Problems in using an adjective checklist to measure fatigue

73 fatigued and 45 unfatigued members of the British Army completed a 16-item adjective checklist, derived from the Nowlis Mood Adjective Checklist. The items had been selected to provide a subjective measure of fatigue. Although the scores could differentiate between the two groups, they did not correlate with an objective measure of fatigue. Significant relationships were found between EPQ-scores and the checklist scores, suggesting that extraverts denied feeling fatigued while neurotics exaggerated their fatigue. Susceptibility to effects of social desirability, as measured by the lie-scale, was also found to decrease self-rated fatigue.     

Central fatigue mechanisms are responsible for decreases in hand proprioceptive acuity following shoulder muscle fatigue

Muscle fatigue is a complex phenomenon, consisting of central and peripheral mechanisms which contribute to local and systemic changes in motor performance. In particular, it has been demonstrated that afferent processing in the fatigued muscle (e.g., shoulder), as well as in surrounding or distal muscles (e.g., hand) can be altered by fatigue. Currently, it is unclear how proximal muscle fatigue affects proprioceptive acuity of the distal limb. The purpose of the present study was to assess the effects of shoulder muscle fatigue on participants’ ability to judge the location of their hand using only proprioceptive cues. Participants’ (N = 16) limbs were moved outwards by a robot manipulandum and they were instructed to estimate the position of their hand relative to one of four visual reference targets (two near, two far). This estimation task was completed before and after a repetitive pointing task was performed to fatigue the shoulder muscles. To assess central versus peripheral effects of fatigue on the distal limb, the right shoulder was fatigued and proprioceptive acuity of the left and right hands were tested. Results showed that there was a significant decrease in the accuracy of proprioceptive estimates for both hands after the right shoulder was fatigued, with no change in the precision of proprioceptive estimates. A control experiment (N = 8), in which participants completed the proprioceptive estimation task before and after a period of quiet sitting, ruled out the possibility that the bilateral changes in proprioceptive accuracy were due to a practice effect. Together, these results indicate that shoulder muscle fatigue decreases proprioceptive acuity in both hands, suggesting that central fatigue mechanisms are primarily responsible for changes in afferent feedback processing of the distal upper limb.     

Changes in the dynamics of tremor during goal-directed pointing.

For successful performance of activities requiring a fine level of manipulative control and dexterity, precise control over the intrinsic oscillations (tremor) in each segment is essential. However, the question of how individuals control (minimize) their tremor during precise postural movements remains unresolved. The aim of this study was to investigate the changes observed in limb tremor during goal-directed postural pointing tasks. Seven subjects attempted to minimize limb tremor during a pointing task whereby progressively greater levels of accuracy were required. Subjects held a small lightweight laser pointer in their extended hand during all tasks, the goal being to maintain the laser emission within a specified target area. Frequency analysis showed that the tremor profile for the hand and index finger was characterized by two prominent frequency peaks, located between 2-4 and 8-12 Hz. When the accuracy requirement of the task increased, there was a significant increase in the amplitude of the 8-12 Hz peak for all segments. Analysis of the time series component of tremor revealed a similar trend with the root mean square (RMS) and approximate entropy (ApEn) of the finger tremor increasing as the accuracy requirement increased. This same pattern was not seen for hand tremor where a small but systematic decrease in both the tremor RMS and ApEn was observed. Overall, it would appear that subjects attempted to reduce tremor at the finger by exerting greater control over the hand (as evidenced by decreased tremor output and increased regularity in the tremor signal). Unfortunately, the consequence of this strategy was that the tremor in the distal effector actually increased. Changes in the tremor output observed as a result of defining an explicit external goal probably resulted from the enhanced visual information provided by the laser emission. However, it would appear that subjects were not able to utilize this feedback effectively to reduce their tremor during the targeting tasks.     

Risk Versus Effort in the Assessment of Motor Fatigue

The choice of probability leffort (COPE) devices require fatigued subjects to choose between risk and effort. In a first experiment, where fatigue was induced by an intense or by a prolonged motor task and where the required effort was perceptual, the fatigue did not generalize to the test mode. A second experiment used motor fatigue of the arm or leg, and tested with arm muscle effort, showing that subjects fatigued with either limb chose riskier alternatives in order to avoid the effort. The data correlated with self-rated fatigue, and closely paralleled earlier work using perceptual fatigue and perceptual effort.     

Directional bias of limb tremor prior to voluntary movement

Taking a cue from recent discoveries of directional bias in microsaccades during visual fixation, we investigated directional bias in tremor during manual pointing. Subjects memorized and then performed patterns of alternating postures and voluntary movements. The directions of the tiny movements occurring during periods of intended stillness were predictive of subsequent target-directed movements such that in the horizontal axis, relative to baseline, the frequency of tremor decreased and the amplitude of tremor increased before horizontal movements, but not before vertical movements. This effect was less pronounced in the finger than in the arm, forearm, and hand. Possible explanations of the effect are based on eye-limb coupling, decreasing stiffness in the axis of forthcoming movement, and release of inhibition. The discovery of directionally specific preparatory activity suggests that the simple task of holding still before moving may provide a new window into the processes that allow for the translation of intentions into actions.     

Sampling frequency and the study of eye-hand coordination in aiming

This study synchronized sampling of point of gaze (PG) and hand movements in a fast aiming task, using a 60- and a 120-Hz sampling frequency. The subjects moved eyes, head, hand, and trunk freely. For limb kinematics, a significant difference between sampling conditions was only found for the number of accelerations in the profile following peak velocity of the hand. For PG movements, no differences were found for initiation time, saccade angle, fixation duration, and overall number of saccades. However, significant differences were observed for saccade duration. Previously, an invariant feature was found for the ratio of PG and hand response times (50%). For both sampling frequencies, a significant correlation and, thus, temporal coupling was found between PG response time and time to peak acceleration for the hand. Depending on the measures required, a 60-Hz sampling of PG and hand movements may provide as meaningful results as a 120-Hz sampling.     

Electromyographic traces of motor unit synchronization of fatigued lower limb muscles during gait

BackgroundThe study of the signal in the frequency domain has shown to be a good tool to identify muscular fatigue. Previous research has shown that the low frequency band and 40 Hz frequency band increase their relative intensity with the onset of fatigue. These findings were obtained in rectus femoris, but the behaviours of other muscles of the lower limb are unknown. In this article we explored the changes in the low frequency and 40 Hz frequency band of lower limb muscles with respect to fatigue.MethodsThirty healthy subjects were recruited to analyse the electromyography (EMG) of biceps femoris, tibialis anterior and gastrocnemius medialis and lateralis of both legs during gait. Four two-minutes walks at a self-selected speed were recorded, the first two walks with a normal muscular function and the last two walks after a fatigue protocol. All the signals were decomposed using wavelet transformations. The signals were normalized in time and spectral intensities normalized to the sum of intensities in the frequency domain. Two frequency bands were studied in each walk: the 40-Hz (34–53 Hz) and the low frequency (< 25 Hz) bands. A ratio of the spectral intensities of those frequency bands at each walk was obtained by dividing the 40-Hz frequency band spectral intensity by the low frequency band spectral intensity. Statistical parametric mapping techniques were used to compare the ratios of the prefatigue walks against the postfatigue walks.ResultsThe results of the Statistical Non-Parametric Mapping (SnPM) analysis of all muscles depict a higher relative spectral intensity in the low frequency band in the comparison of fatigue versus prefatigue recordings except for the right gastrocnemius lateralis. The critical thresholds F* were exceeded by multiple suprathreshold clusters with p values <0.05, showing that the low frequency band increased its relative spectral intensity in the case of fatigue.ConclusionThe obtained results suggest that the low frequency band increases its relative spectral intensity in all the studied muscles when fatigue onsets. This increase in relative spectral intensity may be linked to an increase in motor unit synchronization promoted by the central nervous system to ensure good motor control.     

Effect of Hand Posture on the Temporal and Kinematic Properties of Pointing and Drawing Movements Executed by Healthy Subjects and by a Patient With Primary Writing Tremor

Healthy individuals (n = 6) and a patient with "pure" primary writing tremor executed pointing and drawing movements while adopting different hand postures. The control subjects and the patient exhibited similar kinematics for most conditions. The patient displayed a severe right hand 4- to 6-Hz tremor and prolonged movements only when drawing with his normal hand posture. His tremor was manifested after a ready cue, in anticipation of a go command. The premovement tremor was abolished when the authors simply eliminated the ready cue and instructed the patient to relax and not think about drawing until he heard the go cue. Thus, the patient's writing tremor depended not only upon the writing or drawing act but also upon the hand position adopted and the intent to write, even in the absence of movement. The present results suggest that (a) similar high-level control mechanisms exist for pointing and drawing in healthy subjects and (b) the patient's deficits are compatible with a higher motor defect in central nervous system structures involved in the control of pointing and drawing movements.     

Adaptation to visual displacement with active and passive limb movements: effect of movement frequency and predictability of movement

Three experiments were performed to evaluate the influence of active and passive limb movements on adaptation to visual displacement. Over a wide frequency range (0·5-1·25 Hz) with constant amplitude, 30°, significant adaptation was achieved with active and passive movements. When arm movement frequency was constant at 1·0 Hz but amplitude of movement was varied, less adaptation was achieved for both active and passive movements than when amplitude was held constant. Even at a frequency above that of most naturally occurring limb movements, 1·67 Hz, and with variable amplitude motion, significant adaptation was achieved with active and passive limb movements. These findings emphasize the importance of visual-proprioceptive discordances for adaptation to visual displacement when only sight of the hand is permitted. Significant differences did not appear between the active and passive movement conditions in any of the experiments.     

Behavioral thresholds for tones during infancy

An adaptive up-down tracking procedure was used in combination with a visually reinforced head turn response to examine auditory sensitivity for 500, 2000, and 8000-Hz tone bursts in infants 6 to 18 months of age. Six- and 10-month-old infants were tested with headphone presentation of stimuli, while 10-, 14, and 18-month-olds were tested in sound field. Infant threshold estimates for both headphone and sound field were within 15 dB of adult comparisons for all frequencies and age groups. Six-month-olds were significantly less sensitive to the 8000-Hz tone than to either of the lower frequency stimuli, but older infants demonstrated approximately equal sensitivity for all three frequencies tested.     

Visual tracking of active and passive movements of the hand

Two experiments were performed to evaluate the influence of movement frequency and predictability on visual tracking of the actively and the passively moved hand. Four measures of tracking precision were employed: (a) saccades/cycle, (b) percent of pursuit movement, (c) eye amplitude/arm amplitude, (d) asynchrony of eye and hand at reversal. Active and passive limb movements were tracked with nearly identical accuracy and were always vastly superior to tracking an external visual target undergoing comparable motion. Proprioceptive information about target position appears to provide velocity and position information about target location. Its presence permits the development of central eye-movement programmes that move the eyes in patterns that approximate but do not exactly match, temporally or spatially, the motion of the hand.     

Modulation of tremor amplitude during deep brain stimulation at different frequencies

Rest tremor was quantified in the index finger tip of 16 patients with Parkinson's disease (PD) receiving deep brain stimulation (DBS) of the ventro-intermediate nucleus (Vim) of the thalamus, the subthalamic nucleus (STN), or the internal part of the globus pallidus (GPi) while being off L-dopa for 12h. Clinically, without DBS, tremor amplitude varied from absent to high. Tremor was recorded continuously for about 5 min under three conditions of DBS repeated twice, namely, effective frequency (E), ineffective frequency (I), and no DBS (O). No changes in tremor were observed across conditions in subjects with little or no tremor. However, in subjects with moderate to large amplitude tremor, DBS decreased tremor amplitude to near normal values within a few seconds. Generally, transitions were progressive and occurred with a varying time delay. Occasionally, tremor escaped from control regardless of the stimulation condition considered. In some cases tremor amplitude in one condition appeared to depend on the preceding condition. Finally, the results were reproducible on two consecutive days. We conclude that tremor control with DBS follows specific dynamical rules, which must be compatible with the hypotheses proposed regarding the underlying mechanisms of DBS.     

Muscle force compensation among synergistic muscles after fatigue of a single muscle

PurposeThe aim of this study was to examine control strategies among synergistic muscles after fatigue of a single muscle. It was hypothesized that the compensating mechanism is specific for each fatigued muscle.MethodsThe soleus (SOL), gastrocnemius lateralis (GL) and medialis (GM) were fatigued in separate sessions on different days. In each experiment, subjects (n = 11) performed maximal voluntary contractions prior to and after fatiguing a single muscle (SOL, GL or GM) while the voluntary muscle activity and torque were measured. Additionally, the maximal single twitch torque of the plantarflexors and the maximal spinal reflex activity (H-reflex) of the SOL, GL and GM were determined. Fatigue was evoked using neuromuscular stimulation.ResultsFollowing fatigue the single twitch torque decreased by −20.1%, −19.5%, and −23.0% when the SOL, GL, or GM, have been fatigued. The maximal voluntary torque did not decrease in any session but the synergistic voluntary muscle activity increased significantly. Moreover, we found no alterations in spinal reflex activity.ConclusionsIt is concluded that synergistic muscles compensate each other. Furthermore, it seems that self-compensating mechanism of the fatigued muscles occurred additionally. The force compensation does not depend on the function of the fatigued muscle.     

Combined recruitment of two fixation chains during cyclic movements of one arm

Voluntary adduction-abduction movements of one arm in the horizontal plane discharge a reaction torque which would rotate the trunk in the direction opposite to arm acceleration. Rotation is impeded by muscular fixation chains that exert forces counterbalancing the reaction torque. We examined how two different fixation chains cooperate in stabilising the trunk during the above movements. Standing subjects (n = 6), with shoulders ante-flexed, performed cyclic adductions-abductions of the right arm (1.5 Hz) while grasping a fixed handle with the left hand. In this set-up, reaction torque is contrasted by: (1) a leg fixation chain, exerting on the ground a torque around the vertical axis (Tz), recorded by a force platform; and (2) a left arm fixation chain, exerting on the handle a force in the medial-lateral direction (Fh), recorded by a load cell. Subjects performed 20 trials (15 cycles each). It was found that Tz and Fh underwent sinusoidal changes at the same frequency as arm movements and contributed in counteracting the reaction torque. The intensity of the handle grip, monitored by EMG activity in the left Flexor Digitorum Superficialis, was changed from trial to trial and kept constant during each trial. As grip strength increased, Fh amplitude increased linearly while amplitude of Tz linearly decreased. In conclusion, voluntarily strengthening the handle grip progressively deviates the postural actions from the legs to the left arm.     

The influence of motor system degradation on the control of handwriting movements: a dynamical systems analysis

The complex dynamics of the human hand/arm system need to be precisely controlled to produce fine movements such as those found in handwriting. This study employs dynamical systems analysis techniques to further understand how this system is controlled when it is functioning well and when it is compromised through motor function degradation (e.g. from tremor). Seven people with and 16 people without multiple sclerosis (MS) participated in this study. Tremor was assessed using spirography with participants being separated into "tremor" (6 people with and 1 person without MS; 2 male, 5 female; age range 40-68) and control (1 person with and 15 people without MS; 5 male, 11 female, age range 18-59) groups. Participants wrote the pseudo-word "lanordam" six times on a digitizer, in a quiet as well as a noisy, mildly stressful environment. Velocity profiles of the pen tip for the best four trials were concatenated and analyzed to determine their dimensionality (a measure of the number of control variables) and Lyapunov exponents (a measure of predictability). Results indicate that the velocity profiles for people with tremor were lower dimensional and had less predictable dynamics than for controls, with no effect of sound condition. Interpreted in the context of related research, it was speculated that the lower dimensionality reflected the loss of control of variables related to the minimization of movement variability, resulting in less predictable movements.     

Personality and perfectionism in chronic fatigue syndrome: A closer look

Objective: To test the hypothesis that people with chronic fatigue syndrome (CFS) would differ significantly from a healthy control group on measures of general personality and perfectionism, specifically on measures of neuroticism and unhealthy perfectionism. Method: A total of 27 female CFS outpatients and 30 female healthy controls completed questionnaires, including the NEO Personality Inventory-Revised, the Multi-dimensional Perfectionism Scale and measures of anxiety and depression. Results: The CFS group was significantly more fatigued, anxious and depressed than healthy controls. They scored significantly higher on neuroticism and unhealthy perfectionism. Healthy and unhealthy perfectionism were positively correlated in the CFS group, but not in the control group. Conclusion: The present study confirms the link between neuroticism and fatigue and finds a link between unhealthy perfectionism and fatigue. A ‘healthy trait’, such as healthy perfectionism, when coupled with evaluative concerns is not necessarily healthy in a fatigued population. Researchers and clinicians should note the context in which apparently benign traits are expressed, and how they interact with other traits.     

Posture-movement responses to stance perturbations and upper limb fatigue during a repetitive pointing task

Localized muscle fatigue and postural perturbation have separately been shown to alter whole-body movement but little is known about how humans respond when subjected to both factors combined. Here we sought to quantify the kinematics of postural control and repetitive upper limb movement during standing surface perturbations and in the presence of fatigue. Subjects stood on a motion-based platform and repetitively reached between two shoulder-height targets until noticeably fatigued (rating of perceived exertion = 8/10). Every minute, subjects experienced a posterior and an anterior platform translation while reaching to the distal target. Outcomes were compared prior to and with fatigue (first vs. final minute data). When fatigued, regardless of the perturbation condition, subjects decreased their shoulder abduction and increased contralateral trunk flexion, a strategy that may relieve the load on the fatiguing upper limb musculature. During perturbations, kinematic adaptations emerged across the trunk and arm to preserve task performance. In contrast to our expectation, the kinematic response to the perturbations did not alter in the presence of fatigue. Kinematic adaptations in response to the perturbation predominantly occurred in the direction of the reach whereas fatigue adaptations occurred orthogonal to the reach. These findings suggest that during repetitive reaching, fatigue and postural perturbation compensations organize so as to minimize interaction with each other and preserve the global task characteristics of endpoint motion.     

Vibrotactile temporal summation for threshold and suprathreshold levels of stimulation

Threshold measurement and matching procedures were used to determine the amount of temporal summation at threshold and suprathreshold levels of vibrotactile stimulation on the thenar eminence of the hand. The frequency of the stimulus was 25, 40, 80, or 200 Hz. At 25 Hz, temporal summation was absent at all intensity levels. Considerable amounts of temporal summation were observed for 80- and 200-Hz stimuli, although the effects decreased as a function of intensity. At 40 Hz, no temporal summation was observed at threshold, but above threshold, a small amount was observed at all intensity levels. The results support a duplex model of mechanoreception in which one of two receptor systems exhibits temporal summation.     

The Treatment of Self-stimulation of a Serverely Mentally Retarded and Deaf-blind Client by Brief Physical Interruption — A Case Report

Abstract

The subject's self-stimulation consisted of high frequent shouting and varied finger, hand and arm stereotypies. The target self-simulatory behavior was shouting.

The first part of the treatment was designed to strengthen alternatives to shouting by using hand/arm stereotypies as reinforcers. The subject could self-stimulate by use of hands and arms when he did not shout. Contingent on shouting, the hand/arm stereotypies were briefly interrupted. This treatment did not reduce the frequency of shouting. The brief physical interruptions, however, seemed to reduce the hand and arm stereotypies.

In the second part of the treatment, the treatment design included brief interruptions of the target behavior. Contingent on shouting, the shouting behavior and the hand and arm stereotypies were briefly interrupted. The frequency of shouting was considerably reduced. In this treatment, the reduction of stereotypies seemed to be related to brief physical interruptions of the self-stimulatory behaviors.     

The effects of trunk extensor and abdominal muscle fatigue on postural control and trunk proprioception in young,healthy individuals

The purpose of this study was to induce both trunk extensor and abdominal muscle fatigue, on separate occasions, and compare their effects on standing postural control and trunk proprioception, as well as look at the effects of a recovery period on these outcome measures. A total of 20 individuals participated, with 10 (5 males and 5 females) completing either a standing postural control or lumbar axial repositioning protocol. Participants completed their randomly assigned protocol on two occasions, separated by at least 4 days, with either their trunk extensor or abdominal muscles being fatigued on either day. Postural control centre of pressure variables and trunk proprioception errors were compared pre- and post-fatigue. Results showed that both trunk extensor and abdominal muscle fatigue significantly degraded standing postural control immediately post-fatigue, with recovery occurring within 2 min post-fatigue. In general, these degradative effects on postural control appeared to be greater when the trunk extensor muscles were fatigued compared to the abdominal muscles. No statistically significant changes in trunk proprioception were found after either fatigue protocol. The present findings demonstrate our body’s ability to quickly adapt and reweight somatosensory information to maintain postural control and trunk proprioception, as well as illustrate the importance of considering the abdominal muscles, along with the trunk extensor muscles, when considering the impact of fatigue on trunk movement and postural control.