Heat stress and workload associated with sugarcane cutting - an excessively strenuous occupation!

Introduction

Chronic kidney disease not associated with traditional risk factors (sometimes called Mesoamerican nephropathy) is prevalent in male agricultural labourers, particularly sugarcane cutters, in Central America and Mexico regions [1]. Strenuous work in a hot environment with dehydration is believed to be a key causal factor [1]. The aim of this study was to assess the level of heat stress and workload in sugarcane cutters.

Methods

45 sugarcane cutters (34(12) y; range 18 - 57 y) from El Salvador were studied during the 2015 harvest (Feb-April). Heart rate (HR, Polar) was recorded in 10-11 workers per day, during 7 workdays. Weather data was collected using two weather stations (Weatherhawk, QuesTemp °34). Outdoor Wet Bulb Globe Temperatures (WBGT) was calculated (WBGT (outdoor) = 0.7WB + 0.2G + 0.1DB) via the QuesTemp °34. HR data were expressed a percentage of maximal HR (%HR_max). A regression equation was used to predict HR_max (208 - 0.7 × age) [2].

Results

Sugarcane cutters worked on average for 7:30 hours (range 3:20 - 9:36 hours). In the field, WBGT reached 32.1°C (95% confidence interval [CI]: 33.0°C to 31.1°C), with 79 % (95% CI: 87 to 71%) of the day spent working at a WBGT above 26°C (threshold limit for continuous harvesting at 100 % [3]). Heart rates averaged 54 %HR_max (95% CI: 57 to 52 %HR_max) across all workdays. Workers spent 4:44 hours (95% CI: 5:19 to 4:09 hours) working at ≥50%HR_max and 2:48 hours (95% CI: 3:21 to 2:15 hours) working <50%HR_max.

Discussion

Sugarcane cutting is repetitive high-intensity work carried out in high heat stress conditions. Workers spent over half the workday (including rest breaks) working at and above 50% of their HR_max. This HR intensity is similar to that exhibited in the first 12 hours of adventure racing (64%HR_max [4]) and higher than that maintained by soldiers during multi-day operations (30 - 40% of aerobic power [5]).

Conclusion

The cardiac strain of sugarcane cutting is similar to that associated with very prolonged, competitive exercise and higher than that typically associated with self-paced hard work. Yet, sugarcane cutters maintain this work intensity daily throughout the harvest (~6 months).

Figure 1

Heart rate (1 min intervals) during one workday for two sugarcane workers.