The Limpopo Low-Level Jet: mean climatology and role in water vapor transport

Low-level jets (LLJs) are well established as critical features of regional climates globally. However, across sub-Saharan Africa, LLJs have received relatively little attention, in part due to a lack of data. Utilizing high-resolution reanalysis data, this paper develops the first climatology of a neglected feature of the southern African circulation – the Limpopo LLJ – and investigates its role in delivering water vapor to the continental interior. We demonstrate that the LLJ has a clear diurnal cycle and is a regular feature of the circulation throughout the year, forming on 80.9% of days. The pressure gradient between southern Mozambique and the continental interior acts as a first-order control on the annual cycle of jet strength, which peaks in October, achieving average maximum windspeeds of 15.8 m.s−1 at the core. Water vapor transport follows the same clear diurnal cycle, with at least 72% occurring over 18:00–08:00, and is closely related to jet strength: On average the strongest jet events advect 1.04 × 1012 kg (1.02 × 1012 kg) more moisture each night than the weakest in October-December (January-March). Strong jet events are typically linked to ridging anticyclones along the east coast of South Africa and are associated with increased rainfall in central and southern Botswana and northern South Africa the following day

The acute and delayed effects of foam rolling duration on male athlete’s flexibility and vertical jump performance

© 2022 The Authors. Published by International Universities Strength and Conditioning Association. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: https://doi.org/10.47206/ijsc.v2i1.90Foam rolling (FR) durations totaling ≤60 s per muscle are reported to acutely increase flexibility and vertical jump performance. However, limited research has investigated whether these benefits can outlast the inactive post-warmup preparatory period that typically separates warmups from the start of sporting competition. Eleven male athletes (height 1.77 0.09 m, body mass 78.0 17.0 kg, age 22 2 years) completed familiarization, followed by three experimental trials in a randomized and counterbalanced repeated measures crossover design. Trials commenced with 5 min jogging, before ankle dorsiflexion range of motion (ADF-ROM), sit and reach (S&R), countermovement jump (CMJ) and squat jump (SJ) baseline testing. Participants then sat inactively for 10 min (control) or performed lower extremity FR totaling either 30 (30FR) or 60 s (60FR) that targeted four agonist-antagonist leg muscles. Testing was then repeated before and after a simulated inactive 15 min post-warmup preparatory period to establish the acute and delayed effects of FR on performance. A two-way repeated measures analysis of variance was used to identify any significant interaction effects between conditions (30FR, 60FR, control) and timepoint (baseline, acute, delayed). No significant condition x timepoint interaction effect was detected for the ADF-ROM (f = 1.63, p = 0.19), S&R (f = 0.80, p = 0.54), CMJ ((f = 0.83, p = 0.99) or SJ (f = 0.66, p = 0.99). Therefore, FR totaling ≤60 s appears insufficient to enhance flexibility or vertical jump performance in male athletes

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

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

A preclinical comparison of oxytocin and the non-peptide oxytocin receptor agonist WAY 267,464 as potential therapeutics for psychiatric disorders

Introduction: Many researchers have proposed that the neuropeptide oxytocin (OT) might be used as a therapeutic to enhance social functioning in psychiatric disorders that feature impaired social behaviour. Despite an increasing number of clinical studies, current evidence in favour of meaningful clinical outcomes with OT is marginal at best. Such results might simply reflect the poor oral bioavailability and blood-brain barrier permeability of OT, as well as its poor selectivity for the oxytocin receptor (OTR) over the vasopressin 1A receptor (V1AR). These problems have encouraged the development of ‘small-molecule’ non-peptide OT ligands that aim to provide improved bioavailability and receptor selectivity relative to OT. One promising candidate is the non-peptide OTR agonist WAY 267,464. Surprisingly, there has been limited preclinical testing of WAY 267,464 to date. The present thesis thus provides a comprehensive in vitro, in vivo and ex vivo comparison of WAY 267,464 and OT in rats. Methods: Chapter 2 compared WAY 267,464 and OT on in vitro receptor pharmacology, social preference and regional brain activation. In Chapter 3, the effects of WAY 267,464 on social recognition memory were examined. Chapter 4 characterised the effects of WAY 267,464, OT and vasopressin (AVP) on body temperature and heart rate using biotelemetry. Chapter 5 examined the long-term effects of adolescent OT pretreatment on methamphetamine (METH) self-administration in adulthood. Results: WAY 267,464 increased social preference and caused similar brain activation to OT. WAY 267,464 prevented the facilitatory effects of AVP on social memory, and blocked OT-induced hypothermia and bradycardia. WAY 267,464 showed a dual agonist/antagonist action at the OTR and V1AR, respectively, while OT and AVP exhibited strong agonist activity at both receptors. Lastly, adolescent OT pretreatment reduced METH responding in adulthood. Conclusions: WAY 267,464 is not a simple OTR agonist, and has potent V1AR antagonist properties that have important implications for its therapeutic potential. Exogenous OT may be a promising pharmacotherapy for drug addiction. However, a better mechanistic understanding of its effects is necessary for the development of targeted medications

The Alpha-1 Adrenergic Receptor Antagonist Prazosin Reduces Binge-Like Eating in Rats

Background: Binge-eating disorder is a pervasive addiction-like disorder that is defined by excessive and uncontrollable consumption of food within brief periods of time. The aim of the current study was to examine the role of the brain noradrenergic system in binge-like eating through the use of the alpha-1 adrenergic receptor antagonist prazosin. Methods: For this purpose, we employed a limited access model whereby male Wistar rats were allowed to nosepoke for either chow (Chow rats) or a sugary, highly palatable food (Palatable rats) for 1 h/day. The effects of prazosin (0, 0.5, 1 and 2 mg/kg, i.p.) were tested in a fixed ratio 1 (FR1) and progressive ratio (PR) schedule of reinforcement. Results: The results show that prazosin preferentially reduced the responses for palatable food in a FR1 reinforcement schedule; when tested in a PR schedule of reinforcement, prazosin increased breakpoint in both Chow and Palatable rats, but more potently and more efficaciously in the latter. Our results suggest that prazosin treatment preferentially increased the motivational properties of the palatable diet. Conclusions: The current findings provide the characterization of the effects of prazosin on binge-like eating and offer support to the existing literature showing the important role of the noradrenergic system in addiction-like behavior

Corticospinal excitability of tibialis anterior and soleus differs during passive ankle movement

The purpose of this study was to assess corticospinal excitability of soleus (SOL) and tibialis anterior (TA) at a segmental level during passive ankle movement. Four experimental components were performed to assess the effects of passive ankle movement and muscle length on corticospinal excitability (MEP/Mmax) at different muscle lengths, subcortical excitability at the level of lumbar spinal segments (LEP/Mmax), intracortical inhibition (SICI) and facilitation (ICF), and H-reflex in SOL and TA. Additionally, the degree of fascicle length changes between SOL and TA was assessed in a subpopulation during passive ankle movement. Fascicles shortened and lengthened with joint movement during passive shortening and lengthening of SOL and TA to a similar degree (p<0.001). Resting motor threshold was greater in SOL compared to TA (p≤0.014). MEP/Mmax was facilitated in TA during passive shortening relative to the static position (p≤0.023) and passive lengthening (p≤0.001), but remained similar during passive ankle movement in SOL (p≥0.497), regardless of muscle length at the point of stimulus (p=0.922). LEP/Mmax (SOL: p=0.075, TA: p=0.071), SICI (SOL: p=0.427, TA: p=0.540) and ICF (SOL: p=0.177, TA: p=0.777) remained similar during passive ankle movement. H-reflex was not different across conditions in TA (p=0.258), but was reduced during passive lengthening compared to shortening in SOL (p=0.048). These results suggest a differential modulation of corticospinal excitability between plantar and dorsiflexors during passive movement. The corticospinal behaviour observed might be mediated by an increase in corticospinal drive as a result of reduced afferent input during muscle shortening and appears to be flexor-biased

Reduced corticospinal responses in older compared with younger adults during submaximal isometric, shortening, and lengthening contractions

The aim of this study was to assess differences in motor performance, as well as corticospinal and spinal responses to transcranial magnetic and percutaneous nerve stimulation, respectively, during submaximal isometric, shortening and lengthening contractions between younger and older adults. Fifteen younger (26 ± 4 yrs, 7 females) and 14 older (64 ± 3 yrs, 5 females) adults performed isometric, and shortening and lengthening dorsiflexion on an isokinetic dynamometer (5°·s−1) at 25 and 50% of contraction type specific maximums. Motor evoked potentials (MEPs) and H-reflexes were recorded at anatomical zero. Maximal dorsiflexor torque was greater during lengthening compared to shortening and isometric contractions (p<0.001), but were not age-dependent (p=0.158). However, torque variability was greater in older compared to young (p<0.001). Background electromyographic (EMG) activity was greater in older compared to younger individuals (p<0.005) and was contraction type dependent (p<0.001). As evoked responses are influenced both by the maximal level of excitation and background EMG activity, the responses were additionally normalised ([MEP/Mmax]/RMS and [H/Mmax]/RMS). The (MEP/Mmax)/RMS and (H/Mmax)/RMS were similar across contraction types, but were greater in young compared to older adults (p<0.001). Peripheral motor conduction times were prolonged in older adults (p=0.003), whilst peripheral sensory conduction times and central motor conduction times were not age-dependent (p≥0.356). These data suggest that age-related changes throughout the central nervous system serve to accommodate contraction type specific motor control. Moreover, a reduction in corticospinal responses and increased torque variability seem to occur without a significant reduction in maximal torque producing capacity during older age

Etiology and Recovery of Neuromuscular Fatigue following Competitive Soccer Match-Play

Aim: Previous research into the etiology of neuromuscular fatigue following competitive soccer match-play has primarily focused on peripheral perturbations, with limited research assessing central nervous system function in the days post-match. The aim of the present study was to examine the contribution and time-course of recovery of central and peripheral factors toward neuromuscular fatigue following competitive soccer match-play. Methods: Sixteen male semi-professional soccer players completed a 90-min soccer match. Pre-, post- and at 24, 48, and 72 h participants completed a battery of neuromuscular, physical, and perceptual tests. Maximal voluntary contraction force (MVC) and twitch responses to electrical (femoral nerve) and transcranial magnetic stimulation (TMS) of the motor cortex during isometric knee-extension and at rest were measured to assess central nervous system (voluntary activation, VA) and muscle contractile (potentiated twitch force, Qtw, pot) function. Electromyography responses of the rectus femoris to single- and paired-pulse TMS were used to assess corticospinal excitability and short-interval intracortical inhibition (SICI), respectively. Fatigue and perceptions of muscle soreness were assessed via visual analog scales, and physical function was assessed through measures of jump (countermovement jump height and reactive strength index) and sprint performance. Results: Competitive match-play elicited significant post-match declines in MVC force (−14%, P < 0.001) that persisted for 48 h (−4%, P = 0.01), before recovering by 72 h post-exercise. VA (motor point stimulation) was reduced immediately post-match (−8%, P < 0.001), and remained depressed at 24 h (−5%, P = 0.01) before recovering by 48 h post-exercise. Qtw,pot was reduced post-match (−14%, P < 0.001), remained depressed at 24 h (−6%, P = 0.01), before recovering by 48 h post-exercise. No changes were evident in corticospinal excitability or SICI. Jump performance took 48 h to recover, while perceptions of fatigue persisted at 72 h. Conclusion: Competitive soccer match-play elicits substantial impairments in central nervous system and muscle function, requiring up to 48 h to resolve. The results of the study could have important implications for fixture scheduling, the optimal management of the training process, squad rotation during congested competitive schedules, and the implementation of appropriate recovery interventions