Durée de la récupération et puissance maximale anaérobie au cours de la journée

Effects of recovery duration (2-3 s, 15 s, 30 s, 1 min, and 2 min) and time of day (9 a.m., 2 p.m., and 6 p.m.) on sprint performance were studied in 9 subjects using a cycle ergometer. The peak power (Ppeak) and the total work performed (W) were determined from changes in instantaneous power, taking into account the inertia of the flywheel. A decrease in Ppeak and W was observed after 15 s and 2-3 s recovery (p < 0.001). A logarithmic relationship (y = 3.92 ln x + 81.5; r = 0.82; n = 9) was found between Ppeak (%Ppeak of the first sprint) and the duration of the recovery (half-time = 14.3 s; SD = 7.6). Data indicated that there was no significant effect of time of day on Ppeak and W, regardless of the duration of recovery. The recovery processes occurred in a very short time and did not seem to be affected by biological rhythms

Stored Electrogenerated Promoters Inducing Sustainable Enhanced Pt Catalyst Activity

This work concerns the investigation of the electrochemical promotion of Pt/YSZ catalyst giving more emphasis to the sustainable enhanced catalytic activity after current interruption. The permanent electrochemical promotion (P-EPOC) of C2H4 combustion over Pt/YSZ is investigated at 375°C under atmospheric pressure. Under anodic polarization, a non-faradaic enhancement of the reaction rate is observed (ρ = 4.2 and Λ = 370). However, after current interruption, the sustainable enhanced catalytic activity (P-EPOC) increases with the holding polarization time (γ =2,2 after 10 hours) giving evidence that a storage mechanism of oxygen promoters is involved in P-EPOC. In fact, a model involving two different types of promoters is proposed. Oδ1- promoters, highly mobile and reactive at the Pt/gas, are proposed to be responsible of EPOC while Oδ2- promoters, slow and very stable at the Pt/gas, are proposed to account for P-EPOC. Further electrochemical investigations of the Pt/YSZ interface realized at both atmospheric pressure and under high vacuum (HV) conditions gave strong evidence that the electrogeneration of the Oδ2- promoters is related to the formation of PtO taking place during an anodic polarization. In fact, the investigations of the O2(g),Pt/YSZ systems at atmospheric pressure, have revealed that, under anodic polarization, two electrochemical reactions take place: PtO formation at the Pt/YSZ interface and O2 evolution at the triple phase boundary (tpb). The current efficiencies of each process (ηPtO and ηO2) are determined allowing estimating the effective rate of PtO formation at the Pt/YSZ interface. In addition, CV-MS and DSCP-MS measurements, performed under HV conditions, have confirmed this process of oxygen storage at the Pt/YSZ interface and reveal a cooperative mechanism between O2 evolution reaction and PtO formation which allows the slow diffusion of oxygen strongly bonded (Oδ2- promoters) toward the Pt/gas interface

Charge storage at the Pt/YSZ interface

The electrochemical behavior of Pt/YSZ electrodes in oxygen containing atmosphere at 450°C has been investigated by double-step chronoamperometry and programmed linear sweep cyclic voltammetry. The response of the O2(g),Pt/YSZ system in these experiments could be separated into a time dependent and a steady state contribution, the former being dominated by pseudocapacitive processes. It is proposed that Pt-O type species were stored via different processes at three different locations in the O2(g),Pt/YSZ system: (1) Build-up of a platinum oxide monolayer at the Pt/YSZ binary interface. (2) Formation of Pt-O species at the triple phase boundary and their spreading-out along the Pt/gas interface. (3) Growth of the platinum oxide layer from the binary Pt/YSZ interface toward the bulk of the platinum electrod

The phenomenon of "permanent” electrochemical promotion of catalysis (P-EPOC)

The phenomenon of electrochemical promotion of catalysis (EPOC) is most often fully reversible. Subsequent to long-lasting polarization, however, the new steady-state open-circuit catalytic activity after current interruption may remain significantly higher than that before polarization. This phenomenon, discovered in our laboratory in the late 1990s and called permanent electrochemical promotion of catalysis (P-EPOC), has been observed on both oxide (IrO2, RuO2) and metal (Rh) catalysts. P-EPOC is out of the state-of-the-art model of reversible EPOC, which considers the gas-exposed catalyst surface as the unique location of charge storage via backspillover of electrochemically generated promoter species accompanied by their consumption in the catalytic reaction (‘sacrificial' promoter). Double step chronoamperometric and linear sweep voltammetric characterization of Pt catalyst deposited on YSZ solid electrolyte revealed the existence of a somewhat delayed oxygen storage occurring at the vicinity of the catalyst/electrolyte interface during prolonged anodic polarization. It is proposed that oxygen stored at this location, hidden for the reactant, and then released during relaxation was at the origin of P-EPOC on the Pt/YSZ catalyst observed in catalytic combustion of ethylene with oxygen. The effect of this ‘hidden' promoter on the catalytic reaction rate was found to be highly non-Faradai

EFFECT OF FATIGUE ON MUSCLE COORDINATION IN REPEATED ALL-OUT BOUTS

The aim of the present study was to analyse the fatigue occurring during repeated all-out short cycling bouts through mechanical and electromyographic (EMG) data and to focus on . inter-muscle coordination. The results showed a significant decrease in peak power output without significant modifications in the EMG activity through sprint repetitions. However, the coordination timing between agonist and antagonist muscles was reduced. In conclusion, power output decreased during high-intensity repeated sprints due to the inability of quadriceps to maintain maximal force and owing to inter-muscle coordination limitations

Solid electrochemical mass spectrometry (SEMS) for investigation of supported metal catalysts under high vacuum

A new experimental set-up, coupling electrochemistry and mass spectroscopic techniques, for the investigation of a solid electrochemical cell under high vacuum conditions (HV) is presented. Two configurations are realized allowing the investigation of both the electrochemical and electrocatalytical behavior of a thin Pt layer on yttria stabilized zirconia (YSZ). We can readily select the atmosphere down to 10−6 Pa partial pressure and determine the response of the system in less than 1s. Under HV conditions, YSZ appears electrochemically active and we have identified, in the cathodic potential domain, the reduction/oxidation process of zirconia and in the anodic domain, the platinum oxidation/reduction and the oxygen evolution reactions. In a catalytic active gas mixture, despite the Faradaic enhancement of the CO oxidation observed over Pt/YSZ during an anodic polarization, an intriguing sustainable enhanced Pt/YSZ catalyst activity is achieved after current interruptio

Investigation of the Pt/YSZ interface at low oxygen partial pressure by solid electrochemical mass spectroscopy under high vacuum conditions

The Pt/YSZ interface was investigated at low oxygen partial pressure under high vacuum (HV) conditions at 400°C. Two different electrochemical techniques were coupled to mass spectrometric gas analysis using a new solid electrochemical mass spectrometric monitoring device. Under cathodic polarization, the lack of oxygen in the gas phase induces the reduction of the YSZ solid electrolyte which acts as oxygen source for the formation of O2− ions migrating to the anode. Under anodic polarization, both platinum oxidation and oxygen evolution reaction are identified. PtOx is formed at both the Pt/YSZ and the Pt/gas interface according to two different mechanisms. At the Pt/YSZ interface, PtOx formation is an electrochemical process following a parabolic growth law, while the presence of PtOx at the Pt/gas interface is related to the diffusion of PtOx formed at the triple phase boundary towards the Pt/gas interface. It is proposed that the side oxygen evolution reaction stabilizes thermodynamically the PtOx diffusion toward the gas exposed interface during the anodic polarizatio

Charge storage at the Pt/YSZ interface

The electrochemical behavior of Pt/YSZ electrodes in oxygen containing atmosphere at 450 A degrees C has been investigated by double-step chronoamperometry and programmed linear sweep cyclic voltammetry. The response of the O-2(g),Pt/YSZ system in these experiments could be separated into a time dependent and a steady state contribution, the former being dominated by pseudocapacitive processes. It is proposed that Pt-O type species were stored via different processes at three different locations in the O-2(g),Pt/YSZ system: (1) Build-up of a platinum oxide monolayer at the Pt/YSZ binary interface. (2) Formation of Pt-O species at the triple phase boundary and their spreading-out along the Pt/gas interface. (3) Growth of the platinum oxide layer from the binary Pt/YSZ interface toward the bulk of the platinum electrode

Electrochemical promotion of CO combustion over Pt/YSZ under high vacuum conditions

Electrochemical promotion of CO combustion over Pt/YSZ was investigated under high vacuum conditions. A galvanostatic step was coupled to mass spectrometric gas analysis using an electrochemical mass spectrometric monitoring device. Non-Faradaic electrochemical promotion of catalysis took place at 300 degrees C while only electrochemical oxidation was observed at 400 degrees C. Oxygen evolution measurements revealed that electrochemical promotion is related to the thermodynamically stable PtOx species over the Pt/gas interface. The polarization time and O-2 pressure show strong influence on the relaxation transient upon current interruption. We propose that during anodic polarization, PtOx is first formed at the Pt/YSZ interface. With prolonged polarization time, the formed PtOx either migrates over the Pt/gas interface inducing electrochemical promotion or diffuses into the Pt bulk leading to the oxygen storage. After polarization, the stored O species is released and acts as sacrificial promoter causing the persistent electrochemical promotion effect. (C) 2011 Elsevier B.V. All rights reserved