Neurophysiological responses and adaptation to muscle shortening and lengthening in young and older adults

Healthy aging is characterised by alterations in the nervous system, leading to decrements in neuromuscular performance, particularly during dynamic contractions. Muscle shortening and lengthening differently modulate the corticospinal output, with the possibility of this modulation being altered in aging adults, which might affect the adaptability of an aging neuromuscular system to maximal lengthening contractions. The aim of this thesis was to elucidate the differences in neurophysiological responses and adaptation to muscle shortening and lengthening between young and older adults. It was hypothesised that the age-related alterations in the nervous system will lead to impaired sensorimotor integration with muscle length changes and reduced corticospinal responses during dynamic contractions, impairing the adaptability of older adults to maximal lengthening contractions. In Study 1, a novel method for assessment of subcortical excitability of descending tracts was developed, followed by investigation of corticospinal responses during passive muscle shortening and lengthening. Corticospinal excitability was modulated by muscle length changes in young adults, likely through inhibitory input of muscle spindle afferents on cortical areas. In contrast, older adults showed no modulation, which may be linked to altered sensorimotor integration. In Study 2, a method for normalising torque outputs during submaximal dynamic contractions was developed, followed by assessment of muscle fascicle behaviour. Subsequently, evoked responses were assessed during submaximal contractions of different types in young and older individuals. Despite preserved maximal torque producing capacity, corticospinal responses were reduced in older compared with younger adults across contraction types, along with increased torque variability during dynamic contractions. Study 3 assessed the contribution of spinal and supraspinal properties in adaptation to repeated bouts of maximal lengthening contractions in young and older adults. Less damage was incurred in older individuals, but the rate of adaptation was similar between young and older adults. However, the corticospinal processes played a limited role in the adaptive response. This work extends the understanding of the modulation of corticospinal networks with muscle shortening and lengthening and age-related alterations in corticospinal pathway during dynamic contractions. It also suggests that the adaptability of an aging neuromuscular system to maximal dynamic contractions remains preserved

Low-threshold motor units can be a pain during experimental muscle pain

Neural control of muscle force while experiencing muscle pain is not fully understood yet. The idea of a differential modulation of the activity across the entire motor unit (MU) pool is highly attractive. However, while lower discharge rates of MUs during low‐force contractions in the presence of pain have been previously observed, much uncertainty remains regarding alterations of the firing behaviour of higher‐threshold MUs

ŠESTAŠI NE ZNAJU UČITI – POMOZIMO IM!

Svaki učitelj svjestan je činjenice da je za uspješno i učinkovito učenje novih sadržaja važno znati učiti te da pritom motivacija za učenje ima veliki značaj. Vrsta i razina motivacije određuju temeljitost učenja i kvalitetu postignutih rezultata. Sve više učitelja primjećuje kod učenika nedostatak motivacije, zasićenost, nezainteresiranost i otpor prema učenju, te da djeca uče samo pod prisilom ili za ocjenu [5]. S obzirom na to da i u našoj školi imamo učenike koji ne znaju učiti i koji nisu motivirani za rad u školi, pripremila sam sklop sačinjen od šest radionica čijom provedbom želim osnažiti učenike i potaknuti ih na učenje, koje će im na ovaj način biti olakšano. U ovom članku predstavljam sadržaj radionica i konačna saznanja

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

ŠESTAŠI NE ZNAJU UČITI – POMOZIMO IM!

Svaki učitelj svjestan je činjenice da je za uspješno i učinkovito učenje novih sadržaja važno znati učiti te da pritom motivacija za učenje ima veliki značaj. Vrsta i razina motivacije određuju temeljitost učenja i kvalitetu postignutih rezultata. Sve više učitelja primjećuje kod učenika nedostatak motivacije, zasićenost, nezainteresiranost i otpor prema učenju, te da djeca uče samo pod prisilom ili za ocjenu [5]. S obzirom na to da i u našoj školi imamo učenike koji ne znaju učiti i koji nisu motivirani za rad u školi, pripremila sam sklop sačinjen od šest radionica čijom provedbom želim osnažiti učenike i potaknuti ih na učenje, koje će im na ovaj način biti olakšano. U ovom članku predstavljam sadržaj radionica i konačna saznanja

Differences in force normalising procedures during submaximal anisometric contractions

Eccentric contractions are thought to require a unique neural activation strategy. However, due to greater intrinsic force generating capacity of muscle fibres during eccentric contraction, the understanding of neural modulation of different contraction types during submaximal contractions may be impeded by the force normalisation procedure employed. In the present experiment, subjects performed maximal isometric dorsiflexion at shorter (80°), intermediate (90°) and longer (100°) muscle lengths, and maximal concentric and eccentric contractions. Thereafter, submaximal concentric and eccentric contractions were performed normalised to either isometric maximum at 90° (ISO), contraction type specific maximum (CTS) or muscle length specific maximum (MLS). When using ISO or MLS for normalisation, mean submaximal eccentric torque levels were significantly lower when compared to CTS normalisation (11 and 7% lower compared to CTS; p = 0.003 and p = 0.018 for ISO and MLS, respectively). These experimentally observed differences closely matched those expected from the predictive model. During submaximal concentric contraction, mean torque levels were similar between ISO and CTS normalisation with similar discrepancies noted in EMG activity. These findings suggest that normalising to ISO and MLS might not be accurate for assessment and prescription of submaximal eccentric contractions

Motor unit discharge rate modulation during isometric contractions to failure is intensity‐and modality‐dependent

The physiological mechanisms determining the progressive decline in the maximal muscle torque production capacity during isometric contractions to task failure are known to depend on task demands. Task-specificity of the associated adjustments in motor unit discharge rate (MUDR), however, remains unclear. This study examined MUDR adjustments during different submaximal isometric knee extension tasks to failure. Participants performed a sustained and an intermittent task at 20% and 50% of maximal voluntary torque (MVT), respectively (Experiment 1). High-density surface EMG signals were recorded from vastus lateralis (VL) and medialis (VM) and decomposed into individual MU discharge timings, with the identified MUs tracked from recruitment to task failure. MUDR was quantified and normalised to intervals of 10% of contraction time (CT). MUDR of both muscles exhibited distinct modulation patterns in each task. During the 20% MVT sustained task, MUDR decreased until ∼50% CT, after which it gradually returned to baseline. Conversely, during the 50% MVT intermittent task, MUDR remained stable until ∼40–50% CT, after which it started to continually increase until task failure. To explore the effect of contraction intensity on the observed patterns, VL and VM MUDR was quantified during sustained contractions at 30% and 50% MVT (Experiment 2). During the 30% MVT sustained task, MUDR remained stable until ∼80–90% CT in both muscles, after which it continually increased until task failure. During the 50% MVT sustained task the increase in MUDR occurred earlier, after ∼70–80% CT. Our results suggest that adjustments in MUDR during submaximal isometric contractions to failure are contraction modality- and intensity-dependent

Generation of Multiple Circular Walls on a Thin Film of Nematic Liquid Crystal by Laser Scanning

We found that multiple circular walls (MCW) can be generated on a thin film of a nematic liquid crystal through a spiral scanning of a focused IR laser. The ratios between radii of adjacent rings of MCW were almost constant. These constant ratios can be explained theoretically by minimization of the Frank elastic free energy of nematic medium. The director field on a MCW exhibits chiral symmetry-breaking although the elastic free energies of both chiral MCWs are degenerated, i.e., the director on a MCW can rotate clockwise or counterclockwise along the radial direction.Comment: 10 pages, 5 figures. Submitted to Chemical Physics Letters 2nd Editio

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