Author ORCID Identifier

https://orcid.org/0000-0001-7047-1287

Date Available

12-12-2026

Year of Publication

2025

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Education

Department/School/Program

Exercise Science

Faculty

Mark G. Abel

Faculty

Haley C. Bergstrom

Abstract

INTRODUCTION: Overexertion-induced musculoskeletal injuries and sudden cardiac events are significant threats to firefighter safety and health. Firefighters must possess adequate cardiorespiratory levels to reduce these risks. High-intensity interval training (HIIT) and continuous steady-state endurance exercise (CEE) are effective types of endurance training. On-duty exercise is often interrupted by emergency calls, thus requiring firefighters to perform rigorous occupational tasks and retain critical operational information in a fatigued state. It is important to elucidate the impact of on-duty exercise on subsequent risk of injury and working memory (WM). PURPOSES: The primary aim of this investigation was to evaluate the acute impact of HIIT and CEE on neuromuscular function. The secondary aim was to identify fitness-based characteristics that are associated with decrements in neuromuscular function and WM. The tertiary aim was to determine the reliability of a novel WM assessment and determine if post-exercise changes in WM were related to neuromuscular function outcomes. METHODS: A convenience sample of firefighters (N=20; Age: 32.9±4.7 yr; Aerobic capacity: 46.7±5.5 mL/kg/min) completed a battery of fitness assessments, followed by two endurance exercise sessions. The CEE session included 30 min of running at 90% of the velocity associated with gas exchange threshold, whereas the HIIT session corresponded with 110% of peak aerobic velocity. Muscular strength and power were assessed with an isometric midthigh pull (IMTP). Neuromuscular function was assessed before and 10 min post-exercise in personal protective equipment using force plate assessments of bilateral and unilateral postural sway, isometric midthigh pull, and modified functional balance test outcomes. WM was assessed by recall of occupationally relevant radio communications. Mixed factor (exercise condition x time) ANOVA assessed differences in dependent variables. Post hoc analyses were performed with paired sample t-tests. Effect sizes were calculated as partial eta squared. The level of significance was set at p < 0.05. Minimal difference (MD) analysis (ICC Method) assessed individual responses to exercise stimuli. Pearson correlation identified correlates of decrements in neuromuscular function and WM. RESULTS: There were no condition, time, or interaction effects on bilateral postural sway (p≥0.20) and unilateral postural sway (p≥0.18), indicating static balance was similar to baseline at 10 min post-HIIT and CEE. IMTP peak force yielded an effect of time (F(1,18)=32.02, p< 0.001, ηp2=0.64, Power=1.0), condition (F(1,18)=5.50, p=0.031, ηp2=0.23, Power=0.60), and interaction (p=0.026). Specifically, peak force decrements were observed following HIIT (relative difference (RD)=-3.9±5.7; p=0.007) and CEE (RD=-7.5±5.4%; p< 0.001). IMTP rate of force development (RFD) analysis yielded an effect of time (F(1,18)=15.58, p< 0.001, ηp2=0.46, Power=0.96), with no effect of condition (p=0.81), or interaction (p=0.41). Specifically, RFD decrements occurred following HIIT (RD=-7.6±15.1%, p=0.004), but not CEE (p=0.09). Regarding balance outcomes, the MD analysis indicated that up to 26% of firefighters were negatively impacted by HIIT, whereas up to 16% were negatively impacted following CEE. Multiple fitness and anthropometric attributes were correlated to decrements in neuromuscular function. The reliability of the WM assessment was poor (ICC=-0.18) and WM was not affected by HIIT or CEE (p≥0.055). CONCLUSIONS: Both HIIT and CEE modalities produced fatiguing effects in strength immediately following exercise but did not impact group-level balance outcomes 10 min post-exercise, which reflects an occupationally relevant emergency response time. These findings indicate that most aerobically fit firefighters may safely perform HIIT and CEE protocols while on duty. PRACTICAL APPLICATIONS: Performing regular on-duty exercise is critical to enhance occupational readiness and safety across the career span. These findings will inform the development of appropriate on-duty exercise recommendations to reduce the risk of exercise-induced overexertion and slip, trip, and fall injuries and maintain WM while performing occupational tasks.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2025.597

Funding Information

This work was supported by the National Strength and Conditioning Association Foundation's Doctoral Student Research Grant in 2023.

This work was supported by the University of Kentucky's Department of Kinesiology and Health Promotion.

Download

Available for download on Saturday, December 12, 2026

Contact Author

Share

COinS