Influence of air flow and skin temperature on sweating at the onset,during and following exercise

The influence of convective air flow (W_v), skin temperature (T¯_sk) and rapid changes in work rate on local and whole body evaporative sweat loss ([mdot]_sw) has been investigated in 4 healthy male subjects using the technique of resistance hygrometry. The results showed that changes in sweat rate, measured from a capsule placed on the chest or subscapular region of the mack [mdot],_w(cap), can be elicted rapidly (t_1/2< ls) at the onset and cessation of exercise through the response is dependent on T¯_stand the prior thermal slate of the subject. During exercise, [mdot]_sw and [mdot]_SW(cap) were correlated and the latter variable showed a close temporal relationship with the increase in core temperature measured either in the rectum (T_re) or oesophagus though the association could be affected by sudden changes in W_V. At low W_V the sensitivity of [mdot]_sw to changes in T_re and T¯_sk appeared to diminish. Sudden decreases in work rate by reducing running speeds from 16kmh^-1 to 8kmh ^-1 and 14 6kmh^-1 to 11 3kmh^-1 produce a transient increase in [mdot]_sw(cap) which persisted for some minutes. The rise in [mdot]_sw(cap) was associated with an increase in T_sk at the capsule site despite the maintenance of W_V at its high (45ms^-1) prior level. The responses of [mdot]_sw(cap) and [mdot]_swwere little affected by directional changes in W_V, they were the same irrespective of whether the subjects ran with a following, or against a head wind. It is concluded that during exercise the integrating and modulating effects of skin temperature from different regions of the body are responsible for the control of sweat loss under conditions of constant central thermal drive. The practical applications of these results are discussed in relation to running outdoors.     

The effects of variation in body temperature on the preferred water temperature and flow rate during showering

The purpose of this study was to investigate the effects of body temperature variations on subjects' preferred water temperature and flow rate during showers. Nine healthy women students took a shower before and after physical exercise (running on a treadmill for 30 min) and water immersion (immersing in the water of 25^°C temperature for 30?min). During each shower, the subject was instructed to adjust both the water temperature and flow rate of a shower to suit their comfort. Rectal temperature and skin temperatures of the subjects, water temperature, and flow rate of the shower were measured during the experiments. The means of preferred water temperature during showers were 40·2^°C and 43·8^°C before and after water immersion respectively, which were significantly different. On the other hand, there was little difference in the preferred water temperature between before and after the treadmill exercise. There were no significant differences in the flow rates between before and after both water immersion and the treadmill exercise. A significant negative relationship was observed between the mean body temperature (T¯_b) and the preferred water temperature during showers (r=?0·439). On the other hand, no significant relationship was found between T¯_b and the preferred flow rate. Moreover, a significant negative relationship was observed between the preferred water temperature and the flow rate during showers (r=?0·528).     

Estimating physical working capacity and training changes in the elderly at the fatigue threshold (PWCft)

The test for estimating physical working capacity at the fatigue threshold (PWC_ft), previously validated for young men, was evaluated for use with elderly men and women. A sample of 27 volunteer subjects (67·6 ± 5·6 years, 11 male, 16 female) was divided into three matched groups: (1) controls (n = 10), (2) low intensity (70% PWC_ft) training group (n = 10) and (3) high intensity (85% PWC_ft) training group (n = 7). The subjects were tested for PWC_ft before and after 10 weeks of exercise training on cycle ergometers (30min/day, 3 days/week). Controls did not exercise but met once a week for a health lecture. No significant pre-test to post-test change was noted in the mean PWC_ft of the control group (78·8-78·5 W); low intensity training resulted in 29·8% improvement in PWC_ft (81·0 to 105·0 W); and the high intensity group realized an improvement of 38·4% (83·6-115·7 W). One-way ANOVA -indicated that the gains made by each of the groups were significantly different (p < 0·01). Post hoc analysis revealed that the gains made by each exercise training group were significantly greater than controls (p <0·05) with no significant difference between high and low intensity groups. Reproducibility of the PWC_ft was excellent (R = 0·976). Since RPE averaged 14·2 at PWC_ft and 64% of subjects provided useful data, this test appears to be useful for evaluating the fitness of the elderly.     

Ergonomics International

It was the purpose of this study to examine whether replacing long pants (P) with shorts (S) would reduce the heat stress of wearing firefighting protective clothing during exercise in a warm environment. Twenty-four Toronto Firefighters were allocated to one of four groups that performed heavy (H, 4.8?km·h^?1, 5% grade), moderate (M, 4.5?km·h^?1, 2.5% grade), light (L, 4.5?km·h^?1) or very light (VL, 2.5?km·h^?1) exercise while wearing their full protective ensemble and self-contained breathing apparatus. Participants performed a familiarization trial followed by two experimental trials at 35°C and 50% relative humidity wearing either P or S under their protective overpants. Replacing P with S had no impact on the rectal temperature (T_re) or heart rate response during heavy or moderate exercise where exposure times were less than 1?h (40.8?±?5.8 and 53.5?±?9.2?min for H and M, respectively while wearing P, and 43.5?±?5.3 and 54.2?±?8.4?min, respectively while wearing S). In contrast, as exposure times were extended during lighter exercise T_re was reduced by as much as 0.4°C after 80?min of exercise while wearing S. Exposure times were significantly increased from 65.8?±?9.6 and 83.5?±?11.6?min during?L and VL, respectively while wearing P to 73.3?±?8.4 and 97.0?±?12.5?min, respectively while wearing S. It was concluded that replacing P with S under the firefighting protective clothing reduced the heat stress associated with wearing the protective ensemble and extended exposure times approximately 10?–?15% during light exercise. However, during heavier exercise where exposure times were less than 1?h replacing P with S was of little benefit.     

Work tolerance and physiological responses to thermal environment wearing protective NBC clothing

Abstract

Six young, healthy male subjects performed a series of experiments in a climatic chamber in different environmental conditions wearing protective ventilated NBC clothing. Ambient temperature, TA, ranged from -20 to 35°C, relative humidity, RH, from 20 to 85%, and air velocity, VA, from 0·1 to 5·0 ms^?1. In addition, thermal radiation, measured by the temperature of the globothermometer, TG, was artificially increased in some experiments. A total of 32 experiments were performed. The subject had to exercise on a bicycle ergometer at a mechanical power of 60 W for 120 min. Heart rate, HR, oxygen uptake, VO₂, skin temperature, T_sk and rectal temperature, T_re, were measured during the experiments together with the temperature of the space between skin and garment, T_u. Sweat loss was determined as the difference of the body weight before and after the experiment. T_u was well correlated with the chamber environmental parameters. During heat exposure work duration began to decrease progressively from a T_u 30°C, reducing to 40 min at the highest thermal load. About the same value of T_u, marked the departure of HR, VO₂, T_sk and T_re from the values measured during the same work load in neutral conditions. Also, during cold exposure at -20°C work duration was reduced below 1 h, but the limit appeared to be the cold at the extremities. From these findings it appears that T_u is a good indicator of the thermal load and is related to the environmental condition by the equation: T_u = 9·93 + 0·56 TA + 0·023 TG + 0·14 RH (T in °C, RH in %. For better comfort and performance T_u should be monitored whenever a subject has to work wearing an NBC garment and the ventilating system must be adequate to fulfil the needs imposed on the subject by an adverse environment, in particular a high relative humidity.     

The effect of aerodynamic handlebars on oxygen consumption while cycling at a constant speed

Abstract

In this study, the oxygen consumption ([Vdot]O₂) of bicycling was measured at a fixed speed (40 km·h^?1on level terrain, with normal and aerodynamic handlebars using a Douglas bag collection system. Eleven elite (USCF category I or 2) men cyclists age 24 to 40 years (X¯=28·5, SD±4·6) performed four consecutive (two with each bar in alternating order) steady state rides at 40 km· h^?1over a 4 km flat course (same direction each trial). Expired gases were collected in a 1501 Douglas bag attached to a following vehicle during the last 45 s (approx. 0·5 km) of each trial. A repeated measures analysis of variance revealed a significant (p<0·02) handlebar effect. Specifically, [Vdot]O₂was 2% lower under the aerodynamic handlebar treatment (X¯=4·26, SD±0·36 1 min^?1when compared with that of the normal handlebar treatment (X¯=4·34, SD±0·35 1 min^?1The results of this study demonstrate that the reported aerodynamic advantage of the aerodynamic handlebars produces a small but significant reduction in the [Vdot]O₂of bicycling at 40 km·h^?1     

Cardiorespiratory and thermoregulatory response of working in fire-fighter protective clothing in a temperate environment

The cardiorespiratory and thermal responses of two intensities of treadmill exercise were compared for brief periods (12 min) in fire ensemble (FE) but without self contained breathing apparatus, and sports ensemble (SE), in a temperature environment. A further experiment explored the responses of subjects exercising in FE over a prolonged period (60 min). Eighteen male firefighters wearing either FE or SE walked on a level treadmill for 6 min at 5 km.h^-1 increasing to 7 km.h^-1 for 6 min. Following a recovery interval of 1 h, the exercise protocol was repeated in the second ensemble; the order of ensemble was balanced. Heart rate (HR), rectal temperature (T_re ), VO _2max and rating of perceived exertion (RPE) were monitored continuously under both ensembles. At 7 km.h^-1, VO ₂ was significantly higher (p<0.05) in FE (36.1 and 39.9 ml.kg^-1.min^-1) than in SE and represented 74% V _{O2 max}. There were no changes T _re. In experiment 2, following a rest interval of at least 36 h, eight subjects in FE walked on the treadmill at 6 km.h ^-1 (gradient 10%) for 60 min also in temperate conditions, where HR, T _re and R PE were recorded at 10-min intervals. During the 60-min exercise in FE, HR reached 161 beats.min ^-1 and T _re increased to 38.38°C. Despite considerable subject discomfort, T _re remained below dangerous levels (38.48°C). When R PE were compared with a physiological strain index (PSI) calculated from T _re and HR data over 60 min, there was no significant difference (p <0.05) with a correlation coefficient (r) of 0.98. The results suggest that R PE and PSI are closely related when exercise is sufficiently prolonged or intense to elevate T _re and HR in fire-fighters wearing FE in temperate conditions. If further investigation confirms this relationship for hot humid conditions in which fire-fighters operate, then with training, it may provide individuals with a valid measure of dangerous levels of perceived heat strain.     

The effect of glycogen depletion on the curvature constant parameter of the power-duration curve for cycle ergometry

For high-intensity cycle ergometer exercise, the relation between power (P) and its tolerable duration (t) has been well characterized by the hyperbolic relationship: (P-θ_F)t = W', or P = W'(1/t)+θ_F, where θ_F may be termed the ‘fatigue threshold’. The curvature constant (W') reflects a constant amount of work which is postulated to be equivalent to a finite energy store that relates to the oxygen-deficit: phosphagen pool, anaerobic glycolysis and oxygen stores. Compared to theta_F, the physiological nature of W' has received little consideration. The purpose of this study was therefore to establish the parameters of the power-duration curve (θ_F and W') for subjects in normal glycogen (NG) and glycogen depleted (GD) states. Seven healthy male subjects (aged 22 to 41 years) each performed four high-intensity square-wave exercise bouts on an electrically braked cycle ergometer under two different muscular glycogen content conditions, i.e. NG and GD states. Subjects performed the following exercise on the evening before the trial day to induce the GD state. Initially, they performed a 75-min cycling exercise at 60% of VO₂max. After a 5-min rest period, they subsequently repeated a 1-min cycling bout at 115% of VO₂max (separated by 1-min rest periods) until the subject could no longer maintain the prescribed pedal rate for the full minute. Subjects then reported to the laboratory after an overnight fast and performed a single high-intensity exercise bout. The GD procedure was repeated four times at 1-week intervals. In the GD state, the respiratory exchange ratio (RER) (VO₂/VCO₂) value during a recumbent control period prior to the trial was significantly lower than that in the NG state [GD: 0.84±0.02, NG: 0.94±0.04, mean±SD]. There was no significant difference for θ_F between GD and NG state [NG: 197.1±31.9 W, GD: 190.6±28.2 W]. W' in contrast was significantly reduced by the GD procedure [NG: 12.83±2.21 kJ, GD: 10.33±2.41 kJ]. The present results indicate that the muscular glycogen store seems to be an important determinant of the curvature constant (W') of the power-duration curve for cycle ergometry.     

Hyperoxia improves maximal exercise with the self-contained breathing apparatus (SCBA)

The effects of hyperoxia on maximal exercise while breathing from a self-contained breathing apparatus (SCBA) were studied in 25 males. Each participant completed three graded exercise tests (GXT) for the assessment of maximal oxygen uptake (Vdot;O _2max): two with 20.95 ± 0.28% O₂ and the third (GXT₄₀) while breathing hyperoxia (40.64 ± 1.29% O₂). No significant differences were found between the two normoxic tests, except for a 16W increase in maximal power output (PO_max) in the second trial (GXT₂₁). Compared to GXT₂₁, hyperoxia significantly increased Vdot;O _2max and PO_max by 10.0 ± 3.8% and 10.2 ± 7.1%, respectively. This was likely due to an increase in O₂ delivery as suggested by the significantly higher oxyhemoglobin saturation. The increase in Vdot;O _2max with hyperoxia was similar to the increase in carbon dioxide production (9.3 ± 6.5%). No other significant differences were found at maximal exercise. However, at the intensity that elicited Vdot;O _2max in GXT₂₁, pulmonary ventilation and SCBA mask pressure were significantly lower during GXT₄₀, suggesting a decrease in the work of breathing. These findings could have significant implications for occupations that involve heavy work with SCBA.     

The accuracy of the critical power test for predicting time to exhaustion during cycle ergometry

The purpose of this study was to determine the relationship between actual time to exhaustion or time limit (AT_LIM) during bicycle ergometry and predicted time to exhaustion (PT_LIM from the Critical Power (CP) test Fourteen males (x¯ ± SD = 22·36 ± 2·13 years) volunteered as subjects for this investigation. The subjects visited the laboratory on seven occasions separated by at least 24 h. The first two visits were used for the determination of CP; during the remaining sessions the subjects rode a Monarch bicycle ergometer at power loadings of CP — 20%, CP, CP + 20%, CP + 40% and CP + 60% for the determination of AT_LIM. Theoretically, power loadings les;CP can be maintained indefinitely without exhaustion and the PT_LIM for power loadings > CP can be estimated from the results of the CP test. The accuracy of the CP test for estimating the time to exhasution during bicycle ergometry was determined by comparing AT_LIM to PT_LIM using correlation coefficients, standard error of estimates and related t-tests. The results of this study indicated that there were no significant (p > 0·05) differences between AT_LIM and PT_LIM for power loadings > CP (AT_LIM vs PT_LIM at CP + 20% = 8·19 ± 3·90 vs 7·13 ± 2·69min, t = 2·106, r =0·893, SEE = l·21min; CP + 40% = 3·60 ± 1·37 vs 3·46 ± 1·18min, t = 0·842, r = 0·882, SEE = 0·556min; CP + 60% = 2·36 ± 0·95 vs 2·32 ± 0·79min; t = 0·328 r = 0·841, SEE = 0·428min). Power curve analyses however, indicated that the CP test overestimated the power loading which could be maintained for 60 min by a mean of approximately 17%.     

The relation between cycling time to exhaustion and anaerobic threshold

Abstract

This study investigated whether the anaerobic threshold (AnT) could be used to predict prolonged work capacity measured as cycling time to exhaustion (= endurance time) and which factors, in addition to relative exercise intensity, could explain variation in endurance time. Theoretical exercise intensities corresponding to certain endurance times were also calculated. The hyperbolic and exponential functions between cycling time and relative work rate (WR[%]), as well as between cyling time and relative oxygen uptake ([Vdot]O₂[%]) were fitted to the pooled data (n = 45) of 17 subjects. The WR(%) and [Vdot]O₂ (%) were expressed as a percentage of the subject's own AnT- and maximum -values. At WR corresponding to AnT (i.e., 70% of WR_max) an average subject could cycle 60 min according to both AnT- or maximum-related exponential function. When prediction was done for an endurance time of 4 h, the AnT-related exponential function gave 2·9%-units ( = 11 W or ～0·15 O₂1 · min^?1) lower intensity level (51% of WR_max than the maximum-related function (54% of WR_max). The WR(%) alone explained 54% and 70% of the variation in endurance time of the AnT-related and maximum-related exponential functions, respectively. Muscle fibre composition and initial blood lactate or relative muscle glycogen depletion (change in muscle glycogen as percentage) increased significantly the explanatory power of these models. The differences between the observed and expected exercise times correlated with blood lactate accumulation (r = ?0·42; p < 0·01), muscle fibre composition (r = 0·33; p < 0·05) and relative muscle glycogen depletion (r = 0·67; p < 0·01). It was concluded that the capacity for prolonged work measured as cycling time to exhaustion can be estimated by AnT-related power output, and that the exponential function model is the most suitable. Prediction power of the model can be improved by multiple regressions including muscle fibre composition, initial blood lactate level and relative muscle glycogen depletion.     

Using trunk posture to monitor heat strain at work

Abstract

This study aimed to determine if trunk posture during walking is related to increases in rectal temperature (T_re). 24 males treadmill walked in one of four conditions (1): 30?min at 3.0?mph and 0% grade, 20?°C and 50% relative humidity (RH), wearing healthcare worker (HCW) PPE; (2): 30?min at 3.0?mph and 0% grade, 27.5?°C and 60% RH, HCW PPE; (3): 30?min at 3.0?mph and 0% grade, 32.5?°C and 70% RH, HCW PPE; and (4): 40?min at 40% VO₂max, 30?°C and 70% RH, wearing firefighter PPE. Trunk posture (Zephyr BioHarness 3) and T_re were measured continuously. T_re was positively related to trunk posture, controlling for covariates (B?=?3.49, p?<?.001). BMI and age moderated this relationship (T_re×age, B?=?0.76, p?<?.001; T_re*BMI, B?=??1.85, p?<?.001). Trunk posture measurement may be useful in monitoring fall potential and magnitude of heat stress of workers in hot environments.

Practitioner Summary: Occupational hyperthermia increases worker risk for heat illness and injury but is difficult to monitor in the field. This investigation shows that trunk posture is independently and positively related to core temperature. Non-invasive measurement or visual inspection of trunk posture could provide novel insight on individual heat strain level.     

DEPARTMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH: HUMAN SCIENCES COMMITTEE

Maximal power output during short term constant velocity cycling and vertical jumping from a force platform has been studied in five healthy young male subjects. From the measurements on the force platform the peak (instantaneous) power output (P), net impulse (I_N ), force (F₁ ). velocity of take-off(V_T ) and height of jump(h) were calculated. The corresponding values for power (H), force (F) and velocity (V) on the bicycle were obtained from analysis of the force-velocity relationship.

The results (mean ± S.D.) showed that on the force platform F₁ P, I_N, V_T and h were 1073± 167N, 2205±310W, 154±17Ns, 2·48+0·15ms^?1 and 31 +4cm. h was positively associated with both I_N (r= +0·77) and P (r = 0·67). The mean maximal power output for cycling was 854W(39%) greater than jumping and was achieved at a 271N (25%) increase in F and a reduction in V. Nevertheless they were closely related.

Platform P(W) = 717·6 + 0·483 bicycle H(W) r= +0·74

A comparison of linear and curvilinear (hyperbolic) analysis of the F/V bicycle data showed that the latter did not reduce the variance of observations and was not, therefore, statistically justifiable (Wilkie 1950). The mean intra-subject variations of P and H were 6·6%± 1·8 and 40%+1·2. The relative values of F and V at H were both found to be approximately 50% of their respective maximal values.

It was concluded that short term power output can be measured simply and accurately in man during the performance of two activities. Rotational movement of the legs as in cycling produces higher values of peak power output then vertically lifting body weight. For the achievement of peak power output in cycling, relative force and speed of movement must both correspond to approximately half of their respective maximal values.     

Validation and adjustment of the mathematical prediction model for human rectal temperature responses to outdoor environmental conditions

Abstract

Models to predict rectal temperature (T_re ) have been based on indoor laboratory studies. The present study was conducted to validate and adjust a previously suggested model for outdoor environmental conditions. Four groups of young male volunteers were exposed to three different climatic conditions (30°C, 65% rh; 31°C, 41% rh; 40°C, 20% rh). They were tested both in shaded and open field areas (radiation: 80 and 900 W-m^?2, respectively) at different work loads (100, 300 and 450 watt). Exercise consisted of two bouts of 10 minutes rest and 50 minutes walking on a treadmill, at a constant speed (1.4m ? s^?1) and different grades. The subjects were tested wearing cotton fatigues and protective garments. Their T_re and heart rate were monitored every 5 min and skin temperature every 15 min, oxygen uptake was measured towards the end of each bout of exercise; concomitantly, ambient temperature, relative humidity and solar load were monitored. We concluded that: (a) the corrected model to predict rectal temperature overestimates the actual measurements when applied outdoors; ( b) radiative and convective heat exchanges should be considered separately when using the model outdoors; ( c) radiative heat exchange should also be considered separately for short-wave radiation (solar radiation) and long-wave emission from the body to the atmosphere. Finally, an adjusted model to be used outdoors was suggested.     

Physiological strain of next generation combat uniforms with chemical and biological protection: importance of clothing vents

This study examined whether vents in the arms, legs and chest of new protective assault uniforms (PTAU) reduced heat strain at 35°C during a low dressed state (DS_low), and subsequently improved tolerance time (TT) after transitioning to DS_high compared with the battle dress uniform and overgarment (BDU+O). Small but significant reductions in rectal temperature (T _re), heart rate and vapour pressures over the thigh and shin were observed during DS_low with vents open (37.9 ± 0.2°C, 120 ± 10 b/min, 3.7 ± 0.4 and 3.5 ± 1.0 kPa) versus closed (38.0 ± 0.1°C, 127 ± 5 b/min, 4.3 ± 0.3 and 4.6 ± 0.5 kPa). During DS_high T _re was reduced and TT increased significantly with the PTAUs (1.1 ± 0.2°C/h and 46 ± 24 min) versus BDU+O (1.6 ± 0.2°C/h and 33 ± 16 min). The vents marginally reduced heat strain during DS_low and extended TT during DS_high compared with BDU+O.

Practitioner Summary: Clothing vents in chemical and biological protective uniforms can assist with heat transfer in situations where the uniforms must be worn for extended periods prior to exposure to a hazardous condition. Once the vents are closed, exposure time is increased and the increase in body temperature reduced.     

A new kayak ergometer based on wind resistance

Abstract

An ergometer for kayak paddlers has been developed and used for winter training, measurements of work capacity and maximal oxygen uptake ([Vdot]O₂ max). Force is transmitted from the paddle by means of a wire connected to a flywheel mounted with six 9 × 9cm blades. Resistance, therefore, is based on wind turbulence generated by the flywheel. The mechanical efficiency of the ergometer at 63% (range 48-77) of [Vdot]O₂ max was 17% (range 16-18) (n= 13). The [Vdot]O₂ max was similar during bicycling (median 4·9; range 4·4-5·4l/min), arm cranking (median 4·8; range 4·3-5·11/min), on-water rowing in a kayak (median 4·7; range 4·0-4·91/min) and during rowing the kayak ergometer (median 4·8; range 4·3-5·21/min), (n = 6, p> 0·05). Work capacity during a 5 min ‘all-out’ test was 272 W (range 253–304 W) on the kayak ergometer (n = 17). The use of the ergometer for training helped to increase the aerobic power during arm exercise of Danish paddlers. Before introduction of the ergometer (February 1986), their VO₂ max was 4·6 (range 3·8-5·2) 1/min while 12 months later, it was 50 (range 4·2–5·7) 1/min (n = 14, p < 0·01). The ergometer has thus been found.useful for training and evaluation of work capacity in kayak paddlers.     

Intermittent microclimate cooling during rest increases work capacity and reduces heat stress

Requirements for special protective equipment while working in hazardous environments can present a significantly increased thermal burden and early onset of physical fatigue. Ambulatory (backpack) or tethered personal cooling can accelerate metabolic heat removal, but is often not practical from an ergonomic standpoint. The efficacy of incorporating personal cooling during non-ambulatory rest periods was evaluated in subjects (n=8) with varying levels of fitness. Treadmill work (≈475 W, 40% [Vdot]O₂max) was alternately performed for 30 min followed by 30 min of rest. Subjects walked and rested under three separate experimental conditions: (1) control (C), in which light clothing was worn; (2) CPE, in which a chemical protective ensemble (CPE) was worn, and (3) CPE plus intermittent microclimate cooling (COOL). The WBGTcondition for all trials was 31°C. During the COOL trial the subjects additionally wore a personal cooling vest which allowed for the circulation of chilled liquid over the torso during rest. Under C conditions, relatively modest changes in rectal temperature (T _re ) were observed, which stabilized over time. CPE wear resulted in a progessive rise in T _re and early fatigue. The addition of intermittent cooling during each rest cycle (COOL trial) significantly attenuated heat storage such that an oscillating, but equilibrated T _re was established and work capacity was at least doubled. Moreover, the perceived cooling effect was appreciable for all subjects. Therefore, intermittent personal cooling provided a useful means of enhancing work productivity and may have application for certain military and industrial personnel performing heavy work in hot environments. This approach should provide a practical alternative for reducing stress/fatigue when work/rest cycles are employed.     

Dead space in the breathing apparatus; interaction with ventilation

Dead space in breathing apparatus may cause increased ventilation and/or CO₂ retention. Interactions between ventilation and dead space were tested in the breathing apparatus of three divers: a full face mask with an oro-nasal cup (AGA), a full face mask without an oro-nasal cup (EXO-26) but designed to minimize dead space, and one mouthpiece. Experiments were performed at three depths; 0, 30 and 45 m seawater (msw). The breathing gas was air except at 30 msw where it was 36 O₂ in N₂. Five certified SCUBA divers were exercised at three levels (0, 50 and 100 W), Ventilation and gas exchange were measured. The dead space in the AGA mask was not influenced by either depth or exercise (mean 0·201). The mean dead space of the EXO-26 was 0·341, but it increased with exercise (p<0·001) and decreased with depth (p<0·03). Since the dead space can vary with ventilation levels it is not sufficient to test breathing apparatus only at rest as is required by the US National Institute of Occupational Safety and Health. The mean ventilation with the EXO-26 was higher than with the AGA by 10% at SOW (p<0·05) and by 12% (p < 0·01) at 100 W. The same comparison for end-tidal CO₂ showed mean increase by 0·30 kPa at the 100-W workload (P < 0·05); changes at other workloads were not statistically significant. Comparisons of the mean inspired PCO₂ to the maximum values considered acceptable by various organizations showed that the mouthpiece was always acceptable, the AGA mask was marginally acceptable or better, while sometimes the EXO-26 was not acceptable.     

Arm strength and impulse generation: Initiation of wheelchair movement by the physically disabled

The initiation of wheelchair movement is a function of starting technique, upper extremity strength and the stabilizing potential of the trunk musculature. This study examined the relation between arm strength, activity level, degree of disability and the maximum impulse generated from a resting position while seated in a wheelchair. Two starting techniques were examined using a force platform.

Sixteen male paraplegic adults (age 28·1 ±6·9 year, supine length l·62±0·16m, total body mass 61·2±16·2 kg) performed three grab starts and three strike starts on a Kistler force platform. For each technique, the processed data were averaged together and impulse in the forward/backward and vertical directions was determined. Isokinetic shoulder flexion and elbow extension moments of force were measured at an angular velocity of 60 degs^?1. Peak power and average power were calculated from digitized values of the moment of force-time curves.

Subjects were classified as highly active (HA, >2 exercise periods per week, N = 8) or less active (LA, N = 8). In addition, the site of spinal cord injury was quantified as a high level lesion (HL, above T10, N = 7) or low level lesion (LL, N = 9). There were no differences (p>0·05) between activity or lesion level groups with respect to age, height, total body mass or skinfold thicknesses. Nor were there significant differences between groups for shoulder and elbow power values. However, shoulder flexion scores for the combined groups were greater than those scores for elbow extension (peak power, 72·9 W versus 49·5 W; average power, 51·8 W versus 37·2 W). The grab start produced more forward impulse (the integral of forward force × time) (152·6 N s) than the strike start (119·5 N s, p < 0·05), but the magnitude of this difference was similar for the several groups. Wheelchair impulse scores were well correlated with strength values in both HA and LA subjects (r=0·74 to 0·89). However, the intercepts of the regression lines were dissimilar between activity groups, suggesting an interaction between activity pattern, muscle force and impulse.     

Exercise testing in children: an alternative approach

In recent years there has been a call for new methods of evaluating the cardiorespiratory responses of children to exercise that complement their everyday exercise patterns. One potential method would be to use a sub-maximal, intermittent, pseudo-random binary sequence (PRBS) exercise test protocol to measure oxygen uptake kinetics (VO_{2 kinetics}). Ten children of mean (SD) age 10.8 (± 1.5) years completed a 20–50 W cycle ergometer protocol of 17-min duration. An estimate of alveolar oxygen uptake (VO₂) was calculated on a breath-by-breath basis. The VO₂ kinetic parameters were expressed in the frequency domain as amplitude ratio and phase delay using standard Fourier techniques. Analysis was restricted to the frequency range 2.2 to 8.9 mHz. The mean (SD) amplitude ratio responses decreased from 10.33 (± 0.73) to 7.42 (± 0.99) ml min^?1 W^?1 and the mean phase delay increased from -26.78° (± 6.37°) to -81.93° (± 10.45°) over the frequency range 2.2-8.9 mHz. Significant correlations (p<0.05) were found between chronological age and amplitude ratio (r= 0.68 and 0.62), and chronological age and phase delay (r= -0.62 and -0.69) at the frequencies of 2.2 and 4.4 mHz, respectively. No significant correlations were found between VO_{2 kinetics} and stature or VO_{2 kinetics} and body mass. The observations demonstrated the use of the PRBS technique to measure VO_{2 kinetics} in the frequency domain in children. This approach may be a useful addition to the tests that are used to quantify the oxygen uptake responses to exercise in children.