Exercise: How much is enough?

Physical activity is potent medicine, and it doesn’t take all that much of it to derive the maximum cardiovascular benefit. You don’t need to run a marathon, climb Mount Everest, or bench press more than Dwayne “The Rock” Johnson. In fact, as little as 30 minutes or jogging twice weekly is enough to lower your cardiovascular risk. A brisk walk for 1 hour for 5 days per week can be enough to lower your heart risk as well.

For most people who want improved health, general sense of well-being, improved mood, less anxiety, better sleep, lower blood pressure, heart risk, and lose weight, then their goal should be to start exercising regularly and achieve around 50-85% of their maximum heart rate. There have been numerous studies showing the positive effects for exercise on all of the previously mentioned health problems. For purposes of tracking your heart rate, vigorous activity is defined as a sustained heart rate around the 70-85% of maximum. Moderate activity is listed as a sustained heart rate around 50-70% of maximum. The maximum rate can be calculated using 220-age x target heart rate. For example, if you are 40, then you would take 220-40=180, then take 80% (vigorous exercise) of 180 which gives you around 144 beats per minute. That is your goal when exercising to give the maximum benefit. For those of you that might not be in the best shape, the goal should be to ease into it. Consider starting at 50% of your maximum, which in this case would be around 90-100 beat per minute, and then push yourself as tolerated every few days to slowly build up to the 80-85% of maximum. It is getting easier and easier to monitor this as most exercise equipment now has heart rate monitors built in. Activity trackers and watches are now also tracking the numbers for us, so it has never been easier.

Recent studies have shown just how little effort is required to give significant cardiovascular risk reduction. One particularly compelling chunk of evidence comes from a Taiwanese government–funded prospective cohort study of more than 416,000 individuals followed for an average of 8 years. A key finding: 15 minutes of moderate-intensity physical activity daily was associated with a 14% reduction in the relative risk of all-cause mortality and a 19% reduction in death caused by cardiovascular disease, compared with that of inactive individuals. Moreover, each additional 15 minutes of daily moderate exercise further reduced mortality by 4%. These benefits extended across the full age spectrum of both sexes and applied to patients with cardiovascular disease (Lancet. 2011 Oct 1;378[9798]:1244-53 <https://pubmed.ncbi.nlm.nih.gov/21846575/> ).

Another study reported data on more than 50,000 adult participants in the Aerobics Center Longitudinal Study based at the Cooper Clinic in Dallas showing that vigorous exercise in the form of running at 6 mph for half an hour twice weekly, or a total of 10 metabolic equivalent of task hours (MET-HR) per week, was associated with a roughly 40% reduction in cardiovascular disease mortality. Importantly, 20, 40,or 50 MET-HR/week of vigorous exercise conferred no further survival benefit (J Am Coll Cardiol. 2014 Aug 5;64[5]:472-81 <https://www.ncbi.nlm.nih.gov/pubmed/25082581> ).

The same group showed that the sweet spot for moderate physical activity in terms of reduced cardiovascular mortality was brisk walking for an hour daily 5 days/week, for a total of 20 MET-HR, which was also associated with roughly a 40% risk reduction compared to inactivity. At that point the benefit plateaued, with no further mortality reduction noted with additional MET-HR of moderate exercise. In another report from the Aerobics Center Longitudinal Study, investigators found that moderate level cardiorespiratory fitness as defined by METs was associated with a 44% reduction in the risk of sudden cardiac death in men and women after adjustment for potential confounders, while high level cardiorespiratory fitness was associated with a closely similar 48% reduction in risk. This applied to individuals who were hypertensive, overweight, and/or had poor health status, as well as to others (Mayo Clin Proc. 2016 Jul;91[7]:849-57 <https://www.ncbi.nlm.nih.gov/pubmed/27378037> ).

Don’t just sit there – stand!

A report on more than 221,000 participants in the Australian 45 and Up Study, with close to 1 million person-years of follow-up, demonstrated a linear inverse relationship between standing time per day and all-cause mortality. In a multivariate analysis adjusted for potential confounders, individuals who stood for 2-5 hours per day had a 10% lower risk of all-cause mortality than did those who stood for less than 2 hours. Standing for 5-8 hours was associated with a 15% relative

risk reduction. And standing for more than 8 hours daily was linked to a 24% reduction in risk (Prev Med. 2014 Dec;69:187-91 <https://pubmed.ncbi.nlm.nih.gov/26921660/> ).

And it’s not just total daily sitting time that’s a risk factor. Prolonged, uninterrupted sedentary time was also associated with a dose-dependent increase in all-cause mortality in a prospective cohort study of nearly 8,000 U.S. adults (Ann Intern Med. 2017 Oct 3;167[7]:465-75

<https://www.ncbi.nlm.nih.gov/pubmed/?term=diaz+km%3B+ann+intern+med.+2017> ).

Get strong

Muscle-strengthening activity on at least 2 days/week is recommended in the federal guidelines because it’s independently associated with decreased all-cause mortality, even in individuals getting sufficient aerobic exercise, as shown in a large national study with 15-years’ follow-up (Prev Med. 2016 Jun;87:121-127 https://www.ncbi.nlm.nih.gov/pubmed/? term=diaz+km%3B+ann+intern+med.+2017> ).

For the time constrained

Jogging is more time-efficient than brisk walking as a way to attain the maximum cardiovascular benefit of exercise. And the so-called “Weekend Warrior” study of nearly 64,000 U.K. adults showed that it’s okay to cram the full week’s worth of exercise into one or two sessions and be done with it. Compared with the inactive study participants, the weekend warriors had a 40% reduction in cardiovascular disease mortality, while individuals who split their physical activity up into three or more sessions per week had a nearly identical 41% relative risk reduction (JAMA Intern Med. 2017 Mar 1;177[3]:335-42 <https://www.ncbi.nlm.nih.gov/pubmed/28097313> ).

Interval training is a standard way for athletes in training to improve their endurance by

alternating short, intense exercise with brief recovery periods. It’s also a time saver: In one classic bicycling study, physically active men were randomized to standardized 2-week programs of sprint interval training or high-volume endurance training on the bike. The training time required to pass a rigorous cycling time trial test was 90% lower in the interval training group (J Physiol. 2006 Sep15;575(Pt 3):901-11 <https://www.ncbi.nlm.nih.gov/pubmed/term=gibalda+mj%3B+j+physiol.+2006> ).

Yoga

For patients who are reluctant to pound the pavement, yoga may provide an alternative form of physical activity with tangible cardiovascular benefits. The Yoga-CaRe trial randomized 3,959 post-MI patients at 29 centers in India to a program of 13 supervised in-hospital yoga classes followed by yoga at home, or to a control group with three educational sessions. The rate of major adverse cardiovascular events over 42 months of follow-up was cut in half, compared with controls, in the 27% of participants who attended at least 10 of the 13 yoga classes. Their quality of life scores were higher, too.