When I read an internet headline that said “compared with the minimum exercise recommendation, the additional benefit of 3 to 5 times more only provided modest additional benefit” my interest was peaked. I tracked down the actual paper, read it and here is what I found out:
Six population-based prospective cohorts (see below) from National Cancer Institute (NCI), that included self-reported physical activity were analyzed to determine how activity affected health.  Slightly more than 660,000 men and women (median age: 62 years; range: 21-98 years) were included with a median follow-up time of 14 years. There were just under 117,000 deaths over the decade plus they analyzed. They did Cox proportional hazards regression with cohort stratification to generate multivariable-adjusted hazard ratios (don’t try this at home unless you hold a degree in mathematics) for amounts of exercise based on the 2008 Physical Activity Guidelines for Americans and applied their findings to the groups that were studied.
2008 Physical Activity Guidelines included:
- 150 minutes/week of moderate intensity activity or
- 75 minutes/week of vigorous intensity activity or
- 500 MET minutes/week or
- 7.5 MET hours/week
Is a Cohort Study?
|A cohort is a sample. A cohort study is when 1 or more samples are studied after the
fact to determine if what they are studying (in this case different amounts of exercise to people from 6 different studies) had any effect on disease outcome.
What Is a MET and How Does It Work?
The exercise guidelines can get confusing because the amount of time a person exercises is different from metabolic equivalent time (MET) that researchers often recommend. A MET is the ratio of the following: energy used during an activity to energy usage at rest.
One MET is defined as the energy required to sit quietly. It uses approximately 1 calorie per kilogram (1 kg = 2.2 lbs.) of bodyweight per hour (1 kcal/kg/bw/hr). A MET is often confused with basal metabolic rate (BMR), which is approximately 10% lower than a MET.
METs have been pre-calculated for a number of activities. They are not exact, but they are close enough for large groups of people to get a general approximation.
- Walking 4 mph is a 5 MET activity.
- If done for 30 minutes, 5 METs x 30 min = 150 MET minutes or 2.5 MET hours of physical activity.
- If done 3x a week, the 7.5 MET hour minimum is achieved in 90 minutes.
- Running a 6:45 mile pace is a 12.5 MET activity.
- If done for 12 minutes, 12.5 METs x 12 min = 150 MET minutes or 2.5 MET hours of physical activity.
- When done 3x/week, the 7.5 hour/week MET minimum is met in 36 minutes.
- A list of MET values for activity can be found here .
See Table 2 for how meeting and exceeding the recommendation affected mortality in the large NCI cohort study.
Researchers also did calculations by age, sex, BMI, race, co-morbity, exercise intensity and more.
Table 2 – NCI Cohort Results
Exercise Level Total Mortality CVD Mort Cancer
1 – 2 times Rx 31% lower 33% lower 21% lower
2 – 3 times 37% lower 41% lower 25% lower
3 – 5 times 39% lower 42% lower 26% lower
5 – 10 times 39% lower 39% lower 28% lower
10 + times 31% lower 29% lower 31% lower
Rx = minimum recommendation
Table 2 NCI Cohort Results
In conclusion, a little exercise does a lot and a lot more does a little more for mortality rates in general. Meaning just doing the 7.5 MET minimum reduced mortality by about 30%. Doing 4 times more exercise was worth an additional 8-10% reduction. Exercising 10 times or more above the minimum began to increase mortality except in cases of cancer. In cancer patients, as exercise increased mortality decreased.
- Arem H, Moore SC, Patel A. et al. Leisure time physical activity and mortality: a detailed pooled analysis of the dose-response relationship. JAMA Intern Med. 2015 Jun;175(6):959-67. doi:10.1001/jamainternmed.2015.0533. PubMed PMID: 25844730; PubMed Central PMCID:PMC4451435
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