Cortical inhibition is reduced following short-term training in young and older adults.

The purpose of this study was to investigate age-related differences in short-term training adaptations in cortical excitability and inhibition. Thirty young (21.9 ± 3.

Experimental and modelling investigation of surface EMG spike analysis.

A pattern classification method based on five measures extracted from the surface electromyographic (sEMG) signal is used to provide a unique characterization of the interference pattern for different motor unit behaviours. This study investigated the sensitivity of the five sEMG measures during the force gradation process. Tissue and electrode filtering effects were further evaluated using a sEMG model.

Short-term training adaptations in maximal motor unit firing rates and afterhyperpolarization duration.

In this study we investigated age- and training-related adaptations in maximal motor unit firing rates and the duration of the motoneuron afterhyperpolarization (AHP) in the dorsiflexor muscles of the foot. Subjects included 30 young (21.9 +/- 3.

Relationships between motor unit size and recruitment threshold in older adults: implications for size principle.

As a part of the aging process, motor unit reorganization occurs in which small motoneurons reinnervate predominantly fast-twitch muscle fibers that have lost their innervation. We examined the relationship between motor unit size and the threshold force for recruitment in two muscles to determine whether older individuals might develop an alternative pattern of motor unit activation. Young and older adults performed isometric contractions ranging from 0 to 50% of maximal voluntary contraction in both the first dorsal interosseous (FDI) and tibialis anterior (TA) muscles.

Relationships between surface EMG variables and motor unit firing rates.

Although surface electromyography (sEMG) is a widely used electrophysiological technique, its physiological interpretation remains somewhat controversial. This study examined the relationship between motor unit firing rates (MUFR) and the root mean square (RMS) amplitude and mean power frequency (MPF) of the sEMG signal in the biceps brachii. Eleven subjects performed maximal isometric elbow flexion while indwelling and sEMG recordings were obtained from the biceps.

Motor unit synchronization in FDI and biceps brachii muscles of strength-trained males.

Motor unit (MU) synchronization is the simultaneous or near-simultaneous firing of two MUs which occurs more often than would be expected by chance. The present study sought to investigate the effects of exercise training, muscle group, and force level, by comparing the magnitude of synchronization in the biceps brachii (BB) and first dorsal interosseous (FDI) muscles of untrained and strength-trained college-aged males at two force levels, 30% of maximal voluntary contraction (MVC) and 80% MVC. MU action potentials were recorded directly via an intramuscular needle electrode.

Relationships between voluntary activation and motor unit firing rate during maximal voluntary contractions in young and older adults.

The extent to which an individual can voluntarily produce maximal muscular force can be estimated using the interpolated twitch technique. Incompleteness of activation is typically attributed to either incomplete recruitment, suboptimal firing rates or both of these mechanisms. The purpose of this study was to assess the relationship between muscle activation and maximal motor unit firing rates.

Motor unit firing behavior during prolonged 50% MVC dorsiflexion contractions in young and older adults.

The purpose of this study was to investigate changes in motor unit firing behavior during prolonged contractions in young and older adults. Motor unit activity was recorded from the tibialis anterior of 16 subjects (8 young and 8 older), while they performed isometric dorsiflexion at 50% MVC until task failure. Mean motor unit firing rate, the standard deviation (SD), and coefficient of variation (CV) of the interspike intervals, and number of doublet discharges were calculated for a total of 52 motor units, tracked for an average of 92.

Experimental and modeling investigation of spectral compression of biceps brachii SEMG activity with increasing force levels.

This study investigated possible motor unit (MU) firing patterns underlying changes in biceps brachii (BB) surface electromyographic (SEMG) activity in 96 participants who performed isometric actions of the elbow flexors at 40%, 60%, 80%, and 100% of maximum voluntary contraction (MVC). We also conducted a modeling investigation to determine the extent to which a model would fit the experimental results. Experimentally, there was a linear increase (277%; p<0.

Equalization filters for multiple-channel electromyogram arrays.

Multiple-channels of electromyogram activity are frequently transduced via electrodes, then combined electronically to form one electrophysiologic recording, e.g. bipolar, linear double difference and Laplacian montages.

Reliability of motor-evoked potentials in the ADM muscle of older adults.

The purpose of this study was to determine the reliability of motor-evoked potentials (MEPs) produced in the abductor digiti minimi (ADM) muscle of male and female older adults, both within and between sessions. The number of trials within a session required to obtain reliable results was also examined. The investigation was conducted on 30 elderly individuals (15 M, 15 F; mean age 76 years).

Modulation of motor unit firing rates during a complex sinusoidal force task in young and older adults.

This study compared motor unit rate coding and muscular force control in the first dorsal interosseous muscle of older (n = 11, mean 72.3 yr) and young (n = 12, mean 18.7 yr) adults.

Motor-evoked potentials following imagery and limb disuse.

This article investigated whether mental imagery training could reduce the detrimental effects produced by limb disuse. Subjects learned a task requiring fifth finger abduction. Motor-evoked potentials (MEPs) were obtained from the abductor digiti minimi muscle using transcranial magnetic stimulation.

Neural adaptations to resistive exercise: mechanisms and recommendations for training practices.

It is generally accepted that neural factors play an important role in muscle strength gains. This article reviews the neural adaptations in strength, with the goal of laying the foundations for practical applications in sports medicine and rehabilitation. An increase in muscular strength without noticeable hypertrophy is the first line of evidence for neural involvement in acquisition of muscular strength.

Doublet discharges in motoneurons of young and older adults.

The purpose of this study was to investigate the occurrence of motor unit doublet discharges in young and older individuals at different rates of increasing force. Participants included eight young (21.9 +/- 3.

Aging, resistance training, and motor unit discharge behavior.

Researchers have alluded the existence of "neural factors" in the expression and development of muscular strength. Candidate neural factors including motor unit recruitment, rate coding, double firing, and motor unit synchronization are discussed in this review. Aging is generally accompanied by lower motor unit discharge rates.

Evidence of self-sustained motoneuron firing in young and older adults.

Motoneurons demonstrate a type of self-sustained firing behavior that seems to be produced by a prolonged period of depolarization caused by intrinsic long-term changes in the motoneuron. Such self-sustained firing behavior has previously been reported in human motor units. The purpose of the present study was to investigate the occurrence of self-sustained firing behavior in older adults.

Decreases in motor unit firing rate during sustained maximal-effort contractions in young and older adults.

Previous studies have suggested that older adults may be more resistant to muscular fatigue than young adults. We sought to determine whether motor unit firing rate might be a factor that determines the response to fatiguing exercise in young and older subjects. Motor unit recordings and muscular forces were obtained from the tibialis anterior (TA) muscle of 11 young and 8 older individuals.

Training-related adaptations in motor unit discharge rate in young and older adults.

Background: This study evaluated changes in motor unit (MU) firing rates in young and older adults during exercise training.

Methods: Vastus lateralis MU discharge rates were measured in 8 young and 7 older adults. Each participant performed isometric knee extension contractions at 10%, 50%, and 100% of maximal voluntary contraction or effort (MVC) on two separate occasions.

Neural issues in the control of muscular strength.

During the earliest stages of resistance exercise training, initial muscular strength gains occur too rapidly to be explained solely by muscle-based mechanisms. However; increases in surface-based EMG amplitude as well as motor unit discharge rate provide some insight to the existence of neural mechanisms in the earliest phases of resistance exercise training. Moreover, other phenomena such as the cross transfer of strength following unilateral exercise and neural changes following limb immobilization also support a role for neural control in muscular strength.

Neuromotor issues in human performance: introduction.

Two current approaches frequently implemented to understand mechanisms involved in motor control are presented in a series of papers. One approach aims at understanding what specific neural mechanisms are responsible for motor behavior Such neural mechanisms might be operative at any of several sites in the nervous system, including spinal sites capable of complex reflex organization, as well as supraspinal sites involved in integrating multiple sensory and motor processes. Alternative approaches involve the assessment of kinematic and other variables used to describe the behavior using dynamical systems theory.

Enhanced motor unit rate coding with improvements in a force-matching task.

These data describe improved modulation of discharge rates (rate coding) of first dorsal interosseous motor units throughout the acquisition of a complex force-matching skill involving isometric index finger abduction. In each of 15 consecutive trials, subjects attempted to match their force to a trajectory consisting of the sum of two sine waves (0.15 and 0.

Reliability of motor-evoked potentials during resting and active contraction conditions.

Purpose: To determine the reliability of motor-evoked potentials (MEP) obtained using transcranial magnetic stimulation (TMS) in the first dorsal interosseous (FDI) and biceps brachii muscles.

Methods: Fourteen college subjects attended the laboratory on three separate days. TMS was used to obtain MEP with the subject relaxed (resting condition) at stimulation intensities of 70%, 85%, and 100% of maximal stimulator output.

Hemispheric differences in the relationship between corticomotor excitability changes following a fine-motor task and motor learning.

Motor performance induces a postexercise increase in corticomotor excitability that may be associated with motor learning. We investigated whether there are hemispheric differences in the extent and/or time course of changes in corticomotor excitability following a manipulation task (Purdue pegboard) and their relationship with motor performance. Single- and paired-pulse (3 ms) transcranial magnetic stimulation (TMS) was used to assess task-induced facilitation of the muscle evoked potential (MEP) and intracortical inhibition (ICI) for three intrinsic hand muscles acting on digits 1, 2, and 5.