A prediction equation for the estimation of cardiorespiratory fitness using an elliptical motion trainer.

OBJECTIVE: In the United States of America, 6.2 million individuals are using elliptical motion trainers in fitness centres. However, graded exercise test protocols to estimate peak oxygen consumption (VO(2peak)) using elliptical motion trainers have not been developed for the general population. METHODS: Fifty-nine subjects (mean age: 23.5 +/- 4.1 years) were randomly divided into a validation (VAL: n = 39) or cross-validation (XVAL: n = 20) group. Peak oxygen consumption (ml x kg(-1) x min(-1)) was measured via indirect calorimetry on an elliptical motion trainer for both groups. Subjects exercised at 150 strides x min(-1) against a resistance of four and a crossramp of 8%. The resistance was increased every two minutes by two units until exhaustion. For the VAL group, a stepwise regression analysis was used to predict VO(2peak) from resistance, maximal heart rate (HR(max)), body mass index (BMI), height and gender (female = 0, male = 1). RESULTS: The prediction equation derived from this study was VO(2peak) (ml x kg(-1) x min(-1)) = 187.39403 + 12.97271 (gender) - 1.45311 (height) - 1.21604 (BMI) - 0.19613 (HR(max)) + 1.57093 (resistance) (R2 = 0.76, SEE = 4.47, p < 0.05). Using this equation, the predicted VO(2peak) of the XVAL group was 45.18 +/- 6.42 ml x kg(-1) x min(-1), while the measured VO(2peak) was 43.55 +/- 6.23 ml x kg(-1) x min(-1) CONCLUSION: No significant difference was found between the measured and predicted VO(2peak) in the XVAL group. Therefore, it appears this protocol and equation will allow individuals to accurately estimate their VO(2peak) without using direct calorimetry. However future studies should investigate the validity of this protocol with diverse populations.

Turnover of cyclic 2,3-diphosphoglycerate in Methanobacterium thermoautotrophicum. Phosphate flux in P1- and H2-limited chemostat cultures.

The archaebacterium Methanobacterium thermoautotrophicum was grown at 65 degrees C in H2- and Pi-limited chemostat cultures at dilution rates corresponding to 3- and 4-h doubling times, respectively. Under these conditions the steady state concentration of cyclic 2,3-diphosphoglycerate was 44 mM in the H2-limited cells and 13 mM in the cells grown under Pi limitation. Flux of Pi into the cyclic pyrophosphate pool was estimated by two 32P-labeling procedures: approach to isotopic equilibrium and replacement of prelabeled cyclic diphosphoglycerate with unlabeled compound. The results unequivocally demonstrate turnover of the phosphoryl groups; either both phosphoryl groups of the cyclic pyrophosphate leave together or the second leaves at a faster rate. The half-life of the rate-determining step for loss of the phosphoryl groups was approximately equal to the culture doubling time. The Pi flowing into the cyclic diphosphoglycerate pool accounted for 19% of the total Pi flux into Pi-limited cells and 43% of the total for H2-limited cells. The high phosphate flux through the large cyclic diphosphoglycerate pool suggests that this molecule plays an important role in the phosphorus metabolism of this methanogen.

Kinetics of phosphate uptake, growth, and accumulation of cyclic diphosphoglycerate in a phosphate-limited continuous culture of Methanobacterium thermoautotrophicum.

The archaebacterium Methanobacterium thermoautotrophicum was grown in continuous culture at 65 degrees C in a phosphate-limited medium at specific growth rates from 0.06 to 0.28 h-1 (maximum growth rate [mu max] = 0.36 h-1). Cyclic-2,3-diphosphoglycerate (cyclic DPG) levels ranged from 2 to 20 mM in Pi-limited cells, compared with about 30 mM in batch-grown cells. The Monod constant for Pi-limited growth was 5 nM. Pi uptake rates were determined by following the disappearance of 32Pi from the medium. Interrupting the H2 supply stopped the uptake of Pi and the release of organic phosphates. Little or no efflux of Pi occurred in the presence or absence of H2. Pi uptake of cells adapted to nanomolar Pi concentrations could be accounted for by the operation of one uptake system with an apparent Km of about 25 nM and a Vmax of 58 nmol of Pi per min per g (dry weight). Uptake curves at 30 microM Pi or above were biphasic due to a sevenfold decrease in Vmax after an initial phase of rapid movement of Pi into the cell. Under these conditions the growth rate slowed to zero and the cyclic DPG pool expanded before growth resumed. Thus, three properties of M. thermoautotrophicum make it well adapted to live in a low-P environment: the presence of a low-Km, high-Vmax uptake system for Pi; the ability to accumulate cyclic DPG rapidly; and a growth strategy in which accumulation of Pi and cyclic DPG takes precedence over a shift-up in growth rate when excess Pi becomes available.

Cyclic-2,3-diphosphoglycerate levels in Methanobacterium thermoautotrophicum reflect inorganic phosphate availability.

Methanobacterium thermoautotrophicum was grown in phosphate-limited chemostat cultures at a dilution rate corresponding to a doubling time of 13.2 h. The cyclic-2,3-diphospho-D-glycerate content of these cells was 8 to 10-fold lower than that of cells grown in batch cultures having a doubling time of 11.5 h. This metabolite accounted for 5% of cell dry weight during batch growth on 2 mM phosphate. In the chemostat the steady-state concentration of phosphate was 4 microM, showing that this methanogen is adapted to highly efficient growth at low phosphate concentrations. Since growth rates were similar in both cultures, the growth rate clearly does not depend on intracellular levels of cyclic-2,3-diphosphoglycerate.