1,721,049 research outputs found
Energy Cost of Human Locomotion on Land and in Water
No full textMaximal absolute speeds in human locomotion range from a minimum of about 7km?h-1 in swimming (100m free style) to over 70km?h-1 in cycling (200m with a flying start), whereas the maximal muscular power of elite athletes competing in these events is essentially equal. Hence these large speed differences depend on the specific characteristics of each form of locomotion. These will be described in some detail with the aim of providing a comprehensive overview of the resulting energy cost of transport under different sets of conditions, such as constant versus accelerated or decelerated speed, uphill versus downhill slopes, the effects of barometric pressure, and of the characteristics of the terrain. The resulting overall picture can be condensed in a limited number of equations allowing us to predict overall energy expenditure as well as maximal speed in the locomotion considered, provided that a few parameters concerning the subject and the environmental conditions in question are known
Oxygen uptake kinetics at work onset: role of cardiac output and of phosphocreatine breakdown
No full textThe hypothesis that variability in individual's cardiac output response affects the kinetics of pulmonary O2 uptake (V̇O2) was tested by investigating the time constants of cardiac output (Q̇) adjustment (τQ), of PCr splitting (τPCr), and of phase II pulmonary O2 uptake (τVO2) in eight volunteers. V̇O2, Q̇, and gastrocnemius [PCr] (by 31P-MRS) were measured at rest and during low intensity two-legged exercise. Steady state V̇O2 and Q̇ increased (ΔV̇O2s=182±58 mL min-1; ΔQ̇=1.3±0.4 L min-1), whereas [PCr] decreased significantly (21±8%). τVO2, τPCr and τQ were significantly different from each other (38.3±4.0, 23.9±2.5, 11.6±4.6s, respectively; p<0.001). τPCr assumed to be equal to the time constant of V̇O2 at the muscle level (τmVO2), was not related to τQ, whereas τVO2 and τQ were significantly related (p<0.05) as were τVO2 and τPCr (p<0.05). Venous blood O2 stores changes, as determined from arterio-to-mixed-venous O2 content, were essentially equal to those estimated as (τVO2-τPCr)ΔV̇O2s. This suggests that cardiac output responses affect O2 stores utilization and hence τVO2: thus τVO2 is not necessarily a good estimate of τmVO2
Mechanical efficiency of cycling with a new developed pedal-crank
No full textThe mechanical efficiency of cycling with a new pedal-crank prototype (PP) was investigated during an incremental test on a stationary cycloergometer. The efficiency values were compared with those obtained, in the same experimental conditions and with the same subjects, by using a standard pedal-crank system (SP). The main feature of this prototype is that its pedal-crank length changes as a function of the crank angle being maximal during the pushing phase and minimal during the recovery one. This variability was expected to lead to a decrease in the energy requirement of cycling since, for any given thrust, the torque exerted by the pushing leg is increased while the counter-torque exerted by the contra-lateral one is decreased. Whereas no significant differences were found between the two pedal-cranks at low exercise intensities (ẇ=50-200W), at 250-300W the oxygen uptake (V̇O2, W) was found to be significantly lower and the efficiency (η=ẇ/V̇O2) about 2% larger (p<0.05, Wilcoxon test) in the case of PP. Even if the measured difference in efficiency was rather small, it can be calculated that an athlete riding a bicycle equipped with the patented pedal-crank could improve his 1h record by about 1km. © 2002 Elsevier Science Ltd. All rights reserved
Interplay among the changes of muscle strength, cross-sectional area and maximal explosive power: Theory and facts
No full textA model has recently been proposed to predict the changes of mechanical power (Ẇ) during a maximal explosive effort (such as a standing high jump off both feet) following an adaptation (e.g. training/de-training). The model is based on the assumption that, all other things being equal (ceteris paribus), the predicted changes in Ẇ depend on the measured changes of muscle force (F) or cross-sectional area (CSA) only. It follows that, if the measured changes in Ẇ are not equal to those predicted by the model, factors other than a change in F (or CSA) must be responsible for this difference. The model does not allow the determination of factors specifically involved in the adaptation process but it helps in discriminating whether an adaptation has taken place at a local level (when the observed changes in F would be attributed to factors other than the observed changes in CSA, e.g. co-contractions, fibre type modifications...), or at a central level (when the observed changes in Ẇ would be attributed to other factors than the observed changes in F, e.g. co-ordination of multiple joints and muscle groups...), or in both regions. In this paper the model has been applied to data reported in the literature on disuse (BR, bed rest), de-conditioning (SF, space flight), strength training (ST) and de-training (DT). The results of these calculations have confirmed previous observations on the determinants of the adaptation process and further suggest: (1) that training for one specific motor task (e.g. ST) could affect the performance of a second task (e.g. a maximal explosive jump) but that, as soon as the trained motor task is terminated (DT), this ability is re-gained; and (2) that neuromuscular impairment in disuse (BR) is closer to de-training than to the de-conditioning brought about by weightlessness (SF). © Springer-Verlag 2002
Cardiovascular and peripheral factors affecting the decay of maximal oxygen uptake across the spectrum of age in humans
No full textPurpose: Maximal oxygen uptake ([Formula: see text]O2max) decays with aging due to decreased maximal cardiac output ([Formula: see text]max) and the development of progressive sarcopenia and mitochondrial dysfunctions. The study aimed to develop a quantitative analysis of central and peripheral factors in eliciting the observed progressive drop of [Formula: see text]O2max across the spectrum of ages ranging from about 30 yy to 85-90 yy. Methods: We applied to [Formula: see text]O2max, [Formula: see text]max, and maximal oxygen cardiovascular delivery ([Formula: see text]aO2max) values obtained from literature, a multifactorial model of [Formula: see text]O2max limitation describing the progressive drop of the PO2 along the pathway from ambient air to mitochondria composed of several steps in series, each of them considered as a resistance (Ri) that must be overcome by a pressure gradient (ΔPi). The proposed analysis allowed us to estimate: (i) the maximal oxygen extraction coefficient (O2ext, max) and (ii) the changes of the peripheral resistance (Rp) hindering O2 muscular utilization. Results: O2ext, max progressively decays from 0.80 at 20 yy to 0.60 at 75-80 yy; Rp almost doubles over the same interval of inspected ages. Conclusions: The analysis implemented using data published in the literature suggests that the progressive increase of Rp remarkably contributes to the observed gradual decay of [Formula: see text]O2max observed with aging, perhaps more than the progressive drop in the maximal cardiovascular transport of oxygen
VII. Maximal muscular power before and after exposure to chronic hypoxia
No full textThe maximal muscular power (both instantaneous, and average, and the cross-sectional area of the left thigh (CSA) were measured on six subjects before (B) and after (A) prolonged exposure to high altitude (above 5000 m asl). Instantaneous maximal muscular power and average maximal muscular power were determined during a standing high jump off both feet on a force platform, and CSA by computed tomography. It was observed that: (1) in B, body weight (BW) = 74.1 ± 5.8 kg, instantaneous maximal muscular power = 3330 ± 460 W (44.8 ± 3.4 W·kg-1). Average maximal muscular power = 1795 ± 395 W (24.6 ± 4.3 W·kg-1), and CSA = 184.5 ± 23.1 cm2; 2) in A, BW = 70.4 + 6.6 kg, instantaneous maximal muscular power = 3005 ± 472 W (42.5 ± 3.6 W·kg-1), (w) = 1531 ± 267 W (21.9 ± 3.1 W·kg-1), and CSA = 163.5 ± 23.1 cm2. Thus, instantaneous maximal muscular power and average maximal muscular power were decreased both in absolute terms (-9.8% and -14.7%, respectively) and per unit BW (-5.1% and -11.0%). However, because of the concomitant decrease in CSA, when expressed per unit cross-sectional area of the muscle, instantaneous maximal muscular power (9.04 ± 0.71 and 9.20 ± 0.72 W ± cm2) and average maximal muscular power (4.87 ± 0.81 and 4.70 ± 0.67 W/cm2) were unchanged. The intrinsic capacity of the muscle to generate explosive power is therefore preserved in A. It is concluded that the decrease in instantaneous maximal muscular power and average maximal muscular power after high-altitude exposure depends only on a net loss of muscle mass
Swimming economy (energy cost) and efficiency
No full textThe energy cost per unit distance (i. e. the economy of swimming, C) is given by the ratio / v where is the net (above resting) metabolic power and v is the swimming speed. The contribution of the aerobic and anaerobic energy sources to in swimming competitions differs according to the distance covered; it is independent of swimming style, gender or skill and depends essentially upon the duration of the exercise. In swimming, C increases with the speed with a non linear function; for a given speed, C is the lowest for the front crawl, followed by the backstroke, the butterfly and the breaststroke. C is essentially determined by the hydrodynamic resistance (Wd): the higher Wd, the higher C; and by the propelling efficiency (ηP): the higher ηP the lower C. Hence, all factors influencing Wd and/or ηP will result in proportional changes in C. The concepts of economy and efficiency are strictly related; hence, this chapter is also devoted to an analysis of the efficiencies in swimming; a summary of the values reported in the literature is also presented from a “historical point of view”. Last but not least the factors setting performance ( max and C) are briefly reviewed in view of a proper planning of swim training
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