Even limited exercise helps

One of the exercise mantras commonly floated about is that adults should get 30 minutes of moderate activity exercise at least five days a week. While this is a good goal, the majority of Americans don't get this amount of exercise¹. And, for a lot of beginning exercisers, exercising for 30 minutes a day probably seems like a huge commitment, if not an insurmountable challenge.

My SO and I have long viewed exercise in the "some is better than none" category, and thus try to do even little amounts whenever we can (e.g., walking to the store instead of driving, always taking the stairs at work, doing our own gardening). A recent paper (Church et al., 2007) has shown, via a randomized, controlled trial, that even small amounts of exercise are better than no exercise at all (at least for the subset of people they tested).

Church et al. divided overweight, post-menopausal women into four groups:

• Control: Did no exercise a week (other than normal walking)
  
• 4kcal/kg: Exercised about 70 minutes a week
  
• 8kcal/kg: Exercised about 135 minutes a week
• 12 kcal/kg: Exercised about 190 minutes a week

Participants were randomly assigned to a condition, and all exercise was performed in a lab². The participants exercised at their given level for six months, at which point physiological data were compared to data taken at the start of the study.

Fitness improvement correlated linearly with the amount of exercise:



Figure 3 from Church et al. (2007)."Percent Change in Fitness Data for Each Study Group. The data represent the least-squares means adjusted for age, ethnicity/race, weight, and peak heart rate. The P values for pairwise comparisons of control with 4-kcal/kg, 8-kcal/kg, and 12-kcal/kg per week groups are P .001 for each variable. P for linear trend across groups .001 for each outcome. Error bars indicate 95% confidence intervals."
So, what this means is that even if you work out for only 20 minutes a day three days a week, you'll almost certainly see fitness benefits. And, once you start working out and getting used to doing it regularly, if you increase your workout durations (say, to 40 minutes a day three days a week), you'll see even more improvements. And, to help scare you into exercising, note that the people who didn't do any exercise actually had a small decrease in fitness³.

So, if you're one of the many sedentary Americans out there, take a look at those graphs and start exercising, even if it's only for a few minutes a day. It'll do ya good!

¹ As in "More than 60 percent of U.S. adults do not engage in the recommended amount of activity (30 minutes a day, 5 days a week)" and "Approximately 25 percent of U.S. adults are not active at all." (data from the 1996 Surgeon General's Report on Physical Activity and Health, specifically from here)
² "Women in the exercise groups alternated training sessions on semi-recumbent cycle ergometers and treadmills." The control (non-exercising) women tracked their daily steps with a pedometer and were "asked to maintain their level of activity during the 6-month study period."
³ In fact, it was the realization that our fitness was slowly declining (and would continue declining until we would no longer be able to walk when we were 70) that finally motivated my SO and me to start regularly exercising (and tracking our exercise goals and progress here) a few years ago.

Church, TS., DP Earnest, JS Skinner, and SN Blair. 2007. Effects of Different Doses of Physical Activity on Cardiorespiratory Fitness Among Sedentary, Overweight or Obese Postmenopausal Women With Elevated Blood Pressure. JAMA. 297:2081-2091. Abstract.