Fitness trackers reveal connections between exercises

Exercise can improve your cognitive and mental health, but not all forms and intensities of exercise affect the brain equally. The effects of exercise are much more nuanced, as specific intensities of exercise over long periods of time are linked to different aspects of memory and mental health, according to a new Dartmouth study. The findings are published in Scientific reports and provides insight into how exercise can be optimized.

“Mental health and memory are central to almost everything we do in our daily lives,” said lead author Jeremy Manning, assistant professor of psychology and brain sciences at Dartmouth. “Our study attempts to build a foundation for understanding how different intensities of physical exercise affect different aspects of mental and cognitive health.”

The researchers asked 113 Fitbit users to complete a series of memory tests, answer some questions about their mental health and share their fitness data from the previous year. They expected that more active people would have better memory and mental health, but the results were more nuanced. People who tend to exercise at a low intensity do better on some memory tasks, while those who exercise at a high intensity do better on other memory tasks. Participants who were more intensely active also reported higher levels of stress, while people who regularly exercised at a lower intensity showed lower levels of anxiety and depression.

Previous research has often focused on the effects of exercise on memory over a relatively short period of time over a few days or weeks, but the Dartmouth researchers wanted to examine the effects over a much longer period of time. Data includes daily step count, average heart rate, how much time spent exercising in different “heart rate zones” as defined by FitBit (rest, out of range, fat burn, cardio or peak) and other information collected over the course of an entire calendar year. Study participants were recruited online from Amazon’s Mechanical Turk, a crowdsourced workforce.

The four types of memory tasks used in the study were designed to examine different aspects of participants’ abilities at different time scales. Two sets of tasks were aimed at testing ‘episodic’ memory – the same type of memory used to remember autobiographical events, such as what you did yesterday. Another set of tasks was designed to test “spatial” memory — the same type of memory used to remember locations, such as where you parked your car. The final set of tasks tests “associative” memory—the ability to remember connections between concepts or other memories.

Participants who were more active in the previous year tended to show better memory performance overall, but the specific areas of improvement depended on the type of activity people were doing. The researchers found that participants who frequently exercised at a moderate intensity tended to do better on episodic memory tasks, while participants who frequently exercised at high intensity did better on spatial memory tasks. Sedentary participants who rarely exercised performed worse on spatial memory tasks.

The researchers also found links between the participants’ mental health and their memory. Participants with self-reported anxiety or depression tended to perform better on spatial and associative memory tasks, while those with self-reported bipolar disorder tended to perform better on episodic memory tasks. Participants who reported higher levels of stress tended to perform worse on the associative memory tasks.

The team has made all of its data and code freely available on Github for anyone who wants to explore or better understand the dataset.

“When it comes to physical activity, memory and mental health, there are really complex dynamics that can’t be summed up in single sentences like ‘walking improves your memory’ or ‘stress hurts your memory,'” says Manning. “Instead, specific forms of physical activity and specific aspects of mental health seem to affect each aspect of memory differently.”

With further research, the team says their findings could have some exciting applications. “For example,” says Manning, “to help students prepare for an exam or reduce symptoms of depression, specific exercise regimens can be developed to help improve their cognitive performance and mental health.”

Manning is available for comment at: [email protected] Gina Notaro, Guarini’18, Thayer’18; Esme Chen ’22; and Paxton Fitzpatrick ’19, Guarini ’26 at Dartmouth also co-authored the study.

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