Hey! Great question. The conclusion regarding aerobic exercise came from lots of the literature I was reading saying something like “the effect went away when compared to aerobic exercise.” I should probably not have said “high intensity,” as I don’t really remember looking specifically at any intensities, but umm—below I’ll list the evidence from my answer that kind of points this out. [all of this is just pulled from my big answer comment so if you want more context, look there for the link, etc]
Having looked at it again to list the evidence, I think the evidence I saw was basically.
A. Comparison: resistance to aerobic = no difference
B. Comparison: aerobic to resistance+aerobic = no difference
So I concluded that
The effect of resistance and aerobic on sleep and cognition don’t seem to be independent (or rather, at the very least they are not additive—comparison B).
I guess my thought was that if resistance = aerobic = resistance + aerobic, then either you’re getting the benefits of resistance training from aerobic exercise or you’re getting the benefits of aerobic exercise from resistance training. The latter just seemed more plausible to me. But I highlighted the specific sentences that led me to this below, so please just see for yourself!
“These benefits of isolated resistance exercise are attenuated when resistance exercise is combined with aerobic exercise and compared to aerobic exercise alone”
“There is limited evidence that combined exercise is better than aerobic exercise alone, and further study is warranted. Data from this review and recent reviews of aerobic exercise [44, 57] suggest that both modalities are effective for improving sleep quality”
first study: “Numerous experimental studies have demonstrated that exercise interventions improve cognitive abilities (Kelly et al., 2014b), but benefits have been more consistent for aerobic training, or combined cardiovascular fitness and resistance training”
and the 2nd study: ““Our review detected no difference between RE and AE in acute effects on brain function.”
Thanks! To be honest I wasn’t nearly as systematic as I would’ve liked. I did keyword searches on Google Scholar and PubMed for resistance training and weight training. On PubMed, I specifically looked for review articles and meta-analysis in one search just to look for big picture studies, but as you can see, results were a bit sparse so I also just searched generally for any articles I could find.
I’m trying to get better at this process (ask a question, research the answer), and I’m in the early phases. Future goals include 1) having a more systematic search process to avoid bias (i guess in theory the results above could be heavily biased if I just didn’t know to use certain search terms), 2) getting into the nitty gritty and actually critiquing studies and meta-analysis themselves (I just trusted blindly here, which is fine for now but it would be cool to get better at parsing methods)
I split my findings into categories and bolded the parts of the studies I found most interesting. I really didn’t take the time to be super critical on study design, etc; I was just taking their findings at face value and seeing what, if the study was true as reported, was being claimed. Enjoy!
Claim: “Chronic resistance exercise improves all aspects of sleep, with the greatest benefit for sleep quality. These benefits of isolated resistance exercise are attenuated when resistance exercise is combined with aerobic exercise and compared to aerobic exercise alone”
“Improvements in sleep quality were observed across all intensities, however, effect sizes for all sleep quality outcomes (significant and non-significant) tend to be larger in studies of high intensity exercise”
The least benefit was sleep duration
Sleep quality was ‘perceived sleep quality’ - measured by subjective ratings
Chronic here means avg. Of 14 weeks with an average of 60 min per session
“There is limited evidence that combined exercise is better than aerobic exercise alone, and further study is warranted. Data from this review and recent reviews of aerobic exercise [44, 57] suggest that both modalities are effective for improving sleep quality “
2. Cognitive Function
The impact of behavioral interventions on cognitive function in healthy older adults: A systematic review
“Numerous experimental studies have demonstrated that exercise interventions improve cognitive abilities (Kelly et al., 2014b), but benefits have been more consistent for aerobic training, or combined cardiovascular fitness and resistance training”
“Aerobic training (n= 13) most consistently transferred to executive function, while strength/resistance training (n = 8) most consistently transferred to cognitive inhibition and visual working memory. Similarly, aerobic/resistance combination training (n = 6) showed most consistent improvements in visual working memory”
Acute Effects of Resistance Exercise on Cognitive Function in Healthy Adults: A Systematic Review with Multilevel Meta-Analysis.
“Compared to NEX, RE had a positive effect on global cognition (SMD: 0.56, 95% CI 0.22–0.90, p = 0.004), but was not superior to AE (SMD: − 0.10, 95% CI 0.01 to − 0.20, p = 0.06)”
NEX = no exercise; AE = aerobic exercise, RE = resistance exercise
“Regarding cognitive sub-domains, RE, compared to NEX, improved inhibitory control (SMD: 0.73, 95% CI 0.21–1.26, p = 0.01) and cognitive flexibility (SMD: 0.36, 95% CI 0.17–0.55, p = 0.004)”
Note — the reference to cognitive inhibition was referred to by the study above as well. Kind of interesting.
“Our review detected no difference between RE and AE in acute effects on brain function. This result is in line with the meta-analysis of Northey et al. , who investigated the effects of chronic exercise on cognition in adults aged 50 years and older.”
Lifting cognition: a meta-analysis of effects of resistance exercise on cognition
Positive effects on composite cognitive scores, screening measures of cognitive impairments, and executive functions. no effect on measures of working memory.
“High heterogeneity was observed in all analyses” and the authors weren’t sure why
Long-Term Effects of Resistance Exercise Training on Cognition and Brain Volume in Older Women: Results from a Randomized Controlled Trial.
Aerobic exercise training has been shown to attenuate cognitive decline and reduce brain atrophy with advancing age. The extent to which resistance exercise training improves cognition and prevents brain atrophy is less known, and few studies include long-term follow-up cognitive and neuroimaging assessments. We report data from a randomized controlled trial of 155 older women, who engaged in 52 weeks of resistance training (either once- or twice-weekly) or balance-and-toning (twice-weekly). Executive functioning and memory were assessed at baseline, 1-year follow-up (i.e., immediately post-intervention), and 2-year follow-up. A subset underwent structural magnetic resonance imaging scans at those time points. At 2-year follow-up, both frequencies of resistance training promoted executive function compared to balance-and-toning (standardized difference [d]=.31-.48). Additionally, twice-weekly resistance training promoted memory (d=.45), reduced cortical white matter atrophy (d=.45), and increased peak muscle power (d=.27) at 2-year follow-up relative to balance-and-toning. These effects were independent of one another. These findings suggest resistance training may have a long-term impact on cognition and white matter volume in older women.
Exercise to reduce work-related fatigue among employees: a randomized controlled trial
Note: This is evidence relating to aerobic, not resistance, exercise.
“Analyses of covariance (ANCOVA) revealed that, at T1, the EI group reported lower emotional exhaustion and overall fatigue than the WLC group, however, only according to PP analyses. Both according to ITT and PP analyses, EI participants showed higher sleep quality, work ability, and self-reported cognitive functioning at T1 compared to WLC participants. Intervention effects were maintained at T2 and T3.”
“The exercise intervention consisted of 1-hour low- intensity running sessions three times a week for a period of six consecutive weeks.”
Exercise, inflammation, and fatigue in cancer survivors
Might be hard to generalize, but just thought it was interesting to point out another setting where exercise reduced fatigue
Effects of Different Exercise Modalities on Fatigue in Prostate Cancer Patients Undergoing Androgen Deprivation Therapy: A Year-long Randomised Controlled Trial.
“Different exercise modes have comparable effects on reducing fatigue and enhancing vitality during ADT. Patients with the highest levels of fatigue and lowest vitality had the greatest benefits.”
4. Stuff I didn’t understand but maybe someone else does
The effects of physical activity and exercise on brain-derived neurotrophic factor in healthy humans: A review
“Evidence from experimental studies suggested that peripheral BDNF concentrations were elevated by acute and chronic aerobic exercise. The majority of the studies suggested that strength training had no influence on peripheral BDNF. The results from most observational studies suggested an inverse relationship between the peripheral BDNF level and habitual physical activity or cardiorespiratory fitness. “
I just included this because I have vague memories of BDNF being related to the psychological effect of exercise, but I’m not well informed enough on this to know the implications.
There does seem to be some effect of resistance training on cognition. These studies separated cognition into a number of subfields (executive function, visual working memory, etc).
Every time I saw a mention of a study that did a controlled comparison of resistance training+aerobic exercise to resistance training alone, the study concluded that these were similar. It really gave me the sense that when it comes to cognitive benefits and fatigue, high intensity aerobic exercise provides the benefit, and resistance training, if it includes high intensity aerobic exercise, can capture that benefit.
The one cognitive effect that was captured by resistance training but not aerobic exercise was cognitive inhibition, which another study also mentioned. I didn’t have time to check how robust a result that was.
One final comment—while I couldn’t really make a strong case for resistance training being obviously better than aerobic training with respect to productivity in any manner, I still think that 1) resistance training probably does have absolute benefits to cognition and energy levels, and 2) there are many reasons to pursue resistance training outside of productivity (for instance, things like osteoporosis risk didn’t come up in a productivity-related search, but would be relevant when I design my own workout plan).
From your post:
This is circular, but is this necessarily a problem? If your choice is a circular justification or eventually hitting a level with no justification, then the circular justification suddenly starts looking pretty attractive.
I think the coherentist article I linked to has some useful perspective here. The quote below is from a section in that article on regress. The first paragraph outlines a view similar to yours and raises an important objection against the circular justification view. The 2nd paragraph raises a potential response.
What is the coherentist’s response to the regress? The coherentist can be understood as proposing that nothing prevents the regress from proceeding in a circle. Thus, A can be a reason for B which is a reason for C which is a reason for A. If this is acceptable, then what we have is a chain of reasons that is never-ending but which does not involve an infinite number of beliefs. It is never-ending in the sense that for each belief in the chain there is a reason for that belief also in the chain. Yet there is an immediate problem with this response due to the fact that justificatory circles are usually thought to be vicious ones. If someone claims C and is asked why she believes it, she may reply that her reason is B. If asked why she believes B, she may assert A. But if prompted to justify her belief in A, she is not allowed to refer back to CC which in the present justificatory context is still in doubt. If she did justify A in terms of C nonetheless, her move would lack any justificatory force whatsoever.
The coherentist may respond by denying that she ever intended to suggest that circular reasoning is a legitimate dialectical strategy. What she objects to is rather the assumption that justification should at all proceed in a linear fashion whereby reasons are given for reasons, and so on. This assumption of linearity presupposes that what is, in a primary sense, justified are individual beliefs. This, says the coherentist, is simply wrong: it is not individual beliefs that are primarily justified, but entire belief systems. Particular beliefs can also be justified but only in a secondary or derived sense, if they form part of a justified belief system. This is a coherence approach because what makes a belief system justified, on this view, is precisely its coherence. A belief system is justified if it is coherent to a sufficiently high degree.
Of course, the key coherentist claim is that an entire belief system can be justified without individual beliefs being justified because the property of being justified is a property of belief systems that emerges from the coherence of multiple beliefs.
Have you checked out any work on coherentist theories of epistemic justification? I definitely haven’t done the work to have an opinion on this, but I remember this dichotomy (foundationalism v. coherentism) being referred to in old introductory epistemology coursework.
cool. I’ll be sure to get something in by the 16th.
Is there a deadline? I’m a bit busy until the end of this week, but I wanted to try my hand at doing some lit review soon anyways. I’ll probably take a shot at this sometime next monday.
Practically speaking, how might I go about checking if a study has been replicated independently?
Thanks for the feedback. Will change the format in the future!
Thanks for the links. I think one concern that keeps popping up is that by reading more analysis of other papers I’m just learning others’ thoughts rather than learning to think my own.
Constantin’s fact post approach does seem like an effective way to cut through that.