22 October 2021

Walking Revisited

Stop the presses! Oh, Darn. Too late. The blog post said walking improved health and lowered the risk of death. But it didn’t say that moderate to vigorous exercise will do much more than walking for your fitness.

Welcome back. A month ago, I blogged about three studies that found walking was great with more steps generally associated with lower all-cause mortality (see Just Keep Walking). That seemed reasonable, but the studies also found no significant association between how fast one walks and mortality after adjusting for total steps per day.

All-cause mortality vs steps per day among U.S. adults age 40 or older (figure used in Just Keep Walking, from jamanetwork.com/journals/jama/fullarticle/2763292).

Though I expressed my surprise, I did find other studies that also reported any level of physical activity, regardless of intensity, was associated with a substantially lower risk of death.

Well, that was last month. In the meantime, news was released of another study that found moderate-vigorous physical activity boosts fitness three times more than walking.

Now that’s not surprising. Shall we look at that study?

Testing Physical Activity for Fitness
A team of investigators led by researchers with Boston and Harvard universities set out to better define the relationship between physical activity and physical fitness.

They enlisted 2,070 Framingham Heart Study participants (age 54 ± 9 years, split between men and women) to test how (1) moderate-vigorous physical activity (exercise), (2) low-moderate physical activity (steps/day walking) and (3) minimizing sedentary physical activity translate to cardiorespiratory fitness.

The participants wore accelerometers to measure the intensity and frequency of exercise, steps/day and sedentary times for two 8-day periods, 7.8 years apart. During the second period the participants’ cardiorespiratory fitness was assessed on a cycle ergometer with breath-by-breath gas exchange data obtained during four stages of exercise, initiation to recovery.

Activity levels and VO2 of 2,070 participants during second period; VO2 measured as milliliters of oxygen used in one minute per kilogram of body weight (from academic.oup.com/eurheartj/advance-article-abstract/doi/10.1093/eurheartj/ehab580/6357860).

Example of cycle ergometer measurement of VO2 (photo from www.endurancedave.com/post/whats-the-best-training-protocol-for-your-fastest-1-hour-cycling-effort).

The principal measure of cardiorespiratory fitness was peak oxygen uptake (VO2), which denotes the highest oxygen uptake reached during exercise to voluntary exhaustion.

Principal Findings
Here are the three study results that I found most interesting:

To achieve the equivalent change in cardiorespiratory fitness, each minute increase in moderate-vigorous physical activity (exercise) would require at least 3 minutes of intermediate cadence walking and at least 14 minutes less sedentary activity. 

Activity levels and VO2 of 2,070 participants during second period (from academic.oup.com/eurheartj/advance-article-abstract/doi/10.1093/eurheartj/ehab580/6357860).
As you would expect, participants with either higher moderate-vigorous physical activity or higher steps/day had higher fitness levels. But this was regardless of how much time they spent sedentary. It appears that much of the negative effect that being sedentary has on fitness may be offset by higher levels of exercise and walking.

Participants with high activity values at one period and low activity values at the other, 7.8 years apart, had equivalent levels of fitness. There may be a “memory effect” of previous physical activity on current levels of fitness.

Wrap Up
The earlier studies reported that increased steps/day was associated with lower rates of mortality, though it tended to reach a limit.

In the recent study, increased steps/day was associated with higher fitness levels. The lead researcher noted there was no evidence of a threshold beyond which higher levels of activity were no longer associated with greater fitness.

Fitness isn’t mortality, but they’re sure related. If you’d like to improve your fitness, try increasing the level of exertion through exercise or by picking up the pace. (The study categorized 60-99 steps/minute as low-level exertion, 100-129 steps/minute as moderate and greater than 130 steps/minute as vigorous.)

Be well and thanks again for stopping by.

Study of physical activity and fitness in European Heart Journal: academic.oup.com/eurheartj/advance-article-abstract/doi/10.1093/eurheartj/ehab580/6357860
Article on study on EurekAlert! website: www.eurekalert.org/news-releases/929580
Cardiopulmonary exercise testing: www.massgeneral.org/medicine/pulmonary/treatments-and-services/cardiopulmonary-exercise-testing

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