Supraspinal Fatigue Impedes Recovery From a Low-Intensity Sustained Contraction in Old Adults

This study determined the contribution of supraspinal fatigue and contractile properties to the age difference in neuromuscular fatigue during and recovery from a low-intensity sustained contraction. Cortical stimulation was used to evoke measures of voluntary activation and muscle relaxation during and after a contraction sustained at 20% of maximal voluntary contraction (MVC) until task failure with elbow flexor muscles in 14 young adults (20.9 ± 3.6 yr, 7 men) and 14 old adults (71.6 ± 5.4 yr, 7 men). Old adults exhibited a longer time to task failure than the young adults (23.8 ± 9.0 vs. 11.5 ± 3.9 min, respectively, P \u3c 0.001). The time to failure was associated with initial peak rates of relaxation of muscle fibers and pressor response (P \u3c 0.05). Increments in torque (superimposed twitch; SIT) generated by transcranial magnetic stimulation (TMS) during brief MVCs, increased during the fatiguing contraction (P \u3c 0.001) and then decreased during recovery (P = 0.02). The increase in the SIT was greater for the old adults than the young adults during the fatiguing contraction and recovery (P \u3c 0.05). Recovery of MVC torque was less for old than young adults at 10 min post-fatiguing contraction (75.1 ± 8.7 vs. 83.6 ± 7.8% of control MVC, respectively, P = 0.01) and was associated with the recovery of the SIT (r = −0.59, r2 = 0.35, P \u3c 0.001). Motor evoked potential (MEP) amplitude and the silent period elicited during the fatiguing contraction increased less for old adults than young adults (P \u3c 0.05). The greater fatigue resistance with age during a low-intensity sustained contraction was attributable to mechanisms located within the muscle. Recovery of maximal strength after the low-intensity fatiguing contraction however, was impeded more for old adults than young because of greater supraspinal fatigue. Recovery of strength could be an important variable to consider in exercise prescription of old populations

Supraspinal Fatigue Is Similar in Men and Women for a Low-Force Fatiguing Contraction

Purpose: This study determined the contribution of supraspinal fatigue to the sex difference in neuromuscular fatigue for a low-intensity fatiguing contraction. Because women have greater motor responses to arousal than men, we also examined whether cortical and motor nerve stimulation, techniques used to quantify central fatigue, would alter the sex difference in muscle fatigue. Methods: In study 1, cortical stimulation was elicited during maximal voluntary contractions (MVC) before and after a submaximal isometric contraction at 20% MVC with the elbow flexor muscles in 29 young adults (20 ± 2.6 yr, 14 men). In study 2, 10 men and 10 women (19.1 ± 2.9 yr) performed a fatiguing contraction in the presence and absence of cortical and motor nerve stimulation. Results: Study 1: Men had a briefer time to task failure than women (P = 0.009). Voluntary activation was reduced after the fatiguing contraction (P \u3c 0.001) similarly for men and women. Motor-evoked potential area and the EMG silent period increased similarly with fatigue for both sexes. Peak relaxation rates, however, were greater for men than women and were associated with time to task failure (P \u3c 0.05). Force fluctuations, RPE, HR, and mean arterial pressure increased at a greater rate for men than for women during the fatiguing contraction (P \u3c 0.05). Study 2: Time to task failure, force fluctuations, and all other physiological variables assessed were similar for the control session and stimulation session (P\u3e 0.05) for both men and women. Conclusions: Supraspinal fatigue was similar for men and women after the low-force fatiguing contraction, and the sex difference in muscle fatigue was associated with peripheral mechanisms. Furthermore, supraspinal fatigue can be quantified in both men and women without influencing motor performance

Caring to make a difference with vulnerable women: the impact of targeted support on birth-related outcomes and experiences

We report findings from a mixed-methods study to compare birth outcomes and experiences between vulnerable women who had or had not received targeted support from a specialist midwifery team and/or a third-sector organisation. Sociodemographic and birth-related outcome data from a 12-month birth cohort were used to explore differences between a) vulnerable and non-vulnerable women; and b) vulnerable women who had and those who had not received targeted support. Seventeen women who had or had not received targeted support were interviewed. Vulnerable mothers were significantly more likely to be younger, from a minority ethnic group, access care later in pregnancy and have a baby born earlier and at a lower birth weight. A higher percentage of women who received targeted support had a spontaneous birth, a vaginal presentation at birth and were less likely to use anaesthesia during labour when compared with unsupported vulnerable women. Targeted support was associated with reassurance, increased parental confidence and wellbeing. Key practice and policy-based implications are considered

Stressor-Induced Increase in Muscle Fatigability of Young Men and Women is Predicted by Strength but Not Voluntary Activation

This study investigated mechanisms for the stressor-induced changes in muscle fatigability in men and women. Participants performed an isometric-fatiguing contraction at 20% maximal voluntary contraction (MVC) until failure with the elbow flexor muscles. Study one (n = 55; 29 women) involved two experimental sessions: 1) a high-stressor session that required a difficult mental-math task before and during a fatiguing contraction and 2) a control session with no mental math. For some participants (n = 28; 14 women), cortical stimulation was used to examine mechanisms that contributed to muscle fatigability during the high-stressor and control sessions. Study two (n = 23; nine women) determined the influence of a low stressor, i.e., a simple mental-math task, on muscle fatigability. In study one, the time-to-task failure was less for the high-stressor session than control (P \u3c 0.05) for women (19.4%) and men (9.5%): the sex difference response disappeared when covaried for initial strength (MVC). MVC force, voluntary activation, and peak-twitch amplitude decreased similarly for the control and high-stressor sessions (P \u3c 0.05). In study two, the time-to-task failure of men or women was not influenced by the low stressor (P \u3e 0.05). The greater fatigability, when exposed to a high stressor during a low-force task, was not exclusive to women but involved a strength-related mechanism in both weaker men and women that accelerated declines in voluntary activation and slowing of contractile properties

Caring to make a difference: vulnerable women

We report findings from a mixed-methods study to compare birth outcomes and experiences between vulnerable women who had/had not received targeted support from a specialist midwifery team and/or a third-sector organisation. Sociodemographic and birth-related/outcome data from a 12-month birth cohort were used to explore differences between a) vulnerable and non-vulnerable women; and b) vulnerable women who had and those who had not received targeted support. Seventeen women who had/had not received targeted support were interviewed. Vulnerable mothers were significantly more likely to be younger, from a minority ethnic group, access care later in pregnancy and have a baby born earlier and at a lower birth weight. A higher percentage of women who received targeted support had a spontaneous birth, a vaginal presentation at birth and were less likely to use anaesthesia during labour when compared with unsupported vulnerable women. Targeted support was associated with reassurance, increased parental confidence and wellbeing. Key practice and policy-based implications are considered

Stressor-Induced Increase in Muscle Fatigability of Young Men and Women is Predicted by Strength but Not Voluntary Activation

This study investigated mechanisms for the stressor-induced changes in muscle fatigability in men and women. Participants performed an isometric-fatiguing contraction at 20% maximal voluntary contraction (MVC) until failure with the elbow flexor muscles. Study one (n = 55; 29 women) involved two experimental sessions: 1) a high-stressor session that required a difficult mental-math task before and during a fatiguing contraction and 2) a control session with no mental math. For some participants (n = 28; 14 women), cortical stimulation was used to examine mechanisms that contributed to muscle fatigability during the high-stressor and control sessions. Study two (n = 23; nine women) determined the influence of a low stressor, i.e., a simple mental-math task, on muscle fatigability. In study one, the time-to-task failure was less for the high-stressor session than control (P \u3c 0.05) for women (19.4%) and men (9.5%): the sex difference response disappeared when covaried for initial strength (MVC). MVC force, voluntary activation, and peak-twitch amplitude decreased similarly for the control and high-stressor sessions (P \u3c 0.05). In study two, the time-to-task failure of men or women was not influenced by the low stressor (P \u3e 0.05). The greater fatigability, when exposed to a high stressor during a low-force task, was not exclusive to women but involved a strength-related mechanism in both weaker men and women that accelerated declines in voluntary activation and slowing of contractile properties

The Vibration Ring

The vibration ring was conceived as a driveline damping device to prevent structure-borne noise in machines. It has the appearance of a metal ring, and can be installed between any two driveline components like an ordinary mechanical spacer. Damping is achieved using a ring-shaped piezoelectric stack that is poled in the axial direction and connected to an electrical shunt circuit. Surrounding the stack is a metal structure, called the compression cage, which squeezes the stack along its poled axis when excited by radial driveline forces. The stack in turn generates electrical energy, which is either dissipated or harvested using the shunt circuit. Removing energy from the system creates a net damping effect. The vibration ring is much stiffer than traditional damping devices, which allows it to be used in a driveline without disrupting normal operation. In phase 1 of this NASA Seedling Fund project, a combination of design and analysis was used to examine the feasibility of this concept. Several designs were evaluated using solid modeling, finite element analysis, and by creating prototype hardware. Then an analytical model representing the coupled electromechanical response was formulated in closed form. The model was exercised parametrically to examine the stiffness and loss factor spectra of the vibration ring, as well as simulate its damping effect in the context of a simplified driveline model. The results of this work showed that this is a viable mechanism for driveline damping, and provided several lessons for continued development

Patient-Reported Outcomes Integrated Within an Electronic Medical Record in Patients With Head and Neck Cancer

PURPOSE: Patient-reported outcome (PRO) tools lead to clinical benefits, including improved overall survival for patients with cancer. However, routine implementation of PROs in clinical practice within the electronic medical record (EMR) by integrated health care delivery systems remains limited. We studied the use of a PRO tool for patients with head and neck cancer (HNC) integrated in an EMR at Kaiser Permanente in Northern California. METHODS: Between August 2017 and December 2019, patients with newly diagnosed HNC were surveyed at baseline, then every 3 months using the Functional Assessment of Cancer Therapy-General 7 and Functional Assessment of Cancer Therapy-Head and Neck (version 4). A medical assistant performed a baseline survey on diagnosis and then notified patients electronically per surveillance protocol. Patients who did not respond to online PRO surveys could complete them via telephone or in-person appointments with medical assistants. Abnormal findings on PRO surveys were referred to appropriate members of the care team or the treating Otolaryngology-Head and Neck Surgery physicians. RESULTS: Two hundred ninety patients received baseline surveys. Patients received up to a maximum of eight subsequent surveys. Of a total of 597 electronic surveys, 585 (97.9%) were completed. The percentage of patients completing each interval survey ranged from 92% to 100%. Multivariate Poisson regression analysis showed patients with English as their primary language and an online secure account were the most likely to complete surveys compared with those patients with non-English as a primary language and without an online account. CONCLUSION: PRO tools can be effectively used within the EMR for patients with HNC with a high response rate provided there is strong engagement from a dedicated member of the care team. This has important implications for designing clinical trials and symptom monitoring in clinical practices that incorporate EMRs

Influence of a low magnetic field on the thermal diffusivity of Bi-2212

The thermal diffusivity of a Bi-2212 polycrystalline sample has been measured under a 1T magnetic field applied perpendicularly to the heat flux. The magnetic contribution to the heat carrier mean free path has been extracted and is found to behave as a simple power law. This behavior can be attributed to a percolation process of electrons in the vortex lattice created by the magnetic field.Comment: 10 pages, 3 figures; to be published in Phys. Rev.