A reliable preloaded cycling time trial for use in conditions of significant thermal stress.

The purpose of this study was to assess the reliability of a 15-min time trial preloaded with 45 min of fixed-intensity cycling under laboratory conditions of thermal stress. Eight trained cyclists/triathletes (41 ± 10 years, VO2 peak: 69 ± 8 mL/kg/min, peak aerobic power: 391 ± 72 W) completed three trials (the first a familiarization) where they cycled at ∼ 55% VO2 peak for 45 min followed by a 15-min time trial (∼75% VO2 peak) under conditions of significant thermal stress (WBGT: 26.7 ± 0.8 °C, frontal convective airflow: 20 km/h). Seven days separated the trials, which were conducted at the same time of day following 24 h of exercise and dietary control. Reliability increased when a familiarization trial was performed, with the resulting coefficient of variation and intraclass correlation coefficient of the work completed during the 15-min time trial, 3.6% and 0.96, respectively. Therefore, these results demonstrate a high level of reliability for a 15-min cycling time trial following a 45-min preload when performed under laboratory conditions of significant thermal stress using trained cyclists/triathletes.

Prediction of the amount and rate of histamine degradation by diamine oxidase (DAO).

Histamine is a biogenic amine that forms in a variety of foods and can cause food poisoning at high concentrations (>500 ppm). In situations where the formation of histamine in food cannot be prevented through refrigeration, diamine oxidase (DAO) enzyme may be used to degrade histamine to safe levels. The aims of this work were to apply DAO in model (buffer) and real (cooked tuna soup used in the manufacture of a fish paste product, Rihaakuru) systems, in order to obtain predictions for the rates and amounts of histamine degradation. The two systems were set up with a constant concentration of histamine (500 mg/L) and the DAO enzyme (2534 units/L) at a temperature of 37°C, agitation at 100 rpm and an incubation time of 10h with variable pH (5-7) and salt concentrations (1-5%). A total of 15 experiments were designed for each system using central composite design (CCD). The data from these experiments were fitted into regression models; initially the data were used to generate an exponential decline model and then the data from this were fitted into a secondary response surface model (RSM) to predict the rate and amount of histamine degradation by DAO. The model system results indicated that DAO activity was not significantly affected by salt (p>0.05), and that activity reached a maximum within the pH range of 6-6.5 with an optimum at pH 6.3. However, the results obtained with the tuna soup model showed that the optimum oxidation of histamine using DAO occurred between pH 6-7 and salt 1-3%. This study defined the conditions for the use of DAO to degrade 500 mg/L of histamine in tuna soup used to manufacture Rihaakuru. The models generated could also be used to predict the rate and amount of histamine degradation in other foods that have similar characteristics to tuna soup.

Growth rates and energy intake of hand-reared cheetah cubs (Acinonyx jubatus) in South Africa.

Growth rate is an important factor in neonatal survival. The aim of this study was to determine growth rates in hand-reared cheetah cubs in South Africa fed a prescribed energy intake, calculated for growth in the domestic cat. Growth was then compared with previously published data from hand-reared cubs in North America and the relationship between growth and energy intake explored. Daily body weight (BW) gain, feed and energy intake data was collected from 18 hand-reared cheetah cubs up to 120 days of age. The average pre-weaning growth rate was 32 g/day, which is lower than reported in mother-reared cubs and hand-reared cubs in North American facilities. However, post-weaning growth increased to an average of 55 g/day. Growth was approximately linear prior to weaning, but over the entire age range it exhibited a sigmoidal shape with an asymptotic plateau averaging 57 kg. Energy intake associated with pre-weaning growth was 481 kJ ME/kg BW(0.75). Regression analysis described the relationship between metabolic BW, metabolisable energy (ME) intake, and hence daily weight gain. This relationship may be useful in predicting energy intake required to achieve growth rates in hand-reared cheetah cubs similar to those observed for their mother-reared counterparts.

Effect of a previous sprint on the parameters of the work-time to exhaustion relationship in high intensity cycling.

The relationships between both metabolic (E) and mechanical (W) energy expended and exhaustion time (t(e)), was determined for 11 well-trained subjects during constant load cycloergometric exercises at 95, 100, 110, 115 % maximal aerobic power performed both from rest and, without interruption, after an all-out sprint of 7 s. These relationships were well described by straight lines: y = a + bt(e), where b was taken as the critical power (metabolic and mechanical) that can be sustained for long periods of time. b was unaffected by the exercise conditions and amounted to 82 - 94 % of maximal aerobic metabolic and mechanical power. The constant a was taken as the anaerobic stores capacity in excess of the O2 deficit. When the test was preceded by the sprint, a (metabolic and mechanical) was reduced to about 60 - 70 % of control values. This reduction was essentially equal to the corresponding E and W output during the sprint. These data support the view that the slope of linear regressions of E and W on t(e) is indeed a measure of the critical power, whereas the y intercept of these same regressions is a measure of the anaerobic capacity.

Oxygen kinetics and modelling of time to exhaustion whilst running at various velocities at maximal oxygen uptake.

The purpose of this study was to characterise the relationship between running velocity and the time for which a subject can run at maximal oxygen uptake (VO2max), (tlimVO2max). Seven physical education students ran in an incremental test (3-min stages) to determine VO2max and the minimal velocity at which it was elicited (vVO2max). They then performed four all-out running tests on a 200-m indoor track every 2 days in random order. The mean times to exhaustion tlim at 90%, 100%, 120% and 140% vVO2max were 13 min 22 s (SD 4 min 30 s), 5 min 47 s (SD 1 min 50 s), 2 min 11 s (SD 38 s) and 1 min 12 s (SD 18 s), respectively. Five subjects did not reach VO2max in the 90% vVO2max test. All the subjects reached VO2max in the runs at 100% vVO2max. All the subjects, except one, reached VO2max in the runs at 120% vVO2max. Four subjects did not reach VO2max in the 140% vVO2max test. Time to achieve VO2max was always about 50% of the time to exhaustion irrespective of the intensity. The time to exhaustion-velocity relationship was better fitted by a 3- than by a 2-parameter critical power model for running at 90%, 100%, 120%, 140% vVO2max as determined in the previous incremental test. In conclusion, tlimVO2max depended on a balance between the time to attain VO2max and the time to exhaustion tlim. The time to reach VO2max decreased as velocity increased. The tlimVO2max was a bi-phasic function of velocity, with a peak at 100% vVO2max.

Maximal endurance time at VO2max.

INTRODUCTION: There has been significant recent interest in the minimal running velocity which elicits VO2max. There also exists a maximal velocity, beyond which the subject becomes exhausted before VO2max is reached. Between these limits, there must be some velocity that permits maximum endurance at VO2max, and this parameter has also been of recent interest. This study was undertaken to model the system and investigate these parameters. METHODS: We model the bioenergetic process based on a two-component (aerobic and anaerobic) energy system, a two-component (fast and slow) oxygen uptake system, and a linear control system for maximal attainable velocity resulting from declining anaerobic reserves as exercise proceeds. Ten male subjects each undertook four trials in random order, running until exhaustion at velocities corresponding to 90, 100, 120, and 140% of the minimum velocity estimated as being required to elicit their individual VO2max. RESULTS: The model development produces a skewed curve for endurance time at VO2max, with a single maximum. This curve has been successfully fitted to endurance data collected from all 10 subjects (R2 = 0.821, P < 0.001). For this group of subjects, the maximal endurance time at VO2max can be achieved running at a pace corresponding to 88% of the minimal velocity, which elicits VO2max as measured in an incremental running test. Average maximal endurance at VO2max is predicted to be 603 s in a total endurance time of 1024 s at this velocity. CONCLUSION: Endurance time at VO2max can be realistically modeled by a curve, which permits estimation of several parameters of interest; such as the minimal running velocity sufficient to elicit VO2max, and that velocity for which endurance at VO2max is the longest.

Sensitivity of a standard host resistance assay using Streptococcus agalactiae for assessing exposure to immunotoxicants in wild cotton rats (Sigmodon hispidus).

Resident small mammals have been used for in situ biomonitoring of contaminated waste sites containing suspected immunotoxicants. Host resistance assays, which involve challenging animals with an actual pathogen, allow for testing of overall immune system function in animals. Because such assays have not been evaluated for use with wild rodent species, it was our objective to assess the efficacy of Streptococcus agalactiae as a pathogenic model for use in a host resistance assay for detecting alterations in immune system function in wild cotton rats (Sigmodon hispidus). The ability of the assay to detect immunosuppression was evaluated by inducing immunosuppression chemically (cyclophosphamide or dexamethasone) and by protein malnutrition. The estimated lethal dose of S. agalactiae that killed 50% of challenged animals (LD50) was 5.76x10(7) colony-forming units (CFUs). Although bacterial agglutination titers indicated that animals developed an antibody response when immunized, immunization was not sufficient to adequately protect animals from a subsequent pathogenic challenge. Sensitivity of the host resistance assay was only suitable for detecting substantial immunosuppression, such as that induced by protein malnutrition or dexamethasone administration.

Tree water use and rainfall partitioning in a mature poplar-pasture system.

Traditionally, poplars (Populus) have been planted to control erosion on New Zealand's hill-slopes, because of their capacity to dry out and bind together the soil, by reducing effective rainfall and increasing evapotranspiration and soil strength. However, the effect of widely spaced poplars on the partitioning of soil water and rainfall has not been reported. This study determined rainfall partitioning for 18 mid-spring days in a mature P. deltoides (Bart. ex Marsh, Clone I78)-pasture association (37 stems per hectare, unevenly spaced at 16.4 +/- 0.4 m) and compared it with a traditional open pasture system in grazed areas of a hill environment. Tree transpiration was measured by the heat pulse technique. A time-driven mathematical model was used to set a zero offset, adjust anomalous values and describe simultaneous sap velocity time courses of trees. The model showed that daylight sap flow velocities can be represented with a nonlinear Beta function (R(2) > 0.98), and differences in the parameters representing the initiation, duration and conformation of the sap velocity can be tested statistically to discern tree transpiration differences during the day. Evapotranspiration was greater for the poplar-pasture association than for the open pasture (2.7-3.0 versus 2.2 mm day(-1)). The tree canopy alone contributed 0.92 mm day(-1) as transpiration and 1.37 mm day(-1) as interception, whereas evapotranspiration of the pasture understory was only 0.4-0.6 mm day(-1). Despite the higher water use of the poplar-pasture association, soil water in the 0-300 mm soil stratum was higher than, or similar to, that of the open pasture. Tree shading decreased evapotranspiration and pasture accumulation under the trees.

Time in human endurance models. From empirical models to physiological models.

This article traces the study of interrelationships between power output, work done, velocity maintained or distance covered and the endurance time taken to achieve that objective. During the first half of the twentieth century, scientists examined world running records for distances from < 100 m to > 1000 km. Such examinations were empirical in nature, involving mainly graphical and crude curve-fitting techniques. These and later studies developed the use of distance/time or power/time models and attempted to use the parameters of these models to characterise the endurance capabilities of athletes. More recently, physiologists have proposed theoretical models based on the bioenergetic characteristics of humans (i.e. maximal power, maximal aerobic and anaerobic capacity and the control dynamics of the system). These models have become increasingly complex but they do not provide sound physiological and mathematical descriptions of the human bioenergetic system and its observed performance ability. Finally, we are able to propose new parameters that can be integrated into the modelling of the power/time relationship to explain the variability in endurance time limit at the same relative exercise power (e.g. 100% maximal oxygen uptake).

Effect of endurance training on blood lactate clearance after maximal exercise.

The aim of this study was to measure serial changes in the rate of blood lactate clearance (gamma2) in response to sequential periods of training and detraining in four male triathletes aged 22-44 years. There were two major phases of training and taper, each lasting 4-5 weeks (training 1 = 5 weeks, taper 1 = 2 weeks, training 2 = 4 weeks and taper 2 = 2 weeks), in preparation for a triathlon competition. The training stimulus absorbed by each subject was carefully quantified from the duration and intensity of the training exercise. A serial weekly measure of each trainee's physical response to training was evaluated as the peak power, termed a 'criterion performance', developed by a subject during a 30 W x min(-1) ramp cycle ergometer test to exhaustion each week. During 30 min of recovery after this test, 13 samples of venous blood were drawn sequentially from a subject to measure the blood lactate recovery curve. The rate constant of blood lactate clearance was estimated by a non-linear least-squares regression technique. In addition, the concurrent time to peak lactate concentration and the peak lactate concentration were also estimated to help define changing lactate kinetics. The criterion performance generally declined throughout each period of incremental training and improved during each taper period, rising iteratively in this way to be clearly above baseline by the end of the second taper. The blood lactate clearance rate increased transiently in early training before declining from the middle of the first training period to the middle of the first taper; thereafter, gamma2 increased above baseline in each trainee throughout the remaining first taper and the major portion of the second training period, decreasing only in the final criterion performance test. The time to peak lactate declined from baseline throughout all phases of training and taper. Peak blood lactate increased in all subjects to the end of the first taper before declining by the end of the second training period, rising again to baseline levels during the second taper. The change in gamma2 was examined relative to the work rate achieved in cycle ergometry above an initial baseline score (deltaCP) and against concurrent peak blood lactate. There was a clear upward shift in gamma2 above baseline throughout the first and second training and taper in two subjects; this was less clear in the remaining two subjects, each of whom had a lower deltaCP. We conclude that this indicates improved lactate clearance, manifest by the change in gamma2 induced by endurance training.

Modeling training and overtraining.

This paper adapts the dose-response research tool, well established in pharmacological studies, to an exercise and performance setting. Training is measured in quantitative units as the dosage inputs, and their effects on fitness, fatigue, overtraining and performance responses are modelled. In this way, one can answer such questions as 'what performance level would be predicted if a certain amount of training was undertaken?' More specifically, athletes and their coaches are interested in designing a training schedule to maximize performance potential at some future date and minimize the risk of overtraining during that time, for some minimal training inputs. This approach leads to the practical recommendation that athletes should train more intensely but only on alternate days, for a 5 month session, in a triangular-shaped training profile, with the heaviest training occurring between weeks 12 and 4 before competition.

Ramp and constant power trials produce equivalent critical power estimates.

The standard critical power test protocol on the cycle ergometer prescribes a series of trials to exhaustion, each at a different but constant power setting. Recently the protocol has been modified and applied to a series of trials to exhaustion each at a different ramp incremental rate. This study was undertaken to compare critical power and anaerobic work capacity estimates in the same group of subjects when derived from the two protocols. Ten male subjects of mixed athletic ability cycled to exhaustion on eight occasions in randomized order over a 3-wk period. Four trials were performed at differing constant power settings and four trials on differing ramp incremental rates. Both critical power and anaerobic work capacity were estimated for each subject by curve fitting of the ramp model and of three versions of the constant power model. After adjusting for inter-subject variability, no significant differences were detected between critical power estimates or between anaerobic work capacity estimates from any model formulation or from the two protocols. It is concluded that both the ramp and constant power protocols produce equivalent estimates for critical power and anaerobic work capacity.

Alternative forms of the critical power test for ramp exercise.

The critical power test provides estimates of two important parameters characterizing work performance; anaerobic work capacity (AWC) and critical power (CP). The CP concept has recently been adapted to a test procedure involving ramp exercise. Just as the constant power format of the CP test can be expressed in several mathematically equivalent forms, so too can the ramp format. This communication illustrates these forms and tests the various AWC and CP estimates so obtained. It is found that three of the four forms provide equivalent estimates for both AWC and CP. It is concluded that provided either endurance time or total work performed is taken as the dependent variable, researchers can expect consistent estimates for both AWC and CP.

A 3-parameter critical power model.

The critical power test is a well-established procedure that provides estimates of two important parameters characterizing work performance; anaerobic work capacity (AWC) and critical power (CP). The concept proscribes a hyperbolic relationship between power output (P) and time to exhaustion (t), given by (P - CP)t = AWC. Since evidence now exists that the procedure overestimates CP and underestimates AWC, this study was undertaken to investigate the effect of relaxing the requirement that the time asymptote necessarily be at zero. Using data from a previous study, it is shown that in so doing, (1) a time asymptote significantly less than zero is obtained, (2) significantly smaller estimates of CP and larger estimates of AWC are obtained, (3) a third parameter is introduced that theoretically represents maximal instantaneous power, (4) it implies that the maximal power that could be developed at any instant is proportional to the amount of AWC remaining at that instant, which in turn implies that (5) at exhaustion not necessary all of AWC is consumed.

The relationship between power output and endurance: a brief review.

It is well established that for work requiring high power output, endurance time is short, and that low power outputs can be maintained for long periods. Parameters describing this relationship are important in characterising work performance and the capacity of humans as a source of mechanical power. The purpose of this paper is to provide a brief review of the available literature investigating this relationship and its parameters. Most experimental data reflect measurements of endurance times over a range of constant power outputs on the cycle ergometer. Early graphical analyses of these data have been superseded by curve fitting, which in turn has led to establishment of the two component hyperbolic model now embodied in the critical power test. This model has been modified and extended in various ways to account for its shortcomings. In addition, a number of different exercise forms have been studied, and the effects of a variety of secondary factors (training status, age, sex, for example) on the parameters have also been investigated.

Effects of clenbuterol and ICI118551, a selective beta 2-antagonist, on the growth of skeletal muscle of suckling rats.

The beta 2-adrenergic agonist, clenbuterol, was administered to lactating rats (4 mg/kg diet) from post-partum day 1 to day 19, or directly injected into neonate rats (0.1 and 1.0 mg/kg body weight) from post-partum day 3 until day 15. Changes in body weight and the skeletal muscles soleus (SOL) and extensor digitorum longus (EDL) were studied in both dams and suckling offspring. Drug treatment consistently increased body weight in dams whilst significantly reducing the growth of their suckling pups. In dams treated with clenbuterol (4 mg/kg of diet) muscle weights and protein contents were significantly increased. Total protein content increased by 16% in SOL and 47% in EDL after 19 days of treatment. In contrast, in their suckling pups, there was a 22% and 26% reduction in protein content of SOL and EDL respectively. Administration of the beta 2-antagonist ICI118551 to these pups failed to prevent these reductions in body and muscle weights. Hence, if clenbuterol did reach the pups via the milk from treated mothers it did not act via conventional beta 2-receptors. Injection of pups with clenbuterol (1.0 mg/kg every 12 h) from litters suckling from untreated dams also resulted in significant reductions in muscle weights and protein contents. Protein content was reduced by 10% in SOL and 13% in EDL after 12 days of treatment. No alteration in fibre type proportion in SOL or EDL resulted from this treatment. Further work is required to determine whether the growth suppression in the two situations occurs via the same mechanism.

Effect of the beta 2-adrenergic agonist clenbuterol on the growth of fast- and slow-twitch skeletal muscle of the dystrophic (C57BL6J dy2J/dy2J) mouse.

Clenbuterol (4mg/kg in diet for 21 days) had no statistically significant effect on whole body growth. It did cause a significant increase (18.2%) in wet weight of the fast twitch muscle extensor digitorum longus (EDL) and a corresponding 14.9% increase in total muscle protein. In transverse sections through dystrophic muscle fibre sizes were more variable than in normal muscle. Clenbuterol treatment resulted in a reduction in the proportion of small diameter fibres, and therefore an increase in mean fibre diameter, in dystrophic EDL. Clenbuterol had no significant effect upon the slow twitch muscle soleus.