European journal of applied physiology
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Eur. J. Appl. Physiol. · Mar 2004
Comparative Study Clinical TrialLimitation of muscle deoxygenation in the triceps during incremental arm cranking in women.
The present study investigated the difference in oxygen kinetics in the exercising muscle between arm cranking and leg cycling in women. Twenty-seven females completed incremental arm cranking and leg cycling tests on separate days. During each exercise, spatially resolved near-infrared spectroscopy was used to measure changes in the tissue oxygen saturation ( SO(2)), oxygenated (oxy-) hemoglobin and/or myoglobin (Hb/Mb), deoxygenated (deoxy-) Hb/Mb, and total Hb/Mb in the triceps during arm cranking and in the vastus lateralis during leg cycling. ⋯ During leg cycling, SO(2) remained decreased near to or until approaching peak oxygen uptake (VO(2peak)). During arm cranking, however, the decrease in oxy-Hb/Mb and increase in deoxy-Hb/Mb stopped at the middle of VO(2peak) (mean 51.4%), consequently resulting in a leveling off in the SO(2 )decrease, although total Hb/Mb continued to increase. These results might suggest that the oxygen demand in the triceps attained the maximum at that intensity, despite an adequate oxygen supply during arm cranking.
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Eur. J. Appl. Physiol. · Nov 2003
Determination of rate-constants as a method to describe passive expiration.
To describe the relaxed expiration by a two-compartment model, we introduced a gas/energy transfer between the lung compartment ( V(1)) and a second one ( V(2)). If V(2) were a real volume, the rate-constants (i.e. the flow/volume ratios) of the compartments would describe a real gas-exchange. Alternatively, if a viscoelastic behaviour of the lung or an energy-exchange between compartments was simulated, V(2) would become a "pseudo-volume". ⋯ In conclusion, our analysis demonstrated that the energy/volume of the second compartment may increase at the beginning of expiration and then decrease, showing a maximum, even though the total curve can only be a decreasing one. In other words, the slowing down of the curve representing expiratory volume is due not only to the longer emptying of the second compartment, but also to the interaction between the two compartments. As presently proposed, this interaction can be represented by either a gas exchange between two actual volumes, or a mechanical energy transfer between the lung and the tissue compartment.
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Eur. J. Appl. Physiol. · Oct 2003
ReviewOxygen transport in blood at high altitude: role of the hemoglobin-oxygen affinity and impact of the phenomena related to hemoglobin allosterism and red cell function.
Altitude hypoxia is a major challenge to the blood O2 transport system, and adjustments of the blood-O2 affinity might contribute significantly to hypoxia adaptation. In principle, lowering the blood-O2 affinity is advantageous because it lowers the circulatory load required to assure adequate tissue oxygenation up to a threshold corresponding to about 5,000 m altitude, whereas at higher altitudes an increased blood-O2 affinity appears more advantageous. However, the rather contradictory experimental evidence raises the question whether other factors superimpose on the apparent changes of the blood-O2 affinity. The most important of these are as follows: (1) absolute temperature and temperature gradients within the body; (2) the intracapillary Bohr effect; (3) the red cell population heterogeneity in terms of O2 affinity; (4) control of altitude alkalosis; (5) the possible role of hemoglobin as a carrier of the vasodilator nitric oxide; (6) the effect of varied red cell transit times through the capillaries.
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Eur. J. Appl. Physiol. · Oct 2003
ReviewHeart rate variability and autonomic activity at rest and during exercise in various physiological conditions.
The rhythmic components of heart rate variability (HRV) can be separated and quantitatively assessed by means of power spectral analysis. The powers of high frequency (HF) and low frequency (LF) components of HRV have been shown to estimate cardiac vagal and sympathetic activities. The reliability of these spectral indices, as well as that of LF/HF ratio as a marker of autonomic interaction at rest and during exercise, is briefly reviewed. ⋯ The increased respiratory activity due to exercise would be responsible of HF modulation of HR via a direct mechanical effect. The changes in LF power observed at medium-high intensity might be the expression of the modifications in arterial pressure control mechanisms occurring with exercise. The finding of opposite trends for LF rhythm in supine and sitting exercises suggests that different readjustments might have occurred in relation to different muscular inputs in the two positions.
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Eur. J. Appl. Physiol. · Sep 2003
Clinical TrialThe force-velocity relationship of the human soleus muscle during submaximal voluntary lengthening actions.
In experiments on isolated animal muscle, the force produced during active lengthening contractions can be up to twice the isometric force, whereas in human experiments lengthening force shows only modest, if any, increase in force. The presence of synergist and antagonist muscle activation associated with human experiments in situ may partly account for the difference between animal and human studies. Therefore, this study aimed to quantify the force-velocity relationship of the human soleus muscle and assess the likelihood that co-activation of antagonist muscles was responsible for the inhibition of torque during submaximal voluntary plantar flexor efforts. ⋯ During lengthening actions, however, plantar flexion torques were not significantly different from isometric regardless of angular velocity. It was concluded that the apparent inhibition of lengthening torques during voluntary activation is not due to co-activation of antagonist muscles. Results are presented as mean (SEM).