Active Voice: Does Incidental Physical Activity Promote Aerobic Fitness?
By K. Ashlee McGuire, Ph.D., and Robert Ross, Ph.D., FACSM

Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.

K. Ashlee McGuire, Ph.D., works on the health promotion, disease and injury prevention team at Alberta Health Services in Calgary, Alberta, Canada. Her work focuses on healthy child and youth development. Robert Ross, Ph.D., FACSM, holds faculty appointments in both the School of Kinesiology and Health Studies and in the Department of Medicine at Queen’s University in Kingston, Ontario, Canada. His research is focused on the characterization and management of obesity and its related comorbidities in adults. This commentary presents McGuire’s and Ross’ views associated with the research article they published in the Nov. 2011 issue of Medicine & Science in Sports & Exercise® (MSSE).

The Physical Activity Guidelines for Americans state that some physical activity is better than none and that adults who participate in any amount of physical activity will experience some health benefits. However, when considering a change in physical activity habits to improve health, many individuals 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, 30 minutes is an overwhelming amount of daily physical activity for an individual who does not typically accumulate structured physical activity. As a consequence, this individual either attempts to engage in a structured physical activity program for a short period before giving up because it is too difficult or decides to continue living an inactive lifestyle without attempting to change his or her physical activity habits. This is a very disheartening, and unfortunately common, situation.

Thus, in the recent report of our study in MSSE, we were interested in exploring the association between incidental physical activity (IPA) and cardiorespiratory fitness (CRF). We defined IPA as random 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 since moderate-to-high levels are associated with a significant reduction in morbidity and mortality, and 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.

We explored this association in a sample of abdominally obese, inactive adults who completed a maximal treadmill test to exhaustion for determination of CRF. Each wore an accelerometer for a week, so we could obtain an objective measure of physical activity. First, IPA was quantified in average minutes per day. Then, to determine whether the components of IPA were important, we broke it down further 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, such as running after the bus or walking up a short flight of stairs).

We found that IPA was significantly associated with CRF, and this association remained true after consideration for other factors that may affect this relationship (e.g., gender, body mass index). When IPA was broken down into light and sporadic moderate physical activity, we found that light physical activity was not associated with CRF. However, sporadic moderate physical activity was significantly associated with CRF. Thus, contrary to current recommendations, our results suggest that moderate-intensity physical activity does not need to be accrued in sustained bouts to influence CRF.

To determine what this meant in terms of risk reduction, we split participants into groups based on amount of sporadic moderate physical activity and compared CRF values. Between groups one (average accumulation of six minutes of moderate physical activity per day) and three (average accumulation of 34 minutes of moderate physical activity per day) there was a one-unit (MET) difference in CRF. While this number sounds small and inconsequential, Kodama’s group recently demonstrated that every one-unit increase in CRF was associated with a 13 percent and 15 percent 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.

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. Thus, health professionals are encouraged to promote all forms of physical activity to improve CRF. Further studies are recommended to determine if the current findings hold true in a more heterogeneous sample and whether IPA is associated with a corresponding improvement in cardiovascular disease risk factors.