. Changes in segmental and motor cortical output with contralateral muscle contractions and altered sensory inputs in humans. J Neurophysiol 90: 2451-2459, 2003; 10.1152/jn.01001.2002. Motor or sensory activity in one arm can affect the other arm. We tested the hypothesis that a voluntary contraction can affect the motor pathway to the contralateral homologous muscle and investigated whether alterations in sensory input might mediate such effects. Responses to transcranial magnetic stimulation [motor-evoked potentials (MEPs)], stimulation of the descending tracts [cervicomedullary MEPs (CMEPs)], and peripheral nerve stimulation (H-reflex) were recorded from the relaxed right flexor carpi radialis (FCR), while the left arm underwent unilateral interventions (5 s duration) that included voluntary contraction, muscle contraction evoked through percutaneous stimulation, tendon vibration, and cutaneous and mixed nerve stimulation. During moderate to strong voluntary wrist flexion on the left, MEPs in the right FCR increased, CMEPs were unaffected, and the H-reflex was depressed. These results are consistent with an increase in excitability of the motor cortex, no effect on the motoneuron pool, and presynaptic inhibition of Ia afferents. In contrast, percutaneous muscle stimulation facilitated both MEPs and the H-reflex. However, muscle contraction produced by a combination of voluntary effort and electrical stimulation also reduced the contralateral H-reflex. After voluntary contractions, the H-reflex remained depressed for 35 s, but after stimulationevoked contractions, it rapidly returned to baseline. Under both conditions, MEPs recovered rapidly. After voluntary contractions, CMEPs were also depressed for approximately 10 s despite their lack of change during contractions. Wrist tendon vibration (100 Hz) did not affect, and 20-Hz median nerve stimulation or forearm medial cutaneous nerve stimulation mildly facilitated, the H-reflex without affecting MEPs. Voluntary wrist extension, similarly to wrist flexion, increased MEPs and depressed H-reflexes. However, ankle dorsiflexion facilitated the H-reflex akin to the Jendrassik maneuver. These data suggest that a unilateral voluntary muscle contraction has contralateral effects at both cortical and segmental levels and that the segmental effects are not replicated by stimulated muscle contraction or by input from muscle spindles or non-nociceptive cutaneous afferents.

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The aim of this study was to characterise the effect of prolonged low doses of recombinant erythropoietin (r-HuEPO) on the responses to submaximal and maximal exercise. Volunteer recreational athletes ( n=21) were divided into three groups: r-HuEPO+intravenous iron (EPO+IV, n=7), r-HuEPO+oral iron (EPO+OR, n=9) and placebo ( n=5). During the 12 week study, r-HuEPO or saline injections were given three times a week for the first 8 weeks and for the final 4 weeks the subjects were monitored but no injections were administered. The r-HuEPO doses were 50 IU x kg(-1) body mass for 3 weeks and 20 IU x kg(-1) body mass for the next 5 weeks. An exercise test comprising three submaximal intensities and then increments to elicit maximal aerobic power (VO2max ) was conducted during weeks 0, 4, 8 and 12. During week 0, the mean intensity of the submaximal stages was 60%, 72% and 81%. Blood taken at rest was analysed twice a week for haematocrit (Hct). The relative increases in at weeks 4, 8 and 12 were 7.7%, 9.7% and 4.5%, respectively, for the EPO+IV group; 6.0%, 4.7% and 3.1% for the EPO+OR group; and -0.5%, -0.1% and -1.0% for the placebo group, where the improvements at week 12 for the EPO+IV and EPO+OR groups remained significantly above week 0 values. The Hct was significantly elevated by 0.06 and 0.07 units at week 3 in the EPO+IV and EPO+OR groups, respectively, and was stable during the 5 weeks of low-dose r-HuEPO. After 8 weeks of r-HuEPO use, plasma lactate concentration tended to be lower at exercise intensities ranging from 60% to 100%. This study confirmed the ability of low doses of r-HuEPO to maintain Hct and at elevated levels.

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Error propagation equations are derived for four different sound-power measurement techniques: hemispherical freefield, reference source, reverberation time, and two surface. The analysis shows the hemispherical freefield and two-surface methods to be governed by the same error equation. Of the four methods examined, the reference-source method is shown to exhibit the strongest dependence on errors in measuring the space averaged sound pressure. The results obtained can be used in planning and executing more accurate sound-power measurements. PACS numbers: 43.85.Fm, 43.50. Cb I NT RO DUCTI ON ' whe reThe measurement of the sound-power emitted by an acoustic source can be accomplished in several different ways. Whatever technique may be used--freefield, reverberation room, reference source, two-surface method, etc.---the sound power must ultimately be computed from other observed parameters. As such, the computed value of the sound power will have an uncertainW which is a function of the uncertainties associated with each of the variables actually measured (spaceaveraged sound pressure, distance, etc.). The manner in which these individual measurement errors influence the error in the computed sound power can be examined by an error propagation analysis applied to the equation used to compute the sound power.Since the different techniques used to find the sound power are based on different equations relating sound power to the experimentally observed quantities, the error propagation will depend on which measurement technique is used. In particular, the propagation of errors associated with the space-averaged sound-pressure level is of special interest as this variable is (1) required for all of the sound-power measurement techniques and (2) subject to non-neglibible errors due to practical considerations.The purpose here is to derive the error propagation equations for four different sound-power measurement techniques: the hemispherical freefield method, the reference-source method, the reverberation time method, and the two-surface method; and to briefly discuss how these equations can be used to estimate the uncertainW in the computed sound-power level. I. ERROR ANALYSISA. Hemispherical freefield method , In this method the source is placed on a reflecting surface in an otherwise freefield and the spatially averaged root-mean-squared sound pressure is measured over a hypothetical hemisphere surrounding the source. The emitted power, in the frequency band of interest, is computed from w =2rYVp,W= emitted power, watts r = radius of hemisphere, m p = spatially averaged root-mean-squared sound pressure, N/m •' pc= characteristic air resistance, N-s/m s . Treating the characteristic air resistance, pc, as a single variable, Eq. (1) can be expanded in partial derivative form as /x W_ 27rr22p 27r2rp 2 27rr •-p 2 pc (ap)+ (at) -• (apc) (2) pc (pc) •-' where the differential quantities Ap, At, and apc represent the variations, or estimated errors, associated with these measured variables. The a W variation is the expect...