Road construction workers perform physically demanding, typically including building frames, laying concrete and asphalt, and operating heavy machinery. These activities result in high metabolic demands, leading to significant internal heat production. When combined with environmental heat stress during warmer periods of the year, road construction workers may experience substantial heat strain, making them susceptible to heat-related illnesses and ultimately heat-related deaths. In fact, construction workers are 13 times more likely to die from heat related illness compared to other occupations. Despite these statistics, no studies have assessed heat strain in road construction workers during the summer. PURPOSE: To quantify heat strain in road construction workers during a typical workday in the summer. METHODS: Seven male road construction workers were monitored for markers heat strain during a typical work day in the summer. Core and skin temperatures were continuously monitored on participants throughout the day, and hydration was assessed via changes in urine specific gravity (USG) and body weight from the beginning to end of the workday. Heat index (HI) was calculated from dry bulb temperature and humidity continuous measurements for the duration of the workday. RESULTS: Two of the seven workers (29%) reached a peak core temperature of greater than 38.0°C, which is a threshold used by OSHA to identify heat exhaustion. Peak values for core temperature were 37.89 ± 0.16°C, with average values being 37.42 ± 0.36°C. Peak values for skin temperature were 36.71 ± 0.62°C, with average values being 34.21 ± 1.43°C. The peak heat index was 34.1°C, with a peak dry bulb temperature of 36.1°C. There were no significant changes in USG (p=0.30), however workers had a significant decrease in body weight (0.85 ± 1.0%) from pre to post-work (p=0.02). There was a moderate, positive correlation between heat index and core temperature (p=0.001, r2=0.38) CONCLUSION: Road construction workers experience significant heat strain while working in the summer, even when working in moderately hot dry conditions. This heat strain is likely dependent upon changes in environmental heat.


Road construction workers perform many different tasks including laying concrete or asphalt, repaving previously built roads, and operating heavy machinery6. Many of these tasks require a considerable degree of physical exertion, resulting in significant metabolic stress15. Previous research indicated that the average energy expenditure of road construction workers corresponds to a level III category of “hard work” according to the National Institute for Occupational Safety and Health’s (NIOSH) “work heaviness classification.”16. These researches further demonstrates that road construction workers experience substantial cardiovascular, musculoskeletal, and metabolic demand, often resulting in fatigue and musculoskeletal work-related injuries15. While these musculoskeletal injuries resulting from mechanical stress of physical labor have been documented, 5,16 less is known about the potential detrimental effects of heat stress associated with the high rates of metabolic demand. In addition to metabolic heat stress, road construction workers are frequently exposed to the challenges of working in outdoor, uncovered environments, with the challenge overcoming excessive heat during warmer periods of the year7.

Since road construction workers perform their job task in outdoor spaces, they are exposed to environmental heat stress during summer months. Environmental heat stress is composed of heat radiation, air temperature, humidity, and air velocity,8which likely all fluctuate throughout a typical work shift outdoors. Furthermore, road construction workers are required to wear protective clothing while working, 2 which may contribute to an impaired ability to dissipate heat 9,19. These factors combined contribute as risk factor for increased heat strain, which is considered the physiological responses to heat stress. 13

Elevated core temperature, a common measure of heat strain, 10,13 is considered a risk factors for heat-related illness18. In fact, the American Conference of Governmental Industrial Hygienists1 has established threshold limits, including recommending that workers maintain a core temperature of less than 38°C 2,17. It is, therefore, not surprising that construction workers as a whole have been found to be thirteen times more likely to die from heat-related illnesses compared to workers of other occupations11. Shockingly, despite these concerns, no previous research has assessed the heat strain experienced by road construction workers experience in the summer. Therefore, the purpose of this study was to report heat strain and heat stress in road construction workers during work in the summer.


Seven male road construction workers in New Mexico agreed to participate in this study. Workers were consented and screened for health risks prior to participating in this study. All data was collected during a single work day, at a single job site in July of 2023. Immediately prior to their work day, workers met with researchers for measurements, including height and weight. Urine was then collected to assess urine specific gravity (USG). Next, workers were given a Polar heart rate chest strap to wear, and an iButton skin temperature device was applied to the chest for continuous heart rate and skin temperature recording, respectively. An ingestible core temperature pill, which continuously recorded core temperature every minute, was given to participants to ingest. Following these initial procedures and measurements, workers engaged in their usual work routines for approximately eight hours and minimal disturbance by researchers occurred during the work shift. At the end of the shift, body weight was measured again in order to calculate percent change in body weight. Urine sample was collected again to measure USG, and all research equipment was removed from subjects. Finally, workers were surveyed to identify their peak and average values throughout the work shift of rating of perceived exertion (RPE) on a scale of 6- “no exertion at all” to 20- “maximal exertion” (Borg, 1982), thermal sensation (TS) on the ASHRAE 9-point scale ranging from “-4-very cold” to “+4-very hot”2 and thermal comfort (TC) on a 5-point scale ranging from 1-Comfortable to 5-Intolerable 13. Heat index, dry bulb temperature, wet bulb temperature, and relative humidity were monitored and recorded continuously in the area which workers were primarily working.

Statistical Analysis:

Data is presented as mean ± standard deviation. Paired samples T-test were conducted to assess differences in USG and body weight between pre- and post-work time points. A Pearson correlation was generated to compare the relationships of heat index and peak core temperature. Significance levels were set at p<0.05.


Seven male construction workers (age = 38.9 ± 13.7 years, height = 169.1 ± 6.0 cm, body weight = 86.1 ± 25.4 kg) completed this descriptive study. All workers were engaged in outdoor activities, in an uncovered environment with limited opportunities for shade. Tasks varied from building forms, pouring concrete, and operating machinery. The maximal heat index was 34.1°C with an average of 28.1 ± 3.7°C. The maximum dry bulb temperature was 36.5°C, and the average was 30.0 ± 4.1°C. The maximum wet bulb temperature was 22.2°C with an average of 15.3 ± 1.1°C. Relative humidity peaked at 50.4 with an average of 24.4 ± 8.3%.

Heat Strain

Figure 1A displays core temperature of all seven workers. Figure 1B presents the average peak core temperature, which was 37.89 ± 0.16°C. Two of seven subjects (29%) reached a peak core temperature greater than 38°C, and the highest value recorded was 38.1°C. The average core temperature throughout the workday was 37.42 ± 0.36°C. The average peak skin temperature was 36.71 ± 0.62°C, and the average skin temperature throughout the workday was 34.21 ± 1.43°C.



Figure 1. Core temperature of road construction workers displayed as A) average core temperature (red line) ± standard deviation (black line) throughout a work shift and B) individual peak core temperature (N=7).


There was no significant difference between USG before (1.020 ± 0.01) and after (1.024 ± 0.01) the work shift (p= 0.30). However, there was a significant decrease in body weight from pre-shift (86.1 ± 25.4 kg) to post-shift (85.3 ± 25.2kg) (p=0.023), with an overall percent body weight loss of 0.85 ± 1.0%.

Perceptions of Exertion, Comfort, and Thermal Environment

The reported peak RPE was 14.1 ± 2.5, corresponding to a perceived exertion just between than “somewhat hard” and “hard (heavy).” The average RPE was 11.6 ± 1.9 corresponding to a perceived exertion of “light.” The peak TC in workers was 2.7 ± 0.8 just below “uncomfortable”, with an average of 2.0 ± 0.6 corresponding to “slightly uncomfortable.” Finally, the peak TS was 3.1 ± 0.4 “hot”, with average TS being 2.2 ±0.5 “warm”.[A2]

Heat Index and Core Temperature Correlation

Figure 2 demonstrates a moderate, positive correlation between heat index and core temperature (p=0.0010, r2=0.3792). The generated equation, core temperature = 36.74 + 0.0256*(heat index), indicates that for every one-degree Celsius increase in heat index, there is an associated increase of 0.0256°C in core temperature in road construction workers[A3] [A4] .

Figure 2. Linear regression between heat index and average core temperature. Core temperature = 36.74 + 0.0256*(heat index).


The purpose of this study was to investigate heat strain in road construction workers during work in the summer and provide novel insight about heat strain measuring core temperature. Our primary finding was that approximately 29% of workers reached a peak core temperature exceeding the 38.0°C threshold recommended by ACGIH1. This finding provides evidence that some road construction workers experience significant heat strain during work in the summer, which puts them at increased risk for heat-related illnesses 18. Additionally, we demonstrated a moderate, positive correlation between heat index and core temperature, indicating that environmental heat is likely related to these elevated peak core temperature values.

An evaluation of exposure limits by 19 suggested based off of their findings that a threshold value of 29.4°C for heat index may be an effective threshold to identify increased risk in outdoor workers for heat-related illness. The peak heat index of 34.1°C recorded in our study was much higher (4.7°C) than this recommended threshold, suggesting that the road workers in this study were at a significant risk for heat-related illness. This elevated risk was reflected by the 29% of the workers reaching a core temperature greater than 38.0°C. Workers appeared to sense this heat strain, as reflected by an average peak TS of 3.1 (“hot”), and the average peak TC was 2.2 (“warm”). These findings indicate that road construction workers may appropriately sense heat stress in relation to heat strain. Conversely, previous research by Runkle et al. (2019) found a mismatch between perception of heat strain and heat strain risk in outdoor workers during the summer. Interestingly, we found that road construction workers had a lower average RPE (11.6 ± 1.9) compared to research done by Roja et al. (2006), who found an average RPE of 15 ± 2. These contrasting values represent a difference of “light” work compared to “hard (heavy)” work, which may be influenced by factors such as workday variation, job sites, environmental conditions and worker population. This is a notable finding, as this difference in perceived exertion may also be indicative of differences in workload, and therefore potentially metabolic heat production.

A limitation of this study was that we had a small sample size of seven workers. Future research is needed in road construction workers on a larger scale is warranted to further quantify their work-related heat strain, explore possible cooling strategies, and identify appropriate risk factors for heat-related illness.

In conclusion, our results demonstrate that some road construction workers experience significant heat strain while working in the summer, with heat strain positively correlated to environmental heat index.


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[A1]Remove the lines from the border.

[A2]Is this correct?

2 is warm and 3 is hot

[A3]These number of core were captured at the same time of the HI measurement, correct?




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