Allison Brager, PhD: Exercise’s Impact on Cardiovascular Health, Circadian Clock


In an interview at SLEEP 2024, Brager talked about the benefits of exercise on cardiovascular health and sleep.

Exercise and other healthy habits are important for cardiovascular health and regulating the circadian rhythm.1

A study published in spring 2023 found physical activity could negate the harmful effects of cardiovascular and all-cause mortality linked to unhealthy sleep duration.2

Allison Brager, PhD, from the Walter Reed Army Institute of Research, presented the interaction between daily behaviors and the circadian system with cardiovascular health at SLEEP 2024, the 38th annual meeting of the Associated Professional Sleep Societies.1

HCPLive sat down with Brager to discuss her research on this topic and how sleep specialists can best support their patients to sustain lifestyle modifications that benefit both sleep and cardiovascular health.

When asked what had the most significant impact on the cardiovascular health in relation to the circadian system, she said exercise.

“I'm biased about this, but it’s also because it’s my area of research, and it’s always been exercise,” Brager said.

She explained exercise has many benefits: improving cardiovascular performance and stabilizing the circadian clock especially if it is done the same time every day. The cardiovascular system impacts exercise performance and people will have different performance outcomes if they exercise at night versus morning, independent of whether they are a morning or evening person.

Brager specifically studies the relationships between cardiovascular health, circadian rhythm, and exercise in the military. Her recent findings showed the military personal who had greater hand grip strength were more likely to have a healthier functioning heart. Her team has also been evaluating transitions from daytime to nighttime operations in the military.

“We basically find that in transitioning to nighttime operations, which is what the US military typically does with training and operations, that there's a drastic decrease in grip strength and other measures of athletic performance that ultimately would require the cardiovascular system in order to perform those activities at peak level,” she said.

Brager also conducted research with the NFL, which showcased exercising at a particular time of the day impacts performance due to the circadian clock.

“[The research showed] teams who are playing games in their biological afternoon, where traditionally, you have a dip in circadian alertness and an increase in fatigue, are more likely to get injured. So again, there's just really close intimate ties between the circadian rhythms performance, with the cardiovascular system being part of this this larger issue.”

However, Brager pointed out exercise is not the only thing that impacts cardiovascular health—sleep and nutrition do too. For sleep, she said its best to go to bed and wake up the same time everyday. It is also good to eat at the same time every day.

“The big thing is routine,” Brager said. “You want to make sure that you are doing the same One thing at a predicted time every day.”

Brager believes exercise is more important now than ever. Recently, they have struggled getting young people to join the military due to lack of fitness. This concerns Brager not for their physical health but their mental health, too.

“I think the lowest hanging fruit is exercise,” Brager said. “You can pay a lot of money for exercise or exercise can be completely free. The healthier you are, the more you exercise, the healthier your heart is, the more the easier it is to exercise. I really think exercise is the pillar of all of this and feeds into the relationship of having a good healthy heart, but also a good healthy sleep.”


  1. Brager, A, Brito, L, Currie, K. Cardiovascular Health and Performance: Daily Behaviors and Their Interaction with the Circadian System. Session presented at SLEEP 2024. Houston, TX. June 1-5, 2024.
  2. Campbell, P. Exercise, Increased Physical Activity Can Blunt the Effects of Poor Sleep Health. HCPLive. March 31, 2023. Accessed June 5, 2024.
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