Biomedical subjects

G Havenith

Publications and source records attributed to G Havenith.

At least 19 recordsLinked to original sources

PubMed2006

Temperature limit values for touching cold surfaces with the fingertip.

OBJECTIVES: At the request of the European Commission and in the framework of the European Machinery Directive, research was performed in five different laboratories to develop specifications for surface temperature limit values for the short-term accidental touching of the fingertip with cold surfaces. METHODS: Data were collected in four laboratories with a total of 20 males and 20 females performing a grand total of 1655 exposures. Each touched polished blocks of aluminium, stainless steel, nylon-6 and wood using the distal phalanx of the index finger with a contact force of 1.0, 2.9 and 9.8 N, at surface temperatures from +2 to -40 degrees C for a maximum duration of 120 s. Conditions were selected in order to elicit varying rates of skin cooling upon contact. Contact temperature (TC) of the fingertip was measured over time using a T-type thermocouple. RESULTS: A database obtained from the experiments was collated and analysed to characterize fingertip contact cooling across a range of materials and surface temperatures. The database was subsequently used to develop a predictive model to describe the contact duration required for skin contact temperature to reach the physiological criteria of onset of pain (15 degrees C), onset of numbness (7 degrees C) and onset of frostbite risk (0 degrees C). CONCLUSIONS: The data reflect the strong link between the risk of skin damage and the thermal properties of the material touched. For aluminium and steel, skin temperatures of 0 degrees C occurs within 2-6 s at surface temperatures of -15 degrees C. For non-metallic surfaces, onset of numbness occurs within 15-65 s of contact at -35 degrees C and onset of cold pain occurs within 5 s of contact at -20 degrees C. The predictive model subsequently developed was a non-linear exponential expression also reflecting the effects of material thermal properties and initial temperature. This model provides information for the protection of workers against the risk of cold injury by establishing the temperature limits of cold touchable surfaces for a broad range of materials, and it is now proposed as guidance values in a new international standard.

Adolescent↗

PubMed2004

Finger skin cooling on contact with cold materials: an investigation of male and female responses during short-term exposures with a view on hand and finger size.

This study investigated the independent effects of hand anthropometry and gender upon contact cooling responses. Subjects were selected for matching hand/finger size between genders, with equal variation between individuals of each group. Fourteen volunteers (7 male, 7 female) participated, touching blocks of aluminium and stainless steel using the first phalanx of the index finger with a contact force of 1.0 N and 9.8 N, at surface temperatures of -2 degrees C and -10 degrees C. Conditions were selected in order to elicit varying rates of skin cooling upon contact. Contact temperature ( T(C)) of the finger-pad was measured over time using a T-type thermocouple. Overall, no significant difference was found between the cooling responses of males and females. In order to investigate whether differences in hand anthropometry correlated with contact cooling response, a multiple regression approach was used. Analyses of the residual variance in contact cooling data, after the effects of material type, surface temperature and finger contact force had been accounted for, showed that, under slow cooling conditions (>45 s to reach T(C)=1 degrees C), hand size correlated significantly with contact cooling response only when represented by index finger volume ( P<0.05), but gender did not. Whilst under fast cooling conditions (<25 s to reach T(C)=1 degrees C), hand size did not correlate significantly with contact cooling response at all, but gender had a significant effect ( P<0.001). Under slow cooling conditions, a larger finger (and in most cases hands) provides a higher heat content, thus giving a slower skin cooling speed. Under fast cooling conditions, the significantly longer time required for males to reach a T(C) of 1 degrees C, despite matching hand and finger size, is attributed to higher epidermal insulation provided by the thicker stratum corneum, combined with the higher starting skin temperature observed in the "slightly cool" environment.

Adaptation, Physiological↗

PubMed2004

Correction of clothing insulation for movement and wind effects, a meta-analysis.

A meta-analysis of the effect of body and air movement on the insulation provided by workwear and cold-weather clothing [1.22 clo (0.189 m2 degrees C W(-1)) < I(T)<4.14 clo (0.642 m2 degrees C W(-1))] using data from different sources was performed. For the effect of walking, datasets could be merged and a single prediction equation produced (r2=0.91). For the effect of wind, and interaction of movement and wind, separate equations were required for regular workwear (r2 = 0.93) and cold-weather clothing (r2 = 0.97). Differences were mainly due to the different amounts of nude surface area. An interaction between wind and walking effects was present (the size of the combined effects is less than the sum of the separate effects), and for cold-weather clothing an effect of clothing air permeability (p) was present (high p --> bigger effect). The resulting prediction equations will be proposed for inclusion in European and ISO standards on protective clothing to assist the user in determining the real-life clothing insulation value.

Humans↗

PubMed2002

Assessment of the risk of heat disorders encountered during work in hot conditions.

OBJECTIVE: To co-ordinate the work of the main European research teams in the field of thermal factors in order to develop and improve significantly the methods presently available for assessing the risks of heat disorders encountered during work in hot conditions. METHOD: Each item from the required sweat rate model was reviewed on the basis of the most recent literature. A database with 1,113 laboratory and field experiments, covering the whole range of hot working conditions, was assembled and used for the validation. RESULTS: Influence of clothing ensemble on heat exchange: methods and formulas were developed that take into account the dynamic effects associated with forced convection and the pumping effect associated with body movements and exercise. Prediction of the average skin temperature: the model used in the required sweat rate standard ISO 7933 was extended to cover more severe conditions with high radiation and high humidity and different clothing and take into account the rectal temperature for the prediction of the skin temperature. Criteria for estimating acceptable exposure times in hot work environments: criteria were reviewed and updated concerning the maximum increase in core temperature and the acceptable water loss, for acclimatised and nonacclimatised subjects. These limits are intended to protect 95% of the population. Measuring strategy: a strategy was developed to assess the risks in any working situation with varying conditions of climate, metabolic rate or clothing. A detailed methodology was developed in three stages: an "observation" method for the recognition of the conditions that might lead to thermal stress; an "analysis" method for evaluating the problem and optimising the solutions; and an "expert" method for in-depth analysis of the working situation when needed. VALIDATION: the different results were used to prepare a revision of the interpretation procedure proposed in the ISO standard 7933. We validated the modified approaches using the database. This involved the whole range of conditions for which the model was extended, namely conditions with high and low radiation, humidity and air velocity as well as fluctuating conditions. Based on these results, the predicted heat strain model was developed: it is presently proposed as an ISO and CEN standard.

Biomechanical Phenomena↗

PubMed2002

Temperature limit values for gripping cold surfaces.

OBJECTIVES: At the request of the European Commission and in the framework of the European Machinery Directive, research was conducted jointly in five different laboratories to develop specifications for surface temperature limit values for the gripping and handling of cold items. METHODS: Four hundred and fourteen experiments were run where male and female subjects were invited to grip for up to 20 min cold bars of different contact coefficients, i.e. polished wood, nylon, stone, steel and aluminium. The air temperature and the bars' initial surface temperatures ranged between 0 and -30 degrees C for the various experiments. While gripping the bars, either only the hand or the whole body was exposed to cold. RESULTS: The data were used to develop a prediction formula and a graph of the surface temperature limit values in order for the skin contact temperature not to reach <15 degrees C. This duration is shown to offer a significant degree of safety with respect to the minimal surface temperature spontaneously tolerated by the subjects. CONCLUSIONS: Experiments and modelling must be pursued to extend these data to other conditions of exposure.

Adult↗

PubMed2001

Individualized model of human thermoregulation for the simulation of heat stress response.

A population-based dynamic model of human thermoregulation was expanded with control equations incorporating the individual person's characteristics (body surface area, mass, fat%, maximal O(2) uptake, acclimation). These affect both the passive (heat capacity, insulation) and active systems (sweating and skin blood flow function). Model parameters were estimated from literature data. Other data, collected for the study of individual differences (working at relative or absolute workloads in hot-dry [45 degrees C, 20% relative humidity (rh)], warm-humid [35 degrees C, 80% rh], and cool [21 degrees C, 50% rh] environments), were used for validation. The individualized model provides an improved prediction [mean core temperature error, -0.21 --> -0.07 degrees C (P < 0.001); mean squared error, 0.40 --> 0.16 degrees C, (P < 0.001)]. The magnitude of improvement varies substantially with the climate and work type. Relative to an empirical multiple-regression model derived from these specific data sets, the analytical simulation model has between 54 and 89% of its predictive power, except for the cool climate, in which this ratio is zero. In conclusion, individualization of the model allows improved prediction of heat strain, although a substantial error remains.

Acclimatization↗

PubMed2001

Development and validation of the predicted heat strain model.

Eight laboratories participated in a concerted research project on the assessment of hot working conditions. The objectives were, among others, to co-ordinate the work of the main European research teams in the field of thermal factors and to improve the methods available to assess the risks of heat disorders at the workplace, and in particular the "Required Sweat Rate" model as presented in International Standard ISO 7933 Standard (1989). The scientific bases of this standard were thoroughly reviewed and a revised model, called "Predicted Heat Strain" (PHS), was developed. This model was then used to predict the minute by minute sweat rates and rectal temperatures during 909 laboratory and field experiments collected from the partners. The Pearson correlation coefficients between observed and predicted values were equal to 0.76 and 0.66 for laboratory experiments and 0.74 and 0.59 for field experiments, respectively, for the sweat rates and the rectal temperatures. The change in sweat rate with time was predicted more accurately by the PHS model than by the required sweat rate model. This suggests that the PHS model would provide an improved basis upon which to determine allowable exposure times from the predicted heat strain in terms of dehydration and increased core temperature.

Algorithms↗

PubMed2000

Criteria for estimating acceptable exposure times in hot working environments: a review.

OBJECTIVES: To revise the criteria used in the present "Required Sweat Rate" standard ISO 7933 (1989) for the prediction of the maximum duration of work in hot environments. METHODS: Review of the literature and in particular, of the bases for the present criteria. RESULTS: A new method is proposed, to take into account the increase in core temperature associated with activity in neutral environments. The prediction of maximum wetness and maximum sweat rates are revised, as well as the limits for maximum water loss and core temperature. CONCLUSION: An improved set of maximum values and limits is described, to be used in the revised version of the ISO 7933 standard. Due to the major modifications to the "Required Sweat Rate" index and in order to avoid any confusion, it is suggested that the revised model be renamed the "Predicted Heat Strain" (PHS) model.

Ergonomics↗

PubMed2000

Validation of a model for prediction of skin temperatures in footwear.

A model for foot skin temperature prediction was evaluated on the basis of 2 experiments on subjects at various environmental temperatures (light seated manual work at -10.7 degrees C (Study 1), and a short walking period in combination with standing and sitting at +2.8 degrees C, -11.8 degrees C and -24.6 degrees C (Study 2), with boots of 3 insulation levels. Insulation of the footwear was measured on a thermal foot model. Predicted and measured data showed a relatively good correlation (r = 0.87) at the 2 colder conditions in Study 2. The environmental temperature of 2.8 degrees C was not low enough at the chosen activity for a considerable foot skin temperature drop. In Study 1 the predicted temperature stayed higher for the whole exposure period and the difference between the predicted and the measured foot skin temperatures grew proportionally with time, while subsequent warm-up curves at room temperature were almost parallel. In Study 1 the correlation was 0.95. However, the paired t-test showed usually significant differences between measured and predicted foot skin temperatures. The insulation values from thermal foot measurements can be used in the model calculations. Lotens' foot model is lacking activity as direct input parameter, however, the blood flow is used instead (effect through Tcore). The Lotens foot model can give reasonable foot skin temperature values if the model limitations are considered. Due to the lack of activity level input, it will be difficult to make any good estimation of foot skin temperature during intermittent exercise. The rate of the foot temperature recovery after cold exposure was somewhat overestimated in the model--the warm-up of the feet of the subjects started later and was slower in the beginning of the warm-up than in the prediction. It could be useful to develop the model further by taking into consideration various wetness and activity levels.

Foot↗

PubMed1999

Exercise- and methylcholine-induced sweating responses in older and younger men: effect of heat acclimation and aerobic fitness.

The purpose of this investigation was to examine the effects of aging and aerobic fitness on exercise- and methylcholine-induced sweating responses during heat acclimation. Five younger [Y group-age: 23 +/- 1 (SEM) years; maximal oxygen consumption (VO2max): 47 +/- 3 ml.kg-1.min-1], four highly fit older (HO group- 63 +/- 3 years; 48 +/- 4 ml.kg-1.min-1) and five normally fit older men (NO group -67 +/- 3 years; 30 +/- 1 ml.kg-1.min-1) who were matched for height, body mass and percentage fat, were heat acclimated by daily cycle exercise (approximately 35% VO2max for 90 min) in a hot (43 degrees C, 30% RH) environment for 8 days. The heat acclimation regimen increased performance time, lowered final rectal temperature (Tre) and percentage maximal heart rate (%HRmax), improved thermal comfort and decreased sweat sodium concentration similarly in all groups. Although total body sweating rates (Msw) during acclimation were significantly greater in the Y and HO groups than in the NO group (P < 0.01) (because of the lower absolute workload in the NO group), the Msw did not change in all groups with the acclimation sessions. Neither were local sweating rates (msw) on chest, back, forearm and thigh changed in all groups by the acclimation. The HO group presented greater forearm msw (30-90 min) values and the Y group had greater back and thigh msw (early in exercise) values, compared to the other groups (P < 0.001). In a methylcholine injection test on days immediately before and after the acclimation, the order of sweat output per gland (SGO) on chest, back and thigh was Y > HO > NO, and on the forearm Y = HO > NO. No group differences were observed for activated sweat gland density at any site. The SGO at the respective sites increased in the post-acclimation test regardless of group (P < 0.01), but on the thigh the magnitude of the increase was lower in the NO (P < 0.02) and HO (P = 0.07) groups than in the Y group. These findings suggest that heat tolerance and the improvement with acclimation are little impaired not only in highly fit older but also normally fit older men, when the subjects exercised at the same relative exercise intensity. Furthermore, the changes induced by acclimation appear associated with an age-related decrease in VO2max. However methylcholine-activated SGO and the magnitude of improvement of SGO with acclimation are related not only to VO2max but also to aging, suggesting that sensitivity to cholinergic stimulation decreases with aging.

Adaptation, Physiological↗

PubMed1999

Clothing convective heat exchange--proposal for improved prediction in standards and models.

Convection is an important determinant for both sensible and evaporative heat exchange. Heat transfer by convection for normal boundary conditions is readily described by simple power functions. Clothing affects convection in various ways and existing characterisation of clothing by its static insulation values produces inaccurate prediction of sensible heat exchange, eventually leading to erroneous risk assessment. The present paper reviews various methods for evaluation of clothing convective (sensible) heat exchange. Based on available data, two equations are proposed for determination of the reduction of the total insulation values obtained under static, still wind conditions as a consequence of wind and walking effects. The equations apply from 0 to 1.84 clo, from 0.2 to 3 m/s and for walking speeds up to 1.2 m/s. The equations are incorporated in ISO 7933 to provide a more realistic and accurate prediction of sensible heat transfer through clothing.

Bias↗

PubMed1999

Heat balance when wearing protective clothing.

This issue of the Annals of Occupational Hygiene is dedicated to the topic of heat stress evaluation. For this evaluation, several evaluation programs and international standards are available. In order to understand the reasoning and underlying theory behind these programs and standards, a basic knowledge of heat exchange processes between workers and their environment is needed. This paper provides an overview of the relevant heat exchange processes, and defines the relevant parameters (air and radiant temperature, humidity, wind speed, metabolic heat production and clothing insulation). Further it presents in more detail the relation between clothing material properties and properties of clothing ensembles made from those materials. The effects of clothing design, clothing fit, and clothing air permeability are discussed, and finally an overview of methods for the determination of clothing heat and vapour resistance is given.

Body Temperature Regulation↗

PubMed1999

Clothing evaporative heat resistance--proposal for improved representation in standards and models.

Clothing heat and vapour resistance are important inputs for standards and models dealing with thermal comfort, heat- and cold-stress. A vast database of static clothing heat resistance values is available, and this was recently expanded with correction equations to account for effects of movement and wind on the static value of heat resistance in order to obtain the dynamic heat resistance of clothing ensembles. For clothing vapour resistance, few data were available so far. Indices for vapour permeability (im) and reduction factors for vapour transfer (Fpcl) of clothing were used instead, using a relation between heat and vapour resistance to derive the clothing vapour resistance from the value for clothing heat resistance. This paper reviews the two commonly used approaches (im and Fpcl), as well as five alternative approaches to the problem. The different approaches were evaluated for their accuracy and their usability. The present paper shows that the currently used relations are not adequate when the wearer of the clothing starts moving, or is exposed to wind. Alternative approaches are shown to improve the determination of dynamic clothing vapour resistance, though some are thought to be too complex. An empirical description of the relation between the clothing permeability index (im) and the changes in clothing heat resistance due to wind and movement was selected as the most promising method for deriving clothing vapour resistance. For this method the user needs to know the static heat resistance, the static im value of the clothing and the wind- and movement-speed of the wearer. This method results in a predicted maximal decrease in clothing vapour resistance by 78%, when clothing heat resistance is reduced by 50%, which is consistent with theoretical expectations and available data.

Bias↗

PubMed1999

The effects of wind and human movement on the heat and vapour transfer properties of clothing.

This paper integrates the research presented in the papers in this special issue of Holmér et al. and Havenith et al. [Holmér, I., Nilsson, H., Havenith, G., Parsons, K. C. (1999) Clothing convective heat exchange: proposal for improved prediction in standards and models. Annals of Occupational Hygiene, in press; Havenith, G., Holmér, I., den Hartog, E. and Parsons, K. C. (1999) Clothing evaporative heat resistance: proposal for improved representation in standards and models. Annals of Occupational Hygiene, in press] to provide a practical suggestion for improving existing clothing models so that they can account for the effects of wind and human movement. The proposed method is presented and described in the form of a BASIC computer program. Analytical methods (for example ISO 7933) for the assessment of the thermal strain caused by human exposure to hot environments require a mathematical quantification of the thermal properties of clothing. These effects are usually considered in terms of 'dry' thermal insulation and vapour resistance. This simple 'model' of clothing can account for the insulation properties of clothing which reduce heat loss (or gain) between the body and the environment and, for example, the resistance to the transfer of evaporated sweat from the skin, which is important for cooling the body in a hot environment. When a clothed person is exposed to wind, however, and when the person is active, there is a potentially significant limitation in the simple model of clothing presented above. Heat and mass transfer can take place between the microclimate (within clothing and next to the skin surface) and the external environment. The method described in this paper 'corrects' static values of clothing properties to provide dynamic values that take account of wind and human movement. It therefore allows a more complete representation of the effects of clothing on the heat strain of workers.

Bias↗

PubMed1998

Relevance of individual characteristics for human heat stress response is dependent on exercise intensity and climate type.

Multiple heterogeneous groups of subjects (both sexes and a wide range of maximal oxygen uptake VO2max, body mass, body surface area (AD),% body fat, and AD/mass coefficient) exercised on a cycle ergometer at a relative (%VO2max, REL) or an absolute (60 W) exercise intensity in a cool (CO 21 degrees C, 50% relative humidity), warm humid (WH 35 degrees C, 80%) and a hot dry (HD 45 degrees C, 20%) environment. Rectal temperature (Tre) responses were analysed for the influence of the individual's characteristics, environment and exercise intensity. Exposures consisted of 30-min rest, followed by 60-min exercise. The Tre was negatively correlated with mass in all conditions. Body mass acted as a passive heat sink in all the conditions tested. While negatively correlated with VO2max and VO2max per kilogram body mass in most climates, Tre was positively correlated with VO2max and VO2max per kilogram body mass in the WH/REL condition. Thus, when evaporative heat loss was limited as in WH, the higher heat production of the fitter subjects in the REL trials determined Tre and not the greater efficiency for heat loss associated with high VO2max. Body fatness significantly affected Tre only in the CO condition, where, with low skin blood flows (measured as increases in forearm blood flow), the insulative effect of fat was pronounced. In the warmer environments, high skin blood flows offset the resistance offered by peripheral adipose tissue. Contrary to other studies, Tre was positively correlated with AD/mass coefficient for all conditions tested. For both exercise types used, being big (a high heat loss area and heat capacity) was apparently more beneficial from a heat strain standpoint than having a favourable AD/mass coefficient (high in small subjects). The total amount of variance in Tre responses which could be attributed to individual characteristics was dependent on the climate and the type of exercise. Though substantial for absolute exercise intensities (52%-58%) the variance explained in Tre differed markedly for relative intensities: 72% for the WH climate with its limited evaporative capacity, and only 10%-26% for the HD and CO climates. The results showed that individual characteristics play a significant role in determining the responses of body core temperature in all conditions tested, but their contribution was low for relative exercise intensities when evaporative heat loss was not restricted. This study demonstrated that effects of individual characteristics on human responses to heat stress cannot be interpreted without taking into consideration both the heat transfer properties of the environment and the metabolic heat production resulting from the exercise type and intensity chosen. Their impact varies substantially among conditions.

Adipose Tissue↗

PubMed1998

Human energy expenditure when walking on a moving platform.

The assumption that working on board ship is more strenuous than comparable work ashore was investigated in this study. Various physiological parameters (VO2, VCO2, VE and HR) have been measured to determine the energy expenditure of subjects walking slowly on a moving platform (ship motion simulator). Twelve subjects (eight men and four women) walked either freely on the floor or on a treadmill at a speed of 1 m x s(-1). Platform motion was either in a heave, pitch or roll mode. These three conditions were compared with a control condition in which the platform remained stationary. The results showed that during pitch and roll movements of the platform, the energy expenditure for the same walking task was about 30% higher than under the stationary control condition (3.6 J x kg[-1] x m[-1] vs 2.5 J x kg[-1] x m[-1], P < 0.05) for both walking on a treadmill and free walking. The heart rate data supported the higher energy expenditure results with an elevation of the heart rate (112 beats x min[-1] vs 103 beats x min[-1], P < 0.05). The heave condition did not differ significantly from the stationary control condition. Pitch and roll were not significantly different from each other. During all experimental conditions free walking resulted in a higher energy cost of walking than treadmill walking (3.5 J x kg[-1] x m[-1] vs 2.7 J x kg[-1] x m[-1], P < 0.05) at the same average speed. The results of this experiment were interpreted as indicating that the muscular effort, needed for maintaining balance when walking on a pitching or rolling platform, resulted in a significantly higher work load than similar walking on a stable or a heaving floor, independent of the mode of walking. These results explain in part the increased fatigue observed when a task is performed on a moving platform.

Adult↗

PubMed1995

The relative influence of body characteristics on humid heat stress response.

The present study was designed to determine the relative importance of individual characteristics such as maximal oxygen uptake (VO2max), adiposity, DuBois body surface area (AD), surface to mass ratio (AD: mass) and body mass, for the individual's reaction to humid heat stress. For this purpose 27 subjects (19 men, 8 women), with heterogeneous characteristics (VO2max 1.86-5.28 1.min-1; fat% 8.0%-31.9%; mass 49.8-102.1 kg; AD 1.52-2.33 m2) first rested (30 min) and then exercised (60 W for 1 h) on a cycle ergometer in a warm humid climate (35 degrees C, 80% relative humidity). Their physiological responses at the end of exercise were analysed to assess their relationship with individual characteristics using a stepwise multiple regression technique. Dependent variables (with ranges) included final values of rectal temperature (Tre 37.5-39.0 degrees C), mean skin temperature (Tsk 35.7-37.5 degrees C), body heat storage (S 3.2-8.1 J.g-1), heart rate (HR 100-172 beat.min-1), sweat loss (397-1403 g), mean arterial blood pressure (BPa, 68-96 mmHg), forearm blood flow (FBF, 10.1-33.9 ml.100ml-1.min-1) and forearm vascular conductance (FVC = FBF/BPa, 0.11-0.49 ml.100ml-1.min-1.mmHg-1). The Tre, Tsk and S were (34%-65%) determined in the main by VO2max or by exercise intensity expressed as a percentage of VO2max (% VO2max). For Tre, AD: mass ratio also contributed to the variance explained, with about half the effect of VO2max. For Tsk, fat% contributed to the variance explained with about two-third the effect of VO2max. Total body sweat loss was highly dependent (50%) on body size (AD or mass) with regular activity level having a quarter of the effect of body size on sweat loss. The HR, similar to Tre, was determined by VO2max (48%-51%), with less than half the effect of AD or AD:mass (20%). Other circulatory parameters (FBF, BPa, FVC) showed little relationship with individual characteristics (< 36% of variance explained). In general, the higher the VO2max and/or the bigger the subject, the lower the heat strain observed. The widely accepted concept, that body core temperature is determined by exercise intensity expressed as % VO2max and sweat loss by absolute heat load, was only partially supported by the results. For both variables, other individual characteristics were also shown to contribute.

Blood Flow Velocity↗

PubMed1995

Age predicts cardiovascular, but not thermoregulatory, responses to humid heat stress.

Cross-section comparisons of the effect of age on physiological responses to heat stress have yielded conflicting results, in part because of the inability to separate chronological age from factors which change in concert with the biological aging process. The present study was designed to examine the relative influence of age on cardiovascular and thermoregulatory responses to low intensity cycle exercise (60 W for 1 h) in a warm humid environment (35 degrees C, 80% relative humidity). Specifically, the relative importance of age compared to other individual characteristics [maximal oxygen uptake (VO2max), physical activity level, anthropometry, and adiposity] was determined by multiple regression analysis in a heterogeneous sample of 56 subjects in which age (20-73 years) and VO2max (1.86-4.44 l.min-1) were not interrelated. Dependent variables (with ranges) included final values of thermoregulatory responses [rectal temperature (Tre, 37.8-39.2 degrees C), calculated heat storage (S, 3.4-8.1 J.g-1), sweat loss (238-847 g.m-2)] and cardiovascular responses [heart rate (HR, 94-176 beats.min-1), forearm blood flow (FBF, 5.3-31.3 ml.100 ml-1.min-1), mean arterial blood pressure (MAP, 68-122 mmHg), and forearm vascular conductance (FVC = FBF.MAP-1, 0.06-0.44 ml.100 ml-1.min-1.mmHg-1). Age had no significant influence on Tre, S, or sweat loss, all of which were closely related to VO2max. On the other hand, HR, MAP, FBF, and FVC were related to both age and VO2max. Anthropometric variables and adiposity had secondary, but statistically significant, effects on MAP, FBF, FVC, and sweat loss.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗