Abstract The rate of motor unit (MU) loss and its influence on the progression sarcopenia is not well understood. Therefore, main purpose this study was to estimate compare numbers MUs in tibialis anterior (TA) young men (∼25 years) two groups older (∼65 years ≥80 years). Decomposition‐enhanced spike‐triggered averaging used collect surface intramuscular electromyographic signals during isometric dorsiflexions at 25% maximum voluntary contraction. mean surface‐MU potential size divided into...

The responsiveness of the human central nervous system can change profoundly with exercise, injury, disuse, or disease. Changes occur at both cortical and spinal levels but in most cases excitability motoneuron pool must be assessed to localize accurately site adaptation. Hence, it is critical understand, employ correctly, methods test humans. Several techniques exist each has its advantages disadvantages. This review examines common that use evoked compound muscle action potentials...

During maximal exercise, supraspinal fatigue contributes significantly to the decline in muscle performance but little is known about intracortical inhibition during such contractions. Long-interval produced by a conditioning motor cortical stimulus delivered via transcranial magnetic stimulation (TMS) 50-200 ms prior second test stimulus. We aimed delineate changes this sustained voluntary contraction (MVC). Eight subjects performed 2 min MVC of elbow flexors. Single and paired...

During fatigue caused by a sustained maximal voluntary contraction (MVC), motoneurones become markedly less responsive when tested during the silent period following transcranial magnetic stimulation (TMS). To determine whether this reduction depends on repetitive activation of motoneurones, responses to TMS (motor evoked potentials, MEPs) and cervicomedullary (cervicomedullary motor CMEPs) were submaximal at constant level electromyographic activity (EMG). In such contraction, some are...

Muscle power is more functionally relevant than static muscle strength, particularly with aging. However, the effect of age on derived from isotonic contractions has been studied sparingly, and it not at all in subjects >75 yr age. Thus purpose was to investigate magnitude causes age-related losses among 13 young (26 yr), old (65 very (84 yr) men. Six different loads were employed create velocity-torque power-torque relationships. Dorsiflexor cross-sectional area assessed via magnetic...

Muscle power is more relevant to the activities of daily living than isometric strength. However, dynamic contractions have received little attention as they relate effect age on muscle fatigue, particularly in very old persons. Thus, purpose this study was investigate fatigue dorsiflexors during a velocity-dependent (isotonic) task 12 young (26 years), (64 and (84 years) men.The protocol involved 25 maximal (as fast possible) at load 20% maximum strength through degrees range motion....

Key Points This study investigated the influence of group III/IV muscle afferents on corticospinal excitability during cycling exercise and focused GABA B neuron‐mediated inhibition as a potential underlying mechanism. The provides novel evidence to demonstrate that afferent feedback facilitates inhibitory intracortical neurons whole body exercise. Firing these interneurons probably contributes development central fatigue physical activity. Abstract We in determining Both under control...

A reduction of blood flow to active muscle will precipitate fatigue, and sustained isometric contractions produce intramuscular compartmental pressures that can limit flow. The present study explored how oxygenation respond at low, moderate, maximal intensities. Over two visits, 10 males (26 ± 2 yr; means SD) performed 1-min dorsiflexion 30, 60, 100% voluntary contraction (MVC) torque. Doppler ultrasound the anterior tibial artery was used record arterial diameter mean velocity calculate...

Abstract The documented impact of contractile level on decomposition‐enhanced spike‐triggered averaging motor unit number estimates (MUNEs) in young adults demonstrates the importance selecting an objective contraction intensity that yields most representative MUNE for a given muscle. Whether same would be ideal altered system (e.g., by aging or disease) has yet to examined. Thus, main purpose this study was compare effects MUNEs from soleus muscle (≈27 years) and old (≈75 men. Using...

With fatiguing exercise, firing of group III/IV muscle afferents reduces voluntary activation and force the exercised muscles. These can also act across agonist/antagonist pairs, reducing in nonfatigued We hypothesized that maintained after a adductor pollicis (AP) contraction would decrease AP ipsilateral elbow flexors. In two experiments ( n = 10) we examined flexors by measuring changes superimposed twitches evoked ulnar nerve stimulation transcranial magnetic motor cortex, respectively....

Motoneurone excitability is rapidly and profoundly reduced during a sustained maximal voluntary contraction (MVC) when tested in the transient silent period which follows transcranial magnetic stimulation (TMS) of motor cortex. One possible cause this reduction fatigue-induced withdrawal excitatory input to motoneurones from muscle spindle afferents. We aimed test if produced by tendon vibration would ameliorate suppression cervicomedullary motor-evoked potential (CMEP) MVC. Seven subjects...

During muscle fatigue, firing of small-diameter afferents can decrease voluntary activation the fatigued muscle. However, these may have a more widespread effect on other muscles in exercising limb. We examined if fatigue-sensitive from elbow extensor same arm reduces torque production and flexors. In nine subjects we flexors by measuring changes superimposed twitches evoked transcranial magnetic stimulation motor cortex during brief (2-3 s) maximal contractions (MVC). Inflation blood...

New Findings What is the central question of this study? Do group III and IV muscle afferents act at spinal or cortical level to affect ability nervous system drive quadriceps muscles during fatiguing exercise? main finding its importance? The excitability motoneurone pool vastus lateralis was unchanged by feedback from afferents. In contrast, these may contribute inhibition cortex. However, corticospinal pathway not directly affected These findings are important for understanding neural...

ABSTRACT Purpose Most studies applying repeated neuromuscular electrical stimulation (NMES) to assess intrinsic contractile properties employ frequencies considerably greater than the mean motor unit discharge rate (MUDR) for a given force level. It is hypothesized that loss increases with frequency, but this has not been evaluated in same pool of participants when other parameters are unchanged. Furthermore, there paucity research investigating possible sex-based differences during an NMES...

Objective— Peroxisome proliferator–activated receptor gamma (PPARγ), a ligand-activated transcription factor, has pleiotropic effects, including regulation of macrophage differentiation and lipid homeostasis. The PPARγ ligands, thiazolidinediones (TZDs), attenuate atherosclerosis in mice by uncertain mechanisms. objective this study was to determine whether activation or its obligate heterodimer, retinoid X (RXR), modulates foam cell formation induced oxidized (ox) lipoproteins. Methods...

The purpose of this study was to compare fatigue and recovery maximal voluntary torque [maximal contraction (MVC)] muscle oxygenation after (Vol) electrically stimulated (ES) protocols equal production. On 1 day, 10 male subjects [25 yr (SD 4)] completed a Vol protocol and, on separate an ES the right dorsiflexors. Each task involved 2 min intermittent (2-s on, 1-s off) isometric contractions at 50% MVC. For protocol, stimulation delivered percutaneously common peroneal nerve frequency 25...

Muscle pain has widespread effects on motor performance, but the effect of voluntary activation, which is level neural drive to contracting muscle, not known. To determine whether induced muscle reduces activation during maximal contractions, elbow flexors was assessed with both motor-point stimulation and transcranial magnetic over cortex. In addition, we performed a psychophysical experiment investigate across wide range submaximal efforts (5-75% maximum). all studies, flexion torque...