In my last blog, I made an unsubstantiated claim that if we don’t exercise, we slowly decay. Within a day or two after writing those words, I came across a pair of articles by Gretchen Reynolds of the New York Times that present scientific evidence backing me up. Is this just a confirmation bias? Am I just seeing what I want to believe? Judge for yourself. Let’s dive into the details of the three studies on the benefits of exercise.
On April 17, 2019, Ms. Reynolds published 10 Years After an Exercise Study, Benefits Persist in which she notes that the benefits of exercise can be more persistent that we might expect – even if we slack off later. She summarizes and presents the results from a Frontiers in Physiology original research article by Duke University researchers Johnson, Slentz, Ross, Huffman and Kraus on the 10 year follow-up to their earlier research on STRRIDE (Studies Targeting Risk Reduction Interventions through Defined Exercise). They note that legacy effects from experiments had been known (when participants benefit from the tightly controlled diet, drugs or other methods under testing), but the legacy effect of exercise was completely unknown. In their original study from 1998-2003, hundreds of sedentary, overweight volunteers between 40 and 60 were split into four* groups:
- Control Group – remained inactive.
- Low exercise group – low to moderate exercise of 14kcal/kg of body weight per week at 40-55% peak oxygen consumption (VO2**). This is basically equivalent to an easy walk.
- Moderate exercise group – Low amount of vigorous exercise of 14 kcal/kg of body weight per week at 65-80% of peak VO2. This is equivalent to a brisk walk or slow jog. Same calorie requirement as the Low exercise group, but they must stress their heart rate and breathing to a higher level.
- Vigorous exercise group – high amount of vigorous exercise of 23 kcal/kg of body weight per week at 65-80% peak VO2. This is still a brisk walk or slow jog, but they have to do nearly 60% more than the moderate exercise group.
Notes:
*The article describes three groups, but the paper actually defines four groups. My blog reflects the original research findings not the summary in the NY Times.
**Peak oxygen consumption or VO2 is determined by placing subjects on a graded treadmill with a 12-lead electrocardiography sensor and a gas exchange (breathing through a pipe into an instrument). Then as the exercise goes up, they measure the respiration, CO2/O2 exchange, and heart rate to determine the perceived exertion. For more details, please check this link from the University of New Mexico.
Each volunteer completed three workout sessions per week for eight months and their aerobic fitness, insulin sensitivity, blood pressure and waist circumference were tracked over that time period. As you can expect, all health markets improved for people who exercised, but not for the people who did not exercise. Ten years later, more than 100 volunteers agreed to join a reunion study. The reunion study also included a questionnaire about current medical condition and how often they normally exercised. The study revealed several important findings.
On average, the BMI had not changed for the volunteers. These volunteers had not suddenly become fit thanks to the study 10 years earlier and all volunteers had lost peak VO2 and became more tired faster.
The control group that had not exercised were, as expected less fit. They had larger waistlines and had lost 10% of their aerobic capacity. This was expected as most people over 40 lose 1% of their aerobic capacity annually.
The casual walking group also appeared to had lost similar aerobic capacity. Combining the low exercise and the control group only marginally improved the average loss to 9.6%.
The two vigorous exercise groups who had stopped working out for 10 years only lost 5% of their aerobic activity! The researchers believe that by reaching a higher peak VO2 max after 8 months of regular exercise created a higher level from which to decline. Even though for subjects who generally returned to an inactive lifestyle, the 8 months of exercise help reduce their decline 50% compared to their peers!
After the first study, some of the patients had taken up exercise. For those patients who indicated that they did ‘no exercise’ at all over the previous 3 months, peak VO2 had declined 12.8% over the 10-year period. For those who exercised three or more times per week the decline averaged 6.1% and those subjects exercising four or more times per week actually gained 5.5% in peak VO2! However, recent exercise only explained 16% of the variance on peak VO2 changes – in other words, recent exercise was a minor contributor in the results. The exercise from 10 years ago corresponded to the current trend more directly.
After reading these heart-health findings, one might be tempted to abandon walking in favor of running. However, only the non-exercising group experienced a gain in waist circumference after 10 years. Both the vigorous and walking exercise groups had much lower waistline increases than their non-exercising peers. It was also found that those who exercised not only lost waist size during training, those that exercised independently also has statistically significant slower increase in waist size over the ten year gap – regardless of how hard they worked out.
Similar benefits were promoted for Mean Arterial Blood Pressure and Fasting Insulin, but here the walkers showed the strongest benefits. None of the groups showed a significant increase in blood pressure over the 10-year period, but the low intensity walkers, moderate and high intensity exercise groups all found significant improvements in their blood pressure after the second study. Yet the walk’s benefited nearly twice as much as the moderate or intense groups: -7.7 mmHg compared with -3.4 mmHg. Interestingly, there was no significant relationship between the change in MAP and self-reported exercise prior to the study, but someone smarter than me will have to figure out what that means. For Fasting Insulin, the control group was the only group to experience an increase in insulin during the initial Strride study. Shockingly, both the control group and the high intensity groups did not change over the next ten years, but the low and moderate exercise groups continued to have a drop in their fasting insulin – even if they did not regularly exercise on their own.
The researchers concluded from their study that the best health benefits came from the moderate intensity exercise group, but that both low and high intensity exercise groups also enjoyed lasting benefits. The researchers admit that they have many other issues to study and I hope we don’t have to wait a decade before they can provide us with more information.
Fortunately, on June 5, 2019, Ms. Reynolds posted further evidence on the benefits of walking in her article Even One Extra Walk a Day May Make a Big Difference. A convenient discovery was made for the busy and the lazy, as it appears that the 10,000 step-a-day standard may be more than what is really needed for health. In a May 2019 study released by Lee, Shiroma, Kamada, Bassett, Matthews, and Buring published in JAMA Internal Medicine, a study of 16,741 older women (mean age 72) found that 4.3 years later women who averaged 4,400 steps per day lowered their mortality rate versus those who took 2,700 steps per day. The benefits increased with the increasing number of steps until they leveled out at 7,500 steps per day. The researchers found that while there was improvement from 4,400 to 7,500 steps per day, bulk of the benefit was achieved with 4,400 steps. Few of the women walked intensively or for exercise so this benefit is accrued simply by being active.
Since this study primarily looked at older women, steps taken and mortality rate, it is difficult to combine with the results of the Strride study above and determine any other benefits. While a savvy commenter pointed out on the JAMA site that since this study only measured people for seven days, it is not certain if the results are truly significant. It is possible that some people were motivated to take more steps simply because they knew it would be measured. However, since the test was designed to test everyday activity, I would counter that the seven days was sufficient to accurately segregate people into inactive, moderately active and very active lifestyles. Still, as the authors themselves point out in an editorial in the BMJ Journals’ British Journal of Sports Medicine, there is no clinically proven link between physical activity and actual mortality. Should we blow off exercise just because there is correlation and no actual link between the two? While the exact number of steps might be artificially contrived from the short duration of the study, and no distinct link between the mortality rate and the number of steps taken, the huge sample population of 16,741 compliant wearers suggests a significant trend. Those who take more steps seem to live longer even if the number of steps is not directly related to living longer. I don’t know about you, but I’m going to shoot for the equivalent of 4,400 to 5,000 steps per day – just in case.
However, I will emphasize that exercise, like investing or medicine, needs to be tailored for the individual. First, as I once overheard – “The bad exercise you do is better than the good exercise you don’t do.” If you are not doing anything, get started doing something. Walking tends to be the easiest for most people, but if you have joint issues, you may need to start with walking in a pool or riding a bike (consult with your doctor. Seriously. I am not able to handle a lawsuit at this time). Second, your motivations and your goals will shape your exercise. If you can get excited about saying ‘I’m running a marathon’ but you can’t get excited about saying ‘I’m going to walk for an hour’ – then by all means, train for the marathon because it will get you going. If you need to lower your insulin, walk. If you are short of breath, maybe jogging, swimming or other intense exercise will provide you with benefits you desire more directly. In all cases, know what your body can handle and, please, check with your doctor if you have medical conditions. There is no benefit to injuring yourself and winding up involuntarily inactive!