Gas exchange in the incubation mounds of megapode birds

Summary The brush turkey (Alectura lathami) and mallee fowl (Leipoa ocellata) are megapode birds that incubate their eggs by burying them in mounds. Respiratory gas exchange between the buried eggs and the atmosphere occurs mainly by diffusion through about 60 cm of decomposing forest litter (brush turkey) or sand (mallee fowl).Gas fluxes in the brush turkey mound are greatly influenced by the respiration of thermophilic microorganisms which consume O₂ at rates over eight times that of all of the eggs. The respiratory exchange ratio ( ) of the microorganisms is 0.75 and theQ ₁₀ for metabolism is 2.56. Fermentation and nitrogen fixation do not occur in the mounds.If the mound becomes too wet, gas tensions near the eggs can become critical because water increases rates of microbial respiration and impedes gas diffusion. However, field mounds are relatively dry, possibly because the adult bird modifies the shape of the mound and affects the entry of rain water. At egg level in field mounds, and are about 132 and 21 Torr, respectively, in both species. Embryonic respiration decreases and increases about 5 Torr in the immediate environment of individual eggs in late development. Due to a high eggshell gas conductance, which increases during incubation, the gas tensions within the shell of late embryos ( ca. 108 Torr, ca. 47 Torr) are not far from the mean values found in species that nest above ground.     

Activity and oxygen consumption during hypoxic exposure in high altitude and lowland sceloporine lizards

Summary Resting rates of O₂ consumption against , exercise endurance times and during recovery from vigorous exercise were measured inSceloporus occidentalis captured near sea level and inS. graciosus captured above 2850 m. Oxygen consumption against was also measured inS. occidentalis captured above 2850 m. When was recorded continuously, as ambient was slowly reduced from 155 Torr, it became directly dependent upon ambient between 110 and 120 Torr. The critical for the high altitude lizards was lower than that for the lowland lizards, which enabled the former to maintain relatively higher 's when ambient was reduced below 120 Torr. The high altitude lizards also had significantly greater endurance when stimulated to exercise at 1600 m ( 130 Torr). Both the higher under hypoxia and the greater endurance roughly parallel a significantly greater maximum in the high altitude lizards. At a simulated altitude of 3600 m ( 100 Torr), maximum and rate of recovery of the O₂ debt calculated from post active were significantly reduced in the lowland but not the high altitude lizards. The effects of simulated altitude conditions on the lowland but not the mountaine animals indicate adaptations to altitude in these sceloporine lizards. We did not find any consistent relationship between organ/body weight ratios or hematocrit and our measures of endurance or the altitude at which the lizards were captured.     

Control of acid-base status in active and dormant land snails,Otala lactea (Pulmonata,Helicidae)

Summary Control of extracellular acid-base status was examined during activity and dormancy inOtala lactea (Pulmonata, Helicidae). Active snails showed little variation in hemolymph pH and at constant temperature. With increase of temperature, hemolymph increased from about 6 Torr at 5°C to 13 Torr at 24°C and pH decreased by about 0.017 pH units/°C, a pattern consistent with alphastat regulation of pH via ventilatory control of .During dormancy, mean hemolymph increased to about 50 Torr. Venous pH declined by about 0.4 units due to hypercapnia and fluctuated more widely than in active snails due to variability of . Hemolymph pH declined further in prolonged dormancy due to progressive metabolic acidosis; after one year of dormancy the mean hemolymph pH was about 0.8 units lower than that of active snails at similar temperature.Active snails exposed experimentally to high showed a large increase in hemolymph [HCO ₃ ^– ]. However, [HCO ₃ ^– ] declined by up to 50% during dormancy, despite the naturally occurring hypercapnia. Hemolymph osmolality and the concentrations of solutes other than [HCO ₃ ^– ] increased with increasing duration of dormancy. Concentrations of magnesium and calcium increased about 2.5 times more rapidly than those of sodium and chloride, indicating that acidosis is partially offset by the dissolution of carbonates from the shell or tissues.     

Reversed bohr and root shifts in hemocyanin of the marine prosobranch,Buccinum undatum: Adaptations to a periodically hypoxic habitat

Summary Oxygen binding properties of the hemocyanin-containing blood ofBuccinum undatum were examined in vitro and in vivo under normoxic ( 150 mmHg) and hypoxic ( 50 mmHg) conditions at 10°C. Blood pH and showed a decrease in vivo under hypoxic conditions. Oxygen uptake at high water , was about 18 ml O₂/kg·h (wet weight) and the critical oxygen tension between 25 and 50 mm Hg. In vitro the O₂ binding to hemocyanin showedn-values independent of pH, while both O₂ affinity and oxygen carrying capacity were strongly pH dependent. Oxygen affinity increased below pH=8.1 and thus showed a pronounced reversed Bohr shift in the physiological pH range (7.5<pH<8.1). The oxygen carrying capacity similarly increased markedly with falling pH in the physiological pH range (reversed Root shift). Astrup titration curves showed a metabolic and respiratory acidosis under hypoxic conditions ( 50 mm Hg). The role of hemocyanin in the transport of oxygen in relation to ambient O₂ availability is discussed.     

Water economy in bird nests

Summary Nest humidity ( ) under an incubating bantam hen was measured at ambient ranging from 1.3 to 25.0 mmHg. Weight loss of eggs was recorded in clutches of varying size. Nest and ambient were also measured in wild incubating willow ptarmigan nests in dry and wet habitats.Nest increased linearly with ambient in a way predictable on the assumption that the water vapour conductance ( ) of brood patch skin, plumage and eggs were constant and independent of ambient . Nest was also dependent of clutch size. Egg dehydration was quantitatively predicted from measured values and the laws of diffusion.Our findings confirm earlier conclusions that the adult bird does not actively regulate nest at varying ambient . Birds can presumably achieve appropriate egg dehydration by a strategy combining nest site, nest construction, egg shell conductance and incubation behaviour which meets the requirements of their breeding climate.Abbreviations water vapur pressure - water vapur conductance - water flux     

Respiration of the emersed shore crab at variable ambient oxygenation

Summary In the intertidal shore crab,Carcinus maenas, pH and values of the prebranchial venous hemolymph, and , the PO₂ values of the arterialized cardiac hemolymph, , were measured, and the ventilatory activity was assessed by measuring the hydrostatic pressures at the exits of the epibranchial cavities, under four environmental conditions: normoxic water, normoxic air, hypoxic gas, hyperoxic gas.In the crab breathing normoxic air, was lower and higher than in animals breathing normoxic water. With the switch to hypoxic gas, ventilation increased and and decreased. With the switch to hyperoxic gas, ventilation decreased, and increased and decreased.Thus these crabs breathing air were not as well oxygenated as when breathing air-equilibrated water, and because of their low , they were relatively hypervetilating and hypocapnic compared to air-breathing vertebrates. Hyperoxic breathing, increasing and reducing ventilatory drive, led to increased . Conversely, was reduced by hypoxic breathing. These observations suggest that the gas exchanger of intertidal crabs is not as successfully designed for air breathing as that of land-colonizing insects and air-breathing vertebrates.     

A comparative study of the mechanism of Na+ and Cl? excretion by the gill ofMugil capito andFundulus heteroclitus: Effects of Stress

Summary In seawater (SW)-adaptedMugil andFundulus, gill effluxes of Na⁺ and of Cl^– and the simultaneously recorded transgill potential (P.D.) differ according to whether they are measured in stressed or rested animals.In rested animals of the two species, transfer to Ringer's solution considerably reduces the P.D. but not . InFundulus, is also decreased. Transfer of the two species from SW to fresh water (FW) reduces and by 75 to 85% and leads to a large inversion of P.D. When K⁺ is added to FW, a gill depolarization occurs, as well as a large increase of and .These results suggest that: 1) the P.D. originates primarily from the diffusion of cations, the gill permeability to Na⁺ ( ) being greater than that to Cl^– ( ), 2) a Cl^–/Cl^– exchange independent of P.D. is associated with the Cl^– pump; 3) Cl^– pump activity is linked to Na⁺/K⁺ exchange which in turn is associated to a Na⁺/Na⁺ exchange diffusion mechanism.In stressed individuals of the two species, the P.D. in SW, as well as the P.D. changes observed during transfer experiments, are considerably reduced. The decrease of and observed after transfer from SW to FW are also minimised. Changes are smaller inFundulus. The decrease of P.D. characterizing stressed animals may be at least in part due to a 3 to 4 fold increase of which becomes equal to in both species.As a result of stress, the K⁺-activated Na⁺ and Cl^– excretion mechanisms are totally inhibited inFundulus and partially so inMugil.Stress response seems more intense inFundulus and recovery from stress faster inMugil.     

Effect of chronic acidosis on discharge frequency of intrapulmonary chemoreceptors in the chicken

Summary In order to determine the pH effect on the discharge of intrapulmonary chemoreceptors (IPC) not mediated through , we determined discharge frequency-ln relationships of 28 IPC from ten adult cockerels made acidotic by ingestion of feed containing 6% NH₄Cl for 2 to 5 days. Blood buffer curves — the relationships between pH and — from these cockerels were shifted in parallel towards acidosis by 0.24 pH units (SE=±0.05) compared to control curves. The average slope of the IPC discharge frequenc-ln relationships was less negative than that reported for similar cockerels with normal acid-base balance and the average intercept was decreased. We conclude that pH has an effect on IPC discharge, independent of changes in ; this effect decreases IPC sensitivity to CO₂. We calculate that a shift towards acidosis in the blood buffer curve of one pH unit causes the slope of the IPC discharge frequency-ln relationship to be less negative by 14.7±3.3 imp (s·ln )^–1 and that for any acidotic shift in the blood buffer curve (pH), the average IPC discharge frequency=[–10.7+(14.7·pH)][ln( /25.5)]+3.37. Since IPC discharge is altered by changes in acid-base balance, IPC may contribute to the implementation of respiration responses during metabolic disturbances.Abbreviation IPC intrapulmonary chemoreceptor     

Altitudinal and seasonal effects on aerobic metabolism of deer mice

Summary I compared the maximal aerobic metabolic rates ( ), field metabolic rates (FMR), aerobic reserves ( -FMR), and basal metabolic rates (BMR) of wild and recently captured deer mice from low (440 m) and high (3800 m) altitudes. To separate the effects of the thermal environment from other altitudinal effects, I examined mice from different altitudes, but similar thermal environments (i.e., summer mice from high altitude and winter mice from low altitude). When the thermal environment was similar, , FMR, and aerobic reserve of low and high altitude mice did not differ, but BMR was significantly higher at high altitude. Thus, in the absence of thermal differences, altitude had only minor effects on the aerobic metabolism of wild or recently captured deer mice.At low altitude, there was significant seasonal variation in , FMR, and aerobic reserve, but not BMR. BMR was correlated with , but not with FMR. The significant positive correlation of BMR with indicates a cost of high , because higher BMR increases food requirements and energy use during periods of thermoneutral conditions.Abbreviations BMR basal metabolic rate - FMR field metabolic rate - partial pressure of oxygen - T _a ambient temperature - T _b body temperature - T _e operative temperature - maximal aerobic metabolic rate     

Gill function in an elasmobranch

Summary Highly efficient oxygen uptake in elasmobranchs, as indicated by frequent excess of over has previously been ascribed to the operation of multicapillary rather than counter-current gas exchange by the gills. Analysis of models shows that, at maximum efficiency, a multicapillary system cannot account for values of greater than . In Port Jackson sharks Heterodontus portusjacksoni) commonly exceeds , which indicates the operation of a functional counter-current at the respiratory surface. The anatomical basis of this counter-current is provided by the demonstration that a continuous flow of water passes between the secondary lamellae into septal canals and thence via the parabranchial cavities to the exterior.Queen Elizabeth II Fellow.     

Physiological mechanisms for underwater endurance: Canada goose (Branta canadensis) versus Pekin duck (Anas platyrhynchos)

Maximum submergence time of Canada geese was 18% of that of similarly sized Pekin ducks. Due to a smaller respiratory system volume the oxygen store of Canada geese was 82% of that of Pekin ducks, accounting for approximately 33% of the difference in underwater survival times. The respiratory properties and volume of the blood were similar in both species. Both species utilised approximately 79% of the respiratory oxygen store and 90% of the blood oxygen store. Therefore, most of the species difference in survival times was due to a less effective oxygen-conserving cardiovascular response (bradycardia, peripheral vasoconstriction) in Canada geese. Duck cardiac chronotropic sensitivity to hypoxia during submergence was twice that observed in geese. Furthermore, a lower hypoxic ventilatory response was observed in geese than in ducks. Density of monoamine varicosities in hindlimb artery walls was lower in geese than ducks. However, electrical stimulation of the hindlimb muscles did not cause ascending vasodilation during submergence in either species, perhaps due to higher levels of catecholamines in submerged geese. We conclude that the major difference between species is higher oxygen chemosensitivity in ducks which effects a much more rapid and efficacious oxygen-conserving response during forced submergence.Abbreviations ATPS · BTPS · STPD CNS central nervous system - EEG electroencephalogram - ECG electrocardiogram - EDTA ethylenediaminetetra-acetic acid - HPLC high performance liquid chromatography - fractional oxygen concentration of inspired air - pre-immersion fractional concentration of oxygen in the respiratory system - pre-emersion fractional concentration of oxygen in the respiratory system - [Hb] haemoglobin concentration - Hct haematocrit - HR heart rate - M _B body mass - M _b brain mass - M _h heart mass - partial pressure of carbon dioxide in arterial blood - partial pressure of oxygen in arterial blood - SPG sucrose-potassium phosphate-glyoxylic acid - t _d maximum underwater survival time - respiratory minute volume - V _pl plasma volume - V _rs respiratory system volume - accessible respiratory system oxygen store - total non-myoglobin-bound oxygen store - V _tb blood volume - blood oxygen store     

Dynamics of cardiorespiratory function in Standardbred horses during different intensities of constant-load exercise

Summary Six Standardbred horses were used to evaluate the time course of pulmonary gas exchange, ventilation, heart rate (HR) and acid base balance during different intensities of constant-load treadmill exercise. Horses were exercised at approximately 50%, 75% and 100% maximum oxygen uptake ( max) for 5 min and measurements taken every 30 s throughout exercise. At all work rates, the minute ventilation, respiratory frequency and tidal volume reached steady state values by 60 s of exercise. At 100% max, the oxygen consumption ( ) increased to mean values of approximately 130 ml/kg·min, which represents a 40-fold increase above resting . At the low and moderate work rates, showed no significant change from 30 s to 300 s of exercise. At the high work rate, the mean at 30 s was 80% of the value at 300 s. The HR showed no significant change over time at the moderate work rate but differing responses at the low and high work rates. At the low work rate, the mean HR decreased from 188 beats/min at 30 s to 172 beats/min at 300 s exercise, whereas at the high work rate the mean HR increased from 204 beats/min at 30 s to 221 beats/min at 300 s exercise. No changes in acid base status occurred during exercise at the low work rate. At the moderate work rate, a mild metabolic acidosis occurred which was nonprogressive with time, whereas the high work rate resulted in a progressive metabolic acidosis with a base deficit of 16 mmol/l by 300 s exercise. It is concluded that the kinetics of gas exchange during exercise are more rapid in the horse than in man, despite the relatively greater change in in the horse when going from rest to high intensity exercise.Symbols and abbreviations E minute ventilation - V _T tidal volume - oxygen uptake - carbon dioxide output - oxygen pulse - ventilatory equivalent for oxygen - ventilatory equivalent for carbon dioxide - R respiratory exchange ratio - HR heart rate - SBC standard bicarbonate - STPD standard temperature and pressure dry - BTPS body temperature and pressure saturated - arterial oxygen content - arteriovenous oxygen content difference - Rf respiratory frequency     

Growth and product formation of actinomycetes cultivated at increased total pressure and oxygen partial pressure

Summary Influence of pressure (P) and oxygen partial pressure ( ) on cultivation of various Streptomyces spp. and Micromonospora purpurea was examined in pressurized air-lift and stirred tank fermenters. The maximum was 2100 mbar. Growth and product formation of all cultures tested were markedly influenced by higher than 1000 mbar. There is evidence that wild strains are more oxygen tolerant than production strains. At a certain the metabolic activities of all cultures were inhibited. However, results obtained with S. aureofaciens and S. rimosus indicated an increase in specific product formation rate at elevated pressure. With increase in oxygen tension incorporation of oxygen into tetracycline molecules was enhanced. Since elevated oxygen tension can either show inhibiting effects or may be used for regulation of product formation and selectivity, the influence of should be determined in an appropriate experimental set-up for each process.Offprint requests to: U. Onken     

Ventilation and gas exchange during rest and exercise in adult green sea turtles

Summary Ventilation and metabolic rate were measured during exercise in adult female green turtles at Tortuguero, Costa Rica. Six turtles were studied at night on the beach while actively covering their nests. Five turtles, captured after nesting, were studied at rest, during 20 min of spontaneous activity, and during recovery from the activity. Arterial blood samples were obtained from the latter animals and analyzed for pH, , O₂ concentration and lactate concentration. Blood was obtained by heart puncture from 8 turtles immediately after nesting and analyzed for blood lactate. Active metabolism ( ) in both groups was almost 10 times the standard resting value (0.024 l/kg·h). The increase in ventilation during exercise, due exclusively to higher breathing frequency, exceeded the increase in , so that the ratio (the air convection requirement), more than doubled. The respiratory exchange ratio, , that averaged 0.56 in the resting turtles, increased to 1.08 during exercise in the captured turtles and was 0.90 in the nesting animals. Arterial and O₂ saturation remained unchanged during exercise, indicating efficient gas exchange in the lungs. Pre-exercise values of all variables were restored 1 h after the end of exercise. Blood acid-base changes associated with activity in the captive turtles were variable and not statistically significant, but suggested partially compensated metabolic acidosis. Lactate concentrations were significantly elevated in the nesting turtles.     

Breathing pattern and growth: comparative aspects

Summary The resting oxygen consumption and breathing pattern of nine newborn and adult species (ranging in body size from mouse to human) have been compared on the basis of data collected from the literature. Minute ventilation is similarly linked to at both ages, the percent of extracted as O₂ about 2.2. Tidal volume/kg is an interspecies constant in newborns and adults, approximately 8 ml/kg. Breathing frequency decreases with the increase in size in a different way at the two ages: large species have newborns breathing at rates 2–3 times above the corresponding adults' values, while in the small species newborns and adults breathe at almost the same rate. Therefore the newborns of the smallest species have both and below the expected values, implying a greater inability to cope with the external demands than newborns of larger species. Several considerations indicate that in the smallest newborns the mechanical properties of the respiratory system could be a constraint to resting ventilations larger than observed. It is therefore possible that their low is the cause, and not the effect, of the relatively small .     

Effects of temperature and altitude on ventilation and gas exchange in chukars (Alectoris chukar)

Summary The effects of ambient temperature (T _a) on ventilation and gas exchange in chukar partridges (Alectoris chukar) were determined after acclimation to low and high altitute (LA and HA; 340 and 3,800 m, respectively).At both LA and HA, oxygen consumption ( ) increased with decreasingT _a atT _a from 20 to –20°C. AtT _a of 35 to 40°C, increased above thermoneutral values at HA but remained constant and minimal at LA. Water loss rates increased rapidly atT _a>30°C at both altitudes as birds began to pant. Ventilation rates (f) during panting were 5-to 23-fold greater than the minimalf at thermoneutralT _a.Increased atT _a below thermoneutrality was supported by increased minute volume (V i) at both altitudes. The change inV i was primarily a function of changing tidal volume (V t), althoughf increased slightly asT _a declined. Oxygen extraction ( ) remained fairly constant atT _a below 20°C at both altitudes. BothV t and were considerably lower when birds were panting than at lowerT _a.Chukars showed few obvious ventilatory adaptations to HA. The 35% change in between 340 and 3,800 m was accommodated by a corresponding change inV i (btps), most of which was accomplished by increasedf at HA, along with a slight increase in .Abbreviations and symbols HA high altitude - LA low altitude - rate of evaporative water loss - oxygen extraction efficiency - f respiratory frequency - V t tidal volume - V i minute volume - BMR basal metabolic rate - MHP metabolic heat production     

Respiratory responses to long-term temperature exposure in the box turtle,Terrapene ornata

Summary In late February, seven box turtles were collected with body temperatures between 7 and 9°C. Ventilation, gas exchange and end-tidal and were recorded at 5, 10, 15 and 25°C, the animals being at each temperature for 2 to 3 weeks. There was a pronounced diurnal rhythm of breathing frequency at all temperatures. At 5°C the mean 24-h frequency was only 3.7 breaths h^–1. At 15°C the frequency was 16 times higher with a 17-fold increase of ventilation. Oxygen uptake only changed from 3.4 to 12.7 ml·kg^–1·h^–1. Consequently, the ratio (ventilation, ml BTPS/O₂ uptake, ml STPD) increased from 12.5 at 5°C to 48 at 15°C, but decreased to 24 at 25°C. The decrease of this ratio during cold exposure contrasts with an increase of the ratio during cooling earlier reported for fresh water turtles,Pseudemys. Cutaneous CO₂ elimination was important at low temperature. This caused a decrease of the pulmonary gas exchange ratio so that end-tidal remained low at 5°C in spite of an end-tidal of only 54 Torr.     

Carbonic anhydrase activity in the blood and the gills of rainbow trout during long-term hypercapnia in hard,bicarbonate-rich freshwater

Summary Carbonic anhydrase (CA) activities in gills and venous blood, acid-base balance, and haematological variables were studied during environmental hypercapnia in rainbow trout (Salmo gairdneri). Batches of 8–10 fish were exposed to about 3 or 13 mmHg in flow-through tests of various duration from 4 h to 80 days.After initial acidosis, blood pH rose above pre-experimental values. At 3 mmHg it became normal again within 21 days, while at 13 mmHg the overshoot lasted for 80 days. In fish acclimated for 3 weeks or more to 13 mmHg , blood HCO ₃ ^– increased four to five times while plasma Cl^– levels were lower and K⁺ higher. Na⁺ levels did not show any consistent trend associated with exposure to hypercapnia. After an initial acidaemia, Hct, Hb, and RBC remained relatively constant.Patterns of change in CA activity differed between gills and erythrocytes. Initially, blood CA decreased at both levels. It then began rising after about 3 weeks and tended to reach pre-experimental values by 80 day's hypercapnia. At 13 mmHg , gill CA increased to twice the pre-experimental level. Compared with blood CA, gill CA appeared to be more specifically involved in fish acclimation to hypercapnia, which demands an increase in blood bicarbonate to provide a sufficient buffering capacity. Increased CA indicates that the gill enzyme may play a more important role than blood CA in acid-base regulation in fish during hypercapnia.Abbreviations CA carbonic anhydrase - Hb haemoglobin - Hct haematocrit value - RBC red blood cells     

Energy requirements of Adélie penguin (Pygoscelis adeliae) chicks

Summary The energy requirements of Adélie penguin (Pygoscelis adeliae) chicks were analysed with respect to body mass (W, 0.145–3.35 kg, n=36) and various forms of activity (lying, standing, minor activity, locomotion, walking on a treadmill). Direct respirometry was used to measure O₂ consumption ( ) and CO₂ production. Heart rate (HR, bpm) was recorded from the ECG obtained by both externally attached electrodes and implantable HR-transmitters. The parameters measured were not affected by hand-rearing of the chicks or by implanting transmitters. HR measured in the laboratory and in the field were comparable. Oxygen uptake ranged from in lying chicks to at maximal activity, RQ=0.76. Metabolic rate in small wild chicks (0.14–0.38 kg) was not affected by time of day, nor was their feeding frequency in the colony (Dec 20–21). Regressions of HR on were highly significant (p< 0.0001) in transmitter implanted chicks (n=4), and two relationships are proposed for the pooled data, one for minor activities ( ), and one for walking ( ). Oxygen consumption, mass of the chick (2–3 kg), and duration of walking (T, s) were related as , whereas mass-specific O₂ consumption was related to walking speed (S, m·s^-1) as .Abbreviations bpm beats per minute - D distance walked (m) - ECG electrocardiogram - HR heart rate (bpm) - ns number of steps - RQ respiratory quotient - S walking speed (m·s^-1) - T time walked (s) - W body mass (kg)     

Use of the force-velocity test to determine the optimal braking force for a sprint exercise on a friction-loaded cycle ergometer

A group of 15 untrained male subjects pedalled on a friction-loaded cycle ergometer as fast as possible for 5–7 s to reach the maximal velocity (V{immax}) against different braking forces (F _B). Power was averaged during a complete crank rotation by adding the power dissipated againstF _B to the power necessary to accelerate the flywheel. For each sprint, determinations were made of peak power output ( ) power output attained atV _max ( ) calculated as the product ofV _max andF _B and the work performed to reachV _max expressed in mean power output ( ). The relationships between these parameters andF _B were examined. A biopsy taken from the vastus lateralis muscle and tomodensitometric radiographs of both thighs were taken at rest to identify muscle metabolic and morphometric properties. The value was similar for allF _B. Therefore, the average of values was defined as corrected maximal power ( ). This value was 11 higher than the maximal power output uncorrected for the acceleration. Whereas the determination did not require high loads, the highest value ( ) was produced when loading was heavy, as evidenced by the -F _B parabolic relationship. For each subject, the braking force ( ) giving was defined as optimal. The , equal to 0.844 (SD 0.108) N · kg⁻¹ bodymass, was related to thigh muscle area (r = 0.78,P < 0.05). The maximal velocity ( ) reached against this force seemed to be related more to intrinsic fibre properties (% fast twitch b fibre area and adenylate kinase activity). Thus, from the determination, it is suggested that it should be possible to predict the conditions for optimal exercise on a cycle ergometer.