Farm workers are at high risk for heat-related illness in hot temperatures, especially during summer crop production. Farming is also physically demanding, further increasing the likelihood of developing heat-related illness. In California, where an estimated 30%-40% of U.S. farm workers are employed, temperatures in the state’s Central Valley – are typically in the 90s in June and July.

In the past, there was limited research on these farm workers’ physical activity and how it contributes to heat-related illness.

Recently, researchers at the University of California, Davis funded by the National Institute for Occupational Safety and Health (NIOSH) estimated the physical activity involved in common, strenuous farm tasks that could contribute to heat-related illness among these workers. They used devices called accelerometers, which are clipped onto a hip belt, to measure step counts per minute (cpm) during tasks over the course of a work shift. They then estimated the time spent in light, moderate, or vigorous activity. Study participants included 575 California workers on 28 farms in the Central and Imperial Valleys during the summers of 2014 and 2015. The farm workers’ average age was 38.6, and most were male and of Latino descent.

The overall average for farm workers was 345 cpm, defined as light activity, according to the study published in the Journal of Occupational and Environmental HygieneExternal. Produce carriers had the highest average level of physical activity, with 700 cpm, and ground pruners, who remove or trim plants, had the lowest number at 150 cpm.

Researchers also found a strong link between higher temperature and physical activity. For example, when the average temperature increased by 10°C (50°F), the average cpm decreased by 135. Other factors associated with decreased physical activity included increased age and tasks such as ground pruning, sorting or separating, and harvesting crops. In contrast, irrigation work and performing more than one task at the same time were associated with more physical activity, along with pay based on work completed, rather than time. These factors could increase the risk for heat-related illness.

Although lower than anticipated, the results could underestimate activity since the farm workers wore accelerometers on their hips, and step counts per minute could have missed movement during upper-body-intensive tasks, such as packing, sorting, and carrying. Nevertheless, this study could help inform efforts to prevent heat-related illness among California farm workers.