Signaling Physical Exertion. Can Observers Detect Physical Exertion from Athletes’ Nonverbal Behavior

Abstract This research examined whether observers can accurately detect physical exertion and how their ratings align with athletes’ self-reports and physiological indicators. Across five independent studies (conducted 2024–2025 in Germany), 276 observers evaluated exertion from short video clips of 103 athletes differing in age (children and adults), exertion stage (rested, medium, high), and activity type (sprinting, running, cycling, workouts, track and field) to test the primary hypothesis that people can detect exertion based on thin slices of behavior. Observers reliably detected exertion based on the results of ANOVA and Pearson correlation analyses: ratings increased with physical load and correlated strongly with both self-reports and heart rate data, indicating reliance on valid perceptual cues. Comparisons showed slightly stronger correlations between self-reports and heart rate than between observer ratings and heart rate. Notably, after highly strenuous tasks, observers tended to underestimate exertion relative to athletes’ self-ratings. These findings highlight the accuracy of thin-slice judgments of exertion while revealing systematic underestimation at peak effort, offering insights with practical implications for sports performance monitoring and training feedback.