A U-Shaped Dose-Response Curve for Resistance Exercise?
A fair number of studies have shown reduced late life mortality to correlate with, or result from, programs of resistance exercise. While a great many studies of aerobic exercise have indicated that at very high levels of exercise there is increased mortality versus more modest programs of exertion, in other words that the dose-response curve is U-shaped, it isn't completely clear that this is also the case for resistance exercise. While a fair number of studies have taken place, there isn't as much evidence to assess. This short paper provides a high level discussion of the present state of knowledge and some references to follow up on for those interested in the details.
Regular physical activity (PA) promotes healthy aging, and activities aiming to increase muscular strength (i.e., resistance exercise, RE) are important PA modalities for achieving health benefits. Previous meta-analyses demonstrated that both RE and muscular strength were associated with mortality benefits, even when RE was performed above the PA targets recommended by current guidelines.
While optimal volumes of endurance-type exercise (aerobic moderate-to-vigorous PA, MVPA) to reduce mortality from all causes have been suggested to amount to or even exceed 700 minutes per week, recent meta-analyses suggest that large amounts of RE may be associated with adverse outcomes. Although these analyses demonstrated an overall inverse association between RE and mortality risk from all causes and/or from cardiovascular diseases (CVD), diabetes, and cancers, this was only true up to a certain threshold of RE volume per week (i.e., there is a U-shaped dose-response relationship between RE and mortality). Should the many individuals engaging in RE volumes exceeding the reported cutoffs for optimal benefits be worried?
Overall, excessive RE may put a small number of individuals at a higher risk for adverse health outcomes, which is similar to the effect of extreme endurance exercise. This risk may vary with age and sex (e.g., while young subjects may be more susceptible than older ones to arterial stiffness following RE, men are much more likely than women to be injured performing RE) and can increase with inappropriate execution of RE, overconfidence, and/or subtle pre-existing comorbidities.
Although low-to-moderate intensity RE is usually well tolerated and widely recommended for individuals with and without cardiovascular disease, heart rate and systolic blood pressure values in cardiac patients are higher during low-intensity as compared to high-intensity RE. As low-intensity RE is typically performed at higher volumes than high-intensity RE, vulnerable individuals performing high volumes of low-intensity RE might be at higher mortality risk than previously assumed.