Contraction intensity and sex differences in knee-extensor fatigability

Females are less fatigable than males during isometric contractions across various muscles and intensities. However, sex differences in knee-extensor fatigability remain relatively unexplored. Purpose: To determine the sex difference in performance fatigability for intermittent, isometric contractions of the knee-extensor muscles. Methods: Eighteen participants (10 males, 8 females) performed intermittent, isometric, knee-extensor contractions at 30% of their maximal voluntary force (MVC) for 30 min and in a separate session at 50% MVC until task-failure. During both fatiguing protocols a MVC was performed every 60s and electromyography (EMG) was recorded during all contractions. Results: At task completion males had a larger reduction in MVC force for the 30% MVC task (−32±15% vs. −15±16%, P=0.042) and the 50% MVC task (−34±8% vs. −24±1%, P=0.045). Furthermore, for the 50% MVC task, females had a longer task duration (937±525 s vs. 397±153 s, P=0.007). The rise in EMG activity and force fluctuations were more rapid for the males than females (P<0.05). When participants were matched for strength post-hoc (n=10), a sex difference in fatigability for both tasks was still evident. Conclusions: Females were less fatigable than males during intermittent, isometric, knee-extensor contractions at moderate relative forces and this difference was independent of strength

Carboniferous barite-fluorite mineralization in the Late Devonian Kinsac Pluton, southern Nova Scotia

Abundant barite ± fluorite ± quartz veins occur along the eastern margin of the Late Devonian Kinsac Pluton, a peraluminous granite that intruded metasedimentary rocks of the Meguma Group. The barite veins, striking 120° with vertical dip, occur in areas of strongly fractured granite, but the veins are not deformed and may contain lenses of comminuted granite. The veins (s 0.6 m wide) are dominated by coarse, cloudy white barite euhedra with or without a late infill of euhedral clear quartz and pink to dark purple fluorite. 40Ar/39Ar step-wise heating of a K-feldspar megacryst in granite immediately adjacent to a barite vein indicates a 354 Ma plateau age for the high-temperature gas fraction and a ca. 320 Ma age for the low-temperature gas fraction. The younger age is interpreted to record partial resetting of K-feldspar due to interaction of the mineral with vein-forming fluids. Fluid inclusions (aqueous, L-V types) hosted by vein fluorite have homogenization temperatures of 100° to 130°C. Last melting of ice indicates salinities of 24 to 28 wt. % equivalent NaCl, but low eutectic temperatures indicate that the fluids are mixed NaCI-CaCI2-FeCI2-MgCI2 brines. Although fluorite-hosted fluid inclusions from the South Mountain Batholith have similar salinities, they homogenize at temperatures of 150° to 160°C. Stable isotopic studies of vein minerals indicate 534Sb„,e = +13 ± 2%o, &#x3B4;l8Oquartz = +22%o and &#x3B4;D for fluid inclusion extracts are -123 to -165 %o. The data are interpreted to indicate that: (1) sulphur was derived from dissolution of Windsor Group evaporites rather than from sulphides in basement rocks; (2) the &#x3B4;18)water of the veins was +8 to +12 %o for 100° to 150°C, which is consistent with either a basinal or metamorphic fluid; (3) the fluids interacted with organic matter to generate the low &#x3B4;D values. Measured 87Sr/86Sr on barite (0.7120; n=2) and fluorite (0.7086) indicate that the fluids exchanged with a radiogenic source, either the Horton Group or the Meguma Group being the most likely reservoir. Collectively the data indicate vein formation during the Early Carboniferous, when the study area was buried under ca. 2-3 km of Carboniferous strata which have subsequently been eroded. Basinal-type fluids were focused into zones of extension which opened as a result of high Pfluid, in concert with sinistral movement on NW-trending faults that crosscut the Meguma Terrane. R&#xC9;SUM&#xC9; On trouve une abondance de filons de barytine ± fluorite ± quartz le long de la marge orientale du pluton du D&#xE9;vonien superieur de Kinsac, granite hyperalumineux qui s'est introduit dans des roches m&#xE9;tas&#xE9;dimentaires du groupe de Meguma. Les filons de barytine. orient&#xE9;s selon un pendage vertical de 120°, se trouvent dans des zones de granite fortement fracturees, mais ils ne sont pas d&#xE9;form&#xE9;s et ils pourraient renfermer des lentilles de granite fragment&#xE9;. Les filons (≤0.6 m) sont domin&#xE9;s par la pr&#xE9;sence de barytine automorphe blanc trouble, grossi&#xE9;re, avec ou sans remplissage tardif de quartz transparent automorphe et de fluorite rose &#xE0; mauve fonc&#xE9;. Un r&#xE9;chauffement progressif 40Ar/39Ar d'un m&#xE9;gacristal de feldspath-K dans le granite imm&#xE9;diatement adjacent a un filon de barytine r&#xE9;v&#xE8;le que la fraction gazeuse &#xE0; haute t&#xE9;mperature &#xE0; un &#xE2;ge plateau de 354 M.A. et que la fraction gazeuse &#xE0; basse temp&#xE9;rature est &#xE2;g&#xE9;e de 320 M.A. L'&#xE2;ge le plus jeune est interpr&#xE9;t&#xE9; comme I'enregistrement d'un r&#xE9;tablissement partiel de feldspath-K du &#xE0; I'interaction du min&#xE9;ral avec des fluides constitutifs de filons. Des inclusions de fluides (aqueux de types L-V) contenues dans de la fluorite filonienne poss&#xE8;dent des temp&#xE9;ratures d'homog&#xE9;n&#xE9;isation de 100° a 130 °C. La derni&#xE9;re fonte des glaces r&#xE9;v&#xE8;le des teneurs en sels &#xE9;quivalant &#xE0; 24 &#xE0; 28 % en poids de NaCl. mais les temp&#xE9;ratures eutectiques basses r&#xE9;v&#xE8;lent que les fluides constituent des saumures m&#xEA;l&#xE9;es de NaCI-CaCI2-FeCl2-MgCl. M&#xEA;me si des inclusions de fluides contenues dans de la fluorite du batholithe du mont South affichent des salinit&#xE9;s analogues, elles s'homog&#xE9;neisent &#xE0; des temp&#xE9;ratures de 150° &#xE8; 160 °C. Des &#xE9;tudes des isotopes lourds des min&#xE9;raux filoniens r&#xE9;v&#xE8;lent que &#x3B4;34Sbarytme = +13 ± 2%o. &#x3B4;18Oquartz = +22%oet que &#x3B4;D des extraits d'inclusions de fluides affichent -123 &#xE0; -165%o. Selon I'interpr&#xE9;tation des chercheurs, ces donn&#xE9;es signifient: (1) que le soufre provient d*une dissolution d’&#xE9;vaporites du groupe de Windsor plut&#xEA;t que de sulfures du socle rocheux; (2) que &#x3B4;18Od’eau des filons repr&#xE9;sentait +8 &#xE0; +12%o &#xE0; des temp&#xE9;ratures de 100° &#xE0; 150°C, ce qui correspond &#xE0; un fluide m&#xE9;tamorphique ou un fluide de bassin; et (3) que les fluides ont interagi avec la mati&#xE8;re organique pour produire de faibles valeurs &#x3B4;D. Le 87Sr/86Sr mesur&#xE9; sur la barytine (0.7120; n=2) et la fluorite (0.7086) signale un &#xE9;change de fluides avec une source radiog&#xE9;nique, soit les groupes de Horton ou de Meguma, qui constituent les reservoirs les plus vraisemblables. Les donn&#xE9;es r&#xE9;v&#xE8;lent collcctivement que les filons se sont form&#xE9;s au debut du Carbonifere inf&#xE9;rieur lorsque le secteur d'&#xE9;tude se trouvait enfoui sous environ deux &#xE0; trois kilom&#xE8;tres de strates du Carbonifere, qui se sont subsequemment &#xE9;rod&#xE9;es. Les fluides de bassin ont &#xE9;t&#xE9; concentr&#xE9;s dans des zones d'extension qui se sont ouvertes sous I'influence de fluidesP &#xE0; teneur eievee de concert avec un mouvement senestre sur les failles orient&#xE9;es vers le nord-ouest entrecoupant le terrane de Meguma. [Traduit par la r&#xE9;daction

Task‐specific strength increases after lower‐limb compound resistance training occurred in the absence of corticospinal changes in vastus lateralis

Neural adaptations subserving strength increases have been shown to be task‐specific, but responses and adaptation to lower‐limb compound exercises such as the squat are commonly assessed in a single‐limb isometric task. This two‐part study assessed neuromuscular responses to an acute bout (Study A) and 4 weeks (Study B) of squat resistance training at 80% of one‐repetition‐maximum, with measures taken during a task‐specific isometric squat (IS) and non‐specific isometric knee extension (KE). Eighteen healthy volunteers (25 ± 5 years) were randomised into either a training (n = 10) or a control (n = 8) group. Neural responses were evoked at the intracortical, corticospinal and spinal levels, and muscle thickness was assessed using ultrasound. The results of Study A showed that the acute bout of squat resistance training decreased maximum voluntary contraction (MVC) for up to 45 min post‐exercise (−23%, P < 0.001). From 15–45 min post‐exercise, spinally evoked responses were increased in both tasks (P = 0.008); however, no other evoked responses were affected (P ≥ 0.240). Study B demonstrated that following short‐term resistance training, participants improved their one repetition maximum squat (+35%, P < 0.001), which was reflected by a task‐specific increase in IS MVC (+49%, P = 0.001), but not KE (+1%, P = 0.882). However, no training‐induced changes were observed in muscle thickness (P = 0.468) or any evoked responses (P = 0.141). Adjustments in spinal motoneuronal excitability are evident after acute resistance training. After a period of short‐term training, there were no changes in the responses to central nervous system stimulation, which suggests that alterations in corticospinal properties of the vastus lateralis might not contribute to increases in strength

Physiological sex differences affect the integrative response to exercise: Acute and chronic implications

The anatomical and physiological differences between males and females are thought to determine differences in the limits of human performance. The notion of studying sex as a biological variable has recently been emphasized in the biosciences as a vital step in enhancing human health. In this review, we contend that the effects of biological sex on acute and chronic responses must be studied and accounted for when prescribing aerobic exercise, much like any intervention targeting the optimization of physiological function. Emerging evidence suggests that the response of physiological systems to exercise differs between males and females, potentially mediating the beneficial effects in healthy and clinical populations. We highlight evidence that integrative metabolic thresholds during exercise are influenced by phenotypical sex differences throughout many physiological systems. Furthermore, we discuss evidence that female skeletal muscle is more resistant to fatigue elicited by equivalent dosages of high‐intensity exercise. How the different acute responses affect the long‐term trainability of males and females is considered, with discussion about tailoring exercise to the characteristics of the individual presented within the context of biological sex. Finally, we highlight the influence of endogenous and exogenous sex hormones on physiological responses to exercise in females. Sex is one of many mediating influences on the outcomes of exercise, and with careful experimental designs, physiologists can advance the collective understanding of diversity in physiology and optimize outcomes for both sexes

The Effect of Phase Change Material on Recovery of Neuromuscular Function Following Competitive Soccer Match-Play

Aim: Cryotherapy is commonly implemented following soccer match-play in an attempt to accelerate the natural time-course of recovery, but the effect of this intervention on neuromuscular function is unknown. The aim of the present study was to examine the effect of donning lower-body garments fitted with cooled phase change material (PCM) on recovery of neuromuscular function following competitive soccer match-play. Methods: Using a randomized, crossover design, 11 male semi-professional soccer players wore PCM cooled to 15°C (PCM cold) or left at ambient temperature (PCM amb; sham control) for 3 h following soccer match-play. Pre-, and 24, 48, and 72 h post-match, participants completed a battery of neuromuscular, physical, and perceptual tests. Maximal voluntary contraction force (MVC) and twitch responses to electrical (femoral nerve) and magnetic (motor cortex) stimulation (TMS) during isometric knee-extension and at rest were measured to assess central nervous system (CNS) (voluntary activation, VA) and muscle contractile (quadriceps potentiated twitch force, Q tw,pot) function. Fatigue and perceptions of muscle soreness were assessed via visual analog scales, and physical function was assessed through measures of jump [countermovement jump (CMJ) height and reactive strength index (RSI)] performance. A belief questionnaire was completed pre- and post-intervention to determine the perceived effectiveness of each garment. Results: Competitive soccer match-play elicited persistent decrements in MVC, VA measured with femoral nerve stimulation, Q tw,pot, as well as reactive strength, fatigue and muscle soreness (P 0.05). The belief questionnaire revealed that players perceived that both PCMcold and PCMamb were moderately effective in improving recovery, with no difference between the two interventions (P = 0.56). Conclusion: Although wearing cooled PCM garments improved MVC and VA 48 h following match-play, the lack of effect on measures of physical function or perceptual responses to match-play suggest that PCM offers a limited benefit to the recovery process. The lack of effect could have been due to the relatively small magnitude of change in most of the outcome measures studied

Menstrual cycle-associated modulations in neuromuscular function and fatigability of the knee extensors in eumenorrheic women

Sex hormone concentrations of eumenorrheic women typically fluctuate across the menstrual cycle and can affect neural function such that estrogen has neuroexcitatory effects, and progesterone induces inhibition. However, the effects of these changes on corticospinal and intracortical circuitry and the motor performance of the knee extensors are unknown. The present two-part investigation aimed to 1) determine the measurement error of an exercise task, transcranial magnetic stimulation (TMS)-, and motor nerve stimulation (MNS)-derived responses in women ingesting a monophasic oral contraceptive pill (hormonally-constant) and 2) investigate whether these measures were modulated by menstrual cycle phase (MCP), by examining them before and after an intermittent isometric fatiguing task (60% of maximal voluntary contraction, MVC) with the knee extensors until task failure in eumenorrheic women on days 2, 14, and 21 of the menstrual cycle. The repeatability of neuromuscular measures at baseline and fatigability ranged between moderate and excellent in women taking the oral contraceptive pill. MVC was not affected by MCP (P = 0.790). Voluntary activation (MNS and TMS) peaked on day 14 (P = 0.007 and 0.008, respectively). Whereas corticospinal excitability was unchanged, short-interval intracortical inhibition was greatest on day 21 compared with days 14 and 2 (P < 0.001). Additionally, time to task failure was longer on day 21 than on both days 14 and 2 (24 and 36%, respectively, P = 0.030). The observed changes were larger than the associated measurement errors. These data demonstrate that neuromuscular function and fatigability of the knee extensors vary across the menstrual cycle and may influence exercise performance involving locomotor muscles. NEW & NOTEWORTHY The present two-part study first demonstrated the repeatability of transcranial magnetic stimulation- and electrical motor nerve stimulation-evoked variables in a hormonally constant female population. Subsequently, it was demonstrated that the eumenorrheic menstrual cycle affects neuromuscular function. Changing concentrations of neuroactive hormones corresponded to greater voluntary activation on day 14, greater intracortical inhibition on day 21, and lowest fatigability on day 21. These alterations of knee extensor neuromuscular function have implications for locomotor activities

ZODIACAL EXOPLANETS IN TIME (ZEIT). III. A SHORT-PERIOD PLANET ORBITING A PRE-MAIN-SEQUENCE STAR IN THE UPPER SCORPIUS OB ASSOCIATION

We confirm and characterize a close-in (${P}_{{\rm{orb}}}$ = 5.425 days), super-Neptune sized (${5.04}_{-0.37}^{+0.34}$ ${R}_{\oplus }$) planet transiting K2-33 (2MASS J16101473-1919095), a late-type (M3) pre-main-sequence (11 Myr old) star in the Upper Scorpius subgroup of the Scorpius–Centaurus OB association. The host star has the kinematics of a member of the Upper Scorpius OB association, and its spectrum contains lithium absorption, an unambiguous sign of youth ($\lt 20$ Myr) in late-type dwarfs. We combine photometry from K2 and the ground-based MEarth project to refine the planet's properties and constrain the host star's density. We determine K2-33's bolometric flux and effective temperature from moderate-resolution spectra. By utilizing isochrones that include the effects of magnetic fields, we derive a precise radius (6%–7%) and mass (16%) for the host star, and a stellar age consistent with the established value for Upper Scorpius. Follow-up high-resolution imaging and Doppler spectroscopy confirm that the transiting object is not a stellar companion or a background eclipsing binary blended with the target. The shape of the transit, the constancy of the transit depth and periodicity over 1.5 yr, and the independence with wavelength rule out stellar variability or a dust cloud or debris disk partially occulting the star as the source of the signal; we conclude that it must instead be planetary in origin. The existence of K2-33b suggests that close-in planets can form in situ or migrate within ~10 Myr, e.g., via interactions with a disk, and that long-timescale dynamical migration such as by Lidov–Kozai or planet–planet scattering is not responsible for all short-period planets

Sex differences in fatigability following exercise normalised to the power-duration relationship

Due to morphological differences, females demonstrate greater fatigue resistance of locomotor muscle during single‐limb and whole‐body exercise modalities. Whilst females sustain a greater relative intensity of single‐limb, isometric exercise than males, limited investigation has been performed during whole‐body exercise. Accordingly, this study established the power‐duration relationship during cycling in 18 trained participants (8 females). Subsequently, constant‐load exercise was performed at critical power (CP)‐matched intensities within the heavy and severe domains, with the mechanisms of fatigability assessed via non‐invasive neurostimulation, near‐infrared spectroscopy, and pulmonary gas exchange during and following exercise. Relative CP (72±5 vs. 74±2% Pmax, p = 0.210) and curvature constant (51±11 vs. 52±10 J·Pmax−1, p = 0.733) of the power‐duration relationship were similar between males and females. Subsequent heavy (p = 0.758) and severe intensity (p = 0.645) exercise time to task failures were not different between sexes. However, females experienced lesser reductions in contractile function at task failure (p≤0.020), and greater vastus lateralis oxygenation (p≤0.039) during both trials. Reductions in voluntary activation occurred following both trials (p<0.001), but were less in females following the heavy trial (p = 0.036). Furthermore, during the heavy‐intensity trial only, corticospinal excitability was reduced at the cortical (p = 0.020) and spinal (p = 0.036) levels, but these reductions were not sex‐dependent. Other than a lower respiratory exchange ratio in the heavy trial for females (p = 0.039), no gas exchange variables differed between sexes (p≥0.052). Collectively, these data demonstrate that whilst the relative power‐duration relationship is not different between males and females, the mechanisms of fatigability during CP‐matched exercise above and below critical power are mediated by sex