Heart rate indicators for assessing physical activity level in the field

Area of Science:

• Exercise Physiology
• Occupational Health
• Biostatistics

Background:

• Assessing physical activity level (PAL) is crucial for understanding health and occupational demands.
• Heart rate (HR) monitoring is a common method for estimating energy expenditure and PAL.
• The reliability and validity of specific HR-based indicators require evaluation across diverse populations and activities.

Purpose of the Study:

• To examine the reliability and validity of heart rate (HR) indicators for assessing physical activity level (PAL).
• To evaluate the %Flex metric as a reliable and valid indicator of PAL in agricultural workers.
• To assess intra-individual variability of PAL using HR monitoring.

Main Methods:

• Monitored daytime heart rates (HR) for 12 days across three agricultural seasons in 16 Thai farmers.
• Calculated the percentage of time HR exceeded a flexed heart rate (%Flex) as a PAL indicator.
• Employed regression analyses and Analyses of Covariance (ANCOVA) to assess reliability and validity.

Main Results:

• The %Flex demonstrated high reliability for assessing PAL at the group level (r > 0.89 for females, r > 0.91 for males).
• Regression analyses showed good reliability for %Flex in assessing individual PAL (R² 0.62-0.97).
• ANCOVA indicated significant differences in PAL slopes among males (P=0.003) but not females, suggesting sex-based variations in HR response.

Conclusions:

• The %Flex is a reliable and valid indicator for assessing group-level PAL and intra-individual variability in physical activity.
• Findings are consistent with previous studies on other populations, supporting the generalizability of %Flex.
• HR monitoring, specifically %Flex, offers a practical tool for evaluating physical activity in agricultural settings.