The Optimum Amount of Exercise
How much should you exercise? This is a good question, and like all good questions, it is best to look at the available evidence to come to a determination. One would hope that current evidence is the basis from which all guidelines are created, however for various bureaucratic and political reasons, guidelines of all sorts, including exercise, are often watered down to make them more palatable to the general public.
Let’s start with the Canadian Physical Activity Guidelines. Here are the condensed recommendations.
- “To achieve health benefits, adults aged 18-64 years should accumulate at least 150 minutes of moderate to vigorous intensity aerobic physical activity per week in bouts of 20 minutes or more.
- It is also beneficial to add muscle and bone strengthening activities using major muscle groups at least 2 days per week.
- More physical activity leads to more health benefits”
Physical Activity Guidelines for Americans are quite similar. These guidelines state that “most health benefits occur with at least 150 minutes (2 hours and 30 minutes) a week of moderate intensity physical activity, such as brisk walking.” However, they go onto state that “additional benefits occur with more physical activity”. Like the Canadian guidelines they state that “both aerobic (endurance) and muscle-strengthening (resistance) physical activity are beneficial”.
So… case closed? Not so fast. This US recommendation is actually down from the previous recommendations of the Surgeon General (30-45 minutes a day). As well, the Centers for Disease Control and Prevention, and the American College of Sports Medicine recommend more than 20 minutes of daily exercise. So what’s up with the 20-minute recommendations? Do we now need less exercise now? Is there new evidence? The hint is that both Canadian and American guidelines clearly state that more physical activity leads to more health benefits. So then, what is the ceiling amount after which gains are no longer seen? Is it diminishing returns after 20 minutes? Is this why they came up with this number?
One of my most recent reads is “How Not to Die”, by Dr Michael Greger. In this book he looks at the current evidence on a host of topics to support steps we can take to maximize our health and minimize our risk of premature death. Dr. Greger mentions that following the current recommendations of 150 minutes of weekly moderate exercise (20 minutes a day) appears to reduce mortality rate by 7% compared to being sedentary, however, he notes that walking 300 minutes a week (40 minutes a day) drops overall mortality by 14%[i]. In other words, doubling the amount of exercise doubled the gains. How far can we push this envelope before we see diminishing returns? Another study found that 60 minutes of daily walking reduced mortality by 24%[ii]. This is pretty much a direct, linear relationship between time spent exercising (from 20 minutes to 60 minutes daily) and the longevity benefits derived. Similar benefits were found by Samitz et al for other moderate exertion activities such as gardening and cycling. Samitz’s meta-analysis of studies on this topic found that health benefits actually improved right on up to 90 minutes a day. It might be that benefits continue on beyond 90 minutes per day, but there is no solid data on this, because few people actually exercise this much.
Dr. Greger proposes the reason that recommendations fall far short of the evidence is that perhaps the powers that be feel that the bar should not be set too high so as not to discourage people from feeling the task of exercising to be insurmountable. Considering that over half of Americans fall short of even 20 minutes of exercise per day, one might understand their perspective. However, as with all things in life, it is impossible to make an informed decision unless you actually have the facts. It would appear that we need more information and more facts on this subject, but one thing for sure is that while 20 minutes a day is better than nothing, it is definitely not the optimal amount of daily exercise. We need to be shooting for at least an hour or more of moderate exercise per day, as well as adding some strength and flexibility training. As for the recommended amount of daily movement/exercise, we do not yet know the optimum amounts, after which we begin to see diminished health returns.
This is what the evidence indicates, and it is based on a large number of well-designed studies. However, it is possible for the motivated individual to find their own personal ceiling level of exercise. Many high-performance athletes reach a point where injuries begin to happen due to over-training. Put simply, the body is breaking down faster than it is being built up. When this happens, athletes need to begin cross-training, or backing off a bit with their routine so that overused areas of the body have time to heal.
Listening to your body will guide you against over-training. What we do know is that the optimum amount of daily exercise is well in excess of 20 minutes or 40 minutes. It is also in excess of 60 minutes per day. Benefits of moderate exercise are still accrued right up to 90 minutes a day.
All in all, the American College of Sports Medicine provides excellent guidance as to the amount and types of exercise to incorporate into your day, including: cardiorespiratory exercise, resistance exercise, flexibility exercise and neuromotor exercise.
One thing is for sure is that most guidelines are conservative, falling far short of the evidence. Perhaps it is time to add a walk into your exercise regime to increase your daily movement time up to the 90-minute mark.
[i] Samitz G, Egger M, Zwahlen M. Domains of physical activity and all-cause mortality: systematic review and dose-response meta-analysis of cohort studies. Int J Epidemiol. 2011 Oct;40(5):1382-400. doi: 10.1093/ije/dyr112. Epub 2011 Sep 5.
[ii] Woodcock J, Franco OH, Orsini N, Roberts I. Non-vigorous physical activity and all-cause mortality: systematic review and meta-analysis of cohort studies. Int J Epidemiol. 2011 Feb;40(1):121-38. doi: 10.1093/ije/dyq104. Epub 2010 Jul 14.