to be accrued in sustained bouts to improve CRF.
What does this mean in terms of risk reduction? To determine this, we split participants into tertiles based on amount of sporadic moderate physical activity and compared CRF values. Between tertiles 1 (average accumulation of 6 minutes of moderate physical activity per day) and 3 (average accumulation of 34 minutes of moderate physical activity per day) there was a 1 MET (3.5 ml/kg/min) difference in CRF. While this number sounds small and insignificant, it was recently demonstrated (Kodama, 2009) that every 1 MET increase in CRF was associated with a 13% and 15% reduction in risk for all-cause mortality and cardiovascular disease, respectively. Thus, in our sample, a difference of approximately 30 minutes of sporadically obtained moderate physical activity may be associated with a significant reduction in morbidity and mortality.
What’s the take-home message?
These results are encouraging and suggest that random, short duration physical activity, which may be more feasible and enjoyable for inactive individuals attempting to engage in physical activity for health benefit, is indeed beneficial.
This study was cross-sectional therefore we unfortunately cannot state that the physical activity caused the improvement in CRF. Also, our study sample was homogenous with respect to phenotype and physical activity levels. Thus, further studies (preferably prospective) are required in a more heterogeneous population.
Nonetheless, I encourage everyone to attempt to increase both the duration and intensity of their incidental physical activity (as Travis and Peter have previously) throughout the day by taking more frequent trips to the water fountain and washroom, paying colleagues personal visits instead of sending emails, and parking further from the building entrance. Every little bit does indeed count!
About the author: Ashlee McGuire recently completed her doctoral studies at Queen’s University (Congrats Ashlee!), where she examined the association of incidental physical activity, sedentary behaviour, and sleep with cardiometabolic risk factors in men and women. Ashlee is also involved in projects aimed at improving access to healthy lifestyle choices within the community and is an avid long distance runner.
McGuire, K., & Ross, R. (2011). Incidental Physical Activity Is Positively Associated With Cardiorespiratory Fitness Medicine & Science in Sports & Exercise DOI: 10.1249/MSS.0b013e31821e4ff2
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