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Updated: Sep 7, 2025

In Vivo Protocol of Controlled Subconcussive Head Impacts for the Validation of Field Study Data
Published on: April 18, 2019
Physical demands and physiological strain of American football referees while officiating
Hayley V MacDonald1, Emily C Colster1, Anne M Mulholland1
1Department of Kinesiology, the University of Alabama, Tuscaloosa, AL, USA.
Objectives:
Certain occupations are associated with greater risk of triggering a sudden cardiac event because of high levels of physical exertion and extreme thermal environments in which they occur. The extent to which sports officials--particularly high school (HS) American football referees--experience these conditions is unknown. Forty-six male HS officials (72% White/Caucasian; age = 48 ± 12 years, body mass index = 31.7 ± 6.6 kg·m-2) were studied to quantify the physiological strain and physical demands of officiating.
Methods:
Referee demographics (e.g., experience, habitual exercise), pre-game urine specific gravity (USG), thermal (peak core temperature [Tcore]) and cardiovascular (average heart rate [HR]) strain, kinematic activity (e.g., total distance, speed, mechanical intensity), and environmental conditions were measured during 10 regular season varsity HS football games (≈2.5 h each) in the Southeastern United States (average wet bulb globe temperature and relative humidity: 18.9 ± 6.0 °C and 78.2% ± 12.1%). Analyses included descriptive statistics, bivariate correlations, and linear regression.
Results:
Referees covered 5.2 ± 1.2 km per game, eliciting average HR and peak Tcore of 71.5% ± 8.0% HRmax and 38.3 ± 0.5 °C, respectively; 38% began games dehydrated (USG = 1.026 ± 0.004). Multiple regression analyses revealed that obesity (β = 0.34), not participating in regular exercise (β = -0.36), and officiating at lower mechanical intensity (β = -0.33) predicted greater cardiovascular strain (all p ≤ 0.03). White/Caucasian race/ethnicity (β = 0.59), younger age (β = -0.46), and obesity (β = 0.28) predicted greater thermal strain (all p ≤ 0.01).
Conclusion:
HS football referees experienced elevated levels of physiological strain while officiating, with individual factors modulating the magnitude of strain. Strategies aimed at reducing obesity, increasing exercise participation, and improving cardiovascular health should be emphasized to mitigate strain and prevent cardiac events.
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Exercise Stress Test
Exercise stress testing, commonly known as a treadmill test, is a noninvasive procedure used to evaluate cardiovascular function and diagnose heart conditions.
Definition
An exercise stress test measures the heart's response to exertion using a treadmill or stationary bicycle. Chest electrodes record the heart's electrical activity through an ECG, and blood pressure is monitored regularly.
Purposes
Estimation of the Physical Quantities

