94 research outputs found
Progressive hyperthermia elicits distinct responses in maximum and rapid torque production
Get PDFObjectivesTo investigate the effect of progressive whole-body hyperthermia on maximal, and rapid voluntary torque production, and their neuromuscular determinants.DesignRepeated measures, randomised.MethodsNine participants performed sets of neuromuscular assessments in HOT conditions (~50°C, ~35% relative humidity) at rectal temperatures (Tre) of 37, 38.5 and 39.5°C and in CON conditions (~22°C, ~5% relative humidity) at a Tre of ~37°C and pre-determined comparative time-points. Electrically evoked twitch (single impulse) and octet (8 impulses at 300 Hz) responses were measured at rest. Maximum voluntary torque (MVT), surface electromyography (EMG) normalised to maximal M-wave, and voluntary activation (VA) were measured during 3-5 s isometric maximal voluntary contractions. Rate of torque development (RTD) and normalised EMG were measured during rapid voluntary isometric contractions from rest.ResultsAll neuromuscular variables were unaffected by time in CON. In HOT, MVT, normalised EMG at MVT and VA were lower at 39.5°C compared to 37°C (p<0.05). Early- (0-50 ms) and middle- (50-100 ms) phase voluntary RTD were unaffected by increased Tre (p>0.05), despite lower normalised EMG at Tre 39.5°C (p<0.05) in rapid contractions. In contrast, late-phase (100-150 ms) voluntary RTD was lower at 38.5°C and 39.5°C compared to 37°C (p<0.05) in HOT. Evoked twitch and octet RTD increased with increased Tre (p<0.05). ConclusionsHyperthermia reduced late-phase voluntary RTD, likely due to reduced neural drive and the reduction in MVT. In contrast, early- and middle-phase voluntary RTD were unaffected by hyperthermia, likely due to the conflicting effects of reduced neural drive but faster intrinsic contractile properties.© 2021, Sports Medicine Australia. Published by Elsevier Ltd. The attached document (embargoed until 19/03/2023) is an author produced version of a paper published in JOURNAL OF SCIENCE AND MEDICINE IN SPORT uploaded in accordance with the publisher’s self-archiving policy. The final published version (version of record) is available online at the link. Some minor differences between this version and the final published version may remain. We suggest you refer to the final published version should you wish to cite from it.</p
Maximal voluntary torque and rate of torque development are not effected by whole-body hyperthermia or ten consecutive days of isothermic heat acclimation.
No full textVoluntary torque production is unaffected by changes in local thermal sensation during normothermia and hyperthermia
Get PDFThis study investigated altered local head and neck thermal sensation on maximal and rapid torque production during voluntary contractions. Nine participants completed four visits in two environmental conditions: at rectal temperatures ∼39.5°C in hot (HOT; ∼50°C, ∼39% relative humidity) and ∼37°C in thermoneutral (NEU; ∼22°C, ∼46% relative humidity) conditions. Local thermal sensation was manipulated by heating in thermoneutral conditions and cooling in hot conditions. Evoked twitches and octets were delivered at rest. Maximum voluntary torque (MVT), normalised surface electromyography (EMG) and voluntary activation (VA) were assessed during brief maximal isometric voluntary contractions of the knee extensors. Rate of torque development (RTD) and EMG were measured during rapid voluntary contractions. MVT (P = 0.463) and RTD (P = 0.061) were similar between environmental conditions despite reduced VA (−6%; P = 0.047) and EMG at MVT (−31%; P = 0.019). EMG in the rapid voluntary contractions was also lower in HOT versus NEU during the initial 100 ms (−24%; P = 0.035) and 150 ms (−26%; P = 0.035). Evoked twitch (+70%; P < 0.001) and octet (+27%; P < 0.001) RTD during the initial 50 ms were greater in the HOT compared to NEU conditions, in addition to a faster relaxation rate of the muscle (−33%; P < 0.001). In conclusion, hyperthermia reduced neural drive without affecting voluntary torque, likely due to the compensatory effects of improved intrinsic contractile function and faster contraction and relaxation rates of the knee extensors. Changes in local thermal perception of the head and neck whilst hyperthermic or normothermic did not affect voluntary torque
The reliability of kinetic and kinematic variables used to analyse normal running gait
No full textThe purpose of this study was to assess the reliability of 24 kinetic and kinematic variables from three synchronized systems used to represent normal running gait. Five male runners (mean 23.4 years, mass 80.2 kg) ran down a runway at a constant velocit
Heat acclimation reduces the effects of whole-body hyperthermia on knee-extensor relaxation rate but does not affect voluntary torque production
No full textPurpose: this study investigated the effects of acute hyperthermia and heat acclimation (HA) on maximal and rapid voluntary torque production, and their neuromuscular determinants. Methods: ten participants completed 10 days of isothermic HA (50 °C, 50% rh) and had their knee-extensor neuromuscular function assessed in normothermic and hyperthermic conditions, pre-, after 5 and after 10 days of HA. Electrically evoked twitch and octet (300 Hz) contractions were delivered at rest. Maximum voluntary torque (MVT), surface electromyography (EMG) normalised to maximal M-wave, and voluntary activation (VA) were assessed during brief maximal isometric voluntary contractions. Rate of torque development (RTD) and normalised EMG were measured during rapid voluntary contractions. Results: acute hyperthermia reduced neural drive (EMG at MVT and during rapid voluntary contractions; P < 0.05), increased evoked torques (P < 0.05), and shortened contraction and relaxation rates (P < 0.05). HA lowered resting rectal temperature and heart rate after 10 days (P < 0.05), and increased sweating rate after 5 and 10 days (P < 0.05), no differences were observed between 5 and 10 days. The hyperthermia-induced reduction in twitch half-relaxation was attenuated after 5 and 10 days of HA, but there were no other effects on neuromuscular function either in normothermic or hyperthermic conditions. Conclusion: HA-induced favourable adaptations to the heat after 5 and 10 days of exposure, but there was no measurable benefit on voluntary neuromuscular function in normothermic or hyperthermic conditions. HA did reduce the hyperthermic-induced reduction in twitch half-relaxation time, which may benefit twitch force summation and thus help preserve voluntary torque in hot environmental conditions.</p
LOWER LIMB TRI-JOINT SYNCHRONY DURING RUNNING: A LONGITUDINAL AGE-BASED STUDY
Get PDFCluster Phase analysis was used to examine age-related changes in synchrony between three joints of the lower limb during running stance. Ten male, endurance athletes (Age = 53.54±2.56 years [M50]) participated in the study at baseline (0 years) and then returned for re-testing after seven years (Age = 60.49±2.56 years [M57]). Lower limb coordinate and ground reaction forces were collected as participants performed running trials at a velocity of 3.83±0.40 m/s contacting the force plate with their preferred limb. Statistical parametric mapping identified that the hip, knee and ankle joint synchrony during the stance phase did not change. However tri-joint synchrony was significantly higher at M57 compared to M50 during the absorption sub-phase of stance. The increased joint synchrony as a function of age could be a mechanism associated with this key injury provoking phase
AN AGE-BASED KINETIC ANALYSIS THAT UNDERPINS JOINT COORDINATION IN RUNNING PERFORMANCE
Get PDFThe purpose of this study was to examine the age-based biomechanics that underpins lower body joint coordination during running gait. A longitudinal approach was adopted and experienced male distance runners (initially with a mean age = 53.34 years) were examined over a seven-year period. Three-dimensional joint coordinate and contact ground reaction force data were collected for running trials with a horizontal velocity = 3.83±0.40 m·s-1. ANOVA showed significant increases (p \u3c 0.03) in knee joint moments at amortisation and peak impact and braking forces. Statistical parametric mapping identified decreased hip moments at ~25-40 % of stance. With age there is an increase requirement to attenuate the passive impact forces which places the lower body musculature under further stress. The changes in hip moments, whilst the hip joint is extending, suggests a shift in power production to the knee and ankle which has been previously reported with faster running (Ferris et al., 2012)
Addiction recovery stories: Ceri Pimblett in conversation with Lisa Ogilvie
No full textPurpose: The purpose of this paper is to examine recovery through lived experience. It is part of a series that explores candid accounts of addiction and recovery to identify important components in the recovery process. Design/methodology/approach: The G-CHIME model comprises six elements important to addiction recovery (growth, connectedness, hope, identity, meaning in life and empowerment). It provides a standard against which to consider addiction recovery, having been used in this series, as well as in the design of interventions that improve well-being and strengthen recovery. In this paper, a first-hand account is presented, followed by a semi-structured e-interview with the author of the account. Narrative analysis is used to explore the account and interview through the G-CHIME model. Findings: This paper shows that addiction recovery is a remarkable process that can be effectively explained using the G-CHIME model. The significance of each component in the model is apparent from the account and e-interview presented. Originality/value: Each account of recovery in this series is unique and, as yet, untold
Mogadiscio dans la guerre civile: rêves d'Etat
No full textQoraagu wuxuu ka hadlayaa dowrka ay ka qaadatay caasimadda Moqdisho dhibaatooyinka dalka ku habsaday kaddib markii ay qarxeen dagaalladii sokeeye 1991.L'autore riflette sul ruolo della capitale somala, Mogadiscio, e sulla relativa evoluzione subita in seguito alla crisi che attraversa il paese dallo scoppio della guerra civile nel 1991.The author reflects on the role of the Somali capital, Mogadishu, and its evolution in relation to the crisis the country is facing since the outbreak of the civil war in 1991
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