Physostigmine: dose-response effects on endurance and thermoregulation during exercise.

We previously reported that the administration of 200 micrograms/kg of physostigmine (PH) to rats exercising on a treadmill resulted in decrements in both endurance (decreased running time to exhaustion) and thermoregulation. However, it was necessary to determine the dose-response effects of PH administration before PH-treated exercising rats could be used as a model with which to examine the relative anticholinergic potency of drugs. In the present work saline, 50, 100, or 200 micrograms/kg of physostigmine salicylate (0%, 40%, 50%, and 60% whole blood cholinesterase inhibition) was administered to rats (N = 12/group) prior to treadmill exercise (26 degrees C, 50% rh, 11 m/min, 6 degrees incline). The saline control group ran for 67 +/- 6 min (mean +/- SE) with a rate of rise of core temperature of 0.051 +/- 0.007 degrees C/min. The run times declined (80%, 64% and 48% of control) as rate of rise of core temperature increased (116%, 180%, and 214% of control) in a dose-dependent manner (50, 100, 200 micrograms/kg PH). Cholinergic symptoms such as salivation, tremors, and defecation were also affected in a dose-dependent manner by PH administration. Since cholinergic symptoms, thermoregulatory effects, and endurance decrements all vary in a dose-dependent manner with physostigmine administration, the exercising rat represents a useful model for examining the relative potency of cholinergic therapies.     

Dynamics of thermographic skin temperature response during squat exercise at two different speeds

Low intensity resistance training with slow movement and tonic force generation has been shown to create blood flow restriction within muscles that may affect thermoregulation through the skin. We aimed to investigate the influence of two speeds of exercise execution on skin temperature dynamics using infrared thermography. Thirteen active males performed randomly two sessions of squat exercise (normal speed, 1 s eccentric/1 s concentric phase, 1 s; slow speed, 5 s eccentric/5 s concentric phase, 5 s), using ~50% of 1 maximal repetition. Thermal images of ST above muscles quadriceps were recorded at a rate of 0.05 Hz before the exercise (to determine basal ST) and for 480 s following the initiation of the exercise (to determine the nonsteady-state time course of ST). Results showed that ST changed more slowly during the 5 s exercise (p=0.002), whereas the delta (with respect to basal) excursions were similar for the two exercises (p>0.05). In summary, our data provided a detailed nonsteady-state portrait of ST changes following squat exercises executed at two different speeds. These results lay the basis for further investigations entailing the joint use of infrared thermography and Doppler flowmetry to study the events taking place both at the skin and the muscle level during exercises executed at slow speed.     

Time-of-day effects of exposure to solar radiation on thermoregulation during outdoor exercise in the heat

High solar radiation has been recognised as a contributing factor to exertional heat-related illness in individuals exercising outdoors in the heat. Although solar radiation intensity has been known to have similar time-of-day variation as body temperature, the relationship between fluctuations in solar radiation associated with diurnal change in the angle of sunlight and thermoregulatory responses in individuals exercising outdoors in a hot environment remains largely unknown. The present study therefore investigated the time-of-day effects of variations in solar radiation associated with changing solar elevation angle on thermoregulatory responses during moderate-intensity outdoor exercise in the heat of summer. Eight healthy, high school baseball players, heat-acclimatised male volunteers completed a 3-h outdoor baseball trainings under the clear sky in the heat. The trainings were commenced at 0900 h in AM trial and at 1600 h in PM trial each on a separate day. Solar radiation and solar elevation angle during exercise continued to increase in AM (672–1107 W/m² and 44–69°) and decrease in PM (717–0 W/m² and 34–0°) and were higher on AM than on PM (both P < 0.001). Although ambient temperature (AM 32–36°C, PM 36–30°C) and wet-bulb globe temperature (AM 31–33°C, PM 34–27°C) also continued to increase in AM and decrease in PM, there were no differences between trials in these (both P > 0.05). Tympanic temperature measured by an infrared tympanic thermometer and mean skin temperature were higher in AM than PM at 120 and 180 min (P < 0.05). Skin temperature was higher in AM than PM at the upper arm and thigh at 120 min (P < 0.05) and at the calf at 120 and 180 min (both P < 0.05). Body heat gain from the sun was greater during exercise in AM than PM (P < 0.0001), at 0–60 min in PM than AM (P < 0.0001) and at 120–180 min in AM than PM (P < 0.0001). Dry heat loss during exercise was greater at 0–60 min (P < 0.0001), and lower at 60–120 min (P < 0.05) and 120–180 min (P < 0.0001) in AM than PM. Evaporative heat loss during exercise was greater in PM than AM at 120–180 min (P < 0.0001). Total (dry + evaporation) heat loss at the skin was greater during exercise in PM than AM (P < 0.0001), at 0–60 min in AM than PM (P < 0.0001) and at 60–120 and 120–180 min in PM than AM (P < 0.05 and 0.0001). Heart rate at 120–150 min was also higher in AM than PM (P < 0.05). Neither perceived thermal sensation nor rating of perceived exertion was different between trials (both P > 0.05). The current study demonstrates a greater thermoregulatory strain in the morning than in the afternoon resulting from a higher body temperature and heart rate in relation to an increase in environmental heat stress with rising solar radiation and solar elevation angle during moderate-intensity outdoor exercise in the heat. This response is associated with a lesser net heat loss at the skin and a greater body heat gain from the sun in the morning compared with the afternoon.     

Impact of muscle injury and accompanying inflammatory response on thermoregulation during exercise in the heat.

This study examined whether muscle injury and the accompanying inflammatory responses alter thermoregulation during subsequent exercise-heat stress. Sixteen subjects performed 50 min of treadmill exercise (45-50% maximal O(2) consumption) in a hot room (40 degrees C, 20% relative humidity) before and at select times after eccentric upper body (UBE) and/or eccentric lower body (LBE) exercise. In experiment 1, eight subjects performed treadmill exercise before and 6, 25, and 30 h after UBE and then 6, 25, and 30 h after LBE. In experiment 2, eight subjects performed treadmill exercise before and 2, 7, and 26 h after LBE only. UBE and LBE produced marked soreness and significantly elevated creatine kinase levels (P < 0.05), but only LBE increased (P < 0.05) interleukin-6 levels. In experiment 1, core temperatures before and during exercise-heat stress were similar for control and after UBE, but some evidence for higher core temperatures was found after LBE. In experiment 2, core temperatures during exercise-heat stress were 0.2-0.3 degrees C (P < 0.05) above control values at 2 and 7 h after LBE. The added thermal strain after LBE (P < 0.05) was associated with higher metabolic rate (r = 0.70 and 0.68 at 2 and 6-7 h, respectively) but was not related (P > 0.05) to muscle soreness (r = 0.47 at 6-7 h), plasma interleukin-6 (r = 0.35 at 6-7 h), or peak creatine kinase levels (r = 0.22). Local sweating responses (threshold core temperature and slope) were not altered by UBE or LBE. The results suggest that profuse muscle injury can increase body core temperature during exercise-heat stress and that the added heat storage cannot be attributed solely to increased heat production.     

Reliability and validity of skin temperature measurement by telemetry thermistors and a thermal camera during exercise in the heat

New technologies afford convenient modalities for skin temperature (T_SKIN) measurement, notably involving wireless telemetry and non-contact infrared thermometry. The purpose of this study was to investigate the validity and reliability of skin temperature measurements using a telemetry thermistor system (TT) and thermal camera (TC) during exercise in a hot environment. Each system was compared against a certified thermocouple, measuring the surface temperature of a metal block in a thermostatically controlled waterbath. Fourteen recreational athletes completed two incremental running tests, separated by one week. Skin temperatures were measured simultaneously with TT and TC compared against a hard-wired thermistor system (HW) throughout rest and exercise. Post hoc calibration based on waterbath results displayed good validity for TT (mean bias [MB]=−0.18 °C, typical error [TE]=0.18 °C) and reliability (MB=−0.05 °C, TE=0.31 °C) throughout rest and exercise. Poor validity (MB=−1.4 °C, TE=0.35 °C) and reliability (MB=−0.65 °C, TE=0.52 °C) was observed for TC, suggesting it may be best suited to controlled, static situations. These findings indicate TT systems provide a convenient, valid and reliable alternative to HW, useful for measurements in the field where traditional methods may be impractical.     

Motor unit activation patterns during isometric, concentric and eccentric actions at different force levels.

Motor unit activation patterns were studied during four different force levels of concentric and eccentric actions. Eight male subjects performed concentric and eccentric forearm flexions with the movement range from 100 degrees to 60 degrees in concentric and from 100 degrees to 140 degrees elbow angle in eccentric actions. The movements were started either from zero preactivation or with isometric preactivation of the force levels of 20, 40, 60 and 80% MVC. The subjects were then instructed to maintain the corresponding relative force levels during the dynamic actions. Intramuscular and surface EMG was recorded from biceps brachii muscle. Altogether 28 motoneuron pools were analyzed using the intramuscular spike-amplitude frequency (ISAF) analysis technique of Moritani et al. The mean spike amplitude was lower and the mean spike frequency higher in the isometric preactivation phase than in the consequent concentric and eccentric actions. When the movements started with isometric preactivation the mean spike amplitude increased significantly (P<0.001) up to 80% in isometric and concentric actions but in eccentric actions the increase continued only up to 60% (P<0.01). The mean spike frequency in isometric preactivation and in concentric action with preactivation was lower only at the 20% force level (P<0.01) as compared to the other force levels while in eccentric action with preactivation the increase between the force levels was significant (P<0.01) up to 60%. When the movement was started without preactivation the mean spike amplitude at 20% and at 40% force level was higher (P<0.01) in eccentric action than in concentric actions. It was concluded that the recruitment threshold may be lower in dynamic as compared to isometric actions. The recruitment of fast motor units may continue to higher force levels in isometric and in concentric as in eccentric actions which, on the other hand, seems to achieve the higher forces by increasing the firing rate of the active units. At the lower force levels mean spike amplitude was higher in eccentric than in concentric actions which might indicate selective activation of fast motor units. This was, however, the case only when the movements were started without isometric preactivation.     

Acute effects of eccentric work on a bicycle ergometer

Dynamics of the delayed-onset muscle soreness after the exercise on a bicycle ergometer with floating seat under predominantly concentric and eccentric conditions was evaluated using three different tests. Depending on the used test, the maximum delayed-onset muscle soreness was recorded on days 1 to 3 after the exercise without significant differences between the groups performing concentric and eccentric work. A trend of a slower development of both the delayed onset of muscle soreness and the corresponding recovery was recorded by the test with a passive pressure on the working muscle group (knee joint extensor muscles). A positive correlation between the delayed-onset muscle soreness and the relative work intensity was found; the relative intensity was assessed according to the decrease in strength during the recovery period. No correlation between the delayed-onset muscle soreness and exercise duration was detected.     

Effect of eccentric exercise on position sense at the human forearm in different postures.

This is a study of the ability of blindfolded human subjects to match the position of their forearms before and after eccentric exercise. The hypothesis tested was that the sense of effort contributed to forearm position sense. The fall in force after the exercise was predicted to alter the relationship between effort and force and thereby induce position errors. In the arms-in-front posture, subjects had their unsupported reference arm set to one of two angles from the horizontal, 30 or 60 degrees , and they matched its position by voluntary placement of their other arm. Matching errors were compared with a task where the arms were counterweighted, so could be moved in the vertical plane with minimal effort, and where the arms were moved in the horizontal plane. In these latter two tasks, the intention was to test whether removal of an effort sensation from holding the arm against gravity influenced matching performance. It was found that, although absolute errors for counterweighted and horizontal matching were no larger than for unsupported matching, their standard deviations, 6.1 and 6.8 degrees , respectively, were significantly greater than for unsupported matching (4.6 degrees ), indicating more erratic matching. The eccentric exercise led, the next day, to a fall in maximum voluntary muscle torque of >or=15%. This was accompanied by a significant increase in matching errors for the unsupported matching task from 2.7 +/- 0.5 to 0.8 +/- 0.7 degrees but not for counterweighted (1.4 +/- 0.2 to -0.2 degrees +/- 1.1 degrees ) or horizontal matching (-1.3 +/- 0.7 degrees to -1.8 +/- 0.7 degrees ). This, it is postulated, is because the reduced voluntary torque after exercise was accompanied by a greater effort required to support the arms, leading to larger matching errors. However, effort is only able to provide positional information for unsupported matching where gravity plays a role. In gravity-neutral tasks like counterweighted or horizontal matching, a change in the effort-force relationship after exercise leaves matching accuracy unaffected.     

Thermal and circulatory responses during prolonged exercise at different levels of hydration

After a control experiment under initial normal hydration (N), five healthy unacclimated subjects were studied to investigate the effects of initial hypo- and hyperhydration on cardiovascular and thermo-regulatory responses to prolonged intermittent exercise in the heat (To = 36 degrees C; Tdp = 10 degrees C; Va = 0.6 m.s-1). Prior hydrohydration (O) was obtained by diuretics and prior hyperhydration (R) by ingestion of 0.5 L of isotonic (ISO) electrolyte sucrose solution 30 min before the experiments (4 h) started. Exercise (70 W) lasted 3 hours, and was periodically interrupted by resting periods (5-10 min). Three dehydration (D) runs were thus performed under the three initial hydration states (O,N,R) without fluid replacement during the exercise period. Four additional rehydration runs were carried out: 2 in each initial hydration level (O, R) included ingestion (at 36 degrees C) of water or ISO-solution during the first 3 hours. Physiological measurements were continuously recorded and hourly blood samples (15 ml) were obtained. Results showed that dehydration increased core temperature and heart rate and provoked blood hypovolemia and hyperosmolarity, the latter being somewhat prevented by prior ISO-ingestion. Dehydration reduced significantly the overall sweat rate only in hypohydrated subjects and the large hyperosmolarity seemed to be responsible for this. The significant Tcore rise during dehydration is unlikely to be the result of a decrease in evaporative heat transfer, which was found only in the case of initial hypohydration. Rehydration during exercise with water or ISO-solution induced different dynamic responses depending on the initial hydration level, but it never restored plasma volume.(ABSTRACT TRUNCATED AT 250 WORDS)     

Non-thermal influences on the control of skin blood flow have minimal effects on heat transfer during exercise

During exercise, circulatory reflexes ensure that the cardiac output is sufficiently elevated to meet the oxygen delivery requirements of the contracting skeletal muscles and the heat delivery requirements of the body to the skin. The latter requirements are met by increasing skin blood flow. These increases are largely driven by elevations in the body temperatures, although non-thermal effects on the control of skin blood flow occur in certain conditions. These effects are largely the consequence of high and/or low baroreflex stimulation. Even in the face of such non-thermal effects, which occur during exercise in the heat, the body's requirements for heat transfer from core to skin are largely met by the increased skin blood flow. Thus, non-thermal effects on the control of skin blood flow are relatively unimportant in the body's overall regulatory response to exercise.     

Pulmonary gas exchange during exercise in women: effects of exercise type and work increment.

Exercise-induced arterial hypoxemia (EIAH) has been reported in male athletes, particularly during fast-increment treadmill exercise protocols. Recent reports suggest a higher incidence in women. We hypothesized that 1-min incremental (fast) running (R) protocols would result in a lower arterial PO(2) (Pa(O(2))) than 5-min increment protocols (slow) or cycling exercise (C) and that women would experience greater EIAH than previously reported for men. Arterial blood gases, cardiac output, and metabolic data were obtained in 17 active women [mean maximal O(2) uptake (VO(2 max)) = 51 ml. kg(-1). min(-1)]. They were studied in random order (C or R), with a fast VO(2 max) protocol. After recovery, the women performed 5 min of exercise at 30, 60, and 90% of VO(2 max) (slow). One week later, the other exercise mode (R or C) was similarly studied. There were no significant differences in VO(2 max) between R and C. Pulmonary gas exchange was similar at rest, 30%, and 60% of VO(2 max). At 90% of VO(2 max), Pa(O(2)) was lower during R (mean +/- SE = 94 +/- 2 Torr) than during C (105 +/- 2 Torr, P < 0.0001), as was ventilation (85.2 +/- 3.8 vs. 98.2 +/- 4.4 l/min BTPS, P < 0.0001) and cardiac output (19.1 +/- 0.6 vs. 21.1 +/- 1.0 l/min, P < 0.001). Arterial PCO(2) (32.0 +/- 0.5 vs. 30.0 +/- 0.6 Torr, P < 0.001) and alveolar-arterial O(2) difference (A-aDO(2); 22 +/- 2 vs. 16 +/- 2 Torr, P < 0.0001) were greater during R. Pa(O(2)) and A-aDO(2) were similar between slow and fast. Nadir Pa(O(2)) was 相似文献   

Effects of exercise in the heat on thermoregulation of Japanese and Malaysian males

The effect of low-intensity exercise in the heat on thermoregulation and certain biochemical changes in temperate and tropical subjects under poorly and well-hydrated states was examined. Two VO2max matched groups of subjects consisting of 8 Japanese (JS) and 8 Malaysians (MS) participated in this study under two conditions: poorly-hydrated (no water was given) and well-hydrated (3 mL x Kg(-1) body weight of water was provided at onset of exercise, and the 15th, 35th and 55th min of exercise). The experimental room in both countries was adjusted to a constant level (Ta: 31.6+/-0.03 degrees C, rh: 72.3+/-0.13%). Subjects spent an initial 10 min rest, 60 min of cycling at 40% VO2max and then 40 min recovery in the experimental room. Rectal temperatures (Tre) skin temperatures (Tsk), heart rate (HR), heat-activated sweat glands density (HASG), local sweat rate (M sw-back) and percent dehydration were recorded during the test. Blood samples were analysed for plasma glucose and lactate levels.The extent of dehydration was significantly higher in the combined groups of JS (1.43+/-0.08%) compared to MS (1.15+/-0.05%). During exercise M sw-back was significantly higher in JS compared to MS in the well-hydrated condition. The HASG was significantly more in JS compared to MS at rest and recovery. Tre was higher in MS during the test. Tsk was significantly higher starting at the 5th min of exercise until the end of the recovery period in MS compared to JS.In conclusion, tropical natives have lower M sw-back associated with higher Tsk and Tre during the rest, exercise and recovery periods. However, temperate natives have higher M sw-back and lower Tsk and Tre during experiments in a hot environment. This phenomenon occurs in both poorly-hydrated and well-hydrated states with low intensity exercise. The differences in M sw-back, Tsk and Tre are probably due to a setting of the core temperature at a higher level and enhancement of dry heat loss, which occurred during passive heat exposure.     

Muscular efficiency during steady-rate exercise: effects of speed and work rate.

In a comparison of traditional and theoretical exercise efficiency calculations male subjects were studied during steady-rate cycle ergometer exercises of "0," 200, 400, 600, and 800 kgm/min while pedaling at 40, 60, 80, and 100 rpm. Gross (no base-line correction), net (resting metabolism as base-line correction), work (unloading cycling as base-line correction), and delta (measurable work rate as base-line correction) efficiencies were computed. The result that gross (range 7.5-20.4%) and net (9.8-24.1%) efficiencies increased with increments in work rate was considered to be an artifact of calculation. A LINEAR OR SLIGHTLY EXPONENTIAL RELATIONSHIP BETWEEN CALORIC OUTPUT AND WORK RATE DICTATES EITHER CONSTANT OR DECREASING EFFICIENCY WITH INCREMENTS IN WORK. The delta efficiency (24.4-34.0%) definition produced this result. Due to the difficulty in obtaining 0 work equivalents, the work efficiency definition proved difficult to apply. All definitions yielded the result of decreasing efficiency with increments in speed. Since the theoretical-thermodynamic computation (assuming mitochondrial P/O = 3.0 and delta G = -11.0 kcal/mol for ATP) holds only for CHO, the traditional mode of computation (based upon VO2 and R) was judged to be superior since R less than 1.0. Assuming a constant phosphorylative-coupling efficiency of 60%, the mechanical contraction-coupling efficiency appears to vary between 41 and 57%.     

Effects of heat acclimatisation on work tolerance and thermoregulation in trained tropical natives

This study aimed to investigate the effects of heat acclimatisation on thermoregulatory responses and work tolerance in trained individuals residing in the tropics. Eighteen male trained soldiers, who are native to a warm and humid climate, performed a total of four heat stress tests donning the Skeletal Battle Order (SBO, 20.5 kg) and Full Battle Order (FBO, 24.7 kg) before (PRE) and after (POST) a 10-day heat acclimatisation programme. The trials were conducted in an environmental chamber (dry bulb temperature: 32 °C, relative humidity: 70%, solar radiation: 400 W/m²). Excluding the data sets of which participants fully completed the heat stress tests (210 min) before and after heat acclimatisation, work tolerance was improved from 173±30 to 201±18 min (∼21%, p<0.05, n=9) following heat acclimatisation. Following heat acclimatisation, chest skin temperature during exercise was lowered in SBO (PRE=36.7±0.3 vs. POST=36.5±0.3 °C, p<0.01) and FBO (PRE=36.8±0.4 vs. POST=36.6±0.3 °C, p<0.01). Ratings of perceived exertion were decreased with SBO and FBO (PRE=11±2; POST=10±2; p<0.05) after heat acclimatisation. Heat acclimatisation had no effects on baseline body core temperature, heart rate and sweat rate across trials (p>0.05). A heat acclimatisation programme improves work tolerance with minimal effects on thermoregulation in trained tropical natives.