Exercise and Stress Reactivity in Animals and Humans: A Meta-Analysis

Ernesto Ramirez

The majority of American experience high levels of stress.

50%believetheirlevelofstresshasincreasedoverthelastfiveyears

Stress & Health

↑ Stress leads to hypertension ↑ Stress leads to atherosclerosis, CHD ↑ Reactivity = heart attack

• Animal studies support these findings

Stress & Immunity

↑ Stress = longer wound healing ↑ Stress = activation of latent viruses ↑ Stress = dysfunctional response to

bacterial challenger ↑ Stress = ↑ sick days (children)

Physiology of Stress

Stress produces a variety of nuerochemical changes involving various endocrine and

catecholamine responses which facilitate changes at specific target tissues.

STRESSOR

Cortex

Thalamus

Hypothalamus

CRH

TRF

ACTH TTH

THY OXY VAP E NE GCs

GABA

5‐HT DA

AdrenalCortex ThyroidGland

PosteriorHypothalamus AnteriorHypothalamus

AdrenalMedulla

Amygdala

TargetTissueResponse

Pituitary

Cross Stressor Hypothesis

Sothman proposed that exercise acts as a stressor. •  Creates a positive adaptation • Generalized pattern carriers over to psychological

stress

Exercise & Stress: Previous Reviews

Two qualitative reviews and three quantitative reviews do not provide a clear consensus. •  Mixed results •  Inclusion of methodologically weak studies

Develop an understanding of the effect of exercise on stress reactivity using meta-analytical techniques.

•  Only randomized controlled trials •  Examine both human and animal literature •  Animal research uses stringent protocols • Allows for a glimpse into mechanisms not

able to be studied in humans

Methods

Literature Search •  Utilized electronic databases (PsychInfo, PubMed, Sport Discus, Dissertation & Thesis, etc.)

•  Key Words: Exercise, Randomized Controlled Trial, Stress, Cardiovascular, Training, Physical Activity, Recovery, Reactivity •  For animal studies: Rat, Wheel Running, Stress, Reactivity, Recovery, Training

•  Cross referenced all studies as well as previously published meta-analyses and reviews.

Methods

Inclusion Criteria Human (Meta I)

• Random assignment to groups •  Include no-treatment control group • Cannot use physiological stressors (i.e. exercise)

Animal (Meta II) • Random assignment to groups •  Include no-treatment control group • Cannot use physiological stressors (i.e. exercise) • Physical Activity/Exercise cannot be forced. Animals

allowed free wheel running.

Effect Size

ES Calculation • Hedges g: •  µexp – µcontrol / SDpooled

•  Corrected ES’s based upon sample size

•  Overall weighted effect size •  Weighted by inverse of variance

•  Homogeneity of variance •  All moderators were examined regardless of

homogeneity

Results

Meta I • 150 studies located; 47 met criteria • 30 used in analysis (lack of data) • Resulted in 33 studies (multiple studies per article) • N = 1,252, avg. N = 39.13 • 196 effect sizes • Overall weighted effect size = -.31 • (95% CI = -.43,-.20)

Results

Meta II • 50 studies located; 34 met criteria • 19 articles had sufficient data • 27 studies included (5 studies has multiple groups) • N = 462, avg N = 17.11 • Overall weighted ES = -.33 • (95% CI = -.15, -.52)

Discussion

1.  Exercise is beneficial for the reduction of stress reactivity in humans.

2. Moderate effect is representative of Grade A, Level 1 evidence.

3. Much more research is needed in this area; 1.  Additional RCTs (only 22% of located studies). 2.  Different populations – unhealthy may need it most. 3.  Incorporation of alternative treatments and stressors 4.  Large sample size. 5.  Investigation of immune system response

Discussion

1.  Chronic free-wheel running leads to moderate reductions in stress reactivity for animals.

2.  Based primarily on neuroendocrine markers of stress system response.

3.  Future research must be more focused: 1.  Training methods to create fitness changes. 2.  Clear and repeatable stress protocols. 3.  Inclusion of “human like” psychological stressor. 4.  Investigation of immune system response

Conclusion

Thisisthefirststudytolookatbothanimalandhumanresearch.• ConsistentfindingsindicatethatexerciseprogramshaveposiJve,observable,andreplicableeffectsontheresponsetostress.• Providessupportfortheuseofanimalstoinves=gatepoten=almechanismsthatlinkexerciseandmentalwell‐being.• Anunderstandingofneuralchangeswhichareunavailableinhumanresearchwillleadtostrongerrecommenda=onsinthefuture.

Thank You