That question has been on my mind, sparked by an ongoing debate in our house.
My husband, Ben, and I are both lovers of data and technology, which we each use on a daily basis to track our workouts.
Here's where the conflicts lies: I wear a heart rate monitor strap and watch, which I use to track the duration and intensity of every cardio workout, and I keep a log of calories burned.
Michelle Lee is a writer and avid home chef, with 20 years of experience focusing on healthy lifestyle, diet and the home kitchen.
When not playing around with words, she loves to cook, spend time with her two children, play cribbage with her husband, and tackle The New York Times crossword puzzle
My aim when I work out is to stay in the middle of my target heart rate and sweat.
My husband's approach could not be more different.
Ben uses his smart phone to track every step throughout the day, aiming for 10,000 steps – he's not concerned much about his heart rate when he works out, and he certainly doesn't track calories burned.
So … the big question is, who's right?
Does intensity matter more? Frequency? Duration? Total movement throughout the day?
My quick survey of the science behind exercise would say we're both right. It depends on how you frame the question and whom you ask.
Exercise and longevity – the research
A study recently published in the Journal of the American Medical Association looked at pooled data from six major population-based studies to examine the relationship between longevity and exercise frequency and intensity.
Data from over 660,000 men and women (mostly middle-aged) was analyzed, looking specifically at how much leisure time physical activity they got, and how exercise levels corresponded with their risk of mortality.
Researchers took the data and broke the participants into groups based on how often and frequently they worked out – ranging from people who got no exercise to people who worked out for 10 times the existing recommendations (meaning for 25 or more hours per week).
Next, they looked at death records spanning 14 years for this same group, to establish how exercise levels affected individual mortality.
Understanding the current guidelines
The U.S. Office of Disease Prevention and Health Promotion takes a science-based approach to developing guidelines for children and adults to improve their health through regular physical activity.
The current guidelines, established in 2008, recommend 150 to 300 minutes of moderate-intensity activity (such as a brisk walk) or 75 to 150 minutes of vigorous-intensity aerobic activity (such as jogging or other intense aerobic activity) weekly for optimal health.
Ideally, these minutes are spread out over most of the days of the week. So, for example, the upper levels of their recommendations would mean a 60-minute walk or a 30-minute run five days a week.
They also recommend muscle-strengthening (also called "resistance") exercises of a moderate to intense level, using most of the major muscle groups, two or more days a week.
Exercise and longevity – the findings
Researchers, looking at activity levels for this 660,000-person pool, found a clear correlation between fitness and longevity.
The big question: How much was enough, and is there such a thing as too much exercise?
Not surprisingly, folks who didn't exercise at all had the highest risk of an early death.
But, more interestingly, people who exercised just a little, meaning they didn't meet the U.S. guidelines, but were still getting some exercise, lowered their risk of an early death by 20%.
Scientists found that individuals at the lower end of the recommendations (150 minutes of moderate activity a week) enjoyed an even lower risk of early death (31%) compared to the non-exercisers.
And what level of exercise was just right?
The greatest benefit was for those who got 450 minutes or almost eight hours (7-1/2) of moderate exercise (usually in the form of a walk) each week.
Participants who exercised a little over an hour a day were 39% less likely to die prematurely than the people who didn't exercise.
And while researchers did not find a point at which too much exercise lead to poorer results, they did see a plateau.
It didn't appear that exercising more than 7-1/2 hours a week netted any benefit in terms of longevity over the people at the 450-minute mark.
So, I'm curious … have you found your sweet spot for hours of exercise per week?
Do you meet the hour-a-day level each week? I'd love to hear from you
about your experiences with exercise ... and your outcomes.
And in terms of our ongoing debate, it would seem that Ben and I are both winners!
His aim to get 10,000 steps probably means about 85 minutes of walking a day, and my goal of 45-60 minutes of intense aerobic activity 4-5 days a week would also put me somewhere within the recommended guidelines.
Arem H, Moore SC, Patel A, Hartge P, Berrington de Gonzalez A, Visvanathan K, Campbell PT, Freedman M, Weiderpass E, Adami HO, Linet MS, Lee IM, Matthews CE. Leisure time physical activity and mortality: A detailed pooled analysis of the dose-response relationship. JAMA Internal Med. 2015 Apr 6.