Applicability of the Reflection Index of Respiration Based on Heart Rate Variability Analysis to Firefighting Activity

Firefighting is one of the most physically demanding and hazardous occupations in any country. When the firefighting activity continues for extended periods of time, firefighters are at risk for a decline in their physical and mental work ability. To ensure their safety, it is important for firefighters to be knowledgeable regarding their own physical condition. We have introduced an index of cardiorespiratory load that reflects respiratory metabolism state, the reflection index of respiration ( RIR ). This index is derived based on data, obtained under designed load activities, performed in a shuttle run test and bicycle ergometer test. Therefore, the applicability and effectiveness of this index to activities involving severe physical activities at a firefighting site, have not yet been evaluated. The RIR was applied in a simulated firefighting activity test, conducted according to a standardized protocol. This standardized firefighting test protocol consisted of 13 activities and required continuous physical activity for 26 min. The following results were obtained. First, RIR showed a good response to load intensity even when the activity loads varied irregularly in time. Second, the variation of the RIR demonstrated a good correlation, both, with the respiratory metabolic state and the blood lactate levels. Third, the RIR presented high sensitivity in response to firefighters’ changes in body movements and respiration, during the simulated firefighting activity test. The proposed index, providing objective information that supplements a firefighter’s subjective assessment of his or her own physical state, could be applied in the prevention of overexertion and is expected to improve the occupational safety of firefighters.