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Fatigue resistance is vital for success in elite road cycling, as repeated, intense efforts challenge the athletes' ability to sustain peak performance throughout prolonged races. The present study combined recurrent performance testing and physiological measures during 6 h simulated racing with laboratory testing to investigate factors influencing fatigue resistance. Twelve male national elite cyclists (25 ± 3 years; 76 ± 6 kg and VO2max of 5.2 ± 0.5 L/min) completed incremental power and maximal fat oxidation tests. Subsequently, they underwent field testing with physiological measures and fatigue responses evaluated through peak sprint power and 5 km time trial (TT) testing after 0, 2, 4, and 6 h of exercise. Peak power declined from 1362 ± 176 W in first sprint to 1271 ± 152 W after 2 h (p < 0.01) and then stabilized. In contrast, TT mean power gradually declined from 412 ± 38 W in the first TT to 384 ± 41 W in the final trial, with individual losses ranging from 2% to 14% and moderately correlated (r2 = 0.45) to accumulated exercise time above lactate threshold. High carbohydrate intake (~90 g/h) maintained blood glucose levels, but post-TT [lactate] decreased from 15.1 ± 2 mM to 7.1 ± 2.3 mM, while fat oxidation increased from 0.7 ± 0.3 g/min at 0 h to 1.1 ± 0.1 g/min after 6 h. The study identifies fatigue patterns in national elite cyclists. Peak sprint power stabilized after an initial impairment from 0 to 2 h, while TT power gradually declined over the 6 h simulated race, with increased differentiation in fatigue responses among athletes.
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Rendimiento Atlético , Ciclismo , Fatiga , Ácido Láctico , Consumo de Oxígeno , Humanos , Ciclismo/fisiología , Masculino , Adulto , Rendimiento Atlético/fisiología , Ácido Láctico/sangre , Adulto Joven , Consumo de Oxígeno/fisiología , Prueba de Esfuerzo , Glucemia/análisis , Resistencia Física/fisiología , Fatiga Muscular/fisiologíaRESUMEN
BACKGROUND: Isometric strength testing is widely applied in sports science. However, we hypothesized that traditional testing procedures with a dual focus on both peak force (PF) and rate of force development (RFD) may compromise the true assessment of early RFD measures and lower the associative value towards vertical jump performance. METHODS: Therefore, PF and RFD were assessed for 47 active participants (24 females, 23 males) with a traditional isometric midthigh pull (IMTP) protocol ("push as hard and fast as possible" over 4 s) and an RFD-specific protocol ("push as fast as possible" over 2 s). IMTP measures were compared to squat (SJ), countermovement (CMJ) and drop-jump (DJ) performance. RESULTS: The RFD-specific protocol provided higher RFD (P<0.05) for time domains up to 100 ms but lower PF (P<0.001). Independent of protocol, SJ and CMJ performance displayed significant, but low-to-moderate correlations with all RFD measures (r=0.30-0.52) as well as PF (r=0.44), whereas DJ did not show any correlation. CONCLUSIONS: In conclusion, an RFD-specific protocol appears relevant for the assessment of RFD in the time domain up to 100 ms. However, the observed associations between RFD/PF measures and vertical jump performance remained low-to-moderate independent of the IMTP test protocol.
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ABSTRACT: Performance in intermittent sports relies on the interplay between multiple physiological systems determining the capacity to perform short explosive efforts as well as repeated intense actions with limited recovery over the course of an entire game. Testing should reflect these demands to allow for sport- and position-specific capacity analyses that eventually may translate into optimized training and improved performance. This may include individual load management and optimized training prescription, intensity targeting for specific positions or individual athletes, as well as benchmarking for monitoring of training progression and enhanced engagement of athletes. This review provides an overview of available tests in different exercise domains identified as relevant (from assessment of single explosive actions to intermittent endurance capacity), forming the basis for recommendations on how to compose a comprehensive yet feasible test battery that may be integrated into the seasonal competition and training plan. The test procedures should cover the performance spectrum of relevance for the individual athlete-also in team sports to account for positional differences. We emphasize the benefits of sport-specific tests, highlight parameters of importance for test standardization, and discuss how the applied test battery may be supplemented with secondary tests directed toward specific energy systems to allow for more in-depth analyses when required (e.g., in terms of an underperforming athlete). The synergy between testing and tracking of match performance (utilizing time-motion or global positioning systems) is highlighted, and although tracking cannot substitute for testing, combining the tools may provide a comprehensive overview of the physiological demands and performance during competition contextualized to the athletes' maximal exercise capacity.
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Rendimiento Atlético , Prueba de Esfuerzo , Acondicionamiento Físico Humano , Humanos , Rendimiento Atlético/fisiología , Acondicionamiento Físico Humano/fisiología , Acondicionamiento Físico Humano/métodos , Prueba de Esfuerzo/métodos , Prueba de Esfuerzo/normas , Resistencia Física/fisiología , AdultoRESUMEN
This study investigated the impact of a multiday heatwave on nocturnal physiology, behavior, and sleep under controlled conditions with comprehensive monitoring of environmental factors and participant activities. Seven young healthy males were confined for ten days in controlled conditions that ranged between hot-to-warm (day:35.4°C, night:26.3°C) during nights 4-6 and temperate (day:25.4°C, night:22.3°C) before (nights 1-3) and after (nights 7-10) the heatwave. Measurements included core and skin temperatures, heart rate, sympathovagal balance, vasomotion indicators, urine samples, blanket coverage, subjective sleep assessments, and partial polysomnography. The average nocturnal core temperature was 0.2°C higher during and after the heatwave compared to the pre-heatwave period, with this difference being more pronounced (+0.3°C) in the first two hours of sleep (p<0.001). For every 0.1°C rise in overnight core temperature, the total sleep time decreased by 14 minutes (pseudo-R2=0.26, p=0.01). The elevated core temperatures occurred despite the participants exhibiting evident thermoregulatory behavior, as they covered 30% less body surface during the heatwave compared to pre- and post-heatwave periods (p<0.001). During the heatwave, mean skin temperature at bedtime was 1.3°C higher than pre-heatwave and 0.8°C higher than post-heatwave periods (p<0.001). No differences in other responses, including heart rate and vasomotion indicators, were observed. The paper details a 20-minute sleepwalking episode that was coupled with marked changes in sleepwalker's thermophysiological responses. In conclusion, the simulated heatwave resulted in higher overnight core temperature which was associated with reduced total sleep time. Behavioral thermoregulation during sleep may serve as a defense against these effects, though more research is needed.
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Exposure to ultraviolet radiation (UVR) leads to skin DNA damage, specifically in the form of cyclobutane pyrimidine dimers, with thymidine dimers being the most common. Quantifying these dimers can indicate the extent of DNA damage resulting from UVR exposure. Here, a new liquid chromatography-mass spectrometry (LC-MS) method was used to quantify thymidine dimers in the urine after a temporary increase in real-life UVR exposure. Healthy Danish volunteers (n = 27) experienced increased UVR exposure during a winter vacation. Individual exposure, assessed via personally worn electronic UVR dosimeters, revealed a mean exposure level of 32.9 standard erythema doses (SEDs) during the last week of vacation. Morning urine thymidine dimer concentrations were markedly elevated both 1 and 2 days post-vacation, and individual thymidine dimer levels correlated with UVR exposure during the last week of the vacation. The strongest correlation with erythema-weighted personal UVR exposure (Power model, r2 = 0.64, p < 0.001) was observed when both morning urine samples were combined to measure 48-h thymidine dimer excretion, whereas 24-h excretion based on a single sample provided a weaker correlation (Power model, r2 = 0.55, p < 0.001). Sex, age, and skin phototype had no significant effect on these correlations. For the first time, urinary thymidine dimer excretion was quantified by LC-MS to evaluate the effect of a temporary increase in personal UVR exposure in a real-life setting. The high sensitivity to elevated UVR exposure and correlation between urinary excretion and measured SED suggest that this approach may be used to quantify DNA damage and repair and to evaluate photoprevention strategies.
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Dímeros de Pirimidina , Rayos Ultravioleta , Humanos , Dímeros de Pirimidina/análisis , Masculino , Adulto , Femenino , Daño del ADN , Persona de Mediana Edad , Espectrometría de Masas , Cromatografía Liquida , Adulto Joven , Exposición a la Radiación/análisis , Voluntarios SanosRESUMEN
INTRODUCTION: This study examined the impact of different upper-torso sportswear technologies on the performance and physiological heat strain of well-trained and national-level athletes during prolonged running in moderately hot conditions. METHODS: A randomized crossover design was employed in which 20 well-trained (n = 16) and national-level (n = 4) athletes completed four experimental trials in moderately hot conditions (35°C, 30% relative humidity). In each trial, participants ran at 70% of their peak oxygen uptake (70% VÌO2peak ) for 60 min, while wearing a different upper-body garment: cotton t-shirt, t-shirt with sweat-wicking fabric, compression t-shirt, and t-shirt with aluminum dots lining the inside of the upper back of the garment. Running speed was adjusted to elicit the predetermined oxygen consumption associated with 70% VÌO2peak . Physiological (core and skin temperatures, total body water loss, and urine specific gravity) and perceptual (thermal comfort and sensation, ratings of perceived exertion, and garment cooling functionality) parameters along with running speed at 70% VÌO2peak were continuously recorded. RESULTS: No significant differences were observed between the four garments for running speed at 70% VÌO2peak , physiological heat strain, and perceptual responses (all p > 0.05). The tested athletes reported larger areas of perceived suboptimal cooling functionality in the cotton t-shirt and the t-shirt with aluminum dots relative to the sweat-wicking and compression t-shirts (d: 0.43-0.52). CONCLUSION: There were not differences among the tested garments regarding running speed at 70% VÌO2peak , physiological heat strain, and perceptual responses in well-trained and national-level endurance athletes exercising in moderate heat.
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Regulación de la Temperatura Corporal , Carrera , Humanos , Aluminio , Temperatura Corporal , Regulación de la Temperatura Corporal/fisiología , Frecuencia Cardíaca/fisiología , Calor , Carrera/fisiología , Temperatura Cutánea , Sudoración , Estudios CruzadosRESUMEN
INTRODUCTION: Male elite cyclists (average VO2 -max: 71 mL/min/kg, n = 18) completed 7 weeks of high-intensity interval training (HIT) (3×/week; 4-min and 30-s intervals) during the competitive part of the season. The influence of a maintained or lowered total training volume combined with HIT was evaluated in a two-group design. Weekly moderate-intensity training was lowered by ~33% (~5 h) (LOW, n = 8) or maintained at normal volume (NOR, n = 10). Endurance performance and fatigue resistance were evaluated via 400 kcal time-trials (~20 min) commenced either with or without prior completion of a 120-min preload (including repeated 20-s sprints to simulate physiologic demands during road races). RESULTS: Time-trial performance without preload was improved after the intervention (p = 0.006) with a 3% increase in LOW (p = 0.04) and a 2% increase in NOR (p = 0.07). Preloaded time-trial was not significantly improved (p = 0.19). In the preload, average power during repeated sprinting increased by 6% in LOW (p < 0.01) and fatigue resistance in sprinting (start vs end of preload) was improved (p < 0.05) in both groups. Blood lactate during the preload was lowered (p < 0.001) solely in NOR. Measures of oxidative enzyme activity remained unchanged, whereas the glycolytic enzyme PFK increased by 22% for LOW (p = 0.02). CONCLUSION: The present study demonstrates that elite cyclists can benefit from intensified training during the competitive season both with maintained and lowered training volume at moderate intensity. In addition to benchmarking the effects of such training in ecological elite settings, the results also indicate how some performance and physiological parameters may interact with training volume.
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Ciclismo , Resistencia Física , Humanos , Masculino , Resistencia Física/fisiología , Ciclismo/fisiología , Consumo de Oxígeno/fisiologíaRESUMEN
The ClimApp smartphone application was developed to merge meteorological forecast data with personal information for individualized and improved thermal warning during heat and cold stress and for indoor comfort in buildings. For cold environments, ClimApp predicts the personal thermal stress and strain by the use of the Insulation REQuired model that combines weather and personal physiological data with additional consideration of the Wind Chill index based on the local weather forecast. In this study, we validated the individualized ClimApp index relative to measurements and compared it with the Universal Temperature Climate Index (UTCI). To this aim, 55 participants (27 females) were exposed to at least 1 h in an outdoor environment of 10 °C or below (average 1.4 °C air temperature, 74.9% relative humidity, and 4.7 m/s air velocity) inputting their activity level and clothing insulation as instructed by ClimApp. The UTCI and ClimApp indices were calculated and compared to the participants' perceived thermal sensation. The ClimApp index root mean square deviation (RMSD) was below the standard deviation of the perceived thermal sensation which indicates a valid prediction and the UTCI RMSD was higher than the standard deviation which indicates an invalid prediction. The correlation of ClimApp and UTCI to the perceived thermal sensation was statistically significant for both models.
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Clima , Teléfono Inteligente , Femenino , Humanos , Temperatura , Tiempo (Meteorología) , Viento , Sensación Térmica/fisiologíaRESUMEN
Despite the frequent occurrence of congested game fixtures in elite ice hockey, the postgame recovery pattern has not previously been investigated. The purpose of the present study was therefore to evaluate the acute decrements and subsequent recovery of skeletal muscle glycogen levels, muscle function and repeated-sprint ability following ice hockey game-play. Sixteen male players from the Danish U20 national team completed a training game with muscle biopsies obtained before, postgame and following ~38 h of recovery (day 2). On-ice repeated-sprint ability and muscle function (maximal voluntary isometric [MVIC] and electrically induced low- (20 Hz) and high-frequency (50 Hz) knee-extensor contractions) were assessed at the same time points, as well as ~20 h into recovery (day 1). Muscle glycogen decreased 31% (p < 0.001) postgame and had returned to pregame levels on day 2. MVIC dropped 11%, whereas 50 and 20 Hz torque dropped 21% and 29% postgame, respectively, inducing a 10% reduction in the 20/50 Hz torque ratio indicative of low-frequency force depression (all p < 0.001). While MVIC torque returned to baseline on day 1, 20 and 50 Hz torque remained depressed by 9%-11% (p = 0.010-0.040), hence restoring the pre-exercise 20/50 Hz ratio. Repeated-sprint ability was only marginally reduced by 1% postgame (p = 0.041) and fully recovered on day 1. In conclusion, an elite youth ice hockey game induces substantial reductions in muscle glycogen content and muscle function, but only minor reductions in repeated-sprint ability and with complete recovery of all parameters within 1-2 days postgame.
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Hockey , Adolescente , Humanos , Masculino , Hockey/fisiología , Resistencia Física/fisiología , Músculo EsqueléticoRESUMEN
BACKGROUND: According to the principle of specific adaptations to imposed demands, training induces specific adaptations that predominantly transfer towards performance tasks of similar physiological and/or biomechanical characteristics. Functional performance improvements secondary to resistance and plyometric training have been hypothesized to be force-vector specific; however, the literature pertaining to this matter appears somewhat equivocal. OBJECTIVE: The objective of the present systematic review with meta-analysis was to synthesize the available body of literature regarding the performance implications of vertically and horizontally oriented resistance- and plyometric training. DATA SOURCES: The review drew from the following sources: PubMed, Web of Science, Scopus, Physiotherapy Evidence Database (PEDro), Cochrane Library, Cumulative Index of Nursing and Allied Health Literature (CINAHL), SPORTDiscus and Google Scholar. STUDY ELIGIBILITY CRITERIA: To qualify for inclusion, studies had to compare the efficacy of vertically and horizontally oriented resistance and/or plyometric training, with one or multiple outcome measures related to vertical/horizontal jumping, sprinting and/or change of direction speed (CODS). STUDY APPRAISAL AND SYNTHESIS: For each outcome measure, an inverse-variance random effects model was applied, with between-treatment effects quantified by the standardized mean difference (SMD) and associated 95% confidence- and prediction intervals. RESULTS: Between-treatment effects were of trivial magnitude for vertical jumping (SMD = - 0.04, P = 0.69) and long-distance (≥ 20 m) sprinting (0.03, P = 0.83), whereas small to moderate effects in favor of horizontal training were observed for horizontal jumping (0.25, P = 0.07), short-distance (≤ 10 m) sprinting (0.72, P = 0.01) and CODS (0.31, P = 0.06), although only the short-distance sprint outcome reached statistical significance. CONCLUSIONS: In conclusion, our meta-analysis reveals a potential superiority of horizontally oriented training for horizontal jumping, short-distance sprinting and CODS, whereas vertically oriented training is equally efficacious for vertical jumping and long-distance sprinting. From an applied perspective, the present analysis provides an advanced basis for weighting of vertical and horizontal force-vector exercises as an integrated component for optimizing sport-specific performances. The present systematic review with meta-analysis was not a priori registered.
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Rendimiento Atlético , Ejercicio Pliométrico , Entrenamiento de Fuerza , Humanos , Rendimiento Atlético/fisiología , Terapia por Ejercicio , Ejercicio Físico , Prueba de EsfuerzoRESUMEN
The present observational study was conducted to uncover potential differences in the risk of experiencing high occupational heat strain during agriculture work between migrants and their native coworkers, as well as to elucidate the factors that may contribute to such differences. The study took place over the period from 2016 through 2019 and involved monitoring 124 experienced and acclimatized individuals from high-income (HICs), upper-middle-income (UMICs), as well as lower-middle- and low-income (LMICs) countries. Baseline self-reported data for age, body stature, and body mass were collected at the start of the study. Second-by-second video recordings throughout the work shifts were captured using a video camera and were used to estimate workers' clothing insulation, covered body surface area, and body posture, as well as to calculate their walking speed, the amount of time they spent on different activities (and their intensity) and unplanned breaks throughout their work shifts. All information derived from the video data was used to calculate the physiological heat strain experienced by the workers. The core temperature of migrant workers from LMICs (37.81 ± 0.38 °C) and UMICs (37.71 ± 0.35 °C) was estimated to be significantly higher compared to the core temperature of native workers from HICs (37.60 ± 0.29 °C) (p < 0.001). Moreover, migrant workers from LMICs faced a 52% and 80% higher risk for experiencing core body temperature above the safety threshold of 38 °C compared to migrant workers from UMICs and native workers from HICs, respectively. Our findings show that migrant workers originating from LMICs experience higher levels of occupational heat strain, as compared to migrant workers from UMICs and native workers from HICs, because they take fewer unplanned breaks during work, they work at a higher intensity, they wear more clothing, and they have a smaller body size.
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Migrantes , Humanos , Calor , Renta , Pobreza , AgriculturaRESUMEN
Performance in short-duration sports is highly dependent on muscle glycogen, but the total degradation is only moderate and considering the water-binding property of glycogen, unnecessary storing of glycogen may cause an unfavorable increase in body mass. To investigate this, we determined the effect of manipulating dietary carbohydrates (CHO) on muscle glycogen content, body mass, and short-term exercise performance. In a randomized and counterbalanced cross-over design, twenty-two men completed two maximal cycle tests of either 1-min (n = 10) or 15-min (n = 12) duration with different pre-exercise muscle glycogen levels. Glycogen manipulation was initiated three days prior to the tests by exercise-induced glycogen depletion followed by ingestion of a moderate (M-CHO) or high (H-CHO) CHO-diet. Subjects were weighed before each test, and muscle glycogen content was determined in biopsies from m. vastus lateralis before and after each test. Pre-exercise muscle glycogen content was lower following M-CHO than H-CHO (367 mmol · kg-1 DW vs. 525 mmol · kg-1 DW, p < 0.00001), accompanied by a 0.7 kg lower body mass (p < 0.00001). No differences were observed in performance between diets in neither the 1-min (p = 0.33) nor the 15-min (p = 0.99) test. In conclusion, pre-exercise muscle glycogen content and body mass were lower after ingesting moderate compared with high amounts of CHO, while short-term exercise performance was unaffected. This demonstrates that adjusting pre-exercise glycogen levels to the requirements of competition may provide an attractive weight management strategy in weight-bearing sports, particularly in athletes with high resting glycogen levels.
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Glucógeno , Músculo Esquelético , Humanos , Masculino , Dieta , Carbohidratos de la Dieta , Ejercicio Físico/fisiología , Glucógeno/metabolismo , Músculo Esquelético/fisiología , Estudios CruzadosRESUMEN
Ballistic actions are imperative in sports where performance depends on power production across a relevant range of contraction- and movement velocities. Force-velocity-power (FvPâ¾) profiling provides information regarding neuromuscular capabilities and vertical performances, but knowledge regarding its associative value towards horizontal movements is scarce. Therefore, we conducted FvPâ¾ profiling and analysed associations with uni- and multidirectional ballistic performance tasks in 27 international- to national-level athletes (18.9 ± 2.6 years, 182.9 ± 7.1 cm and 79.2 ± 11.9 kg). Low to moderate correlations were observed between theoretical maximal power (P-max) and horizontal acceleration (R = -0.43), speed (R = -0.64), sprint (R = -0.60) and agility (R = -0.59) performances. Force-velocity imbalance (FvIMB) significantly (P ≤ 0.05) strengthened the correlations towards sprinting ability (from -0.60 to -0.74) and agility (from -0.59 to -0.68), however, both correlations remaining weaker than for jumping performances (R = 0.78-0.86). In conclusion, FvPâ¾ profiling provides information of importance for horizontal and vertical performances with a significant positive effect of P-max, but negative effect of FvIMB. Assessment of lower-extremity neuromuscular capabilities through FvPâ¾ profiling and associated development of training programmes targeting compensation of either force- or velocity deficit may benefit the ability to utilise a given power potential.
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Rendimiento Atlético , Carrera , Humanos , Pierna , Fenómenos Biomecánicos , Fuerza Muscular , Extremidad InferiorRESUMEN
PURPOSE: This study evaluated how extended match time (90 + 30 min) affected physiological responses and fatigue in male soccer players. METHODS: Twenty competitive players (mean ± SD: age, 20 ± 1 yr; maximal oxygen uptake, 59 ± 4 mL·min -1 ·kg -1 ) completed an experimental match with their activity pattern and heart rate assessed throughout the game, whereas countermovement jump performance and repeated sprint ability were tested and quadriceps muscle biopsies and venous blood samples were taken at baseline and after 90 and 120 min of match play. RESULTS: Less high-intensity running (12%) was performed in extra time in association with fewer intense accelerations and decelerations per minute compared with normal time. Peak sprint speed was 11% lower in extra time compared with normal time, and fatigue also manifested in impaired postmatch repeated sprint ability and countermovement jump performance (all P < 0.05). Muscle glycogen declined from 373 ± 59 mmol·kg -1 dry weight (dw) at baseline to 266 ± 64 mmol·kg -1 dw after 90 min, with a further decline to 186 ± 56 mmol·kg -1 dw after extra time ( P < 0.05) and with single-fiber analyses revealing depleted or very low glycogen levels in ~75% of both slow and fast twitch fibers. Blood glucose did not change during the first 90-min but declined ( P < 0.05) to 81 ± 8 mg·dL -1 after extra time. Plasma glycerol and ammonia peaked at 236 ± 33 mg·dL -1 and 75 ± 21 µmol·L -1 after the extra period. CONCLUSIONS: These findings demonstrate exacerbated fatigue after extra time compared with normal time, which seems to be associated with muscle glycogen depletion, reductions in blood glucose levels, and hyperammonemia. Together, this points to metabolic disturbances being a major part of the integrated and multifaceted fatigue response during extended soccer match play.
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Rendimiento Atlético , Carrera , Fútbol , Humanos , Masculino , Adulto Joven , Adulto , Fútbol/fisiología , Rendimiento Atlético/fisiología , Glucemia , Carrera/fisiología , Glucógeno , Fatiga MuscularRESUMEN
Adaptation to heat stress and hypoxia are relevant for athletes participating in Tour de France or similar cycling races taking place during the summertime in landscapes with varying altitude. Both to minimize detrimental performance effects associated with arterial desaturation occurring at moderate altitudes in elite athletes, respectively, reduce the risk of hyperthermia on hot days, but also as a pre-competition acclimatization strategy to boost blood volume in already highly adapted athletes. The hematological adaptations require weeks of exposure to manifest, but are attractive as an augmented hemoglobin mass may improve arterial oxygen delivery and hence benefit prolonged performances. Altitude training camps have in this context a long history in exercise physiology and are still common practice in elite cycling. However, heat-acclimation training provides an attractive alternative for some athletes either as a stand-alone approach or in combination with altitude. The present paper provides an update and practical perspectives on the potential to utilize hypoxia and heat exposure to optimize hematological adaptations. Furthermore, we will consider temporal aspects both in terms of onset and decay of the adaptations relevant for improved thermoregulatory capacity and respiratory adaptations to abate arterial desaturation during altitude exposure. From focus on involved physiological mechanisms, time course, and responsiveness in elite athletes, we will provide guidance based on our experience from practical implementation in cyclists preparing for prolonged stage races such as the Tour de France.
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In a series of three companion papers published in this Journal, we identify and validate the available thermal stress indicators (TSIs). In this third paper, we conducted field experiments across nine countries to evaluate the efficacy of 61 meteorology-based TSIs for assessing the physiological strain experienced by individuals working in the heat. We monitored 372 experi-enced and acclimatized workers during 893 full work shifts. We continuously assessed core body temperature, mean skin temperature, and heart rate data together with pre/post urine specific gravity and color. The TSIs were evaluated against 17 published criteria covering physiological parameters, practicality, cost effectiveness, and health guidance issues. Simple meteorological parameters explained only a fraction of the variance in physiological heat strain (R2 = 0.016 to 0.427; p < 0.001), reflecting the importance of adopting more sophisticated TSIs. Nearly all TSIs correlated with mean skin temperature (98%), mean body temperature (97%), and heart rate (92%), while 66% of TSIs correlated with the magnitude of dehydration and 59% correlated with core body temperature (r = 0.031 to 0.602; p < 0.05). When evaluated against the 17 published criteria, the TSIs scored from 4.7 to 55.4% (max score = 100%). The indoor (55.4%) and outdoor (55.1%) Wet-Bulb Globe Temperature and the Universal Thermal Climate Index (51.7%) scored higher compared to other TSIs (4.7 to 42.0%). Therefore, these three TSIs have the highest potential to assess the physiological strain experienced by individuals working in the heat.
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In a series of three companion papers published in this Journal, we identify and validate the available thermal stress indicators (TSIs). In this first paper of the series, we conducted a systematic review (registration: INPLASY202090088) to identify all TSIs and provide reliable information regarding their use (funded by EU Horizon 2020; HEAT-SHIELD). Eight databases (PubMed, Agricultural and Environmental Science Collection, Web of Science, Scopus, Embase, Russian Science Citation Index, MEDLINE, and Google Scholar) were searched from database inception to 15 April 2020. No restrictions on language or study design were applied. Of the 879 publications identified, 232 records were considered for further analysis. This search identified 340 instruments and indicators developed between 200 BC and 2019 AD. Of these, 153 are nomograms, instruments, and/or require detailed non-meteorological information, while 187 can be mathematically calculated utilizing only meteorological data. Of these meteorology-based TSIs, 127 were developed for people who are physically active, and 61 of those are eligible for use in occupational settings. Information regarding the equation, operating range, interpretation categories, required input data, as well as a free software to calculate all 187 meteorology-based TSIs is provided. The information presented in this systematic review should be adopted by those interested in performing on-site monitoring and/or big data analytics for climate services to ensure appropriate use of the meteorology-based TSIs. Studies two and three in this series of companion papers present guidance on the application and validation of these TSIs, to guide end users of these indicators for more effective use.
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In a series of three companion papers published in this Journal, we identify and validate the available thermal stress indicators (TSIs). In this second paper of the series, we identified the criteria to consider when adopting a TSI to protect individuals who work in the heat, and we weighed their relative importance using a Delphi exercise with 20 experts. Two Delphi iterations were adequate to reach consensus within the expert panel (Cronbach's α = 0.86) for a set of 17 criteria with varying weights that should be considered when adopting a TSI to protect individuals who work in the heat. These criteria considered physiological parameters such as core/skin/mean body temperature, heart rate, and hydration status, as well as practicality, cost effectiveness, and health guidance issues. The 17 criteria were distributed across three occupational health-and-safety pillars: (i) contribution to improving occupational health (55% of total importance), (ii) mitigation of worker physiological strain (35.5% of total importance), and (iii) cost-effectiveness (9.5% of total importance). Three criteria [(i) relationship of a TSI with core temperature, (ii) having categories indicating the level of heat stress experienced by workers, and (iii) using its heat stress categories to provide recommendations for occupational safety and health] were considered significantly more important when selecting a TSI for protecting individuals who work in the heat, accumulating 37.2 percentage points. These 17 criteria allow the validation and comparison of TSIs that presently exist as well as those that may be developed in the coming years.
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BACKGROUND: Cold-induced vasodilation (CIVD) is a phenomenon that refers to a paradoxical increase in finger temperature that sometimes occurs during cold exposure. The aim of this study was to compare CIVD responses between women and men, during exposure to different environmental conditions. METHODS: Seven men and seven women participated in a matched controlled study consisting of a familiarization protocol followed by three experimental sessions (cool (10.8 °C WBGT), thermoneutral (17.2 °C WBGT), and hot (27.2 °C WBGT)). In each session, participants were asked to immerse their left hand and foot in warm water (35 ± 1 °C) for five minutes. Thereafter, the left hand and foot were immersed in cold water (8 ± 1 °C) for 40 min. After that, the left hand and foot were removed from the water and participants remained seated for five minutes. RESULTS: For a matched thermal stress, women experienced an elevated cardiovascular strain (heart rate and in some cases mean arterial pressure) and higher frequency of CIVD reactions (men: 31 vs. women: 60) in comparison to their male counterparts. CONCLUSIONS: The present study demonstrated that women experienced elevated cardiovascular strain and higher frequency of CIVD reactions, particularly in the toes, compared to their male counterparts during cold-water immersion.