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Shock Therapy

Runner’s high – a brief, deeply relaxing state of euphoria following intense exercise – may be a popular humblebrag, but it’s one firmly rooted in science. Studies have found that acute bouts of aerobic exercise can reduce anxiety and, though the mechanism behind these anxiolytic effects is still not fully understood, researchers believe the endocannabinoid (eCB) system plays a role (1). 

In a bid to learn more, researchers at the University of Wisconsin-Madison, USA, analyzed the effect of acute aerobic exercise on a particularly vulnerable population – women with PTSD. The randomized, counterbalanced study assessed the women’s anxiety and fear ratings in response to specific threatening stimuli (predictable and unpredictable electric shock administration). It also monitored participants’ moods and their circulating concentrations of eCBs following 30 minutes on a treadmill at 70–75 percent maximum heart rate and in a quiet control condition. Study participants included those with and without a history of trauma, with a particular focus on women with PTSD.

The results? Anxiety and fear ratings to predictable and unpredictable threats were significantly (p<.05) lower following exercise compared with quiet rest, and analyses indicated that those with greater increases in circulating eCBs had greater reductions in anxiety and fear ratings to both types of threat following exercise. The women also reported significant (p<.05) reductions in fatigue, confusion, and total mood disturbance, as well as an increase in positive affect.

Both the PTSD group and non-trauma controls reported significant (p<.05) increases in vigor, with additional mood improvements following exercise for the PTSD group, including decreases in anxiety, negative affect, tension, anger, and depression. The bottom line? Aerobic exercise appears to offer impressive psychological benefits, potentially due to increased concentrations in circulating eCBs. Could we see exercise form part of a comprehensive treatment plan for individuals with PTSD in the future? Perhaps.


We reached out to lead author Kevin Crombie, Postdoctoral Research Associate in the Department of Pharmacology and Toxicology, University of Wisconsin-Madison, USA, to find out more

Why did you focus specifically on women with PTSD?

That’s a great question! Women are more than twice as likely to develop a diagnosis of PTSD following exposure to trauma. Furthermore, the majority of individuals with PTSD in this study had experienced interpersonal violence (e.g., physical or sexual assault). Although individuals can develop PTSD following exposure to a broad range of traumatic events, epidemiological evidence suggests that interpersonal violence exposure (which is more common in women than men) is a more potent risk factor than other forms of trauma.

Additionally, among individuals with PTSD, comorbid depression and anxiety rates are often greater in women than in men. Although this study – and the majority of our previous research investigations – focused primarily on women with PTSD stemming from interpersonal violence exposure, we feel that future research should also examine men and individuals with other types of trauma exposure. PTSD is a debilitating mental health disorder, so the more research that can be done, the better!  

Is there a reason you studied responses to both predictable and unpredictable threats?  

Most research examining the anxiolytic effects of exercise has focused on general anxiety levels, either prior to and following an acute bout of exercise or before and after a long-term exercise intervention. These studies have been instrumental in improving our understanding of the anxiolytic effects of exercise, but we wanted to ask a slightly different question. We wanted to know whether an acute bout of aerobic exercise influences anxiety and fear responses to specific threats (as opposed to more general anxiety).

As such, we administered a common lab-based task known as the NPU threat task, which allowed us to examine fear ratings to predictable threats ( in which the participant knew when a shock was going to occur) and anxiety ratings to unpredictable threats (in which participants did not know when shocks would occur). In a lot of ways, this was very much a lab-based basic science research project; we primarily wanted to determine whether aerobic exercise is capable of influencing fear and anxiety ratings to predictable and unpredictable threats, and whether or not there may be a role for the endocannabinoid system in such effects.

What do your findings tell us about exercise and the eCB system?

Our findings contribute to a growing body of literature that suggests that moderate-intensity aerobic exercise increases circulating concentrations of endocannabinoids and that these increases are often associated with psychological improvements such as improved mood. In this study’s case, that included reduced fear and anxiety ratings to predictable and unpredictable threats. There is still a ton of work that needs to be done in this area (in fact, the first human exercise and endocannabinoid study was published in 2003), but there are some really great researchers trying to fully understand the therapeutic potential of increased endocannabinoid concentrations following exercise. See here, here and here.

Do you plan on continuing this work in the future? 

Absolutely! We have several ongoing projects examining the role of exercise as part of a comprehensive treatment plan for individuals with PTSD. Specifically, we are currently using computational modeling and neuroimaging approaches to examine whether moderate-intensity aerobic exercise performed shortly after fear extinction training (a lab-based model of commonly administered exposure-based therapies) improves memory consolidation and prevents the return of fear in women with PTSD.

We recently finished some pilot studies that provide preliminary evidence in support of this notion, but we now want to take a deeper dive. In addition to exercise, we are also examining pharmacological manipulations to the endocannabinoid system as a potential method for enhancing extinction learning, which may improve our targeting of the endocannabinoid system and, ultimately, increase the efficacy of exposure-based therapies. See here and here.

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  1. K Crombie et al., Ment Health Phys Act, 20, 100366 (2021). PMID: 34149867.
About the Author
Phoebe Harkin
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