Cognitive Benefits of Exercise

Tl;dr: roughly speak­ing, ~2 hours/​week of mixed car­dio and strength train­ing may in effect raise your IQ by ~2.7 points.

I spent a few hours try­ing to roughly es­ti­mate the cog­ni­tive benefits of aer­o­bic ex­er­cise. The best liter­a­ture re­view I could find about the type/​mag­ni­tude of the benefits re­ports the fol­low­ing effects:

  • At­ten­tion/​pro­cess­ing speed (with com­bined strength train­ing): g = .25, P = .026

  • Ex­ec­u­tive func­tion: g = .123, P = .018

  • Work­ing mem­ory (with com­bined strength train­ing): g = .228, P = .028

  • Me­mory: g = .128, P = .026

Work­ing mem­ory and at­ten­tion/​pro­cess­ing speed, but not ex­ec­u­tive func­tion or non-work­ing mem­ory, ap­peared to benefit more from a com­bi­na­tion of aer­o­bic ex­er­cise and strength train­ing than aer­o­bic ex­er­cise alone (g = .288 ver­sus g = −0.042, and g = .250 ver­sus g = .098, re­spec­tively).

Th­ese are pretty sub­stan­tial benefits—how much do they cost to ac­quire? In my fa­vorite world, I would have found a graph de­pict­ing cog­ni­tive benefit as a func­tion of hours of ex­er­cise per month, to get a sense of diminish­ing re­turns. In the ac­tual world, the best I could find was this lit re­view of stud­ies in­volv­ing 11k old peo­ple, which re­ports a find­ing that vaguely hints at what that graph might look like: all stud­ies which re­ported no cog­ni­tive benefits from ex­er­cise in­volved less than 52 hours of ex­er­cise over six months, while stud­ies which did show cog­ni­tive benefit in­volved a me­dian of 52 hours.

Nor­mally I would have been skep­ti­cal these re­sults would gen­er­al­ize to young peo­ple, but the first (Smith et al.) re­view stud­ies rel­a­tive gains in im­prove­ment be­tween young and old pop­u­la­tions, and finds no differ­ence (ex­cept for work­ing mem­ory, where older peo­ple benefit more). So my guess is that the re­sults of Os­man et al. are at least mostly ap­pli­ca­ble across age groups.

Both stud­ies re­port that nei­ther in­ten­sity of ex­er­cise nor study length (which ranged from weeks to 1.5 years) cor­re­lated with im­proved cog­ni­tion; Os­man et al. re­ports that the only thing which did cor­re­late was num­ber of hours ex­er­cised over six months. In other words, from what I un­der­stand, you don’t have to ex­er­cise very hard to get the benefits, you just have to log a cer­tain num­ber of hours—maybe 52 over six months, or ~8.5/​month. And while con­tin­u­ing to ex­er­cise af­ter that pre­sum­ably en­sures these benefits con­tinue, they prob­a­bly won’t in­crease fur­ther.

So, to make a very crude es­ti­mate: If we as­sume the av­er­age of the effect sizes listed above (.18) is about the size of the effect on in­tel­li­gence in gen­eral, then do­ing 8.5 hours/​month of mixed car­dio and strength train­ing should in effect in­crease your in­tel­li­gence by about .18 σ, or ~2.7 IQ points.

If any­one has a bet­ter es­ti­mate, I’d love to see it!

Thanks to Con­nor Flex­man for helping me in­ter­pret fre­quen­tist ar­cana.