Once and for All: Aerobic Exercise Increases Brain Size

Meta-analysis confirms aerobic exercise is like Miracle-Gro for human brain.

Posted Nov 14, 2017

 Anton Balazh/Shutterstock
Source: Anton Balazh/Shutterstock

For over a decade, researchers have suspected that aerobic exercise boosts cognitive function and maintains brain health via neurogenesis (the birth of new neurons). Neurogenesis is believed to bulk up gray matter volume, prevent neural atrophy, and increase the size of certain brain regions.

Some neuroscientists even refer to aerobic exercise as “Miracle-Gro for the brain." But there are also some naysayers who have fueled a constructive "correlation does not imply causation" debate as to whether or not aerobic exercise actually causes the human hippocampus (a memory hub) to increase in size.

Finally, a new first-of-its-kind meta-analysis confirms that aerobic exercise does, in fact, increase hippocampal volume in the human brain. The findings of this report, "Effect of Aerobic Exercise on Hippocampal Volume in Humans: A Systematic Review and Meta-Analysis," were published online ahead of print, Nov. 4, 2017, in the journal NeuroImage

For this meta-analysis, an international team of researchers systematically reviewed 14 clinical trials which involved brain scans of 737 people before and after aerobic exercise programs or under control conditions. More specifically, the team examined effects of aerobic exercise, which included stationary bicycling, walking, and treadmill running. The length of the aerobic interventions ranged from three to 24 months with a spectrum of two to five moderate-to-vigorous physical activity (MVPA) sessions per week.

Typically, brain health decreases as we get older. The average brain shrinkage experienced by men and women is approximately five percent per decade after age 40. The good news is that aerobic exercise increases hippocampal volume and can improve memory function along with maintaining overall brain health as we age.

What Makes Aerobic Exercise Like Miracle-Gro for the Human Brain? 

Brain-derived neurotrophic growth factor (BDNF) is a protein released during aerobic exercise which acts like "Miracle-Gro" neuron fertilizer. BDNF promotes both neurogenesis and functional connectivity between brain regions via neuroplasticity.

Fabio Berti/Shutterstock
Source: Fabio Berti/Shutterstock

Countless animal studies on rats and mice have consistently shown that physical exercise increases the size of the hippocampus. However, until recently the empirical evidence of aerobic activity increasing hippocampal volume in humans has been inconsistent. That said, the current meta-analysis reaffirms a significant effect of aerobic exercise on left hippocampal volumes in the human brain. In a statement, lead author, NICM postdoctoral research fellow, Joseph Firth, said, “this study provides some of the most definitive evidence to date on the benefits of exercise for brain health.”

Firth concludes that along with improving regular 'healthy' brain aging, the results of this new systematic review and meta-analysis have implications for the prevention of aging-related neurodegenerative disorders such as Alzheimer's and dementia. Notably, aerobic exercise is one of the very few 'proven' methods for maintaining gray matter (GM) brain volume and white matter (WM) functional connectivity into older age.

If you need one more reason to stay physically active on a regular basis, hopefully, the growing mountain of empirical evidence showing that aerobic exercise increases brain size will inspire you to move more. 


Firth, Joseph, Brendon Stubbs, Davy Vancampfort, Felipe Schuch, Jim Lagopoulos, Simon Rosenbaum, and Philip B. Ward. "Effect of Aerobic Exercise on Hippocampal Volume in Humans: A Systematic Review and Meta-Analysis." NeuroImage (Published online ahead of print: November 4, 2017) DOI: 10.1016/j.neuroimage.2017.11.007

Wrann, Christiane D., James P. White, John Salogiannnis, Dina Laznik-Bogoslavski, Jun Wu, Di Ma, Jiandie D. Lin, Michael E. Greenberg, and Bruce M. Spiegelman. "Exercise Induces Hippocampal BDNF Through a PGC-1α/FNDC5 Pathway." Cell Metabolism (First published online: October 10, 2013) DOI: 10.1016/j.cmet.2013.09.008

Kramer, Arthur F., Kirk I. Erickson, and Stanley J. Colcombe. "Exercise, Cognition, and the Aging Brain." Journal of Applied Physiology (2006) DOI: 10.1152/japplphysiol.00500.2006

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