The danger of an inadequate water intake during prolonged exercise A novel concept re-visited

To prevent thermal injuries during distance running, the American College of Sports Medicine proposes that between 0.83 and 1.65 l of water should be ingested each hour during prolonged exercise. Yet such high rates of fluid intake have been reported to cause water intoxication. To establish the freely-chosen rates of fluid intake during prolonged competitive exercise, we measured fluid intake during, body weight before and after, and rectal temperature after competition in a total of 102 runners and 91 canoeists competing in events lasting from 170-340 min. Fluid intakes during competition ranged from 0.29-0.62 l.h-1; rates of water loss ranged from 0.69-1.27 l.h-1 in the runners; values were lower in the canoeists. Mean post-race rectal temperatures ranged from 38.0-39.0 degrees C. There was no relationship between the degree of dehydration and post-race rectal temperature. We conclude that hyperthermia is uncommon in prolonged competitive events held in mild environmental conditions, and that exercise intensity, not the level of dehydration, is probably the most important factor determining the postexercise rectal temperature. During prolonged exercise in mild environmental conditions, a fluid intake of 0.5 l.h-1 will prevent significant dehydration in the majority of athletes.     

Kinetics of heart rate and catecholamines during exercise in humans The effect of heart denervation

To elucidate the role of factors other than the nervous system in heart rate (f _c) control during exercise, the kinetics off _c and plasma catecholamine concentrations were studied in ten heart transplant recipients during and after 10-min cycle ergometer exercise at 50 W. Thef _c did not increase at the beginning of the exercise for about 60 s. Then in the eight subjects who completed the exercise it increased following an exponential kinetic with a mean time constant of 210 (SEM 22) s. The two other subjects were exhausted after 5 and 8 min of exercise during whichf _c increased linearly. At the cessation of the exercise,f _c remained unchanged for about 50 s and then decreased exponentially with a time constant which was unchanged from that at the beginning of exercise. In the group of eight subjects plasma noradrenaline concentration ([NA]) increased after 30 s to a mean value above resting of 547 (SEM 124) pg · ml^–1, showing a tendency to a plateau, while adrenaline concentration ([A]) did not increase significantly. In the two subjects who became exhausted an almost linear increase in [NA] occurred up to about 1,300 pg · ml^–1 coupled with a significant increase in [A]. During recovery an immediate decrease in [NA] was observed towards resting values. The values of thef _c increase above resting levels determined at the time of blood collection were linearly related with [NA] increments both at the beginning and end of exercise with a similar slope, i.e. about 2.5 beats · min^–1 per 100 pg · ml^–1 of [NA] change. These findings would seem to suggest that in the absence of heart innervation the increase inf _c depends on plasma [NA].     

Influence of fluid intake on endurance running performance A comparison between water, glucose and fructose solutions

The aim of the present study was to compare the influence of drinking water, a carbohydrate-electrolyte solution, containing additional free glucose (Glucose) or the same carbohydrate-electrolyte solution containing additional fructose (Fructose), on running performance. Twelve endurance-trained recreational runners volunteered to take part in this study; 9 completed the three and all 12 completed two trials. The subjects were randomly assigned to one of the three trials: Water, Glucose or Fructose. In each trial the subjects were required to run 30 km as fast as possible on a motorized treadmill, instrumented so that they could control its speed. The carbohydrate-electrolyte solutions contained a total of 50 g carbohydrate, 20 g as a glucose polymer. The Glucose solution contained an additional 20 g free glucose and the Fructose solution contained an additional 20 g fructose rather than glucose. The osmolality of the Glucose and Fructose solutions was approximately 300-320 mosmol and the energy equivalent of both solutions was 794 kJ.l-1. The subjects ingested 1 l fluid throughout each run. The running times were not significantly different, being 129.3 (+/- 17.7) min, 124.8 (+/- 14.9) min and 125.9 (+/- 17.9) min for Water, Glucose and Fructose respectively. There was a decrease (P less than 0.05) in running speed over the last 10 km of the Water trial from 4.14 (+/- 0.55) to 3.75 (+/- 0.86) m.s-1, which did not occur in the carbohydrate trials. Blood glucose concentrations during the Water trial decreased from 15 km onwards and at the end of the run they were significantly (P less than 0.05) lower than the value recorded at 15 km.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dispersal of adult female fig wasps 1. Arrivals and departures

Ficus burtt-davyi, like most other fig species (Ficus, Moraceae), is exclusively pollinated by its own unique species of fig wasp, in this caseElisabethiella baijnathi (Chalcidoidea, Agaonidae). Because fig crop development on any one tree is usually synchronised, the small and short-lived female wasps have to migrate and find other trees bearing figs which are at suitable stage of development for oviposition. However, the likelihood of successful location and subsequent arrival at a new host tree is dependent on distance and the effect of environmental factors such as wind and temperature. This study examines the relationship between ambient temperatures and the timing of fig wasps emergence from their natal figs and the commencement of their dispersal flight. The behaviour of the wasps arriving at figs which were ready to be pollinated was also examined. The female wasps did not appear to distinguish between the figs and other parts of the tree when in flight. However, after landing on the tree their search for figs was more directed as they visited more figs than leaves. Short-range recognition of figs appears to be by contact chemo-reception, but the wasps showed a preference for entering figs which did not already contain a female wasp.     

Eccentric and concentric torque-velocity relationships during arm flexion and extension Influence of strength level

Forty men were tested with a computerized dynamometer for concentric and eccentric torques during arm flexion and extension at 0.52, 1.57, and 2.09 rad.s-1. Based on the summed concentric and eccentric torque scores, subjects were placed into a high strength (HS) or low strength (LS) group. The eccentric and concentric segments of the torque-velocity curves (TVCs) were generated using peak torque and constant-angle torque (CAT) at 1.57 and 2.36 rad. Angle of peak torque was also recorded. Compared to LS, HS had significantly greater estimated lean body mass (+10.2 kg) and approximately 25% greater average torque output. Reliability of the peak torque scores on 2 days in 20 subjects was r greater than or equal to 0.85. The difference between observed torques and the mathematically computed criterion torque scores averaged 1% for three validation loads that ranged from 11.4 to 90.4 kg. Statistical analysis revealed that torque output in LS plateaued at low concentric velocities and was also flattened with increasing eccentric velocities. Conversely, torque output for HS increased with decreasing concentric velocities and increased with increasing eccentric velocities. The method of plotting the TVCs for peak or CAT did not influence the pattern of TVC. Eccentric flexion peak torque occurred at a significantly shorter muscle length (1.88 rad) than concentric torque (2.12 rad). This difference was also present for extension; it was 1.88 rad for eccentric and 2.03 rad for concentric torque.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hypoxia-induced fibre type transformation in rat hindlimb muscles Histochemical and electro-mechanical changes

Twelve male Sprague-Dawley rats (21 days old) were randomly assigned into two experimental groups: sea level control (CONT) and hypobaric hypoxia (HYPO). The HYPO rats were kept in an hypobaric chamber maintaining a simulated altitude of 4000 m (61.1 kPa). After 10 weeks of treatment, the rat hindlimb muscles [soleus (SOL) and extensor digitorum longus (EDL)] were subjected to histochemical and electro-mechanical analyses. Results indicated that compared to CONT the HYPO SOL muscle had a significantly greater relative distribution of fast-twitch-oxidative-glycolytic (FOG) fibres (28.9% SEM 2.0 vs 18.3% SEM 1.8, P less than 0.01) with a significant decrease in slow twitch oxidative fibre distribution (69.5% SEM 2.4 vs 82.9% SEM 3.1, P less than 0.01). Compared to CONT the HYPO EDL muscle also manifested a significant increase in FOG fibre distribution (51.6% SEM 0.8 vs 46.6% SEM 1.1, P less than 0.01), but this was accompanied by a significant decrease in fast twitch glucolytic fibres (44.3% SEM 0.9 vs 49.2% SEM 1.7, P less than 0.05). These histochemical fibre type transformations accompanied significant and expected changes in the electro-mechanical parameters tested in situ, e.g. maximal twitch force, maximal rate of force development, contraction time, half relaxation time, force: frequency curve, and fatigability. It was concluded that chronic hypobaric hypoxia could have a potent influence upon the phenotype expression of muscle fibres.     

Introduction Ecological implications of flower–pollinator interactions in tropical rain forest ecosystems

This article introduces the special issue on flower–pollinator interactions in the tropics deriving from the 19th symposium of the Society of Population Ecology, held at Ohmi-shirahama, Shiga, Japan, in October 1999.     

Skeletal muscle damage during tourniquet-induced ischaemia The initial step towards atrophy after orthopaedic surgery?

Muscle biopsies from the vastus lateralis muscle of patients who had undergone anterior cruciate ligament surgery under conditions of tourniquet-induced ischaemia were examined under the electron microscope at different periods of time up to 90 min of ischaemia. The severity of the alterations in ultrastructure appeared to depend on the period of ischaemia. The pathological changes consisted of accumulation of lysosomes, persistent intrafibre oedema, and some extracellular oedema. Signs of fibre necrosis were found after 90 min of ischaemia. Capillary ultrastructure was only altered with regard to some swelling of the endothelium and marked thickening of the basement membrane. It was concluded that skeletal muscle could be severely affected even during relatively short periods of ischaemia, which might facilitate the development of muscle atrophy during immobilization after orthopaedic surgery.     

Psychiatric Ethics and a Politics of Compassion The Case of Detained Asylum Seekers in Australia

Australia has one of the harshest regimes for the processing of asylum seekers, people who have applied for refugee status but are still awaiting an answer. It has received sharp rebuke for its policies from international human rights bodies but continues to exercise its resolve to protect its borders from those seeking protection. One means of doing so is the detention of asylum seekers who arrive in Australia by boat. Health care providers who care for asylum seekers in these conditions experience a conflict of “dual loyalty,” whereby their role in preserving and maintaining the health of patients can run counter to their employment in detention facilities. Many psychiatrists who have worked in the detention setting engage in forms of political activism in order to change the process of seeking refuge.     

Role of trace elements in primary arterial hypertension Is mineral water style or prophylaxis?

A negative relationship between water hardness and cardiovascular mortality rate was demonstrated and became a source of interest regarding minerals and trace metals in the pathogenesis of atherosclerosis, cardiovascular diseases, and arterial hypertension. Higher incidences of sudden death, cerebrovascular diseases, arterial hypertension, and coronary heart disease have been reported in soft water areas. Amajor research effort has been devoted to the problem in an attempt to find a protective factor in hard water or a detrimental factor or element in soft water. The roles of calcium, magnesium, cobalt, lithium, vanadium, silicon, manganese, and copper have been considered potentially beneficial, whereas those of cadmium, lead, silver, zinc, and thallium have been considered potentially harmful. Cobalt and zinc have been attributed both roles. In the present article, the role of trace quantities of several elements in mineral water in the etiopathogenesis of primary arterial hypertension is reviewed.     

Selection ofAzolla forms resistant to the water lily aphid,Rhopalosiphum nymphaeae Life history of Rhopalosiphum nymphaeae

Genotypic and environmentally determined differences inSalix viminalis L. suitability forDasineura marginemtorquens (Bremi) (Diptera: Cecidomyiidae) growth and survival were investigated in laboratory and field experiments. Earlier studies have documented high neonate larval mortality on certainS. viminalis genotypes. Here we present results from laboratory experiments which show no difference in larval establishment behaviour on resistant and susceptible willow genotypes. These data indicate that larvae are not able to detect the plant characteristic responsible for resistance. In a field study insect performance was measured on willow shoots of dissmilar size. Adult body size was positively correlated to willow shoot length. In turn, body size was positively correlated to potential fecundity. These results are discussed in relation to observed high densities ofD. marginemtorquens in vigorously growing willows cultivated for biomass production.     

Associational refuges among corals mediate impacts of a crown-of-thorns starfish Acanthaster planci outbreak Indirect positive interactions in communities

Interactions among coral populations can moderate the impact of coral predator outbreaks, enhancing community resilience and recovery. This study used predator-exclusion cages and neighbour removals in a field experiment to test how indirect interactions between populations of three coral taxa, Acropora, Pocillopora, and Porites, influenced their survival during an outbreak of the crown-of-thorns starfish, Acanthaster planci, in Moorea, French Polynesia. High densities of corals enhanced survival by generating associational refuges: physical structures that impeded Acanthaster and protected corals, and by simple density-dependent prey dilution that reduced predation rates. Acanthaster showed feeding preferences, resulting in varying intensities of predation on corals, which (1) influenced the type and strength of the associational refuge among corals and (2) resulted in significant loss of the competitive dominants to the benefit of the competitive inferiors. The result was a set of indirect positive interactions (IPIs) that prevented Acanthaster from eradicating Acropora and may have enhanced Porites, a relatively weak competitor among corals. IPIs probably play a key role in many ecosystems, especially in coral reefs in which corals act as engineer species, to reduce impacts of perturbations and enhance community resilience. This study illustrates the importance of IPIs in community regulation with a new conceptual model.     

Interrelationships among various measures of upper body strength assessed by different contraction modes Evidence for a general strength component

Two studies were conducted in 83 college men to determine the degree of generality of individual differences in upper body muscular strength assessed by different testing modes. In study 1 (N = 43), correlations were computed between four measures of upper body strength using the bench press movement, maximal isokinetic (0.09 rad.s-1), maximal fast (0.126 m.s-1) and slow (0.037 m.s-1) hydraulic, and one repetition maximum (1-RM) free weight bench press (BP). Compared to free weight BP, maximal strength during isokinetic and slow hydraulic BP was approximately 29% and approximately 8% larger, and fast hydraulic BP strength was approximately 63% lower (p less than 0.05). Simple linear regression of isokinetic BP on 1-RM BP yielded r = 0.79, error of prediction (SE) = 12%, and generality = 81%. The corresponding averaged values for the regression of slow and fast hydraulic BP on free weight 1-RM BP were r = 0.77, SE = 13.5%, and generality = 84%. In Study 2 (N = 40), testing included maximal isokinetic concentric and eccentric arm flexion and extension at 0.524, 1.570, and 2.094 rad.s-1. The ratio of concentric to eccentric torque at the 3 speeds averaged 0.68 (flexion) and 0.70 (extension), and eccentric torques were 32% and 30% greater than concentric torques (p less than 0.05). The linear regression between concentric vs. eccentric flexion and extension torques at the three velocities yielded an average r = 0.80, SE = 13.7%, and generality = 73%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Photo-induced electron transfer between hypocrellins and nano-sized semiconductor CdS —EPR study on the kinetics of photosensitized reduction in HA-CdS and HB-CdS systems

Both HA-CdS and HB-CdS (Hys-CdS, Hys represents HA, HB) complex systems were established according to the dynamics of heterogeneous electron-transfer process m = E_{S^* /S⁺} - E < 0\mu = E_{S^* /S^ + } - E< 0 . In these systems, the electron transferring from¹Hys* to conduction band of CdS is feasible. Determined from the fluorescence quenching, the apparent association constants (K_app) between Hypocrellin A (HA), Hypocrellin B. (HB) and CdS sol. were about 940 (mol/L)⁻¹, 934 (mol/L)⁻¹, respectively. Fluorescence lifetime measurements gave the rate constant for the electron transfer process from¹HA*,¹HB* into conduction band of CdS semiconductor as 5.16 × 10⁹ s⁻¹, 5.10 × 10⁹ s⁻¹, respectively. TEMPO (2,2,6,6-tetramethy-1-piperdinyloxy), a stable nitroxide radical, was used in the kinetic study of the reduction reaction taking place on the surface of a CdS colloidal semiconductor, kinetics equation of the reaction was determined with the electron paramagnetic resonance (EPR) method, and the reaction order of TEMPO is zero. When Hys were added, the rate of EPR increased greatly. By comparing rate constants, the Hys-CdS systems were revealed to be about 350 times more efficient than CdS sol. alone in the photoreduction of TEMPO under visible light. It suggests that Hys can be used as efficient sensitizers of a colloidal semiconductor in the application of solar energy.