27 December 2018


by Ian McCarthy 0

Let’s be real: it seems to have become popular in the fitness industry to brag about not doing cardio, or doing only very little. While this is completely understandable – most people seem to dislike cardio, so the idea of not doing it at all is attractive – it’s also foolish. While resistance training certainly…

Let’s be real: it seems to have become popular in the fitness industry to brag about not doing cardio, or doing only very little. While this is completely understandable – most people seem to dislike cardio, so the idea of not doing it at all is attractive – it’s also foolish.

While resistance training certainly confers a variety of health benefits (some, such as increased bone mineral density, likely being somewhat unique), I would suggest skepticism toward the conclusion that lifting alone is sufficient to maximize all health outcomes. However, it is not my intention in writing this piece to explicitly argue for the absolute necessity of cardio in addition to resistance training to maximize all health outcomes. Rather, I simply wish to draw attention to the literature on cardio’s cognitive and mental health benefits, as it’s my impression these benefits are profoundly neglected – even in the evidence-based fitness community. Thus, a discussion of these benefits will make up the remainder of this review. Specifically, aerobic exercise has been shown to:

● Improve symptoms of depression in as little as ten days, although the relevant study lacked a control group (leaving the door open to the influence of a meaning response, i.e. a positive change in depressive symptoms caused by the subjective meaning of the cardiovascular intervention, rather than an improvement mediated by the treatment itself) and involved significant interindividual variability (for example, some subjects didn’t show a readily-discernible improvement in symptoms). Nonetheless, the pooled change from baseline is impressive, especially given the extremely condensed timeline.

● Maintain cerebral blood flow relative to prolonged sitting, plausibly allowing for optimal cognitive functioning; the brain is disproportionately metabolically active, and an adequate blood supply allows for ideal nutrient delivery.

● Improve attention and processing speed, executive functioning, and memory (although, notably, not working memory – roughly equivalent to short-term memory).

● Transiently boost positive affect (the experience of positive thoughts and feelings) immediately following exercise, especially when positive affect is initially low. In lay terms, exercise boosts mood more when one’s mood is initially ‘bad’. It’s worth noting this benefit resulted specifically from low intensity cardio, of durations less than 35 minutes, suggesting a potentially unique benefit to low intensity cardio of low-to-moderate duration.

● Produce robust improvements in positive-activated affect (PAA; equivalent to positive affect, liveliness, happiness, positive engagement, revitalization, positive well-being, vitality, pleasantness, activation, vigor, energy, or thought-related positive affect, depending on the relevant study) over a period of 4-32 weeks, regardless of exercise frequency, intensity, or duration. Even subjects with the highest baseline PAA – essentially the happiest subjects – report significant benefits in the overwhelming majority of cases. It’s worth underlining that this boost in PAA – this improvement in mood – appears to be one of the benefits of aerobic exercise which arises most consistently in the relevant research.

● Decrease social anxiety and depression, and improve subjective well-being, in those with social anxiety disorder. This is a striking result, as social anxiety, unlike generalized anxiety, is specific to social contexts, and the traditional treatment consists of controlled exposure to relevant anxiety-inducing situations; thus, one might not assume that aerobic exercise – performed in a potentially non-social context – would be beneficial.

● Reduce worry symptoms in those with generalized anxiety disorder (GAD), with remission (full recovery) achieved in 40% of cases. Admittedly, and bizarrely, simply being placed on a waitlist – in other words, not being treated in any sense, not even with a placebo – resulted in remission in 30% of cases in the relevant study; this result potentially diminishes the practical significance of the 40% rate of remission achieved in the aerobic exercise group, although aerobic exercise nonetheless remains ~33% more likely to cause remittance of GAD per this dataset.

● Reduce anxiety sensitivity (sensitivity to anxiety-related physiological sensations, such as elevated heart rate or sweating) in those with elevated anxiety sensitivity at baseline. Of note is the fact high-intensity cardiovascular exercise outperformed low-intensity exercise for this outcome, perhaps because of high-intensity exercise’s greater effects on the aforementioned physiological conditions.

● Improve anxiety and depression in those with panic disorder, although clomipramine (a tricyclic antidepressant) proved more effective and better-tolerated, as 0% of subjects in the antidepressant group dropped out, versus over 30% in the exercise group. Unfortunately, and I say this without wishing to be dismissive of those who use medication of any kind, exercising will always require more effort than taking medication, and one does need to be willing to exert substantial effort if they desire to experience the beneficial effects of consistent exercise.

● Reduce frequency of alcohol consumption in alcohol-dependent subjects.

● Reduce self-reported marijuana consumption by approximately 50% after only ten exercise sessions, even when subjects aren’t seeking treatment for marijuana dependence. Consistent with this result, the same pool of subjects reported significantly reduced cravings for marijuana. The reduction in self-reported marijuana consumption is particularly notable, as the subjects were in no way required or requested to reduce their marijuana consumption during the study. Thus, the (purported) reduction in marijuana use was entirely voluntary.

● Increase dopamine receptor availability in methamphetamine abusers. For context, chronic use of methamphetamine, a dopamine releasing agent (DRA), causes downregulation (a reduction in number and/or sensitivity) of dopamine receptors, and this is borne out by research showing lower dopamine receptor availability in long-term methamphetamine abusers relative to healthy (non-methamphetamine-using) control subjects. This downregulation results in a diminished response to both normal and methamphetamine-induced releases of dopamine – keep in mind dopamine is still secreted in the absence of dopamine-releasing drugs, just at a lower rate – causing users to have to consume progressively higher dosages of methamphetamine to create the same subjective drug experience, and potentially causing depressive symptoms in the absence of drug use. Thus, the ability for aerobic exercise to increase dopamine receptor availability in methamphetamine abusers represents an important reversal of drug-induced neurostructural damage.

(Note: in the interest of full disclosure, it should be recognized that at least one meta-analysis has concluded that “Aerobic exercise demonstrated no significant effect for the treatment of anxiety disorders”, although this conclusion seems questionable given the concurrent conclusion that “Exercise is more effective than placebo or wait-list conditions.”, as well as the fact that the control conditions in some studies consisted of psychotherapy, psychoeducation, or meditation, rather than non-treatment conditions.)

As you can see, the cognitive and emotional benefits of aerobic exercise 1) are well-substantiated, 2) extend across numerous domains, including executive functioning, memory, mood, depression, anxiety, and drug (ab)use, and 3) achieve real-world significance.

As such, the belief that not doing cardio is worth bragging about is a belief it’s worth bragging about not doing something good for you. Moving forward, I hope that all of us in the evidence-based community can push ourselves and others to adhere more steadfastly to a truly evidence-based worldview, rather than one unduly influenced by that which is simply desirable.

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