Exercise, Fitness, and Cognition Under Extreme Stress

High stress can make attention feel expensive. Sleep fragments, pain lingers, and the brain starts dropping small administrative tasks like a bad intern. Exercise may help, but a 2024 randomized trial in forcibly displaced adults at risk for PTSD adds an uncomfortable condition: attendance alone did not improve cognition. Participants needed to improve cardiorespiratory fitness (CRF) for cognitive gains to appear.

That finding comes from a secondary analysis of the SALEEM randomized controlled trial, the first exercise RCT in this population. It does not prove that fitness is the only route to a sharper mind under stress. It does suggest that, in this unusually high-stress setting, the physiological response to training mattered more than simply completing sessions.

The trial found a mediated effect, not a direct one

SALEEM tested 10 weeks of a structured exercise and sport intervention in forcibly displaced adults at risk for PTSD. The cognitive endpoint was attentional processing speed. The intervention had no statistically significant direct effect on that endpoint; the reported p values were at least .332.

Yet the researchers' mediation analysis found that improvement in CRF fully mediated the pathway between the intervention and cognitive benefit. In practical terms, participants whose fitness improved also showed cognitive improvement, while session participation without a measurable CRF gain did not yield a cognitive return in that analysis.

This is an interesting result, but its design sets firm limits. The parent trial was powered for PTSD symptoms, not cognitive or pain mediation. Secondary mediation analyses can produce unstable estimates when the study lacks adequate power for that question. The result identifies a plausible pathway worth testing directly; it does not establish a universal training law for trauma-exposed people, stressed office workers, or anyone else.

SALEEM does not show that every form of movement must raise CRF to help cognition. It shows that CRF improvement statistically explained the cognitive benefit observed in this particular 10-week intervention.

Why fitness could matter when stress is high

CRF is not itself a brain molecule. It is a measurable marker of how the cardiovascular, respiratory, and autonomic systems respond to sustained aerobic work. Those systems interact with stress biology, which gives the SALEEM result a credible biological rationale without turning it into proof of mechanism.

In chronically stressed young adults, Looser et al. (2023) found that higher CRF was associated with better-preserved working memory, and heart-rate variability partially mediated that association. Heart-rate variability reflects autonomic regulation; the observational design means it cannot show that improving fitness caused the working-memory difference. Still, it supports the possibility that aerobic training may help restore autonomic flexibility disrupted by chronic stress.

Other populations provide related, but indirect, mechanistic evidence. A 2025 meta-analysis in people with depression found that moderate-intensity aerobic exercise most reliably elevated brain-derived neurotrophic factor, or BDNF, a protein involved in synaptic plasticity. Read the Zhu et al. review as evidence about a biomarker in depression, not proof that BDNF caused cognitive recovery after trauma.

A separate meta-analysis of randomized trials in mild cognitive impairment found that physical activity reduced IL-6 and TNF-α while increasing BDNF and IGF-1. Lower inflammatory signaling and higher neurotrophic signaling could plausibly support cognition, but these participants had mild cognitive impairment, not PTSD risk. Population differences matter: trauma exposure, depression, neurodegeneration, and healthy aging do not share the same biology or circumstances.

Structural evidence also remains preliminary. In people with Parkinson's disease, Petkus et al. (2022) reported that thalamic volume statistically mediated the association between VO2max and cognitive performance. That cross-sectional finding cannot establish direction of cause and effect, and Parkinson's disease is not a model for displacement-related stress.

Pain: a signal, not a result

SALEEM also examined chronic pain. Greater exercise adherence showed a trend toward lower pain, with β = −.14 and p = .065. Because this missed the conventional .05 threshold and came from a secondary analysis, it is hypothesis-generating rather than evidence that the program reduced pain. The direction fits hypotheses about movement, inflammation, and pain regulation, but the trial did not settle the question.

Fitness is one pathway, not the whole story

The strongest challenge to a CRF-only explanation comes from the 18-month EXERT trial in adults with mild cognitive impairment. Aerobic exercise and low-intensity stretching and balance training produced statistically equivalent cognitive outcomes. If aerobic fitness were required for every cognitive benefit of exercise, that result would be hard to explain.

Several explanations remain possible. Structured movement can reduce sedentary time, create regular social contact, demand attention and motor learning, or change inflammatory signaling without producing large CRF gains. A 2022 meta-analysis of multicomponent exercise also found cognitive benefit in older adults with cognitive impairment when programs combined aerobic, resistance, and balance work. Those evidence bases involve cognitive impairment rather than trauma exposure, so they do not overturn SALEEM. They do rule out treating its mediation model as the only possible mechanism.

Cognitive outcomes also vary by domain. In cognitively normal older adults, Frost et al. (2021) found that executive-function gains associated with CRF change after high-intensity exercise were domain-selective. Improving fitness may help some cognitive tasks more than others; "cognition" is too broad to function as a single endpoint.

Biology may further divide the response. In an aerobic-exercise RCT, Barha et al. (2023) found executive-function improvement in women without the BDNF Val66Met polymorphism, while men did not show benefit regardless of genotype. This does not establish who will respond to training under trauma-related stress, but it cautions against assuming one BDNF-based mechanism applies equally to everyone.

What to do with this evidence

If stress is high, keep moving—but judge the plan by adaptation, not by whether a workout appeared in an app. For people who can safely train, aerobic work that gradually improves CRF is a reasonable priority. A 2025 systematic review of RCTs in healthy older adults identified at least 150 minutes per week of moderate-to-vigorous activity as the training profile most consistently associated with executive-function gains, with aerobic training outperforming resistance training. That is a useful benchmark from Lin et al., not a validated prescription for displaced or trauma-exposed adults.

Pairing aerobic training with resistance and balance work also makes sense, because non-aerobic movement may carry cognitive benefits through other routes. Track an actual fitness measure when feasible—such as a standardized walking, cycling, or VO2-based assessment—rather than assuming that more sessions automatically equal more adaptation.

The evidence supports exercise as a sensible part of recovery under stress, not as a substitute for trauma-informed mental-health care, medical evaluation of chronic pain, adequate sleep, or safety. SALEEM's most useful lesson is narrower: under extreme stress, the body's training response may be the part that matters most for attention. We need larger trials designed to test that claim before treating it as settled.