Firefighting tasks may require near maximal levels of cardiorespiratory fitness. Previous research has indicated that body fat percentage (BF%) and aerobic capacity (VO_2peak) are related to the performance of firefighting tasks. Since a standard submaximal treadmill test for firefighters is terminated at 85% of maximal heart rate (MHR), key performance information relating to maximal cardiorespiratory effort may not be measured in a submaximal test. The purpose of this study was to examine the relationships between body composition and time spent running at intensities greater that 85% MHR. Height, weight, body mass index (BMI; kg/m²), BF%, MHR (bpm), VO_2peak (mL/kg/min), predicted VO_2peak (P-VO_2peak; mL/kg/min), submaximal treadmill test time (WFI_sub Test Time; min), and maximal treadmill test time (WFI_max Test Time; min) were collected in fifteen active-duty firefighters. The results indicated that significant relationships (p < 0.05) existed between BF% and VO_2peak, BF% and WFI_max Test Time, BF% and T_diff, and VO_2peak and WFI_max Test Time. P-VO_2peak was not significantly different than VO_2peak, and the WFI_max Test Time was significantly longer than the WFI_sub Test Time. These results indicate that a submaximal treadmill test may reasonably predict VO_2peak, but key information about physiological work at intensities greater than 85% MHR may be missed when using submaximal effort tests.

The purpose of this study was to compare heart rate recovery (HRR) after a maximal treadmill (MAX-TM) and three-minute all-out (3MT) test between firefighters (FF) and a control (CON) group. Nine male CON and nine male FF participants completed height (m), weight (kg), body fat percent (BF%), normalized handgrip (GRIP_NORM, kg/kg), and MAX-TM with direct gas analysis to capture aerobic capacity (VO_2PEAK, mL/kg/min). A shuttle-sprint 3MT was used to measure critical velocity (CV, m/s) and D′ (m). Non-linear models determined HR decay (HRR_τ), HR asymptote (HR_∞), and HR amplitude (HR_amp). Two-way GROUP (FF vs. CON) by TEST (MAX-TM vs. 3MT) repeated measures ANOVAs indicated a significant TEST (F = 7.004, p = 0.018) effect on HR_amp. When divided by VO_2PEAK classification (FITNESS), a significant TEST effect was observed (F = 7.661, p = 0.014) on HR_amp. VO_2PEAK was significantly related to CV (r = 0.583, p = 0.011), GRIP_NORM (r = 0.668, p = 0.002), and BF% (r = −0.890, p < 0.001). Complete autonomic nervous system recovery may depend on the intensity of task demands and cardiorespiratory fitness.

Mendelson, BJ, Ebersole, KT, Brau, SD, and Ebersole, NT. Performance and physiologic responses to repeated 3-minute all-out shuttle tests. J Strength Cond Res 39(9): e1059–e1066, 2025—The purpose of this investigation was to examine changes in performance capacity in repeated all-out efforts. Ten participants (24.00 ± 4.32 years, 79.71 ± 46.05 kg, 1.79 ± 0.102 m) completed a maximal treadmill test with direct breath-by-breath and heart rate (HR) analysis to capture maximal aerobic capacity (V̇ o ₂ peak, mL·kg ⁻¹ ·minute ⁻¹ ) and HR (HR _PEAK-TM , bpm). Participants also completed three 30-meter shuttle sprint 3-minutes all-out test (3 MT) bouts, from which critical velocity (CV, m·second ⁻¹ ), anaerobic work capacity ( D′, m), maximal sprint speed (S _MAX , m·second ⁻¹ ), and the difference between S _MAX and CV (S _MAX-CV , m·second ⁻¹ ) were calculated. The 30-second end-3MT average HR (HR _END-3MT , bpm), pretest blood lactate (LA ⁻ _PRE , mmol·L ⁻¹ ), and post-test blood lactate (LA ⁻ _POST , mmol·L ⁻¹ ) captured physiologic responses to the 3 MT session. Repeated measures ANOVAs (⍺ = 0.05) indicated that CV ( F = 1.401, p = 0.270) did not significantly change across bouts, but D′ ( F = 7.271, p = 0.005) and S _MAX ( F = 7.474, p = 0.004) significantly decreased across bouts. HR _END-3MT was significantly lower than HR _PEAK-TM ( F = 11.961, p < 0.001), and the LA ⁻ _POST did not significantly change across bouts ( p > 0.05). Correlation analysis indicated that V̇ o ₂ peak was significantly related to CV in bout 1 ( r = 0.745, p = 0.013) and bout 3 ( r = 0.746, p = 0.013). CV may be a repeatable level of performance but the ability to work more than the CV is significantly diminished in repeated all-out efforts. Further research is needed to examine methods to improve repeatability of D' .

Background: The purpose was to determine the ventilatory and metabolic demands in percentage-based heart rate (HR) zones in active-duty firefighters. Methods: Male career firefighters (n = 48, 38.17 ± 9.02 years, 1.79 ± 0.05 m, 88.27 ± 12.50 kg) completed a maximal treadmill test while wearing chest strap monitors to measure physiological responses corresponding to Zone 1 (50–59%), Zone 2 (60–69%), Zone 3 (70–79%), Zone 4 (80–89%), and Zone 5 (90–100%) based on age-predicted maximal HR. Aerobic capacity (VO_2PEAK, mL·kg⁻¹·min⁻¹), average minute ventilation (V_E, L·min⁻¹), and respiratory exchange ratio (RER) in each zone was measured via indirect calorimetry. Linear mixed models determined significant differences in V_E, RER, and time in zone (min). Results: Significant relationships emerged between VO_2PEAK and average RER in Zone 5 (r = −0.33) and time in Zone 3 (r = 0.45), Zone 4 (r = 0.41), and Zone 5 (r = 0.41). A significant HR zone effect emerged in V_E (F = 516.01, p < 0.001) indicating that V_E increased as zone intensity increased. After controlling for VO_2PEAK, a significant HR zone effect emerged in RER (F = 11.90, p < 0.001), indicating that average RER increased as zone intensity increased. No HR zone effect was found for time in zone (F = 1.18 p = 0.332) after controlling for VO_2PEAK. Conclusions: A practical cardiovascular workload measure, such as percentage-based HR zones determined from treadmill testing, have distinct ventilatory and metabolic responses. Higher aerobic capacity is related to greater time spent working in higher HR zones.

Recruitment of firefighters is, in part, hindered due to attrition from fire academies. This study explored initial fitness differences between those who graduated (GRAD) or were released (REL) from the academy. During the first week of the academy, recruits (N = 407; GRAD = 354, REL = 53; 26.6 ± 7.2 yrs; 177.6 ± 8.6 cm; 87.9 ± 17.2 kg) completed an assessment battery including: body composition using skinfold calipers to estimate percent body fat (BF) and fat-free mass (FFM); shoulder mobility via Apley’s scratch test (APLEY); aerobic fitness (VO_2peak) and heart rate recovery (HRR_1min) estimated from the five-minute Forestry step test; muscular strength via the sum of right and left handgrip (SHG); and muscular endurance via a paced two-minute push-up test (PU). A t-test identified age differences between GRAD and REL, followed by separate ANCOVAs for each fitness measure, and logistic regression to identify the ability of fitness measures to predict academy outcome. GRAD had a lower age and BF and a higher FFM, VO_2peak, SHG, and PU, but did not differ in APLEY or HRR_1min. The full model predicting release was significant; age, BF, and FFM were significant predictors. These results provide pre-fire academy preparation guidance for optimizing the potential for successful academy completion.