1,721,096 research outputs found
Passive hyperthermia reduces maximal but not explosive torque production
No full textIntroduction: hyperthermia can reduce maximal voluntary force/torque (MVT) of skeletal muscle due to reduced neural activation (Todd et al., 2005). Rate of force/torque development (RTD) may be a more functionally relevant measure of neuromuscular performance than MVT; however, the effect of hyperthermia on RTD has received little attention. Primary determinants of RTD include neural activation and electrically evoked involuntary RTD (Maffiuletti et al., 2016), and whilst neural activation may decrease with hyperthermia, increased muscle temperature improves involuntary RTD, so it is unclear how voluntary RTD will be affected by hyperthermia. This study aimed to investigate the effects of progressive passive whole-body hyperthermia on MVT and voluntary RTD, as well as the neural and contractile factors contributing to any effects.Methods: nine male participants completed two trials; one involving passive heating to a rectal temperature (Tre) of 39.5˚C (HOT) and the other (CON) where Tre was maintained at ~37˚C. The same neuromuscular measurements of the knee extensors were completed when participants first entered the chamber (Tre ~37˚C; Base), and at Tre=38.5˚C (ModHyp) and Tre=39.5˚C (SevHyp), in the HOT trial, and at equivalent time points into the CON trial. MVT, voluntary activation (VA) determined via interpolated twitch, and EMG at MVT normalised to maximal M-wave (EMGMVT) were measured during MVCs. Explosive voluntary RTD and normalised EMG were measured over 0-50 (RTD50; EMG50) and 0-100 (RTD100; EMG100) from torque/EMG onsets during explosive contractions. Involuntary RTD50 was measured during evoked octets at 300Hz.Results: in the HOT trial, MVT declined throughout and was 15% lower at SevHyp than Base (P=0.016), which coincided with declines in EMGMVT (-44%; P<0.005) and VA (-16%; P<0.005) from Base to SevHyp. In contrast, voluntary RTD50 and RTD100 remained unaffected in the HOT trial (P>0.05), despite 23-31% decreases in EMG50 and EMG100 from Base to SevHyp (P<0.001). Involuntary RTD50 however, increased from Base to ModHyp (10%; P<0.001) and from ModHyp to SevHyp (4%; P<0.001). There were no changes in any dependent variables throughout the CON trial.Conclusion: as expected MVT declined as a result of passive hyperthermia which was largely due to reduced neural activation (i.e., EMGMVT and VA). In contrast, this study provides novel evidence that voluntary RTD was largely unaffected by passive hyperthermia, despite considerable reductions in explosive neural activation, which likely occurred due to the increased involuntary RTD, and thus cancelling out of neural and contractile effects.<br/
Head and neck cooling does not improve maximal voluntary torque or rate or torque development during brief maximal voluntary contractions in the heat
No full textIntroduction: maximal voluntary torque (MVT) is impaired when hyperthermic due to a reduction in the central nervous system’s capacity to voluntarily drive the available force capacity of muscle. Rate of torque development (RTD) is considered more functionally relevant than MVT in some situations and neural drive is a key determinant of RTD. Head and neck cooling can improve endurance performance when hyperthermic, but its effects on neural drive are unclear. The purpose of this study was to investigate head and neck cooling on thermal perception during whole-body hyperthermia on MVT, RTD, neural drive and the contractile properties of the muscle.Method: 9 participants completed two trials in HOT conditions (50°C, 40% RH), involving light exercise before passive heating to a rectal temperature (Tre) of 39.5°C. During one trial, the head and neck was continuously cooled (HOTcool) using a towel soaked in ice water. At Tre=39.5°C neuromuscular measurements were completed to assess MVT, voluntary activation and EMG at MVT normalised to maximal M-wave. Voluntary RTD and normalised EMG were measured over 0-50, 0-100, 0-150 and 0-200 ms. Involuntary RTD at 0-50 ms was measured during evoked octets at 300 Hz. Thermoregulatory and perceptual variables were measured throughout.Results: MVT and RTD, and their neuromuscular determinants were unaffected by cooling (P > 0.05). Neck (-20%) and head (-12%) temperature were lower in HOTcool, as were thermal sensation of the head (-36%) and body (-12%) and thermal comfort (body) (-23%). Time to target Tre was increased (71%) in HOTcool, and not all participants were able to reach 39.5°C. Tre (-0.3%) and skin temperature (-6%) were lower in HOTcool (P < 0.05), but heart rate was similar (P > 0.05).Conclusions: head and neck cooling did not affect MVT, RTD, or the neuromuscular determinants of these functional variables despite improving perceptions of thermal strain.<br/
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Design and optimization of a multi-particle accelerator beam transport and delivery system for material irradiation in nuclear and fusion science
Get PDFThesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, February 2012."December 2011." Cataloged from PDF version of thesis.Includes bibliographical references (p. 129-131).A beam delivery and transport system were designed for the use in MIT Materials Test Facility (M2TF). The purpose of this beam delivery system was to design a 36 MeV Proton Cyclotron for DPA accumulation and a 100 MeV Helium Cyclotron for irradiation failure and volumetric helium accumulation simulation. The purpose of the beam transport system was to incorporate the two cyclotrons into the beam transport system and transport their beams to the target chamber, the location of the target sample. The cyclotrons were designed using Opera-3D and Acfields. The beam transport system was designed using TRANSPORT. The shielding analysis for the entire facility was designed using SolidWorks and calculated with MCNP/X The design specification of M2TF with respect to beam energy, current density, and control were achieved based on these design tools and previously developed analytic methods. The design process for the cyclotrons resulted in a 4.3T lsochronous Proton Cyclotron and 3.9T Isochronous Helium Cyclotron. A beam transport system connected the cyclotrons to the target chamber with three doublet quadrupoles and one dipole bending magnet The shielding calculation proved the total effect dose rate in rem/year for the final design facility was safe for operational workers.by Tyler Christopher Sordelet.S.M
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