Passive temperature lability in the elderly

Thermoregulatory responses of nine healthy elderly [seven men and two women; mean age (SD) 73.9 (4.8) years] were compared to those of nine young adult men [26.6 (5.2) years]. They exercised on a cycle ergometer for 20 min at an intensity inducing a heart rate equivalent to 65% of their predicted maximum, and were thereafter immersed in 28°C water. The exercise was conducted to elevate tympanic temperature (T _ty) and initiate a steady rate of sweating. The post-exercise immersion period induced gradual cooling ofT _ty, and changes inT _ty relative to resting levels (ΔT _ty) at which sweating abated and shivering commenced were defined as the ΔT _ty thresholds for the cessation of sweating (T _sw) and onset of shivering (T _sh), respectively. In addition toT _ty, oxygen uptake ( ; 1 · min⁻¹), sweating rate (g · m⁻² · min⁻¹), and forehead skin blood perfusion were also measured during the trials. The mean (SD)T _sw occurred at a significantly (P <0.005) higher ΔT _ty [0.48 (0.18)°C] in the elderly than in the young adults [0.21(0.06)°C], while the Tsh occurred at significantly (P < 0.005) lower ΔT _ty in the elderly [ −0.64 (0.34)°C] than in young adults [−0.22 (0.10)°C]. Decreases in ΔT _ty below the shivering threshold were met with a significantly (P <0.01) reduced . The range of temperature lability between Ts, andT _sh, defined as the null-zone, was significantly greater in the elderly [1.12 (0.39)°C] than in the young adults [0.43 (0.12)°C], and the slope of the vasoconstrictor response in the null-zone was significantly (P <0.001) lower in the elderly subjects. The present study demonstrates a greater passive core temperature lability in older individuals, since the effector responses of sweating and shivering were initiated at higher and lower levels ofT _ty, respectively. The magnitudes of the effector responses beyond the thresholds were also significantly reduced, suggesting that the elderly may be more susceptible to hypo-/hyperthermia during periods of endogenous and/or exogenous thermal stress.     

Effects of passive heat adaptation and moderate sweatless conditioning on responses to cold and heat

Summary Two series of experiments were performed in physically untrained subjects. In series A (heat adaptation, HA), seven male subjects were adapted to dry heat (five consecutive days at 55‡ C ambient air temperature (T_a) for 1 h · day⁻¹) under resting conditions. Before and after HA, the subjects' shivering responses were determined in a cold test (T_a+10 to 0‡ C). In series B, eight male subjects underwent mild exercise training (five consecutive days at a heart rate, HR, of 120b · min⁻¹) under T_a conditions individually adjusted (T_a + 15 to +5‡ C) to prevent both sweating and cold sensations. Before and after “sweatless training≓, the subjects were subjected to a combined cold and heat test. During HA the thresholds for shivering, cutaneous vasodilatation (thumb and forearm) and sweating were shifted significantly (p<0.05) towards lower mean body temperatures ( ). The mean decrease in threshold was 0.36‡ C. “Sweatless training≓ resulted in a mean increase in work rate (at HR 120b · min⁻¹) and oxygen pulse of 13 and 8%, respectively. However, “sweatless training≓ did not change the threshold for shivering or sweating. Neither HA nor “sweatless training≓ changed the slopes of the relationships of shivering and sweating to . It is concluded that the previously reported lowering of shivering and sweating threshold in long-distance runners is not due to an increased fitness level, but is essentially identical with HA. The decreased shivering threshold following HA is interpreted as “cross adaptation≓ produced by the Stressors cold and heat. This study was supported by the Deutsche Forschungsgemeinschaft (Br 184/16-3)     

Gender differences in physiological reactions to thermal stress

Following an extensive anthropometric evaluation, thermoregulatory responses were studied in nine men and nine women who performed immersed exercise with post-exercise rest in 28°C water. During the post-exercise period esophageal temperature (T _es), oxygen consumption, heat flux and skin blood perfusion were monitored at 10s intervals, with average minute values used for calculations. The T _es (relative to restingT _es) at which sweating abated and shivering commenced were defined as the T _es thresholds for the cessation of sweating and onset of shivering, respectively. No significant gender differences were evident in the sweating and shivering threshold T _es values, or the magnitude of the null-zone. Usingz-tests for parallelism the rates of core cooling across the null-zone were not found to differ significantly between genders, nor were the slopes of the perfusion: T _es responses across the null-zone or the post-threshold shivering responses (ml·kg^–1·min^–1·°C^–1). The slope of the sweating response (measured from immersion until sweat cessation; g·m^–2·min^–1°C^–1) was, however, significantly lower in the female than in the male samples (z = 3.93;P < 0.01). Despite the gender-related dimorphic distribution of adipose tissue, both men and women lost equal proportions of their total heat flux from central and peripheral measurement sites. Performing a standardized regression using the rate of core cooling across the null-zone as the dependent variable and gender as a dummy variable, gender and adipose tissue mass were not found to be significant factors in determining the rate of core cooling, while mass ( = 1.73;P < 0.05) and muscle mass ( = 1.86;P < 0.05) did contribute significantly to the rate of core cooling. It was concluded that, except for the quantitative differences in the sweating response, men and women respond to deviations in core temperature in a similar manner, with mass and muscle mass modifying this response.     

Dynamics of sweating in men and women during passive heating

Summary The dynamics of sweating was investigated at rest in 8 men and 8 women. Electrical skin resistance (ESR), rectal temperature (T_re) and mean skin temperature were measured in subjects exposed to 40‡ C environmental temperature, 30% relative air humidity, and 1 m · s⁻¹ air flow. Sweat rate was computed from continuous measurement of the whole body weight loss. It was found that increases in T_re, and mean body temperature were higher in women than in men by 0.16, 0.38 and 0.21‡ C, but only the difference in δ was significant (p<0.05). The dynamics of sweating in men and women respectively, was as follows: delay (t_d) 7.8 and 18.1 min (p<0.01), time constant (Τ) 7.5 and 8.8 min (N.S.), inertia time (t_i) 15.3 and 26.9 min (p<0.002), and total body weight loss 153 and 111 g · m⁻² · h⁻¹ (p<0.001). Dynamic parameters of ESR did not differ significantly between men and women. Inertia times of ESR and sweat rate correlated in men (r=0.93, p<0.001), and in women (r=0.76, p<0.02). In men, δ T_re correlated with inertia time of sweat rate (r=0.81, p<0.01) as well as with the inertia time of ESR (r=0.83, p<0.001). No relation was found between δ T_re and the dynamics of sweating in women. It is concluded that the dynamics of sweating plays a decisive role in limiting δ T_re in men under dry heat exposure. The later onset of sweating in women does not influence the rectal temperature increase significantly. In women, δ T_re is probably limited by a complex interaction of sweating, skin blood flow increase, and metabolic rate decrease. This work was supported by the Centre National de la Recherche Scientifique and Polish Academy of Siences     

Influence of the menstrual cycle on the sweating response measured by direct calorimetry in women exposed to warm environmental conditions

Summary The whole body sweating response was measured at rest in eight women during the follicular (F) and the luteal (L) phases of the menstrual cycle. Subjects were exposed for 30-min to neutral (N) environmental conditions [ambient temperature (T _a) 28°C] and then for 90-min to warm (W) environmental conditions (Ta, 35°C) in a direct calorimeter. At the end of the N exposure, tympanic temperature (T _ty) was 0.18 (SEM 0.06)°C higher in the L than in the F phase (P<0.05), whereas mean skin temperature ( ) was unchanged. During W exposure, the time to the onset of sweating as well as the concomitant increase in body heat content were similar in both phases. At the onset of sweating, the tympanic threshold temperature (T _{ty, thresh}) was higher in the L phase [37.18 (SEM 0.08)°C] than in the F phase [36.95 (SEM 0.07)°C;P<0.01]. The magnitude of the shift inT _ty, thresh [0.23 (SEM 0.07)°C] was similar to the L-F difference inT _ty observed at the end of the N exposure. The mean skin threshold temperature was not statistically different between the two phases. The slope of the relationship between sweating rate andT _ty was similar in F and L. It was concluded that the internal set point temperature of resting women exposed to warm environmental conditions shifted to a higher value during the L phase compared to the F phase of the menstrual cycle; and that the magnitude of the shift corresponded to the difference in internal temperature observed in neutral environmental conditions between the two phases.     

Residual analysis in the determination of factors affecting the estimates of body heat storage in clothed subjects

Body heat storage can be estimated by calorimetry (from heat gains and losses) or by thermometry [from changes (Δ) in mean body temperature (T _b) calculated as a weighted combination of rectal (T _re) and mean skin temperatures (T _sk)]. If an invariant weighting factor ofT _re andT _sk were to be used (for instance, ΔT _b = 0.8 · ΔT _re + 0.2 · ΔT _sk under hot conditions), body heat storage could be over- or underestimated substantially relative to calorimetry, depending on whether the subject was wearing light or protective clothing. This study investigated whether discrepancies between calorimetry and thermometry arise from methodological errors in the calorimetric estimate of heat storage, from inappropriate weightings in the thermometric estimate, or from both. Residuals of calorimetry versus thermometric estimates were plotted against individual variables in the standard heat balance equation, applying various weighting factors toT _re andT _sk. Whether light or protective clothing was worn, the calorimetric approach generally gave appropriate estimates of heat exchange components and thus heat storage. One exception was in estimating latent heat loss from sweat evaporation. If sweat evaporation exceeded 650 g·h⁻¹ when wearing normal clothing, evaporative heat loss was overestimated and thus body heat storage was underestimated. Nevertheless, if data beyond this ceiling were excluded from the analyses, the standard 4:1 weighting matched calorimetric heat storage estimates quite well. When wearing protective clothing, the same 4:1 weighting approximated calorimetric heat storage with errors of less than approximately 10%, but only if environmental conditions allowed a subject to exercise for more than 90 min. The best thermometric estimates of heat storage were provided by using two sets of relative weightings, based upon the individual's metabolic heat production ( in kilojoules per metre squared per hour): {4 − [( )· ] 2}:1 for an initial, thermoneutral environment and {4 + [( ) · ] · 5}: 1 for a final, hot environment; the optimal value of lay between 450 and 500 kJ m⁻² · h⁻¹. We concluded that the accuracy of thermometric estimates of heat storage can be improved by modifying weighting factors ofT _re andT _sk according to the environment, type of clothing, and metabolic rate.     

Influence of the menstrual cycle and oral contraceptives on thermoregulatory responses to exercise in young women

Summary Thermoregulatory responses to exercise in relation to the phase of the menstrual cycle were studied in ten women taking oral contraceptives (P) and in ten women not taking oral contraceptives (NP). Each subject was tested for maximal aerobic capacity ( ) and for 50% exercise in the follicular (F) and luteal (L) phases of the menstrual cycle. Since the oral contraceptives would have prevented ovulation a quasi-follicular phase (q-F) and a quasi-luteal phase (q-L) of the menstrual cycle were assumed for P subjects. Exercise was performed on a cycle ergometer at an ambient temperature of 24° C and relative air humidity of 50%. Rectal (T _re), mean skin ( ), mean body ( ) temperatures and heart rate (f _c) were measured. Sweat rate was estimated by the continuous measurement of relative humidity of air in a ventilated capsule placed on the chest, converted to absolute pressure (PH₂O_chest). Gain for sweating was calculated as a ratio of increase inPH₂O_chest to the appropriate increase inT _re for the whole period of sweating (G) and for unsteady-state (G_u) separately. The did not differ either between the groups of subjects or between the phases of the menstrual cycle. In P, rectal temperature threshold for sweating (T _{re, td}) was 37.85° C in q-L and 37.60° C in q-F (P < 0.01) and corresponded to a significant difference fromT _re at rest. TheT _re, andf _c increased similarly during exercise in q-F and q-L. No menstrual phase-related differences were observed either in the dynamics of sweating or in G. In NP,T _{re, td} was shorter in L than in F (37.70 vs 37.47° C,P<0.02) with a significantly greater value fromT _re at rest. The dynamics and G for sweating were also greater in L than in F. The G_u was 36.8 versus 16.6 kPa · ° C^–1 (P<0.01) while G was 6.4 versus 3.8 kPa · ° C^–1 (P<0.05), respectively. TheT _re, andf _c increased significantly more in phase F than in phase L. It was concluded that in these women performing moderate exercise, there was a greater temperature threshold and larger gains for sweating in phase L than in phase F. Intake of oral contraceptives reduced the differences in the gains for sweating making the thermoregulatory responses to exercise more uniform.     

Hyperpnoea and CO2 sensitivity of the respiratory centres during exercise

Summary The aim of this study was to specify whether exercise hyperpnoea was related to the CO₂ sensitivity of the respiratory centres measured during steady-state exercise of mild intensity. Thus, ventilation , breathing pattern [tidal volume (V _T), respiratory frequency (f), inspiratory time (T _I), total time of the respiratory cycle (T _TOT),V _T/T _I,T _I/T _TOT] and CO₂ sensitivity of the respiratory centres determined by the rebreathing method were measured at rest (SCO_{2 re}) and during steady-state exercise (SCO_{2 ex}) of mild intensity [CO₂ output =20 ml·kg⁻¹·min⁻¹] in 11 sedentary male subjects (aged 20–34 years). The results showed that SCO_{2 re} and SCO_{2 ex} were not significantly different. During exercise, there was no correlation between and SCO_{2 ex} and, for the same , all subjects had very close values normalized for body mass (bm), regardless of their SCO_{2 ex} ( =1.44 l·min⁻¹·kg⁻¹ SD 0.10). A highly significant positive correlation between SCO_{2 ex} andV _T (normalised for bm) (r=0.80,P<0.01),T _I (r=0.77,P<0.01) andT _TOT (r=0.77,P<0.01) existed, as well as a highly significant negative correlation between SCO_{2 ex} and (normalised for bm^−0.25) (r=−0.73,P<0.01). We conclude that the hyperpnoea during steady-state exercise of mild intensity is not related to the SCO_{2 ex}. The relationship between breathing pattern and SCO_{2 ex} suggests that the breathing pattern could influence the determination of the SCO_{2 ex}. This finding needs further investigation.     

Control of sweating during the human menstrual cycle

Summary Thermoregulatory responses were studied in seven women during two separate experimental protocols in the follicular (F, days 4–7) phase and during the luteal (L, days 19–22) phase of the menstrual cycle. Continuous measurements of esophageal temperature (T _es), mean skin temperature ( ), oxygen uptake and forearm sweating ( ) were made during all experiments. Protocol I involved both passive heat exposure (3 h) and cycle exercise at ∼80% peak during which the environmental chamber was controlled atT _a=50.0° C, rh=14% (P _w=1.7 kPa). In protocol II subjects were tested during thirty-five minutes of exercise at ∼85% peak atT _a=35° C and rh=25% (P _w=1.4 kPa). The normal L increase in restingT _es (≈0.3° C) occurred in all seven subjects. was higher during L than F in all experiments conducted at 50° C. During exercise and passive heat exposure, theT _es threshold for sweating was higher in L, with no change in the thermosensitivity (slope) of toT _es between menstrual cycle phases. This rightward or upward shift inT _es threshold for initiation of sweating averaged 0.5° C for all experiments. The data indicate the luteal phase modulation in the control of sweating in healthy women is also apparent during severe exercise and/or heat stress.     

Effect of aerobic capacity on sweat rate and fluid intake during outdoor exercise in the heat

We measured the aerobic capacity, sweat rate and fluid intake of trained athletes during outdoor exercise and examined the relationship between aerobic capacity and thermoregulatory responses at high ambient temperatures. The maximal aerobic capacity ( ) of the subjects, nine male baseball players of college age, was determined by maximal exercise tests on a cycle ergometer. The subjects practised baseball regularly without drinking fluids from 1330 to 1530 hours. After 30 min rest, they played a baseball game with free access to a sports drink at 15°C from 1600 to 1830 hours. At a mean ambient temperature of 36.7 (SEM 0.2)°C, the mean percentage of body mass loss (m _b) and increase of oral temperature (T _o) from 1330 to 1530 hours was 3.47 (SEM 0.12)% and 0.81 (SEM 0.14)°C, respectively. The sweat loss from 1330 to 1830 hours was 56.53 (SEM 1.56)ml · kg^–1 of body mass (M _b) while the mean fluid consumption was 44.78 (SEM 2.39)ml · kg^–1 ofm _b, with recovery of 76.08 (SEM 2.81)% of sweat loss. The was significantly inversely correlated withm _b, fluid intake and rehydration amount, but showed no correlation withT _o. These results would suggest that at a given exercise intensity in subjects with a higher aerobic capacity body temperature is maintained with a lower sweating rate than that in subjects with a lower aerobic capacity.     

Seasonal variation in sweating responses of older and younger men

Eight older (60–65 years) and six younger (20–25 years) men were exposed to a standard heat stress for 60 min in summer, autumn, winter, and spring. The test consisted of placing the lower legs and feet in a 42°C water bath while sitting in constant environmental conditions (30°C and 45% relative humidity). The increase of rectal temperature (T _re) was significantly greater (P < 0.05) in autumn, winter, and spring than in summer for the older group, but significantly greater only in winter than in summer for the younger group (P < 0.05). The T _re was greater for the older group in all seasons, but of significance only in autumn and spring (P < 0.01). There were no significant season-related differences for metabolic heat production (m) and mean skin temperature ( _sk) during the heat test in the respective groups, although the m and _sk were lower for the older group in all seasons (P < 0.01). In the older group total body sweating rate (m_sw) divided by T _re (total m_sw/T _re) decreased from summer to winter (P < 0.02) and did not differ between winter and spring, whereas total m_sw/T _re in the younger group increased in spring after decreasing from autumn to winter (P < 0.03). The variations of the value, local sweating rate on the back and thigh divided by T _re (back m_sw/T _re and thigh m_sw/T _re), were similar to those of the total m_sw/T _re in each group, except for back m_sw/T _re in the younger group, which did not increase from winter to spring. The total m_sw/T _re, back m_sw/T _re and thigh m_sw/T _re were significantly less for the older group in summer, autumn and spring (P < 0.05). The range of seasonal variations was significantly less for the older group (P < 0.001). The results indicated that, compared with younger men in older men, the enhancement of sweating function toward summer occurred later and its reduction toward winter occurred earlier despite a smaller range of seasonal variation and that older men had a somewhat lesser capability to maintainT _re when challenged by heat stress in all seasons.     

Fat energy use and plasma lipid changes associated with exercise intensity and temperature

Summary The effect of 60 min of exercise at two intensities (50 and 60% ) and temperatures (0 and 22° C) on changes (A) in plasma lipids {triglycerides (TG), glycerol (GLY), total cholesterol (TC), and HDL-cholesterol (HDL-C)} was examined. Subjects were 10 men aged 27±7 years ( , % fat=12.2%±7.1%). and respiratory exchange ratio results indicated that total energy and fat energy use were similar at the two temperatures. Changes in plasma volume (%ΔPV) were different (P<0.05) at the two temperatures (22° C: −2.3% vs 0° C: 1.1%). Combining the data at each temperature revealed that the increases in concentrations were greater (P<0.05) at 22° C (ΔTG=0.22, ΔGLY=0.20, ΔTC=0.14, ΔHDL-C=0.05 mmol 1⁻¹) vs 0° C (ΔTG=0.10, ΔGLY=0.12, ΔTC=0.05, ΔHDL-C=0.02 mmol 1⁻¹). Combining the data for each intensity revealed that the increases in concentration were greater (P<0.05) at 60% for ΔTG and ΔHDL-C. The 60% C bout produced greater changes (P<0.05) than all other bouts for ΔTC and ΔHDL-C (0.21 and 0.08 mmol 1⁻¹, respectively). Only ΔTG and ΔGLY were greater at 22° C when adjusted for %ΔPV. These metabolic and plasma lipid results indicate that cold exposure does not act synergistically with exercise to further stimulate fat metabolism.     

Thermal exchanges during sleep in anhidrotic ectodermal dysplasia

Summary Anhidrotic ectodermal dysplasia is a congenital syndrome characterized by the absence of sweat glands. A sweating test was performed on such a patient and proved his inability to sweat. Thermal exchanges during night sleep were then measured in this patient and compared with data obtained from a healthy control subject. Ambient conditions were as follows: dry bulb temperature 32.2°C, relative humidity 30%–40%, wind speed 0.7 m·s⁻¹. Polysomnographic recordings showed normal sleep patterns in both subjects, but a “first night effect” in the patient. Rectal (T _re) and mean skin temperatures and loss of mass were monitored continuously throughout the 8-h sleep recording. Loss of mass averaged 34.1 g·h⁻¹ in the patient vs 78.1 g·h⁻¹ in the control subject. No relationship with sleep stages was observed in the patient, in contrast to the control subject who experienced a decrease in evaporation during rapid eye movement sleep. Body temperatures varied little in the patient, but decreased until the 6th h of sleep in the control subject. On two occasions there was a 0.3°C fall in theT _re of the patient during two slow wave sleep (SWS) phases, while and loss of mass did not change. As thermolytic processes had not varied on these two occasions, it was concluded that the fall inT _re indicated a concomitant decrease in metabolic heat production, in agreement with the assumption that SWS represented a state of energy conservation.     

Time-of-day effect on nonthermal control of sweating response to maintained static exercise in humans

To investigate the influence of nonthermal factors in the time-of-day effect on the sweating response to maintained static exercise, eight healthy male subjects performed handgrip exercise at 20%, 35% and 50% maximal voluntary contraction (MVC) for 60 s at 0600 hours (morning) and at 1800 hours (evening). Oesophageal temperature (T _oes) before the experiment showed a diurnal rhythm [mean (SEM)] [36.3 (0.1) (morning) compared to 36.8 (0.1) °C (evening), P<0.01]. Experiments were conducted with subjects in a state of mild hyperthermia during which the mean skin temperature (T _sk) was kept constant at 35.5–36.5 °C using a water-perfused suit to activate sudomotor responses. The T _oes and mean T _sk remained stable during the pre-exercise, handgrip exercise and recovery periods. The response in sweating rate (ΔSR) on the chest and forearm to handgrip exercise increased significantly with increasing exercise intensity in both the morning and evening tests (P<0.05). The ΔSR on the palm did not change significantly with increasing exercise intensity in the morning test (P>0.1). During handgrip exercise at 50% MVC only, ΔSR on the chest, forearm and palm in the evening was significantly higher than in the morning (P<0.05). On the other hand, mean arterial blood pressure and the rating of perceived exertion during 50% MVC handgrip exercise were not significantly different between the morning and evening (P>0.1). These results indicate the presence of a time-of-day effect on nonthermal control of the sweating response to isometric handgrip exercise, and that this effect is dependent on exercise intensity. Electronic Publication     

Relationship between core temperature and skin blood flux in lower limbs during prolonged arm exercise in persons with spinal cord injury

The purposes of the present study were to examine the response of the skin blood flux (SBF) in the paralyzed lower limbs of persons with spinal cord injury (PSCI) and to clarify the relationship between the SBF and core temperature during prolonged arm exercise. Eight male PSCI with lesions from T6 to L5 and six male control subjects (CS) participated in this study. The subjects rested for 60 min and then performed arm-cranking exercise at 20 W for 30 min at 25 °C. The tympanic membrane temperature (T _ty) and SBF in the anterior thigh (SBFT) and in the posterior calf (SBFC) were continuously measured throughout the experiment. The SBFC did not change in either PSCI or CS during the experiment. The SBFT in four PSCI with high lesions (T6 to T12), remained unchanged during exercise. The SBFT in the other four PSCI with low lesions (T12 to L5, SBFT+) began to elevate markedly when the T t, exceeded a threshold temperature of 36.69 °C. The pattern of increase of SBFT in SBFT+ was similar to that in CS, although onset of the increase in SBFT was delayed and the peak of SBFT during exercise was significantly lower in comparison with the CS. We consider that these differences between the SBFT+ and CS were largely attributable to the lowerT _ty in the former group, which took a prolonged time to reach the threshold of 36.69 °C.     

Energy consumption of paraplegic locomotion using reciprocating gait orthosis

The energy cost of walking using a reciprocating gait orthosis (RGOII) with functional electrical stimulation (FES) was assessed in 14 patients with spastic complete paraplegia from six rehabilitation centres. Before and after training asing RGOII with FES, the subjects performed a progressive maximal test on an arm-crank ergometer to obtain their laboratory peak oxygen uptake heart rate (HR) and blood lactate concentration changes. At the end of the training session, oxygen uptake was measured during a walking test with orthosis at different speeds (6 min steady state at 0.1 m · s⁻¹, followed by 2-min stages at progressively increasing speeds up to exhaustion). Of the subjects 4 repeated this test using orthosis without FES. At a speed of 0.1 m · s⁻¹, represented 47 (SD 23)% of , mean HR was 137 (SD 21) beats · min⁻¹ and mean blood lactate concentration 2.4 (SD 1.4) mmol · l⁻¹. Maximal speed ranged from 0.23 to 0.5 m · s⁻¹. At maximal speed, was 91 (SD 18) % of mean HR reached 96 (SD 7)% and mean blood lactate concentration only 52 (SD 19)% of the maximal values measured during the laboratory test. Walking without electrical stimulation induced an increase in HR but there was no difference in and blood lactate compared to walking with stimulation. The training period did not result in any improvement in maximal physiological data. We concluded that the free cadence walking speed with orthosis remains much lower than that of able-bodied people or wheelchair users. The metabolic cost at a given speed is much higher even if, using a stimulation device, the cardiovascular stress is reduced.     

Skeletal muscle properties and performance in elite female track athletes

Summary Selected biochemical and physiological properties of skeletal muscle were studied in light of performance capabilities in 24 elite female track athletes. The feasibility of quantifying end point histochemistry and relating oxidative staining density (reduced nicotinomide adenine dinucleotide diaphorase: NADH-D) to whole body maximal oxygen consumption ( max) was also investigated, while muscle fiber types, classified according to alkaline APTase stains, were studied and related to muscle oxidative capacity (succinate dehydrogenase: SDH), max and “in vivo” torque-velocity properties. Muscle biopsies were taken from the vastus lateralis of each subject and maximal knee extensor torques were recorded at 30‡ from full extension at four selected velocities. While results confirm earlier reports on skeletal muscle properties and performance it was concluded that end point histochemistry could be reliably quantified and that an “oxidative” stain such as NADH-D correlates extremely well with max (r=0.86,p<0.001) whereas correlations between %slow twitch fibres (alkaline ATPase stain) and max were lower (r=0.44,p<0.05). Additionally, as knee extension velocity increased from 0–1.7 rad·s⁻¹ angle specific extensor torque production did not decline as observed in vitro and pentathletes displayed significantly larger torques at all velocities when compared to the other athletes. These data confirm that while myofibrillar ATPase staining correlates with force-velocity properties of muscle, max is better correlated with quantified oxidative staining. Supported in part by a Public Health Service Biomedical Research Support Grant to UCLA, Public Health Service Grant 10423 and by the National Aeronautics and Space Administration (NASA)     

Human thermoregulatory function during exercise and immersion after 35 days of horizontal bed-rest and recovery

The present study evaluated the effect of 35 days of experimental horizontal bed-rest on exercise and immersion thermoregulatory function. Fifteen healthy male volunteers were assigned to either a Control (n=5) or Bed-rest (n=10) group. Thermoregulatory function was evaluated during a 30-min bout of submaximal exercise on a cycle ergometer, followed immediately by a 100-min immersion in 28°C water. For the Bed-rest group, exercise and immersion thermoregulatory responses observed post-bed-rest were compared with those after a 5 week supervised active recovery period. In both trials, the absolute work load during the exercise portion of the test was identical. During the exercise and immersion, we recorded skin temperature, rectal temperature, the difference in temperature between the forearm and third digit of the right hand (T_{forearm-fingertip})— an index of skin blood flow, sweating rate from the forehead, oxygen uptake and heart rate at minute intervals. Subjects provided ratings of temperature perception and thermal comfort at 5-min intervals. Exercise thermoregulatory responses after bed-rest and recovery were similar. Subjective ratings of temperature perception and thermal comfort during immersion indicated that subjects perceived similar combinations of Tsk and Tre to be warmer and thermally less uncomfortable after bed-rest. The average (SD) exercise-induced increase in Tre relative to resting values was not significantly different between the Post-bed-rest (0.4 (0.2)°C) and Recovery (0.5 (0.2)°C) trials. During the post-exercise immersion, the decrease in Tre, relative to resting values, was significantly (P<0.05) greater in the Post-bed-rest trial (0.9 (0.5)°C) than after recovery (0.4 (0.3)°C). T_{forearm-fingertip} was 5.2 (0.9)°C and 5.8 (1.0)°C at the end of the post-bed-rest and recovery immersions, respectively. The gain of the shivering response (increase in O₂ relative to the decrease in Tre; O₂/Tre) was 1.19 l min^–1°C^–1 in the Recovery trial, and was significantly attenuated to 0.51 l min^–1°C^–1 in the Post-bed-rest trial. The greater cooling rate observed in the post-bed-rest trial is attributed to the greater heat loss and reduced heat production. The former is the result of attenuated cold-induced vasoconstriction and enhanced sweating rate, and the latter a result of a lower shivering O₂ response.     

Cardiac frequency in miners recorded during four to five work shifts

Cardiac frequency (f _c) was recorded in 101 coal-face miners [mean age 32.7 (range 21–49) years, mean height 169.6 (range 150–185) cm, mean body mass 76.9 (range 54–106) kg, mean maximal cardiac frequency (f _cmax) 180.2 (range 154–197) beats min⁻¹, mean maximal oxygen uptake 2.93 (range 1.9–4.0) l · min⁻¹] with a small-size, nonintrusivef _c counter, during the five (n = 76) or at least four (n = 25) work-shifts in a week. Thef _cmax and were determined during a progressive test to exhaustion on a treadmill. Overall (four to five work-shifts) mean work-timef _c (f _c) was 97.7 (range 74.9–122.4) beats · min⁻¹, restingf _c (f _{c rest}) 59.1 (range 50–75) beats · min⁻¹, work-time increase inf _c (f _c —f _{c rest}) 38.5 (range 21.1–55.8) beats · min⁻¹ and percentage off _c reserve used (f _{c reserve} =f _{c max} —f _crest)32.0(range 18.5–50.9). Multiple regression analysis showed thatf _c andf _c —f _{c rest}, as dependent variables, correlated with predicted percentage of CO lung diffusion capacity, (D _LCO_SB%) (r = −0.334 andr = −0.273, respectively) but not with age,f _{c max}, , · kg⁻¹ body mass, effort test Δoxygen uptake/Δf _c or percentage of forced expiratory volume in 1 s as independent variables. The percentage off _{c reserve} used as dependent variable, correlated withD _LCO_SB (r = − 0.265) andf _{c max} (r = − 0.227) but not with any of the other variables listed. Individual differences in worktimef _c are thus large and virtually unpredictable. Other physiological variables not taken in account here (i.e. sense of effort, fatigue perception) as well as psychological ones (work satisfaction, motivation) may have played a role in those differences. At peaks of effort, some subjects reachedf _c values within the range off _{c max}.     

Noninvasive measurement of arterial elasticity in various human limbs

Arterial elasticity expressed by such indices as volume elastic modulus E_v and compliance C_a were noninvasively measured in various human limb segments; the upper arms, forearms, fingers, thighs, calves and toes. These indices are defined, respectively, as and C_a=ΔV/ΔP, where ΔP is pulse pressure, mean arterial volume and ΔV its pulsatile variation. ΔP was calculated from systolic P_as and mean P_am arterial pressures determined by volume oscillometric sphygmomanometry using the following equation: and the ΔV were detected by electrical admittance plethysmography at various transmural pressure P_t levels controlled by a compression cuff. The values obtained in these limb segments were compared with each other at P_t levels 0,30 and 60 mm Hg and the differences between them were discussed.