Abstract
ObjectivesFollowing predictions from life history theory, we sought to identify acute trade‐offs between reproductive effort (as measured by psychological arousal) and somatic maintenance (via functional measures of innate immunity) during conditions of severe energetic imbalance.MethodsSixty‐six male ultramarathon runners (ages 20 to 37 years) were sampled before and after a lengthy race. Saliva and sera were collected for testosterone and immunological analyses (hemolytic complement activity and bacterial killing ability). Lean body mass was assessed by bioelectrical impedance, and libido was measured using a slideshow of arousing and neutral images.ResultsFollowing predictions, there was a significant decrease in salivary testosterone levels (109.59 pg/mL versus 97.61 pg/mL, P < .001) and arousal scores in response to provocative images (5.40 versus 4.89, P = .001) between prerace and postrace time points. Additionally, participant bacterial killing ability (P = .035) and hemolytic complement activity (P = .021) increased between prerace and postrace.ConclusionsDecreased libido and testosterone with concomitant heightened innate immune responses suggest a shift in energetic priorities away from reproduction and toward maintenance/defense during a period of energetic stress.
Highlights
Maintenance, defense, growth, and storage under conditions of limited environmental resources (Reznick, Nunney, & Tessier, Life history theory predicts the existence of trade-offs between 2000; Stearns, 1992)
Recent work suggests that high levels of energy expenditure cause metabolic adaptation to reduce total energy output (Pontzer et al, 2016), and the high energetic costs of locomotion necessitated by ultramarathons are expected to necessitate physiological trade-offs
The study was approved by the University of Cambridge Human Biology Research Ethics Committee
Summary
Sixty-six male ultramarathon runners (ages 20 to 37 years) were sampled before and after a lengthy race. Saliva and sera were collected for testosterone and immunological analyses (hemolytic complement activity and bacterial killing ability). Lean body mass was assessed by bioelectrical impedance, and libido was measured using a slideshow of arousing and neutral images
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