Taken together, those results suggest that more fatigable Type II motor units are involved in men, resulting in greater lactic acid and ions accumulations during fatigue. This difference in muscle's metabolic and ionic state could be responsible for a greater reflex-induced decrease of motor units firing rates in men compared with boys. This firing rate decrease could be explained using the "muscular wisdom" hypothesis and would express a nervous command adaptation to sustain a maximal contraction.

The relationship between the amount of work (Wlim) performed at the end of constant-power exhausting exercise and exhaustion time (tlim) has been studied for supramaximal exercise [105%, 120%, 135% and 150% of the individual maximal aerobic power, (MAP)] performed on a Monark cycle ergometer in nine men. The Wlim--tlim relationship was described by a linear relationship (Wlim = a + b . tlim). Intercept a was roughly equivalent to the work produced during a 1-min exercise performed at MAP. Slope b was equal to 79% of MAP. Intercept a has been correlated with the total amount of work (AW) performed during a 30-s all-out test supposed to assess anaerobic capacity. Intercept a was significantly (p less than 0.05) correlated with AW. The anaerobic capacity was not depleted at the end of the all-out test, as the mechanical power at the 30th s of this test was approximately equal to twice MAP. However, AW was significantly higher than intercept a. It was likely that the value of intercept a was an underestimation of the maximal anaerobic capacity because of the inertia of the aerobic metabolism. Indeed, an exponential model of the Wlim--tlim relationship, which takes the interia of the aerobic metabolism into account, shows that a linear approximation of the Wlim--tlim relationship yields a systematic underestimation of the anaerobic capacity. Consequently, intercept a of the Wlim--tlim relationship is not a more accurate estimation of the anaerobic capacity than the AW performed during a 30-s all-out test.(ABSTRACT TRUNCATED AT 250 WORDS)

International Journal of Occupational Medicine and Environmental AbstractRecording and analyzing eye movements provide important elements for understanding the nature of the task of driving a vehicle. This article reviews the literature on eye movement strategies employed by drivers of vehicles (vehicle control, evaluation of the situation by analyzing essential visual elements, navigation). Special focus was placed on the phenomenon of conspicuity, the probability of perceiving an object in the visual field and the factors that determine it. The article reports the methods of oculographic examination, with special emphasis on the non-invasive technique using corneal reflections, and the criteria for optimal selection of the test apparatus for drivers in experimental conditions (on a driving simulator) and in real conditions. Particular attention was also paid to the helmet -or glass-type devices provided with 1 or 2 high definition (HD) camcorders recording the field of vision and the direction of gaze, and the non-contact devices comprising 2 or 3 cameras and an infrared source to record eye and head movements, pupil diameter, eye convergence distance, duration and frequency of eyelid blinking. A review of the studies conducted using driver eye-tracking procedure was presented. The results, in addition to their cognitive value, can be used with success to optimize the strategy of drivers training.