Hi guys,
So lately I’ve been digging into the physical activity guidelines and evidence for meeting both aerobic and resistance training components. With aerobic activity, we pretty much see a linear reduction in disease and mortality risk (even as far as 17,000 steps per day in one paper) with no ceiling of benefit. However, I have come across a couple of papers suggesting a J-shaped curve with regards to resistance training and all-cause or CV mortality.
Muscle-strengthening activities and risk of cardiovascular disease, type 2 diabetes, cancer and mortality: A review of prospective cohort studies - PubMed)%2C
Depending on which paper you look at, the benefits of “muscle-strengthening activities” seem to peek at around 60-150 minutes per week (1-2 sessions) for CVD, cancer, and overall mortality. The association is more linear for Diabetes, however (which sort of makes sense). This seems in line with the recommended amount of RT in the physical activity guidelines.
My question is, with regards to general health, is this a cause for concern for people who may be dedicating several hours per week to resistance training? I know J-shaped curves sometimes disappear in epidemiology when we use superior methodology to tease stuff out (sodium, cholesterol etc). Could this J-shaped curve be due to people who do more resistance training having less time or neglecting aerobic exercise? If the J-shaped curve is accurately reflective of a causal effect of a high amount of RT and increased risk of disease/death, does this mean it may be beneficial to sub out some resistance training volume for more aerobic work?
Anyway, look forward to hearing your thoughts!
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Hey Tom,
These are interesting questions. Unfortunately I have not spent a very large amount of time wading through this literature to be able to speak very authoritatively on it.
Your observations are correct regarding the aerobic activity findings, although previous papers have suggested “J-shaped curves” for that as well. I think there are numerous methodological concerns with these types of studies (which I know you are already familiar with from the nutrition side of things) and remain skeptical of these findings that strengthening activities would have a unique mortality-increasing effect beyond a certain threshold. I also don’t love quantitating “muscle-strengthening activities” in terms of minutes per week; as you can imagine this really does not tell you much about the actual activity being performed. Steroid use may also be a consideration in these data sets, although perhaps not a massive one at the population level.
To your final question – if someone’s primary goal is maximizing health and longevity, and they were strength training, say, 5x per week with zero conditioning work … then sure, I could make a strong case to incorporate some aerobic activity (although I’m still not sure I have a strong basis to recommend it be 1:1 substituted). But I would still have a hard time telling them to reduce their strength training from 5x to 2x because of a J shaped curve association.
Hope this makes sense.
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Thanks, Austin. Makes perfect sense!
A somewhat related question. Do you have any thoughts on occupational vs leisure-time physical activity? I’ve seen numerous papers reporting a “physical activity paradox” where greater occupational physical activity is associated with worse outcomes, a few papers where there is no increased risk (once socio-economic factors are adjusted for), and even a study where high levels of occupational PA modestly contributed to longevity in men. So my take away from these studies is that occupational physical activity, in general, may still be beneficial, but isn’t as beneficial as leisure-time physical activity (possibly because OPA can’t be dosed/scaled to current abilities and you can’t always reduce activity or take time off when needed if your recovery capabilities are hampered).
So if an individual is working a very active job, I may still advise them to meet PA guidelines in their leisure time, but adjust for the role they are doing. So if they’re a postman and already walking 15,000 steps per day, the focus may be on them incorporating some higher intensity conditioning work or meeting resistance training guidelines, rather than getting them to do even more low-intensity aerobic work. On the other hand, if they’re a construction worker, it may make more sense to incorporate lower intensity conditioning activities (like walking) during their leisure time. Does this approach seem sensible?
Yeah, I find it an interesting observation and one for which we don’t have a good mechanistic understanding/explanation. This paper discusses some potential ideas that are plausible (particularly #5, IMO).
So if an individual is working a very active job, I may still advise them to meet PA guidelines in their leisure time, but adjust for the role they are doing. So if they’re a postman and already walking 15,000 steps per day, the focus may be on them incorporating some higher intensity conditioning work or meeting resistance training guidelines, rather than getting them to do even more low-intensity aerobic work. On the other hand, if they’re a construction worker, it may make more sense to incorporate lower intensity conditioning activities (like walking) during their leisure time. Does this approach seem sensible?
Yep, to the extent the person is willing to add leisure time physical activity, I would first prioritize filling in the biggest “gap” vs. the PA guidelines. So the postman would first prioritize getting in 2 days of strength training before I even considered adding any other conditioning work. These can be tough situations though, as many people do not feel they have the time, energy, or resources to add in leisure activity on top of physically demanding occupations when balancing other demands/responsibilities (family, etc.), which is understandable.