Influence of training status on maximal accumulated oxygen deficit during all-out cycle exercise

The influence of training status on the maximal accumulated oxygen deficit (MAOD) was used to assess the validity of the MAOD method during supramaximal all-out cycle exercise. Sprint trained (ST; n = 6), endurance trained (ET; n = 8), and active untrained controls (UT; n = 8) completed a 90 s all-out variable resistance test on a modified Monark cycle ergometer. Pretests included the determination of peak oxygen uptake ( O_2peak) and a series (5–8) of 5-min discontinuous rides at submaximal exercise intensities. The regression of steady-state oxygen uptake on power output to establish individual efficiency relationships was extrapolated to determine the theoretical oxygen cost of the supramaximal power output achieved in the 90 s all-out test. Total work output in 90 s was significantly greater in the trained groups (P<0.05), although no differences existed between ET and ST. Anaerobic capacity, as assessed by MAOD, was larger in ST compared to ET and UT. While the relative contributions of the aerobic and anaerobic energy systems were not significantly different among the groups, ET were able to achieve significantly more aerobic work than the other two groups, while ST were able to achieve significantly more anaerobic work. Peak power and peak pedalling rate were significantly higher in ST. The results suggested that MAOD determined during all-out exercise was sensitive to training status and provided a useful assessment of anaerobic capacity. In our study sprint training, compared with endurance training, appeared to enhance significantly power output and high intensity performance over brief periods (up to 60 s), yet few overall differences in performance (i.e. total work) existed during 90 s of all-out exercise.     

Anaerobic capacity determined by maximal accumulated O2 deficit

We present a method for quantifying the anaerobic capacity based on determination of the maximal accumulated O2 deficit. The accumulated O2 deficit was determined for 11 subjects during 5 exhausting bouts of treadmill running lasting from 15 s to greater than 4 min. The accumulated O2 deficit increased with the duration for exhausting bouts lasting up to 2 min, but a leveling off was found for bouts lasting 2 min or more. Between-subject variation in the maximal accumulated O2 deficit ranged from 52 to 90 ml/kg. During exhausting exercise while subjects inspired air with reduced O2 content (O2 fraction = 13.5%), the maximal O2 uptake was 22% lower, whereas the accumulated O2 deficit remained unchanged. The precision of the method is 3 ml/kg. The method is based on estimation of the O2 demand by extrapolating the linear relationship between treadmill speed and O2 uptake at submaximal intensities. The slopes, which reflect running economy, varied by 16% between subjects, and the relationships had to be determined individually. This can be done either by measuring the O2 uptake at a minimum of 10 different submaximal intensities or by two measurements close to the maximal O2 uptake and by making use of a common Y-intercept of 5 ml.kg-1.min-1. By using these individual relationships the maximal accumulated O2 deficit, which appears to be a direct quantitative expression of the anaerobic capacity, can be calculated after measuring the O2 uptake during one exhausting bout of exercise lasting 2-3 min.     

Oxygen deficits incurred during 45, 60, 75 and 90-s maximal cycling on an air-braked ergometer

The aims of this study were to determine the most appropriate duration for the measurement of the maximal accumulated O₂ deficit (MAOD), which is analogous to the anaerobic capacity, to ascertain the effects of mass, fat free mass (FFM), leg volume (V _leg) and lower body volume (V _1b) on anaerobic test performance, to examine the reproducibility for peak power output ( ) or maximal anaerobic power using an air-braked cycle ergometer and to produce approximations for the percentages of aerobic and anaerobic metabolism during exercise of short duration but high intensity. A group of 12 endurance trained cyclists [mean age 25.1 (SD 4.6) years; mean body mass 73.43 (SD 7.12) kg; mean maximal oxygen consumption 5.12 (SD 0.35) l·min^–1; mean body fat 12.5 (SD 4.1) %] accordingly performed four counterbalanced treatments of 45, 60, 75 and 90 s of maximal cycling on an air-braked ergometer. The mean O₂ deficit of 3.52 l for the 45-s treatment was significantly less (P < 0.01) than those for the 60 (3.75 l), 75 (3.80 l) and 90-s (3.75 l) treatments. These data therefore indicate that in predominantly aerobically trained subjects the O₂ deficit attains a plateau after 60 s of maximal cycling on an air-braked ergometer. Statistically significant interclass correlation coefficients (P<0.05) between the anthropometric variables (mass, FFM, V _leg and V_1b) and or maximal anaerobic power (0.624–0.748) and MAOD (ml) or anaerobic capacity (0.666–0.772) furthermore would suggest the relevance of taking into account muscle mass during anaerobic tests. Intraclass correlation coefficients (0.935–0.946; all P<0.001) would indicate a high degree of reliability for the measurement of . The relative importance of anaerobic work decreased from 60% for the 45-s test to 40% for the 90-s one. Hence our study showed that both aerobic and anaerobic metabolism contributed significantly during all-out tests of 45–90 s duration.     

Effect of end-point cadence on the maximal work-time relationship

This study examined the effect of end-point cadence on the parameters of the work-time relationship determined for cycle ergometry. Eight male subjects completed four maximal tests on an electrically-braked cycle ergometer that regulated a constant power output independent of cadence. The power outputs imposed ranged between an average of 259 W and 403 W, whereas the corresponding durations ranged between 139 s and 1691 s. During each test subjects were required to maintain a cadence of 80–90 rpm. Accumulated time to end-point cadences of 70, 60 and 50 rpm were recorded. The four work-time determinations for each of three end-point cadences were used to determine linear relationships between work and time, yielding both a y-intercept, which represents anaerobic work capacity, and a slope, which is termed critical power (CP), for each end-point cadence. There was a significant increase in the y-intercept as end-point cadence decreased from 70 to 60 rpm (F[1,7]=36.7, p < 0.001) or 70 to 50 rpm (F[1,7]=80.1, p < 0.001), but not from 60 rpm to 50 rpm (F[1,7]=3.28, p > 0.05). In contrast, there was no effect of end-point cadence on CP (F[2,14]=1.89, p < 0.05). These results demonstrate that the end-point cadence selected to terminate tests only affects the y-intercept of the work-time relationship. To control for this effect, the cadence at which each test is terminated should be standardised if determination of anaerobic work capacity, as represented by the y-intercept, is required.     

Oxygen deficit is related to the exercise time to exhaustion at maximal aerobic speed in middle distance runners

The purpose of this study was to show the relationship between oxygen deficit and the time to exhaustion (tlim) at maximal aerobic speed (MAS). The minimum speed that elicits VO(2max) was assumed to be the maximal aerobic speed (MAS). Fourteen subelite male runners (mean (SD: age = 27 +/- 5 yrs: VO(2max) = 68.9 +/- 4.6 ml kg (-1). min ( -1); MAS = 21.5 +/- 1 km h (-1) ) participated in the study. Each subject performed an incremental test to determine and MAS. The subjects ran to exhaustion at velocities corresponding to 100 and 120 % MAS. Oxygen deficit was measured during the period exercise to exhaustion at 120% of MAS and was calculated from the difference between O(2) demand and the accumulated O 2 uptake. The tlim values at 100% MAS were correlated with the values of tlim at 120% MAS (r = 0.52). The results reveal that the oxygen deficit was related to the time to exhaustion at MAS and indicate that the greater the oxygen deficit, the greater the time to exhaustion at MAS. It was also noted that the adjustment of oxygen consumption is related to the oxygen deficit. In other words, the subjects who have an important anaerobic capacity are the most efficient during an exercise time to exhaustion at MAS. The time limit values can be expressed by a linear regression making intervene MAS and anaerobic capacity. This conclusion could be of great interest in the training of middle distance runners.     

A simple,reliable method to determine the mean gait speed using heel markers on a treadmill

Gait speed is an essential parameter of gait analysis. Our study proposed a simple and accurate method to extract a mean gait speed during walking on a treadmill using only kinematic data from markers placed on the heels of the participants’ feet. This method provided an attractive, simple method that remains resistant to errors in treadmill calibration. In addition, this method required only two markers, since heel markers are essential to gait analysis, and the proposed method is robust enough to differentiate among various gait speeds (mean error <1%).     

An enzymatic method to determine receptor-mediated endocytosis

Many studies have measured receptor-mediated endocytosis using radiolabeled ligands or antibodies. Upon ligation and cross-linking, the labeled ligand or antibody is endocytosed and the internalization of the radioisotope is assayed after stripping the uninternalized ligand from the cell membrane. This study reports on an enzymatic assay to measure receptor-mediated endocytosis and compares it with the radioactive method. The results show that receptor-mediated endocytosis measured using the peroxidase conjugated antibody is two fold higher than that measured with a radiolabeled antibody. Thus, approximately 38% endocytosis of CD3 is measured using an ¹²⁵I-labeled antibody, whereas approximately 79% endocytosis is detected by peroxidase conjugated antibody method. Similar increases are also found with CD2 receptor-mediated endocytosis. Our study has demonstrated that the enzymatic method could be employed in determining receptor-mediated endocytosis. In addition to increased sensitivity, the enzymatic assay eliminates the use of radioactive materials.     

Increasing maximal heart rate increases maximal O2 uptake in rats acclimatized to simulated altitude

Gonzalez, Norberto C., Richard L. Clancy, Yoshihiro Moue,and Jean-Paul Richalet. Increasing maximal heart rate increases maximal O₂ uptake in ratsacclimatized to simulated altitude. J. Appl.Physiol. 84(1): 164-168, 1998.Maximal exerciseheart rate (HR_max) is reducedafter acclimatization to hypobaric hypoxia. The lowHR_max contributes to reducemaximal cardiac output(_max) andmay limit maximal O₂ uptake(O_{2 max}). Theobjective of these experiments was to test the hypothesisthat the reduction in_max afteracclimatization to hypoxia, due, in part, to the lowHR_max, limitsO_{2 max}. Ifthis hypothesis is correct, an increase in _max wouldresult in a proportionate increase inO_{2 max}. Rats acclimatized to hypobaric hypoxia [inspiredPO₂(PI_O2) = 69.8 ± 3 Torr for 3 wk] exercised on a treadmill in hypoxic (PI_O2 = 71.7 ± 1.1 Torr) or normoxic conditions(PI_O2 = 142.1 ± 1.1 Torr). Each rat ran twice: in one bout the rat was allowed to reach itsspontaneous HR_max, which was 505 ± 7 and 501 ± 5 beats/min in hypoxic and normoxic exercise,respectively; in the other exercise bout,HR_max was increased by 20% to the preacclimatization value of 600 beats/min by atrial pacing. This resulted in an ~10% increase in_max, since theincrease in HR_max was offset by a10% decrease in stroke volume, probably due to shortening of diastolicfilling time. The increase in_max was accompanied by a proportionate increase in maximal rate of convective O₂ delivery(_max × arterial O₂ content), maximal workrate, and O_{2 max} inhypoxic and normoxic exercise. The data show that increasingHR_max topreacclimatization levels increasesO_{2 max}, supportingthe hypothesis that the lowHR_max tends to limitO_{2 max} after acclimatization to hypoxia.

     

一种优化的测定过氧化氢酶活性的方法

建立了一种优化的化学发光技术测定过氧化氢酶(CAT)活性的方法,并用此法检测40只正常家兔红细胞中过氧化氢酶活性为6.421±1.43K/gHb.采用H\-2O\-2-鲁米诺发光体系,探讨了反应时间、底物浓度、样品浓度、样品保存等因素对测定的影响,得到较好的线性和重复性.     

An improved method to determine serine palmitoyltransferase activity

Serine palmitoyltransferase (SPT) catalyzes the condensation of l-serine and palmitoyl-CoA, which is the rate-limiting step in the de novo synthesis of sphingolipids. SPT activity is commonly measured by monitoring the incorporation of radiolabeled l-serine into 3-ketodihydrosphingosine. In this article, we introduce several adaptations of the established protocol to improve sensitivity, reproducibility, and practicability of the assay. A significant improvement of this new protocol is the possibility to measure SPT activity in total cell lysate instead of microsomes. The assay is furthermore extended by the introduction of a nonradioactive, HPLC-based detection protocol. The suggested HPLC method offers several advantages, most importantly, a 20-fold lower detection limit compared with the radioactive assay and the possibility to use an internal standard to correct for variation in the extraction.     

Physiological responses of young and elderly men to prolonged exercise at critical power

The critical power (CP) of a muscle group or individual may represent the highest rate of work which can be performed for an extended period. We investigated this concept in young (n = 13, 24.5 years) and elderly (n = 12, 70.7 years) active men by first determining CP and then comparing responses elicited by 24 min of cycle exercise at power outputs (omega) corresponding to CP. Values from the final 2 min of the 24-min ride were expressed relative to maximal values established in a ramp test. CP for the elderly was only 65% that for the young, but on a relative basis, it was significantly higher both in terms of omega (67 vs 62% of omega max) and oxygen consumption (VO2) (91.5 vs 85.2% of maximum oxygen consumption). There were no group differences in relative values for ventilation (VE), heart rate or respiratory exchange ratio (R). During the 24-min ride, VO2 and R achieved a plateau in both groups, while VE, blood lactate and arterial PCO2 continued to change in the young. It was concluded that CP can be determined in active elderly men, but that CP may not represent a true non-fatiguing work rate in either young or elderly men.     

Reliability of urine lactate as a novel biomarker of lactate production capacity in maximal swimming

Context: Postexercise urine lactate may be a novel biomarker of lactate production capacity during exercise.

Objective: To evaluate the reliability and utility of the urine lactate concentration after maximal swimming trials between different training protocols (6?×?50?m and 3?×?100?m) and training states (active and nonactive swimmers).

Materials and methods: Lactate and creatinine were determined by spectrophotometry in blood and urine.

Results: Blood and urine lactate concentrations were correlated in-between training protocols and in participants of different training states. The reliability of the urine lactate concentration was moderate for one of the training protocols and good or moderate for the two training states. Additionally, it was lower than that of the blood lactate concentration, and did not improve after normalizing to the urine creatinine concentration.

Discussion and conclusion: Although promising as a biomarker of lactate production capacity, urine lactate requires further research to improve its reliability.     

A facile method to determine the CO2/O2 specificity factor for ribulose bisphosphate carboxylase/oxygenase

A rapid method to determine the CO₂/O₂ specificity factor of ribulose 1,5-bisphosphate carboxylase/oxygenase is presented. The assay measures the amount of CO₂ and O₂ fixation at varying CO₂/O₂ ratios to determine the relative rates of each reaction. CO₂ fixation is measured by the incorporation of the moles of¹⁴CO₂ into 3-phosphoglycerate, while O₂ fixation is determined by subtraction of the moles of CO₂ fixed from the moles of RuBP consumed in each reaction. By analyzing the inorganic phosphate specifically hydrolyzed from RuBP under alkaline conditions, the amount of RuBP present before and after catalysis by rubisco can be determined.     

An alternative method of estimating the cranial capacity of Olduvai Hominid 7

The cranial capacity of Olduvai Hominid 7 is estimated to be 690 cc, with a standard uncertainty range of 538 to 868 cc. The estimate is derived from a systematic consideration of the relationships between Bregma-Asterion chords and cranial capacities obtained from a large sample of Homo sapiens and Pan troglodytes and from available fossil hominids. The estimation technique is applicable to other characters and specimens.     

A method to determine 18 O kinetic isotope effects in the hydrolysis of nucleotide triphosphates

A method to determine 18 O kinetic isotope effects (KIEs) in the hydrolysis of GTP that is generally applicable to reactions involving other nucleotide triphosphates is described. Internal competition, where the substrate of the reaction is a mixture of 18 O-labeled and unlabeled nucleotides, is employed, and the change in relative abundance of the two species in the course of the reaction is used to calculate KIE. The nucleotide labeled with 18 O at sites of mechanistic interest also contains 13C at all carbon positions, whereas the 16 O-labeled nucleotide is depleted of 13C. The relative abundance of the labeled and unlabeled substrates or products is reflected in the carbon isotope ratio (13C/12C) in GTP or GDP, which is determined by the use of a liquid chromatography-coupled isotope ratio mass spectrometer (LC-coupled IRMS). The LC is coupled to the IRMS by an Isolink interface. Carbon isotope ratios can be determined with accuracy and precision greater than 0.04% and are consistent over an order of magnitude in sample amount. KIE values for Ras/NF1(333)-catalyzed hydrolysis of [beta18 O3,13C]GTP were determined by change in the isotope ratio of GTP or GDP or the ratio of the isotope ratio of GDP to that of GTP. KIE values computed in the three ways agree within 0.1%, although the method using the ratio of isotope ratios of GDP and GTP gives superior precision (<0.1%). A single KIE measurement can be conducted in 25 min with less than 5 microg nucleotide reaction product.     

An adaptation of the LMS method to determine expression variations in profiling data

One of the major issues in expression profiling analysis still is to outline proper thresholds to determine differential expression, while avoiding false positives. The problem being that the variance is inversely proportional to the log of signal intensities. Aiming to solve this issue, we describe a model, expression variation (EV), based on the LMS method, which allows data normalization and to construct confidence bands of gene expression, fitting cubic spline curves to the Box-Cox transformation. The confidence bands, fitted to the actual variance of the data, include the genes devoid of significant variation, and allow, based on the confidence bandwidth, to calculate EVs. Each outlier is positioned according to the dispersion space (DS) and a P-value is statistically calculated to determine EV. This model results in variance stabilization. Using two Affymetrix-generated datasets, the sets of differentially expressed genes selected using EV and other classical methods were compared. The analysis suggests that EV is more robust on variance stabilization and on selecting differential expression from both rare and strongly expressed genes.     

Aerobic and anaerobic energy during a 2-km race simulation in female rowers

The maximal aerobic power (VO2max) and maximal anaerobic capacity (AODmax) of 16 female rowers were compared to their peak aerobic power (VO2peak) and peak anaerobic capacity (AODpeak, respectively) during a simulated 2-km race on a rowing ergometer. Each subject completed three tests, which included a 2-min maximal effort bout to determine the AODmax, a series of four, 4-min submaximal stages with subsequent progression to VO2max and a simulated 2-km race. Aerobic power was determined using an open-circuit system, and the accumulated oxygen deficit method was used to calculate anaerobic capacities from recorded mechanical power on a rowing ergometer. The average VO2peak (3.58 l min(-1)), which usually occurred during the last minute of the race simulation, was not significantly different (P > 0.05) from the VO2max (3.55 l min(-1)). In addition, the rowers' AODmax (3.40 l) was not significantly different (P > 0.05) from their AODpeak (3.50 1). The average time taken for the rowers to complete the 2-km race simulation was 7.5 min, and the anaerobic system (AODpeak) accounted for 12% of the rowers' total energy production during the race.