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Biomedical subjects

C Moia

Publications and source records attributed to C Moia.

9 recordsLinked to original sources
PubMed1999

Oxygen cost of dynamic leg exercise on a cycle ergometer: effects of gravity acceleration.

A model of the metabolic internal power (Eint) during cycling, which includes the gravity acceleration (ag) as a variable, is presented. This model predicts that Eint is minimal in microgravity (0 g; g=9. 81 m s-2), and increases linearly with ag, whence the hypothesis that the oxygen uptake (VO2) during cycling depends on ag. Repeated VO2 measurements during steady-state exercise at 50, 75 and 100 W on the cycle ergometer, performed in space (0 g) and on Earth (1 g) on two subjects, validated the model. VO2 was determined from the time course of decreasing O2 fraction during rebreathing. The gas volume during rebreathing was determined by the dilution principle, using an insoluble inert gas (SF6). Average VO2 for subject 1 at each power was 0.99, 1.21 and 1.52 L min-1 at 1 g (n=3) and 0.91, 1.13 and 1.32 L min-1 at 0 g (n=5). For subject 2 it was 0.90, 1.12 and 1. 42 L min-1 at 1 g, and 0.76, 0.98 and 1.21 L min-1 at 0 g. These values corresponded to those predicted from the model. Although resting VO2 was lower at 0 g than at 1 g, the net (total minus resting) exercise VO2 was still smaller at 0 g than at 1 g. This difference reflects the lower Eint at 0 g.

Adult↗
PubMed1998

Effects of prolonged bed rest on cardiovascular oxygen transport during submaximal exercise in humans.

The hypothesis was tested that prolonged bed rest impairs O2 transport during exercise, which implies a lowering of cardiac output Qc and O2 delivery (QaO2). The following parameters were determined in five males at rest and at the steady-state of the 100-W exercise before (B) and after (A) 42-day bed rest with head-down tilt at -6 degrees: O2 consumption (VO2), by a standard open-circuit method; Qc, by the pressure pulse contour method, heart rate (fc), stroke volume (Qh), arterial O2 saturation, blood haemoglobin concentration ([Hb]), arterial O2 concentration (CaO2), and QaO2. The VO2 was the same in A and in B, as was the resting fc. The fc at 100 W was higher in A than in B (+17.5%). The Qh was markedly reduced (-27.7% and -22.2% at rest and 100 W, respectively). The Qc was lower in A than in B [-27.6% and -7.8% (NS) at rest and 100 W, respectively]. The CaO2 was lower in A than in B because of the reduction in [Hb]. Thus also QaO2 was lower in A than in B (-32.0% and -11.9% at rest and at 100 W, respectively). The present results would suggest a down-regulation of the O2 transport system after bed rest.

Adult↗
PubMed1997

The decrease of maximal oxygen consumption during hypoxia in man: a mirror image of the oxygen equilibrium curve.

1. Endurance athletes (E) undergo a marked reduction of arterial O2 saturation (Sa,O2) at maximal exercise in normoxia, which disappears when they breathe hyperoxic mixtures. In addition, at a given level of hypoxia, the drop in maximal O2 consumption (VO2,max) is positively related to the individual normoxic VO2,max. 2. These data suggest that the curve relating VO2,max to PI,O2 may be steeper and perhaps less curved in E than in sedentary subjects (S) with low VO2,max values because of the greater hypoxaemia in the latter, whence the hypotheses that (i) the relationship between VO2,max and PI,O2 may be set by the shape of the oxygen equilibrium curve; and (ii) the differences between E and S may be due to the different position on the oxygen equilibrium curve on which these subjects operate. These hypotheses have been tested by performing a systematic comparison of the VO2,max or Sa,O2 vs. PI,O2 relationships in E and S. 3. On ten subjects (five S and five E), VO2,max was measured by standard procedure during cycloergometric exercise. Sa,O2 was measured by finger-tip infrared oximetry. Arterialized blood PO2 (Pa,O2) and PCO2 (Pa,CO2) were determined in 80 microliters blood samples from an ear lobe. The subjects breathed ambient air or a N2-O2 mixture with an inspired O2 fraction (FI,O2) of 0.30, 0.18, 0.16, 0.13 and 0.11, respectively, VO2,max was normalized with respect to that obtained at the highest FI,O2. 4. The relationships between Sa,O2 or normalized VO2,max and FI,O2 (or PI,O2) had similar shapes, the data for E being systematically below and significantly different from those for S. Linear relationships between Sa,O2 and normalized VO2,max, statistically equal between E and S, were found. 5. We conclude that the relationships between either VO2,max or Sa,O2 and FI,O2 (or Pa,O2) may indeed be the mirror images of one another, implying a strict link between the decrease of VO2,max in hypoxia and the shape of the oxygen equilibrium curve, as hypothesized.

Adult↗
PubMed1995

Loss of muscle oxidative capacity after an extreme endurance run: the Paris-Dakar foot-race.

We measured changes in maximal oxygen uptake capacity (VO2max), ventilation, heart rate, plasma lactate and speed at the end of an incremental exercise test as a consequence of a relay foot race from Paris to Dakar in 6 subjects. Additionally, anthropometric measurements were taken and muscle biopsies from M. vastus lateralis were obtained before and after the race. The latter were analyzed with morphometric methods for fiber size, capillarity and muscle ultrastructural composition. Weight specific VO2max was significantly reduced from 62.4 to 60.5 ml/min.kg after the race while absolute VO2max and the other endurance related functional variables remained unchanged. Body fat, thigh cross-sectional area and thigh volume showed tendential reduction immediately after the race but regained pre-race values within a few days. Fiber size and capillarity were not affected by the race. Volume density of total mitochondria was significantly reduced from 6.98 to 4.89% of fiber volume. Both subsarcolemmal and interfibrillar mitochondria were significantly reduced by 59 and 21%, respectively. The volume density of satellite cell was increased about three-fold whereas the content of lipofuscin remained constant. It is concluded that extreme endurance events such as a multi-stage relay race may induce a considerable loss of oxidative capacity of skeletal muscle tissue.

Adipose Tissue↗
PubMed1992

Effects of temperature on the maximal instantaneous muscle power of humans.

The maximal instantaneous muscle power (wi,max) probably reflects the maximal rate of adenosine 5'-triphosphate (ATP) hydrolysis (ATPmax), a temperature-dependent variable, which gives rise to the hypothesis that temperature, by affecting ATPmax, may also influence wi,max. This hypothesis was tested on six subjects, whose vastus lateralis muscle temperature (Tmuscle) was monitored by a thermocouple inserted approximately 3 cm below the skin surface. The Wi,max was determined during a series of high jumps off both feet on a force platform before and after immersion up to the abdomen for 90 min in a temperature controlled (T = 20 +/- 0.1 degrees C) water bath. Control Tmuscle was 35.8 +/- 0.7 degrees C, with control Wi,max being 51.6 (SD 8.7) W.kg-1. After cold exposure, Tmuscle decreased by about 8 degrees C, whereas wi,max 27% lower. The temperature dependence of Wi,max was found to be less (Q10 less than 1.5, where Q10 is the temperature coefficient as calculated in other studies) than reported in the literature for ATPmax. Such a low Q10 may reflect an increase in the mechanical equivalent of ATP splitting, as a consequence of the reduced velocity of muscle contraction occurring at low Tmuscle.

Adenosine Triphosphate↗
PubMed1990

Energy cost and efficiency of sculling a Venetian gondola.

Oxygen uptake was measured on four male subjects during sculling gondolas at constant speeds from approximately 1 to approximately 3 m.s-1. The number of scullers on board in the different trials was one, two or four. Tractional water resistance (drag, D, N) was also measured in the same range of speeds. Energy cost of locomotion per unit of distance (C, J.m-1), as calculated from the ratio of O2 uptake above resting to, increased with v according to a power function (C = 155.2.v1.67; r = 0.88). Also D could be described as a power function of the speed: D = 12.3.v2.21; r = 0.94). The overall efficiency of motion, as obtained from the ratio of D to C, increased with speed from 9.2% at 1.41 m.s-1 to 14.5% at 3.08 m.s-1. It is concluded that, in spite of this relatively low efficiency of motion, the gondola is a very economic means. Indeed, at low speeds (approximately 1 m.s-1), the absolute amount of energy for propelling a gondola is the same as that for waking on the level at the same speed for a subject of 70 kg body mass.

Adult↗
PubMed1990

Oxygen transport system before and after exposure to chronic hypoxia.

Maximal VO2 on the treadmill (VO2max) and on the bicycle ergometer (VO2peak), maximal cardiac output (Qmax), by a CO2 rebreathing method, maximal heart rate (HRmax), blood hemoglobin concentration (Hb), and hematocrit (Hct) were measured on six subjects before (B) and 3 weeks after (A) prolonged exposure to chronic hypoxia. It was observed that after high-altitude exposure VO2max, VO2peak, and Qmax were lower (P less than 005) than before [A: 4.13 +/- 0.67; 3.28 +/- 0.41 and 16.89 +/- 2.49 (l/min +/- SD); B: 4.39 +/- 0.39; 3.53 +/- 0.34 and 21.81 +/- 1.27, respectively], whereas Hb and Hct were larger (A: 162 +/- 8 g/l and 0.46 +/- 0.02; B: 142 +/- 7 and 0.41 +/- 0.02) and HRmax was unchanged (178 +/- 7 vs 175 +/- 9 bts/min). Thus, the calculated stroke volume of the heart and the Hb flow at VO2 peak were lower in A than in B (95 +/- 15 vs 124 +/- 7 ml and 2,723 +/- 307 vs 3,129 +/- 196 g/min) (P less than 0.05, respectively), whereas the arteriovenous O2 difference was greater in A than in B (195 +/- 16 vs 162 +/- 19 ml O2/l; P less than 0.05). At any given submaximal work load, VO2 and HR were the same in B and in A, whereas Q was lower in A by approximately 2-3 l/min. However, because of the increased Hb, leading to a higher arterial O2 content, at any work load the O2 flow remained unchanged.

Acclimatization↗
PubMed1986

The energetics of endurance running.

Maximal O2 consumption (VO2max) and energy cost of running per unit distance (C) were determined on the treadmill in 36 male amateur runners (17 to 52 years) who had taken part in a marathon (42.195 km) or semi-marathon (21 km), their performance times varying from 1.49 to 226 and from 84 to 131 min, respectively. VO2max was significantly (2p less than 0.001) greater in the marathon runners (60.6 vs 52.1 ml . kg-1 . min-1) while C was the same in both groups (0.179 +/- 0.017, S.D., mlO2 . kg-1 . m-1 above resting), and independent of treadmill speed. It can be shown that the maximal theoretical speed in endurance running (vEND) is set by VO2max, its maximal sustainable fraction (F), and C, as described by: vEND = F . VO2max . C-1. Since F was estimated from the individual time of performance, vEND could be calculated. The average speed of performance (vMIG) and vEND (m . s-1) were found to be linearly correlated: vMIG = 1.12 + 0.64 vEND (r2 = 0.72; n = 36). The variability of vMIG explained by vEND, as measured by r2, is greater than that calculated from any one regression between vMIG and VO2max (r2 = 0.51), F . VO2max (r2 = 0.58), or VO2max . C-1 (r2 = 0.63). The mean ratio of observed (vMIG) to theoretical (vEND) speeds amounted to 0.947 +/- 0.076 and increased to 0.978 +/- 0.079 (+/- S.D.; n = 36) when the effects of air resistance were taken into account. It is concluded that vEND = F . VO2max . C-1 is a satisfactory quantitative description of the energetics of endurance running.

Adolescent↗