IntroductionHigher work rates may be sustainable when maintaining target rating of perceived exertion (RPE) compared to maintaining target heart rate (THR) during high-intensity interval training (HIIT) exercise in hot conditions, but may also result in greater thermal strain and cardiovascular drift, as well as greater decrements in maximal oxygen uptake (V˙O2max).PurposeTo test the hypotheses that maintaining target RPE compared to THR during HIIT in the heat results in 1) smaller work rate adjustments, 2) greater thermal and cardiovascular strain, and 3) larger decreases in V˙O2max.MethodsEight adults (4 women) completed a graded exercise test on a cycle ergometer in 22°C and then 4 cycling trials in 35°C, consisting of an 8-min warm-up at 70% maximal heart rate (HRmax) or 12 RPE followed by 1 (15HR and 15RPE) or 5 (43HR and 43RPE) rounds of HIIT (1 round = 4 min work at 90% HRmax or 17 RPE and 3 min recovery at 70% HRmax or 12 RPE) totaling 15 min or 43 min of exercise, respectively. Each trial ended with a GXT to measure V˙O2max.ResultsIn the 43-min trials work rate decreased from the first to the fifth work interval in both conditions, but by a non-significant, yet moderately larger (ES = 0.53) amount during 43HR (46 ± 29 W) compared to 43RPE (30 ± 28 W). From the first to fifth work interval HR increased over time by 12 b⋅min–1 in 43RPE (p < 0.001), but did not increase during 43HR (p = 0.36). Rectal temperature increases were not different between conditions (43HR = 0.7°C, p < 0.001; 43RPE = 0.8°C, p < 0.001). V˙O2max decreased 15.6% (ES = 0.41) between 15RPE and 43RPE (p = 0.005), but it was not different over time during the HR-based trials [6.5%, ES = 0.16 (α adjusted for multiple comparisons = 0.0125) p = 0.03].ConclusionMaintaining target RPE and THR require considerable declines in work rate during HIIT in the heat, with ∼53% larger declines needed to maintain THR. The mitigation of cardiovascular drift in the THR trial may have contributed to the preservation of V˙O2max.

INTRODUCTION/PURPOSE:The purpose of this study was to test the hypothesis that cardiovascular (CV) drift and associated decrements in maximal oxygen uptake (V̇O 2max ) are greater in high-fit compared with low-fit women during exercise at the same %V̇O 2max , but comparable at the same rate of metabolic heat production. METHODS:Six high-fit (HI) and six low-fit (LO) women cycled in 35°C for 15 or 45 min at the same relative intensity (60% V̇O 2max ; 15REL and 45REL) or fixed rate of heat production (500 W; 15FX and 45FX), immediately followed by a graded exercise test to measure V̇O 2max . The separate 15- and 45-min trials permitted measurements of V̇O 2max over the same time interval as CV drift. RESULTS:During 45REL, higher heat production in HI (496 ± 51 vs 364 ± 44 W in LO) resulted in greater end-exercise core temperature (38.7°C ± 0.4°C vs 38.2°C ± 0.1°C, P = 0.03), greater increases in HR (15 bpm (10%) vs 10 bpm (6%), P = 0.03) and decreases in stroke volume (11 mL per beat (16%) vs 5 mL per beat (8%), P = 0.001), and larger reductions in V̇O 2max (16% vs 5%, P = 0.04) compared with LO. During 45FX, temperature responses, CV drift, and decreased V̇O 2max were not different between groups (all P > 0.05), despite differences in %V̇O 2max (60% vs 75% for HI and LO, respectively). CONCLUSIONS:We conclude metabolic heat production modulates the CV drift-V̇O 2max relationship, independent of fitness level. These results support previous findings showing the magnitude of CV drift is proportional to reductions in V̇O 2max .

Heart rate drifts upward over time during interval exercise and during exercise in hot conditions. As such, work rate must be lowered to maintain target heart rate. The purpose was to characterize acute work rate adjustments during high-intensity interval training based on target heart rate. Seven humans (three females) completed five study visits: a graded exercise test on a cycle ergometer to measure maximal heart rate (HRmax) in ∼22 °C and four trials performed in ∼22 °C (TEMP) or ∼35 °C (HOT), consisting of an 8 min warm-up at 70% HRmax followed by one (15TEMP and 15HOT) or five (43TEMP and 43HOT) rounds of high-intensity interval training (one round = 4 min work at 90% HRmax and 3 min recovery at 70% HRmax) totaling 15 min or 43 min of exercise, respectively. Work rate was lowered 33 ± 20 W ( p = 0.005) in 43TEMP and 56 ± 30 W ( p = 0.003) in 43HOT between the first and fifth work intervals. Thermal strain (0.2 °C higher rectal temperature, p = 0.01) and cardiovascular strain (6 beats·min–1 larger increase in heart rate from first to fifth recovery interval, p = 0.01) were greater in 43HOT versus 43TEMP. Using target heart rate during high-intensity interval training may reduce the training stimulus, especially in hot environments, but it may also limit thermal strain and enable participants to complete the prescribed workout despite the heat.

Heart rate (HR) drifts upward over time during interval exercise and during exercise in hot conditions. As such, work rate must be lowered to maintain target HR (THR). Additionally, prolonged exercise in the heat can result in reduced maximal oxygen uptake (V̇O2max). PURPOSE: To characterize work rate adjustments during high-intensity interval training (HIIT) in a temperate and hot environment based on THR and to test the hypotheses that in a hot versus temperate environment 1) work rate must be lowered to a greater extent to maintain THR, 2) there will be greater thermal and cardiovascular strain, 3) V̇O2max will decrease to a greater extent. METHODS: Four men and 3 women completed the study, which began with a control graded exercise test (GXT) on a cycle ergometer to measure maximal HR (HRmax) and V̇O2max in 22 °C. The remaining two 15-min and two 43-min trials were counterbalanced and separated by ≥48 h. Each consisted of an 8-min warm-up (WU) at 70% HRmax followed by 1 or 5 rounds of HIIT (4 min at 90% HRmax; 3 min at 70% HRmax) and then a GXT to measure V̇O2max, performed in ~22 °C (TEMP) or ~ 35 °C (HOT): 15TEMP and 15HOT = WU and 1 round of HIIT; 43TEMP and 43HOT = WU and 5 rounds of HIIT. The separate 15- and 43-min trials were intended to measure V̇O2max before and after, respectively, cardiovascular and thermal strain ensued. RESULTS: Work rate had to be lowered 33 ± 20 W (p = 0.005) in 43TEMP and 56 ± 30 W (p = 0.003) in 43HOT between the first and final work intervals to maintain THR (p = 0.008 for the interaction effect and paired samples t-test comparing change scores between 43TEMP and 43HOT). From the first to final recovery interval, thermal and cardiovascular strain were greater in 43HOT versus 43TEMP: 0.2 °C higher rectal temperature (p = 0.01 for t-test comparing change scores); 6 b/min larger increase in HR (11 b/min versus 5 b/min; p = 0.01 for interaction effect). V̇O2max was 0.2 L/min lower in the heat (p = 0.001 for main effect of condition) and 0.2 L/min lower over time (p = 0.02 for main effect of time), but the decrease was not different between conditions (p = 0.29 for interaction). CONCLUSIONS: Using THR during HIIT may reduce the training stimulus, especially in hot environments, but it may also limit thermal strain and enable participants to complete the prescribed workout.

Heart rate (HR) and rating of perceived exertion (RPE) drift upward over time during exercise in hot conditions. As such, work rate must be lowered to maintain target intensity. PURPOSE: To characterize work rate adjustments during high-intensity interval exercise (HIIE) in the heat based on target HR and target RPE and to test the hypotheses that 1) work rate must be lowered to a greater extent to maintain target HR than to maintain target RPE and 2) greater thermal and cardiovascular strain will result from maintaining target RPE compared to target HR during HIIE in hot conditions. METHODS: 5 adults [3 men, (mean ± SD) age = 26 ± 8 y] completed two 43-min trials on a cycle ergometer in 35 °C. Exercise intensity was prescribed based on a target HR (HR-based) or target RPE (RPE-based). After an 8-min warm-up at 70% HRmax or an RPE of 12, subjects completed 5 rounds of HIIE (4 min of work at 90% HRmax or an RPE of 17 and 3 min of recovery at 70% HRmax or an RPE of 12). Three more subjects are anticipated to participate in the study. RESULTS: Percent change in power output from the first to last work bout was greater during HR-based trials (-31% ± 8%; -52 ± 35 W) compared to RPE-based trials (-14% ± 22%; -25 ± 29 W) (p = 0.045). By design, HR remained constant from the first to final work bout during the HR-based trial [4% ± 4% (6 ± 6 beats/min) increase, p = 0.073], but it increased 12% ± 5% (18 ± 8 beats/min; p = 0.006) during the RPE-based trial. Although work rate and cardiovascular responses were different between trials, the increases in rectal temperature over time (1.1 ± 0.5 °C for HR-based and 1.1 ± 0.3 °C for RPE-based) were not different (p = 0.29). CONCLUSIONS: These data show that method of exercise prescription affected work rate adjustments and cardiovascular strain, but not thermal strain during HIIE in hot conditions. Work rate had to be lowered ~27 W (108%) more to maintain target HR than to maintain target RPE, which may have practical significance in terms of the metabolic stimulus of the exercise and potentially compromised training adaptations. On the other hand, maintenance of a higher metabolic intensity during the RPE-based trial resulted in a 3 times greater increase in HR over time which may have implications for reduced maximal oxygen uptake associated with cardiovascular drift.

Acute kidney injury (AKI) following extreme high-volume functional resistance exercise (HVFRE) has been observed. However, the breadth of programing within this exercise style and concomitant risk factors make causality unclear. PURPOSE: Measure markers of AKI after a standardized HVFRE workout. METHODS: Participants [n = 38 (10 female), 175 ± 9 cm, 79 ± 14 kg, 29 ± 9 y, with HVFRE experience of 3.7 ± 1.7 y] performed a HVFRE workout (1-mile run, 100 pull-ups, 200 push-ups, 300 body-weight squats, and 1-mile run). Exclusion criteria were current injury, renal disease, and no previous completion of the intervention HVFRE workout. Spot urine and blood samples were taken at five time points surrounding the workout (24 hr-pre, immediately-pre, immediately-post, 24 hr-post, and 48 hr-post). 24 hr urine was collected over three days (day before, day of, and day after workout) Spot urine was analyzed for protein and blood with reagent strips, blood was analyzed for interleukin-18 (IL-18), chitinase-3-like protein 1 (YKL-40), creatine kinase (CK), myoglobin (MYO), and 24 hr urine for neutrophil gelatinase-associated lipocalin (uNGAL) with enzyme-linked immunosorbent assays. RESULTS: HVFRE duration and intensity were 65 ± 14 min and 77.0 ± 11.7 %HRR, respectively. IL-18 (+27.4 ± 38.6 pg/mL) and YKL-40 (+14.6 ± 5.5 ng/mL) were elevated immediately-post exercise only in comparison to the immediately-pre time point (p < 0.01). There were no significant changes in corrected uNGAL from day-before, to day-of [+5.39 ± 21.47 (ng/ml)/(ml/min), p = 0.15] or day after exercise [+2.82 ± 15.46 (ng/ml)/(ml/min), p = 0.31]. Spot urine samples showed increased incidence of proteinuria (84%, p < 0.01) and hematuria (22%, p = 0.02) immediately following the bout of exercise. Significant increases from immediately-pre (224 ± 129 U/L; 69 ± 27 ng/mL) to all post exercise time points up to 48 hr (1380 ± 2354 U/L, p = 0.01; 283 ± 400 ng/mL, p < 0.01) were observed for CK and MYO, respectively. Nine of 38 subjects (24%) demonstrated CK > 5x resting at ≥1 post workout time point. CONCLUSION: Proteinuria, hematuria, IL-18 and YKL-40 increase immediately following HVFRE and return to baseline within 24 hr. CK and MYO remained elevated for at least 48 hr following the bout of exercise demonstrating some risk for AKI following this specific HVFRE.

Introduction: Agricultural workers laboring in thermally stressful environments are at increased risk for kidney injury and chronic kidney disease of unknown origin (CKDu), and their environmental and occupational exposures have been considered to be important risk factors. This study examined the effects of repeated kidney stress from the simultaneous strain of work and other factors experienced by workers in Guatemala during a typical workweek. Methods: We collected data from 107 sugarcane workers across 7 consecutive work shifts. Data included information on daily occupational, meteorological, environmental, and lifestyle factors. We used multivariable linear mixed models to evaluate associations of these factors with percent change in creatinine. Results: We observed that increasing wet bulb globe temperature (beta = 2.5%, 95% confidence interval [CI] = 0.3%, 4.7%) and increasing diastolic blood pressure (beta = 6.2%, 95% CI = 0.9%, 11.6%) were associated with increases in creatinine across the shift, whereas consumption of water from chlorinated dormitory tanks as compared to artesian well water (beta = -17.5%, 95% CI = -29.6%, -5.4%) and increasing number of rest breaks (beta = -5.8%, 95% CI = -9.0%, -2.6%) were found to be protective against increases in creatinine. Workers reporting drinking tank water had lower concentrations of urine creatinine-corrected arsenic, lead, uranium, and glyphosate compared to workers reporting the use of well water or municipal water. Conclusion: These results reinforce the need to focus on preventive actions that reduce kidney injury among this worker population, including strategies to reduce heat stress, managing blood pressure, and examining water sources of workers for nephrotoxic contaminants.

Background: Maintaining euhydration is beneficial for health, safety, and physical performance [1]; however, it may also improve subjective feelings [2, 3]. Objective: The aim of this study was to evaluate the relationship between changes in self-reported thirst and alertness in people undergoing changes in drinking water volume. Methods: Subjects (mean ± SD) (n = 115, 59 males, 32 ± 10 years; 24.6 ± 4.4 kg·m−2) visited the lab 3 times over 10 days: V1, a baseline visit prior to participants were drinking ad libitum; V2, following 3 days of fluid restriction (1 L·d−1, 250 mL was consumed in the morning prior to the visit); and V3, the morning following a prescribed increase in water intake. The increase in water intake at V3 varied by group assignment: control group (CON) maintained 250 mL, while LOW and HIGH groups (n = 45 each) consumed 496 ± 82 mL and 878 ± 125 mL, respectively. At each visit, subjects indicated on an open-ended visual analog scale (VAS) how thirsty and alert they felt and were measured in millimeters (mm). Four, two-way ANOVAs (group × visit) for change in thirst and alertness between V1–V2 and V2–V3 were completed. A repeated-measures correlation (rrm) procedure was completed for change in alertness and thirst from V1 to V2 and V2 to V3 [4]. The study was approved by the University of Wyoming’s Institutional Review Board (protocol #20160524EJ01208), and all subjects provided written informed consent. Results: Groups were similar at baseline (V1) for fluid intake, thirst, and alertness (all p ≥ 0.17). Fluid restriction (V2) resulted in a main effect of visit for thirst and alertness (both p < 0.01), with no main effect of group. Thirst increased (35 ± 35 mm) and alertness decreased (−19 ± 31 mm) from V1 to V2. The prescribed increase in water intake (V3) revealed a significant interaction of visit and group for thirst and alertness (both p < 0.01) (Table 1). Independent-samples t tests with a Bonferroni correction revealed that HIGH reduced thirst (−38 ± 37 mm) and increased alertness (18 ± 25 mm), while no change was observed for LOW (thirst, −7 ± 37 mm; alertness −1 ± 24 mm) and CON (thirst, −6 ± 23 mm; alertness 0 ± 23 mm; all p < 0.01) (Fig. 1). There was no difference between LOW and CON (both p > 0.92). Repeated-measures correlation analysis revealed an inverse relationship between change in alertness and thirst (rrm [114] = −0.53, 95% CI [−0.65, −0.38], p < 0.01). Conclusion: A reduction in water intake resulted in an increase in thirst and decrease in alertness. Following 3 days of fluid restriction, 750–1,000 mL of water intake was needed to decrease thirst and increase alertness. Overall, an inverse relationship was observed between self-reported thirst and alertness.

Rates of anemia among agricultural workers, who are also at risk for kidney injury and chronic kidney disease of unknown cause (CKDu), are unknown. We evaluated body composition through the sum of three skinfolds among 203 male sugarcane cutters and assessed the relationship of variables related to nutrition, anemia (hemoglobin < 13 g/dL), and elevated hemoglobin A1c (HbA1c ≥ 5.7%) with estimated glomerular filtration rate (eGFR) using linear regression. Eleven percent of workers were at the level of essential body fat (2–5%). Anemia was present among 13% of workers, 70% of which were normochromic normocytic, a type of anemia suggesting potential underlying chronic disease. Anemia was more common among those with lower BMI and fat free mass. The prevalence of elevated HbA1c was 21%. A moderate negative correlation was found between hemoglobin and HbA1c (Pearson’s r = −0.32, p < 0.01) which suggests that HbA1c values should be interpreted with caution in populations that have high rates of anemia. Twelve percent of workers had reduced kidney function with an eGFR < 90 mL/min/1.73 m2. On average, the eGFR was 18 mL/min per 1.73 m2 lower [(95% CI:−24, −12), p < 0.01)] for those with anemia than those without, and 8 mL/min per 1.73 m2 lower among those with elevated HbA1c [(95% CI: −13, −2), p < 0.01]. Results will inform future studies examining the role of anemia in the evaluation of CKDu and interventions to improve nutrition for workers in low-resource settings.

Intense physical demands and hot environments—reflected by elevated cardiovascular strain—may contribute to the high rates of kidney disease in sugarcane cutters. PURPOSE: To evaluate the cardiovascular strain of cutting sugarcane. METHODS: During the harvest, 45 male Guatemalan sugarcane cutters (mean ± SD, 28 ± 6 y, 55 ± 5 kg, 158 ± 5 cm, systolic blood pressure (BP) = 111 ± 12 mm Hg, diastolic BP = 64 ± 9 mm Hg) wore a heart rate (HR) monitor for a workday. Serum creatinine (SCr) and urine neutrophil gelatinase-associated lipocalin (NGAL), indicators of kidney function, were measured pre- and post-work. Average, peak, and minimum HR were calculated before and after lunch. Paired samples t-tests were completed to evaluate if the HR response to work and rest were different before and after lunch. Average and peak age-predicted HR reserve (HRR) were calculated and categorized (very light <30%, light 30-39%, moderate 40-59% or vigorous 60-89%). One-way ANOVAs were used to compare change, excluding categories with n < 5, in SCr and NGAL from pre- to post-work between HRR categories. RESULTS: Work duration (including breaks) = 8.8 ± 1.3 h. Lunch lasted 0.72 ± 0.25 h. Average HR during work = 111 ± 8 bpm. Peak HR = 147 ± 13 bpm. Average HR was higher after lunch (114 ± 11 bpm) compared to before (108 ± 7 bpm; t[43] = 5.14, p < 0.01). Peak HR was not different before (141 ± 10 bpm) vs after lunch (146 ± 16 bpm; t[43] = 0.48, p = 0.63). Minimum HR was higher after lunch (79 ± 12 bpm) compared to before (69 ± 9 bpm; t[43] = 5.8, p < 0.01). Peak HRR = 68 ± 9%. Average HRR = 40 ± 6%. SCr increased by 0.09 mg/dL (t[44] = 2.31, p = 0.03) and NGAL decreased by 10.3 ng/mL (t[38] = -2.97, p = 0.01) pre- to post-work. Changes in SCr and NGAL from pre- to post-work did not differ among groups based on peak (SCr: F[1] = 0.77, p = 0.39; NGAL: F[1] = 1.24, p = 0.27) or average (SCr: F[1] = 0.91, p = 0.35; NGAL: F[1] = 0.98, p = 0.76) HRR. CONCLUSIONS: Although changes in SCr and NGAL were not different based on intensity of work, average and minimum HR were higher after lunch indicating increased cardiovascular strain in the afternoon. FUNDING: This study was supported by Centers for Disease Control and Prevention (CDC) (U19 OH011227) and National Institutes of Health (NIH) (R21 ES028826), and in part by Pantaleon, Guatemala City.

The purposeful distribution of speed, power, or energy is termed as the pacing or pacing strategy and is recognized as a key determinant in optimal run performance. There is no agreement on the best pacing strategy for all runners and race types. Thus, the challenge posed to runners and practitioners is pacing strategy selection and in-race adherence. This review briefly discusses pacing strategy types and selection considerations. More importantly, we overview factors influencing pacing and translate key findings from research into useable evidence-based recommendations for pacing strategy preparation and adherence during competition.

Background: Iodine deficiency is not seen as a public health concern in the US. However certain subpopulations may be vulnerable due to inadequate dietary sources. The purpose of the present study was to determine the dietary habits that influence iodine status in young adult men and women, and to evaluate the relationship between iodine status and thyroid function. Methods: 111 participants (31.6 ± 0.8 years, 173.2 ± 1.0 cm, 74.9 ± 1.7 kg) provided 24 h urine samples and completed an iodine-specific Food Frequency Questionnaire (FFQ) for assessment of urinary iodine content (UIC) as a marker of iodine status and habitual iodine intake, respectively. Serum Thyroid Stimulating Hormone (TSH) concentration was evaluated as a marker of thyroid function. Spearman correlational and regression analysis were performed to analyze the associations between iodine intake and iodine status, and iodine status and thyroid function. Results: 50.4% of participants had a 24 h UIC < 100 µg/L). Dairy (r = 0.391, p < 0.000) and egg intake (r = 0.192, p = 0.044) were the best predictors of UIC, accounting for 19.7% of the variance (p ≤ 0.0001). There was a significant correlation between UIC and serum TSH (r = 0.194, p < 0.05) but TSH did not vary by iodine status category (F = 1.087, p = 0.372). Discussion: Total dairy and egg intake were the primary predictors of estimated iodine intake, as well as UIC. Iodized salt use was not a significant predictor, raising questions about the reliability of iodized salt recall. These data will be useful in directing public health and clinical assessment efforts in the US and other countries.

PURPOSE: The extent to which groundskeepers experience heat strain, dehydration, and accompanying declines in kidney function during work in hot-humid conditions is unknown. METHODS: Hydration, cardiovascular, and internal body temperature measures were assessed in 20 groundskeepers (18 men; mean±SD age=38±8 y, body mass index=32±8 kg/m2) during work on 2 summer days. Before (PRE) and after (POST) the work shift, resting blood pressure (BP) and heart rate (HR) were measured and urine and blood samples were collected. At POST, fluid intake was recalled for the previous 24 h. Gastrointestinal temperature (TGI) was recorded every 5 min via ingestible telemetric sensor. RESULTS: Average highest daily wet bulb globe temperature=39.1±3.5 °C. In 45% of subjects, PRE BP>130/80 mm Hg on Day 1 (D1) and Day 2 (D2). Highest HR and TGI achieved across both days were 143±15 bpm and 37.7±0.3 °C, respectively. On D1 and D2, urine specific gravity (USG; 1.021±01) and urine color (UCOL; 6±1) did not change PRE to POST (all P>0.28), but subjects began the workday “underhydrated” (concentrated urine but normal serum osmolality (Sosm)]—62% had USG≥1.020 and 95% had UCOL≥4 despite Sosm=292±5. Fluid intake=2.3±1.6 L during work and consisted of 70% water and 25% sugar sweetened beverages. No subject lost ≥2% of body mass on D1 or D2. For 6 subjects, estimated glomerular filtration rate at PRE was ≤60 mL/min/1.73m2 averaged across D1 and D2. Although serum creatinine did not change statistically from PRE to POST across days (all P>0.18), 5 subjects had increases ≥0.3 mg/dL, signifying an acute kidney injury (AKI). CONCLUSIONS: While hyperthermia was not prevalent, subjects began and ended the workday underhydrated. Hypertension, obesity, and low water intake may have contributed to the overall low kidney function and AKIs observed. Using urine color as a self-assessment tool could be a beneficial intervention improve hydration status and kidney function.Funded by NIOSH

Climate change is increasing the number of hot days to which outdoor workers are exposed, thereby increasing their risk of heat illness. Currently, continuous monitoring of core temperature (Tc) is expensive, invasive, and impractical. The BioModule is a non-invasive physiological monitor that uses heart rate to provide an estimation of Tc, but its accuracy is unknown. PURPOSE: To test the association between measured gastrointestinal temperature (TGI) and estimated core temperature (Tc-est) from the BioModule device during outdoor work in a hot environment. METHODS: Twenty groundskeepers (18 men; mean±SD age = 38±8 y, body mass index = 31.5±7.5 kg/m2) swallowed an ingestible temperature sensor and strapped on a BioModule before work. TGI was collected every 15 minutes during the workday; Tc-est was determined by a 1-min average from the same time of day. Data collection occurred in Alabama during July and August (31.4±3.1 °C WBGT). Relationship between TGI and Tc-est was quantified using the repeated measures correlation coefficient (rrm). Agreement (bias±1.96 SD) between TGI and Tc-est was evaluated using the Bland-Altman method for repeated observations. RESULTS: There was a moderate, positive relationship between TGI and Tc-est (rrm = 0.56, p < 0.001). Agreement analysis indicated that Tc-est overestimated TGI (0.28±0.58 °C). The error between Tc-est and TGI was larger at lower temperatures, as indicated by a strong negative trend (Pearson’s r = −0.73). CONCLUSION: The BioModule provides an estimation of Tc that may be helpful as a guide during outdoor work in hot environments but should not be used for safety considerations or measurement of Tc . Funded by the Deep South Center for Occupational Safety and Health, a National Institute for Occupational Safety and Health Education and Research Center.

Objectives: To evaluate impact of electrolyte supplementation on hydration status and health outcomes in Guatemalan agricultural workers performing heavy work under hot climatic conditions. Methods: A 3-week pragmatic trial was conducted with a group of 50 workers during the 2017 to 2018 sugarcane harvest. Workers received an electrolyte hydration intervention during 2 of the 3 weeks. Blood and urine samples were collected each week. Results: Increased electrolyte intake resulted in less muscle injury. Kidney function was maintained across the intervention period. Workers were adequately hydrated and average electrolyte levels remained in normal ranges. Mild indications of hyponatremia occurred at higher levels of fluid intake. Conclusions: This trial demonstrates the feasibility of maintaining workers’ electrolyte levels under extremely hot and humid conditions while mitigating muscle injury. Electrolyte supplementation should be added to standard workplace water, rest, and shade interventions to protect workers.

Agricultural workers worldwide exposed to heat stress could be at the risk of kidney injury, which could lead to chronic kidney disease of an unknown origin (CKDu). Hydration has been promoted as a key measure to reduce kidney injury. In the presence of a hydration intervention, the incidence of acute kidney injury (AKI) was calculated in a sugarcane worker population in Guatemala and several risk factors were evaluated. We measured kidney function at the beginning and end of the work shift at three time points in 517 sugarcane workers. We defined AKI as an increase in serum creatinine of 26.5 µmol/L or 50% or more from the pre-shift value. Associations between AKI and risk factors were examined, including interactions with hydration status. The prevalence of dehydration post-shift (> 1.020 specific gravity) was 11% in February, 9% in March, and 6% in April. Cumulative incidence of AKI was 53% in February, 54% in March, and 51% in April. AKI was associated with increasing post-shift specific gravity, a dehydration marker, (OR 1.24, 95% CI 1.02–1.52) and with lower electrolyte solution intake (OR 0.94, 95% CI 0.89–0.99). Dehydration and insufficient electrolyte consumption are risk factors for AKI. However even well-hydrated sugarcane workers routinely experience AKI. While hydration is important and protective, there is a need to understand other contributors to risk of AKI and identify prevention strategies with these workers.