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

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 degrees C, relative humidity, RH, from 20 to 85%, and air velocity, VA, from 0 center dot 1 to 5 center dot 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, Tsk, and rectal temperature, Tre, were measured during the experiments together with the temperature of the space between skin and garment, Tmu. Sweat loss was determined as the difference of the body weight before and after the experiment. Tmu was well correlated with the chamber environmental parameters. During heat exposure work duration began to decrease progressively from a Tmu > 30 degrees C, reducing to 40 min at the highest thermal load. About the same value of Tmu marked the departure of HR, VO2, Tsk and Tre from the values measured during the same work load in neutral conditions. Also, during cold exposure at -20 degrees 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 Tmu is a good indicator of the thermal load and is related to the environmental condition by the equation: Tmu = 9 center dot 93 + 0 center dot 56 TA + 0 center dot 023 TG + 0 center dot 14 RH (T in degrees C, RH in %). For better comfort and performance Tmu 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 energy cost of level cross-country skiing and the effect of the friction of the ski.

Oxygen consumption [(VO2) in ml.kg-1.min-1], blood lactate concentration ([La] in mM) and dynamic friction of the skis on snow [(F) in N] were measured in six athletes skiing on a level track at different speeds [(v) in m.min-1] and using different methods of propulsion. The VO2 increased with v and F, the latter depending mostly on snow temperature, as did [La]. The VO2 was very much affected by the skiing technique. Multiple regression equations gave the following results: with diagonal stride (DS), VO2 = -23.09 + 0.189 v + 0.62 N; with double pole (DP), VO2 = -30.95 + 0.192 v + 0.51 N; and with the new skating technique (S), VO2 = -32.63 + 0.171 + 0.68 N. In terms of VO2 DS is the most expensive technique, while S is the least expensive; however, as F increases, S, at the highest speed, tends to cost as much as DP. At speeds from 18 to 22 km.h-1, the speeds measured in the competitions, the F for DS and DP can represent from 10% to 50% of the energy expenditure, with F ranging from 10 to 60 N; with S this range increases to 20%-70%. This seems to depend on the interface between the skis and the snow and on the different ways the poles are used.

Maximal anaerobic (lactic) capacity and power of the horse.

Blood lactate concentrations were determined in 16 horses (three Thoroughbreds, seven Standardbreds and six polo ponies) before and 5 mins after they galloped over distances of 200, 300 and 400 m at maximal speed. The highest net lactate concentration (delta Lamax) of 14 to 15 mmol/litre was attained by the polo ponies and the highest speed by the Thoroughbreds. The maximal rate of lactate production (delta Låmax) was about 35 mmol/litre X min for the polo ponies and 20 to 25 mmol/litre X min for the Standardbreds and the Thoroughbreds. Values for delta Lamax and delta Låmax were similar to those measured in human athletes after exhaustive work. delta Låmax increases with the speed (v) and can be described by the equation delta Lå = a (v-v1), where a is a proportionality constant representing the amount of lactate needed to cover a unit distance and v1 the theoretical speed at which delta Lå = 0 X v1 was highest for the Thoroughbreds and lowest for the polo ponies; this difference could be caused by the effect of training and/or to genetic differences among the different breeds of horses X v1 could be a useful index of the fitness of a horse following a training programme.

Energy sources in alpine skiing (giant slalom).

The energy cost of a giant slalom event was measured in eight skiers of national level. The lap lasted on average 82 s. VO2 was measured during the first, the second and the last third of the lap in different trials and also during recovery from a complete lap. Blood lactate was measured at the end of a lap. From the data obtained it was possible to calculate that: a) VO2, as measured during the lap, would correspond at steady state to 80% of the VO2max of the subjects; b) the total metabolic power delivered during the lap should be equal to about 72 ml O2 X kg-1 X min-1, corresponding to 120% of VO2max of the subjects. Considering the short duration of the trial and the power output delivered during maximal efforts on a bicycle ergometer, it appears that the giant slalom is not a very high energy demanding event.

Equation of motion of a cyclist.

Tractional resistance (RT, N) was determined by towing two cyclists on a racing bike in "fully dropped" posture in calm air on a flat track at constant speed (5--16.5 m/s). RT increased with the air velocity (v, m/s): RT = 3.2 + 0.19 V2. The constant 3.2 N is interpreted as the rolling resistance and the term increasing with v2 as the air resistance. For a given posture this is a function of the body surface (SA, m2), the air temperature (T, degree K), and barometric pressure (PB, Torr). The mechanical power output (W, W) can then be described as a function of the air (v) and ground (s) speed: W = 4.5.10(-2) Ps + 4.1.10(-2) SA (PB/T)v2 s, where P is the overall weight in kg. With a mechanical efficiency of 0.25, the energy expenditure rate (VO2, ml/s) is given by: VO2 = 8.6.10(-3) Ps + 7.8.10(-3) SA (PB/T)v2 s (1 ml O2 = 20.9 J). As the decrease of VO2max with altitude is known from the literature, this last equation allows the calculation of the optimal altitude for top aerobic performance. The prediction derived from this equation is consistent with the present 1-h world record.

A method for the in situ measurement of the electrical quantities in frog skin.

A method allowing the measurement of the electrical quantities related to the physiological functions of the frog skin in situ is presented. The method allows the performance of several experiments on the same pithed animal, which remains alive for a number of days. The preparation is very stable, and the electrical potential difference and short-circuit current values are higher than in isolated skin. The theory of measurement and the possible systematic errors are discussed. The possibilities of the method are evaluated on comparing the pH and temperature dependence of the electrical quantities in situ with previous measurements on isolated skin.

Hemoglobin-oxygen equilibrium at different hemoglobin and 2,3-diphosphoglycerate concentrations.

Hemoglobin-oxygen equilibrium curves at constant pH, ionic strength, and temperature were determined (a) on 2,3-DPG-free solutions at various hemoglobin (Hb) concentrations, (b) on solutions at various Hb concentrations but constant 2,3-DPG/Hb molar ratio, (c) on solutions at constant hemoglobin concentration but various 2,3-DPG/Hb molar ratios, and (d) on hemolysates at various Hb concentrations. Under all conditions the shape of the equilibrium curve was the same (n = 2.62 +/- 0.04, 33 experiments). Half-saturation pressure (P 1/2) did not change with increasing Hb concentration in case (a), whereas P 1/2 was linearly related to Hb concentration in case (b). In case (c) at 200 g/l Hb, P 1/2 increased sharply as 2,3-DPG/Hb molar ratio increased up to 0.4 but changed little as the ratio was further increased up to 1.5. This behavior is very different from that observed in diluted (5 g/l) solutions. P 1/2 of the hemolysates was also linearly related to Hb concentration but the slope was about twice that for case (b). These results cannot be explained by linked function theory or by a dimer-tetramer equilibrium. It is suggested that intermolecular interactions in the presence of organic phosphates may be responsible for the observed changes in Hb affinity for oxygen.

Energy cost of speec skating and efficiency of work against air resistance.

The energy expenditure during speed ice skating (PB=650 mmHg; T=-5 degrees C) was measured on 13 athletes (speed range: 4-12 m/s) from VO2 and (for speeds greater than 10 m/s) from blood lactic acid concentration. The energy spent (O2 equivalents) per unit body wt and unit distance (Etot/V, ml/kg-min) increases with the speed (v, m/s): Etot/v=0.049 + 0.44 X 10(-3) V2. At 10 m/s, Vtot/v amounts then to 0.093 ml/kg-m: about half the value of running. The constant 0.049 ml/kg-m is interpreted as the energy spent against gravitational and inertial forces. The term 0.44 X 10(-3) v2 indicates the energy spent against the wind, the constant 0.44 X 10(-3) ml-s2-kg-1-m-3 being a measure of k/e, where k is the coefficient relating drag to v2, and e the efficiency of work against the wind. From a direct estimate of k in a wind tunnel, e was calculated as 0.11. In running, skating, and cycling k/e is similar (approximately 0.020 ml-s2-m-3 per m2 body area), hence at a given speed the energy spent against the wind is equal. On the contrary, the energy spent against other forces decreases in the above order: 0.19, 0.05, 0.018 ml-m-1 per kg body wt. This explains the different speeds attained in these exercises with the same power output.