Better cardiorespiratory fitness may help the brain work more efficiently after intense exercise.
Exercise is known to support brain health, but the biological link between fitness and brain function is still being clarified. A new study tested whether improving cardiorespiratory fitness changes the brain-derived neurotrophic factor (BDNF, a protein involved in brain signaling) response to hard exercise and alters brain activity during cognitive tasks.
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In this randomized study, 49 sedentary adults aged 18 to 55 were enrolled, but the final analyses included only 20 to 23 participants due to dropouts and missing data. They were assigned either to a 12-week cycling program or to a control group that kept its usual activity habits. The cycling group trained four times per week, with the program becoming more intense over time. Both groups visited the lab at the start of the study, week 6, and week 12 to complete a VO2max test (a hard cycling test used to measure cardiorespiratory fitness) and cognitive tasks. Before and about 30 minutes after each test, blood samples were taken. At weeks 6 and 12, the researchers also estimated prefrontal brain activity (activity in the front part of the brain involved in attention, self-control, and other "executive" thinking skills) during the cognitive tasks using fNIRS, a wearable imaging method that tracks blood-oxygen changes near the surface of the brain.
- Fitness improved in the cycling group, but not the control group: VO2max increased from 28.8 to 32.2 ml/kg/min after 12 weeks of cycling, while it changed from 29.8 to 27.7 ml/kg/min in the control group.
- Resting BDNF levels did not clearly rise in either group.
- After 12 weeks, only the cycling group showed clearly higher serum BDNF levels 30 minutes after the VO2max test. In the control group, serum BDNF levels changed little.
- Participants in the cycling group who gained more VO2max tended to show a larger serum BDNF increase after the VO2max test at week 12.
- Participants were faster on some thinking tasks after the VO2max test, but BDNF changes were not clearly linked to better cognitive performance, and the cycling program did not clearly improve cognitive performance overall.
- BDNF was linked to an estimated brain-activity pattern that may reflect greater efficiency: In the cycling group, people with higher BDNF measures showed a larger drop in estimated prefrontal brain activity after the VO2max test than before it during attention and self-control tasks, without a clear link to worse performance. The same overall pattern was not seen in the control group.
The study results suggest that becoming fitter may change how the brain responds to a demanding workout. Higher cardiorespiratory fitness may make the body more capable of mounting a BDNF response when exercise creates a strong physiological challenge. This matters because BDNF is involved in several processes relevant to brain health, including brain-cell signaling, blood-vessel function, metabolism, and the ability of connections between brain cells to adapt. Supporting these processes may help the brain maintain efficient function during cognitive tasks.
The study was small, and the brain-imaging correlations were exploratory, so the findings need replication in larger groups. The blood sample was collected about 30 minutes after exercise, which may have missed each person's peak BDNF response. Even so, the study suggests that cardiorespiratory fitness may shape the BDNF response to intense exercise and how it relates to short-term brain function. My BDNF protocol includes additional lifestyle strategies that may improve cognitive performance and support healthy brain aging.