Longevity Briefs: Are Physical Exercise Recommendations Too Low?

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

The problem:

Even a small amount of exercise correlates with significant reduction in risk of age-related diseases and mortality compared to no exercise at all. At higher levels of physical activity, diminishing returns start to kick in, with exercise eventually becoming harmful at extremely high levels. Official health guidelines generally recommend people aim for 150 minutes of moderate-to-high intensity exercise per week, as this is an achievable goal for most people that correlates with significant benefits. However, studies investigating this relationship often overlook the variation that exists between individuals and their responsiveness to exercise.

Exercise isn’t synonymous with fitness. Genetic and environmental factors can influence how physically fit someone is regardless of exercise, and can also influence how well they respond to exercise training. Cardiorespiratory fitness (CRF) is the body’s ability to deliver oxygen to muscles during exercise, and it is strongly correlated with reduced risk of cardiovascular diseases (CVD) like heart attacks and strokes. If two people exercise the same amount, but one has superior CRF, then research suggests that person is better protected against CVD. In this study, researchers set out to shed light on how cardiorespiratory fitness and physical activity levels interact to influence cardiovascular risk.

The discovery:

Researchers looked at data from the UK Biobank, a vast anonymised collection of health information from UK residents. The study used data from 17,088 participants with an average (mean) age of 57.4 years. The data included accelerometer readings which allowed researchers to estimate the weekly physical activity levels of participants. The metric of cardiorespiratory fitness used was VO2max, which is defined as the rate of oxygen consumption per kilogram of body weight during maximal physical exertion. VO2max is an excellent measure of overall cardiorespiratory fitness because it depends on how quickly the lungs can get oxygen into the blood, how quickly the heart can circulate that blood to the muscles, and how quickly the muscles can consume that oxygen.

Researchers then studied the relationship between VO2max, weekly moderate-to-vigorous exercise duration and cardiovascular events like heart attacks and strokes over a median follow-up of 7.85 years (meaning half of participants were followed up for longer than this). They found that compared to no exercise, meeting the 150 min/week guidelines was generally associated with an approximate 9% reduction in risk of cardiovascular events, consistent with previous studies. However, this was modified by VO2max. Someone doing 150 minutes of exercise a week needed to achieve a VO2max of around 23 mL/kg/min in order to reduce their cardiovascular risk by 10% compared to the least active, least fit participants (see below for a more detailed explanation). On the other hand, 150 minutes of exercise per week with a VO2max of around 18 mL/kg/min resulted in comparatively less risk reduction.

This relationship persisted for higher activity levels. In other words, the amount of risk reduction you gain from doing more physical activity depends on your cardiorespiratory fitness. The researchers also noted that while 150 minutes usually reduced risk by around 9%, doing 3-4 times that amount of exercise (up to 600 minutes a week) brought the risk reduction up to 30% or more, so there was still significant benefit to be gained past the recommended activity of 150 minutes per week.

The implications:

This research could imply that people don’t always respond to exercise in the same way, meaning that activity recommendations are somewhat simplistic. It may be necessary to do more than 150 minutes of moderate-to-vigorous activity per week to gain the advertised benefits. Doing more than 150 minutes per week is also expected to yield substantial improvements regardless of your cardiorespiratory fitness. Does this mean that the 150 minute recommendation is insufficient? Not necessarily – 150 minutes is still a good ‘entry level’ amount of exercise. As around 25% of the UK population do less than 30 minutes of exercise per week, raising this level to 150 minutes, would still yield substantial benefits. If people believe that they need to do more than this, they may be discouraged from taking that first step.

While this is one possible interpretation, people with high physical activity but low cardiorespiratory fitness could represent those who have only recently started exercising, or who have reduced cardiorespiratory fitness as a result of some health condition and are attempting to compensate through exercise. The authors attempted to control for some confounding factors, but it is not possible to prove cause and effect in an observational study such as this one. Accelerometers may also fail to capture some types of exercise, such as resistance training, which could also explain the appearance of some participants having high fitness despite low physical activity.