SJ. The differential effects of fatigue on reflex response timing and amplitude in males and females. Journal of Electromyography and Kinesiology. 2002; 12:351-360 Abstract:We examined the effects of fatigue on patellar tendon reflex responses in males and females. A spring-loaded reflex hammer elicited a standardized tendon tap with the knee positioned in an isokinetic dynamometer and flexed to 85°. We recorded vastus lateralis activity (SEMG) and knee extension force production at the distal tibia (force transducer). Reflex trials were performed before and after (immediate, 2, 4, and 6 min) an isokinetic fatigue protocol to 50% MVC (90°/s). For each event, pre-motor time (PMT), electromechanical delay (EMD), and total motor time (TMT) were obtained, as well as EMG amplitude (EMGamp), time to peak EMG (EMGtpk), peak force amplitude (Famp), time to peak force (Ftpk), EMG:force ratio (E:F), and rate of force production (Frate=N/ms). TMT increased significantly in females following fatigue, while males showed no change. The increased TMT was due to an increased EMD with fatigue, while PMT was unaffected. EMGamp and Famp were somewhat diminished in females yet significantly augmented in males following fatigue, likely accounting for the differential changes in EMD noted. Results suggest males and females may respond differently to isokinetic fatigue, with males having a greater capacity to compensate for contraction force failure when responding to mechanical perturbations.

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We examine the global accuracy of the commonly used multizone approach to inferring elemental abundances from nebular spectra. We use a large model grid of constant-density models to construct ''ionization correction factors'' (i CF 's) for several ions with bright optical lines. The emission lines from the model suite were analyzed as coming from a two-zone nebula, with temperatures and densities based on diagnostic line ratios. These were used to infer the ionic abundances responsible for the emission lines, to which the i CF 's were applied. The procedure was also applied to model grids simulating blister-type H ii regions, as well as individual dense knots. Comparison of the model elemental abundances to those inferred from their line emission show large deviations with respect to the demonstrated accuracy of the analysis procedure; in addition, the inaccuracies of the three models follow significantly different trends, defeating any secondary correction appropriate for arbitrary nebulae. We thus strongly favor other methods for determining abundances from observations; e.g., direct modeling of photoionized nebulae or their small-scale structures.

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