# Comparison of Ventilatory and Metabolic Demands Across Percentage-Based Heart Rate Zones in Firefighters

## TL;DR

The study found that higher heart rate zones in firefighters lead to increased ventilatory and metabolic demands, with better aerobic capacity linked to longer time spent in intense zones.

## Contribution

This study provides new insights into how different heart rate zones affect ventilatory and metabolic responses in firefighters.

## Key findings

- Higher heart rate zones correlate with increased minute ventilation.
- Aerobic capacity is associated with longer time spent in higher intensity heart rate zones.
- Respiratory exchange ratio increases with higher heart rate zone intensity.

## Abstract

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 (VO2PEAK, mL·kg−1·min−1), average minute ventilation (VE, L·min−1), and respiratory exchange ratio (RER) in each zone was measured via indirect calorimetry. Linear mixed models determined significant differences in VE, RER, and time in zone (min). Results: Significant relationships emerged between VO2PEAK 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 VE (F = 516.01, p < 0.001) indicating that VE increased as zone intensity increased. After controlling for VO2PEAK, 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 VO2PEAK. 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.