69 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/
The effect of head and neck per-cooling on neuromuscular fatigue following exercise in the heat
Full text linkThe effect of localised head and neck per-cooling on central and peripheral fatigue during high thermal strain was investigated. Fourteen participants cycled for 60 min at 50% peak oxygen uptake on 3 occasions: thermoneutral control (CON; 18 °C), hot (HOT; 35 °C), and HOT with head and neck cooling (HOTcooling). Maximal voluntary force (MVF) and central activation ratio (CAR) of the knee extensors were measured every 30 s during a sustained maximal voluntary contraction (MVC). Triplet peak force was measured following cycling, before and after the MVC. Rectal temperatures were higher in HOTcooling (39.2 ± 0.6 °C) and HOT (39.3 ± 0.5 °C) than CON (38.1 ± 0.3 °C; P < 0.05). Head and neck thermal sensation was similar in HOTcooling (4.2 ± 1.4) and CON (4.4 ± 0.9; P > 0.05) but lower than HOT (5.9 ± 1.5; P < 0.05). MVF and CAR were lower in HOT than CON throughout the MVC (P < 0.05). MVF and CAR were also lower in HOTcooling than CON at 5, 60, and 120 s, but similar at 30 and 90 s into the MVC (P > 0.05). Furthermore, they were greater in HOTcooling than HOT at 30 s, whilst triplet peak force was preserved in HOT after MVC. These results provide evidence that central fatigue following exercise in the heat is partially attenuated with head and neck cooling, which may be at the expense of greater peripheral fatigue. Novelty Central fatigue was greatest during hyperthermia. Head and neck cooling partially attenuated the greater central fatigue in the heat. Per-cooling led to more voluntary force production and more peripheral fatigue.© 2020, The Author(s). This is an author produced version of a paper published in APPLIED PHYSIOLOGY NUTRITION AND METABOLISM 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 textThe effect of hyperthermia with localised head and neck cooling on neuromuscular function
No full textIntroduction: hyperthermia reduces volitional force production, voluntary muscle activation and agonist-electromyography (EMG) during a sustained maximal voluntary contraction (MVC) [1], [2]. This reduction in neuromuscular function may explain a reduced exercise capacity in the heat. Cooling of the neck has been shown to improve running capacity in the heat [3]; however the mechanism is unknown. The aim of the study was to investigate whether localised cooling of the head and neck during hyperthermia would affect neuromuscular function following 60 min of cycling in the heat. Methods: fourteen male participants exercised on a cycle ergometer for 60 min at 50% ̇V̇O2max in three experimental conditions; hot (35 °C, 50% rh; HOT), hot with head and neck cooling (35 °C, 50% rh; HOTcooling) and control (18 °C, 50% rh; CON). Immediately after the cycling bout, participants performed a 120-s sustained isometric MVC of the knee extensors of their dominant limb. Neuromuscular activation was assessed during the MVC at 5, 30, 90 and 120-s by superimposing supra-maximal triplet (3 impulses at 100 Hz) contractions by electrical stimulation of the femoral nerve, and calculating the central activation ratio (CAR). EMG amplitude (normalised to maximal M-wave) of the 3 superficial quadriceps heads was recorded throughout the MVC. Rectal temperature (Tre) was measured throughout each condition.Results: Tre was raised in both the HOT (39.27 (0.52) °C) and HOTcooling (39.19 (0.56) °C) trials vs CON (38.07 (0.28) °C) immediately post cycling (P <0.001) and remained elevated during the 120-s MVC. Force declined throughout the MVC in all conditions (Fig 1). The decline in force was on average 18 and 13.6% greater in HOT and HOTcooling respectively compared to CON (Fig.1; P <0.001 for both). This was similar for voluntary activation, with significant reductions in HOT vs CON trials across all time points (P <0.001). Normalised agonist EMG showed significant differences between HOT vs CON throughout the first 60-s of contraction; thereafter a reduced neural drive in all conditions was similar.Discussion: cooling had no physiological effect on Tre during hyperthermia trials. HOT appeared to show the greatest decline in voluntary force and was associated with a greater decline in CAR and normalised EMG in comparison to CON. The higher force output for HOTcooling may be explained by improved neural drive of the central nervous system to voluntarily activated muscles.Conclusion: localised head and neck cooling improves neuromuscular function of the knee extensors during a sustained MVC under hyperthermic conditions. <br/
Voluntary torque production is unaffected by changes in local thermal sensation during normothermia and hyperthermia
Full text linkThis 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
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
A classical test theory and item response theory analysis of the DSM-IV symptom criteria for a major depressive episode using data from the National Comorbidity Survey--Replication
No full textFormal psychiatric symptom criteria are used to delineate the boundary between “normal” and “abnormal” behavior. In North America, the current official psychodiagnostic criteria for a multitude of psychiatric disorders are codified in the Diagnostic and Statistical Manual of Mental Disorders (4th Edition, text revision) (APA, 2000). Psychodiagnostic symptom criteria are indicators of psychopathological constructs that are clearly latent, however, it is somewhat astonishing that formal psychometric techniques that have been developed to model latent constructs have not been used to develop and evaluate psychodiagnostic symptom criteria (Aggen, Neale, & Kendler, 2005; Zimmerman, McGlinchey, Young, & Chelminski, 2006a, 2006b). There are two main psychometric paradigms that are currently in use: classical test theory and item response theory (Crocker & Algina, 1986). Classical test theory has been extensively used on both cognitive constructs and noncognitive constructs (Crocker & Algina, 1986; Embretson & Hershberger, 1999). Item response theory is considered to be theoretically superior to classical test theory and it has revolutionized the creation and evaluation of cognitive constructs (Crocker & Algina, 1986; Embretson & Hershberger, 1999; McDonald, 1999). However, item response theory has not been extensively utilized for the creation and evaluation of noncognitive constructs, even though it holds great promise in this regard (Reise, 1999; Reise & Henson, 2003). The proposed study will use classical test theory and item response theory to assess the psychodiagnostic symptom criteria for depression as found in the Diagnostic and Statistical Manual of Mental Disorders (4th Edition, text revision) (APA, 2000). The data to be used in the proposed study was collected in the National Comorbidity Survey – Replication, which was a nationally representative epidemiological community survey (Kessler et al., 2004; Kessler & Merikangas, 2004). The results of such a study will give a sophisticated psychometric perspective on the psychodiagnostic symptom criteria of depression that has not yet been available and it will provide valuable information on improving and refining future diagnostic symptom criteria of depression.Ph.D.Includes abstractVitaIncludes bibliographical referencesby Anthony P. Pawla
Rate of torque development scaled to maximum torque available is velocity dependent
Full text linkThe influence of angular velocity on rate of torque development (RTD) is unknown, despite the inverse, curvilinear torque-velocity relationship for angle- and velocity-specific maximum available torque (Tmax) being well-established. This study investigated the relationship between angular velocity and RTD scaled to Tmax. In 17 participants, tetanic contractions (100-Hz) of the knee extensors were evoked as the knee was passively extended at different iso-velocities between 0º.s-1 to 200º.s-1. Each condition consisted of evoking 0.25-s contractions without pre-activation (for measuring RTD) commencing as the knee passed 95º of extension, and 1.25-s contractions with pre-activation (for measuring Tmax), commencing 1 s prior to the knee reaching 95º. Torque at 100 ms after torque onset (T100) and peak RTD (RTDpeak) in the contractions without pre-activation were normalised to Tmax. The torque-velocity relationship for T100 was flat in comparison to an inverse, curvilinear relationship for Tmax, resulting in linear increases in normalised T100 and RTDpeak with increased velocity. Results also showed normalised T100 and RTDpeak were likely overestimated due to shortening-induced force depression (FD) which would be greater in contractions with- than without- pre-activation. However, these effects of FD cannot explain the faster normalised RTD with increased velocity, as the relative difference in work done (a proxy for FD) between contractions with and without pre-activation decreased – and thus the overestimation of normalised RTD metrics likely decreased – with increased velocity. In conclusion, RTD scaled to Tmax increases with increased velocity, which appears to be an intrinsic contractile property independent of the effects of force depression. © 2021, Elsevier. This is an author produced version of a paper published in Journal of Biomechanics 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
Rate of force development: physiological and methodological considerations
No full textThe evaluation of rate of force development during rapid contractions has recently become quite popular for characterising explosive strength of athletes, elderly individuals and patients. The main aims of this narrative review are to describe the neuromuscular determinants of rate of force development and to discuss various methodological considerations inherent to its evaluation for research and clinical purposes. Rate of force development (1) seems to be mainly determined by the capacity to produce maximal voluntary activation in the early phase of an explosive contraction (first 50–75 ms), particularly as a result of increased motor unit discharge rate; (2) can be improved by both explosive-type and heavy-resistance strength training in different subject populations, mainly through an improvement in rapid muscle activation; (3) is quite difficult to evaluate in a valid and reliable way. Therefore, we provide evidence-based practical recommendations for rational quantification of rate of force development in both laboratory and clinical settings. © 2016, The Author(s)
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