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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Several investigations have demonstrated that localized muscle fatigue (LMF) causes an increase in postural sway measures during quiet stance. Since many falls are likely the result of a postural perturbation, this study investigated the effects of LMF on balance recovery from sagittal plane postural perturbations. Thirty-two participants (16 young, 16 older) were tested. Postural perturbations were administered with ballistic pendulums before and after exercises to fatigue the lumbar extensors and plantar flexors. Measures of balance recovery were based on the center of pressure (COP) and center of mass (COM) trajectories and the maximum perturbation that could be withstood without stepping. A covariate analysis that included initial conditions at the time of the perturbation was also performed. The results demonstrated changes in the COM trajectory that were consistent with an LMF-induced decrement in the ability to recover from the perturbations without stepping. Interpretation of the COP trajectory was presented in light of the COM and indicated a modified postural control strategy following LMF.
Gait Posture 2009 Jun
PMID:Effects of localized muscle fatigue on recovery from a postural perturbation without stepping. 1916 59

The aim of this study was to compare the effects of acute muscle fatigue of the ankle and knee musculature on postural control by immediate measures after performing fatiguing tasks (POST condition). One group of subjects (n = 8) performed a fatiguing task by voluntary contractions of the triceps surae (group TRI) and the other (n = 9) performed a fatiguing task by voluntary contractions of the quadriceps femoris (group QUA). Each muscle group was exercised until the loss of maximal voluntary contraction torque reached 50% (isokinetic dynamometer). Posture was assessed by measuring the centre of foot pressure (COP) with a force platform during a test of unipedal quiet standing posture with eyes closed. Initially (in PRE condition), the mean COP velocity was not significantly different between group TRI and group QUA. In POST condition, the mean COP velocity increased more in group QUA than in group TRI. The postural control was more impaired by knee muscle fatigue than by ankle muscle fatigue.
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PMID:Effects of knee and ankle muscle fatigue on postural control in the unipedal stance. 1928 26

The purpose was to examine the effects of localized muscle and whole-body fatigue on indices of single-leg balance between healthy young men (n=10) and women (n=10). Subjects performed 10, 10-s single-leg balance trials on a force platform prior to performing each of three conditions (local, whole-body, and control), in a randomized order, on separate days. Localized muscle and whole-body fatigue consisted of single-leg, weight-bearing heel raises on an inclined platform, and exercise on a rowing ergometer, respectively, to the point of volitional failure. During the control condition, subjects remained in a seated position for 5 min. Immediately following each condition, five, 10-s, single-leg balance trials were performed. The localized muscle and whole-body fatigue protocols produced significant (p<0.05) increases in medial/lateral (M/L) and total sway (TS). Men experienced a greater (p<0.05) increase in anterior/posterior (A/P) sway following the localized muscle, than whole-body, fatigue protocol, whereas A/P sway increased more following the whole-body, than localized muscle, fatigue protocol for the women. Total sway variability increased significantly (p<0.05) more following the localized muscle fatigue protocol than the whole-body fatigue protocol for both men and women. The major findings of the present investigation demonstrated that measures of postural control, namely M/L, A/P sway and total sway, were adversely affected following fatiguing exercise, with differential effects between men and women.
Gait Posture 2009 Jul
PMID:The effects of localized muscle and whole-body fatigue on single-leg balance between healthy men and women. 1932 99

Military personnel are often required to carry all of their personal supplies and equipment for long distances during both training and combat situations, creating many biomechanical and postural challenges for these individuals. In addition to other problems such as generalized fatigue and the development of stress fractures, significant external loads may also affect a soldier's postural sway. The purpose of this study was to assess changes in postural sway as a consequence of wearing a military backpack in females. Forty-three female subjects between the ages of 18 and 25 volunteered to participate. There were two conditions: unloaded and while wearing an 18.1 kg military backpack. Each subject stood with two feet on a force platform for 30s under both conditions while center of pressure (COP) data were collected. COP path length increased 64%, medial-lateral excursion increased 131%, anterior-posterior excursion increased 54%, and COP area increased 229% with addition of the backpack (p<0.0001 for all of these measures). These data show that wearing 18.1 kg of external weight in a military backpack increases the postural sway of females, which may in turn increase the likelihood of falls and injury.
Gait Posture 2009 Jul
PMID:Changes in postural sway as a consequence of wearing a military backpack. 1940 10

Although previous studies have investigated the effects of bilateral muscle fatigue on bipedal postural control, whether and how the central nervous system could adapt to unilateral muscle fatigue for controlling bipedal stance remains to be investigated. The purpose of the present experiment was designed to address this issue by assessing the effect of unilateral muscle fatigue induced on the hip's abductors of the dominant leg on bipedal standing. Twenty-four young healthy adults stood barefoot, feet together, with their eyes closed and were asked to sway as little as possible. The experimental group (n=12) executed this postural task in two conditions, pre- and post-fatigue. In the post-fatigue condition, the measurements were performed immediately after a designated fatiguing exercise for the hip abductors of their dominant leg. For the control group (n=12), this fatiguing exercise was replaced by a laying rest period corresponding to the fatiguing exercise. The distribution of the body weight and plantar centre of foot pressure (CoP) displacements from the non-fatigued and fatigued leg were recorded along the mediolateral and anteroposterior axes using a plantar pressure data acquisition system. Results of the experimental group showed that unilateral muscle fatigue induced on the hip's abductors of the dominant leg had different effects on the plantar CoP displacements (1) under the non-fatigued and fatigued legs, yielding larger displacements under the non-fatigued leg only, and (2) in the anteroposterior and mediolateral axes, yielding larger displacements along the mediolateral axis only. These observations could not be accounted for by any asymmetrical distribution of the body weight on both legs which were similar for both pre- and post-fatigue conditions. The observed postural responses could be viewed as an adaptive process to cope with an unilateral alteration in the hip neuromuscular function induced by the fatiguing exercise for controlling bipedal stance. The increase in CoP displacements observed under the non-fatigued leg in the fatigue condition could reflect enhanced exploratory "testing of the ground" movements with sensors of the non-fatigued leg's feet, providing supplementary somatosensory inputs to the central nervous system to preserve/facilitate postural control in condition of altered neuromuscular function of the dominant leg's hip abductors induced by the fatiguing exercise.
Gait Posture 2009 Jul
PMID:Postural adaptation to unilateral hip muscle fatigue during human bipedal standing. 1940 11

The aim of this study was to investigate how and why age and localized muscle fatigue affect postural control using model-based simulations. A balance control model, based on an optimal control strategy, was used to simulate trials of quiet upright stance both pre-fatigue and following induced ankle plantarflexor fatigue. Empirical data were obtained from an earlier study that included both younger and older participants. Effects of age and ankle fatigue were determined from center-of-pressure (COP) measures and fitted model parameters. Though some discrepancies existed, the simulated effects of age and ankle fatigue were consistent with experimental findings in terms of trends in COP-based measures with age and ankle fatigue. Changes in both COP-based measures and model parameters were used to infer potential underlying causal mechanisms for the observed effects of age and ankle fatigue. For example, the model-based simulations indicated that sensory delay time increased with age and ankle fatigue by 31.1% and 2.9%, respectively, suggesting a potentially important role for such delay in postural control and fall risks.
Gait Posture 2009 Nov
PMID:Model-based assessments of the effects of age and ankle fatigue on the control of upright posture in humans. 1972 89

To assess the effectiveness of a tongue-placed electrotactile biofeedback system to improve ankle force sense following plantar-flexor muscles fatigue, 11 young healthy adults were asked to perform an isometric contra-lateral force ankle-matching task in two experimental conditions of No fatigue and Fatigue of the plantar-flexor muscles and two conditions of No biofeedback and Biofeedback. The underlying principle of the biofeedback consisted of supplying subjects with supplementary information about the force developed by the plantar-flexor muscles through electrical stimulation of the tongue. Measures of the overall accuracy and the variability of the force ankle-matching performances were determined using the absolute error and the variable error, respectively. Results showed that (1) the Fatigue condition yielded increased absolute and variable errors relative to the No fatigue condition in the No biofeedback condition, whereas (2) no significant difference between the two No fatigue and Fatigue conditions was observed in the Biofeedback condition. These results suggest that subjects were able to integrate augmented sensory information delivered through electrotactile stimulation of the tongue to suppress the adverse effect of plantar-flexor muscles fatigue on ankle force sense.
Gait Posture 2009 Nov
PMID:Effectiveness of a tongue-placed electrotactile biofeedback to improve ankle force sense following plantar-flexor muscles fatigue. 1972 92

This study compared the gait characteristics of individuals walking in heat while wearing firefighting equipment in fatigued and non-fatigued states. Nineteen subjects performed a 50-min treadmill protocol in a heated room while gait patterns were recorded using a digital video camcorder. Forty gait cycles were analyzed near the beginning (9 min) and at the end (39-49 min) of exercise. Spatio-temporal gait variables including step frequency, step length, swing time, stance time, cycle time and double-support time were determined. Gait variability was quantified by the standard deviation (SD) and coefficient of variation (CV) of each variable. Left-right symmetry was calculated using the symmetry index (SI) and symmetry angle (SA). Paired t-tests (alpha = 0.05) were performed to identify difference between the beginning and the end of the protocol for each measured variable. Spatio-temporal gait characteristics did not differ between the beginning and the end of exercise. Gait variability of the double-support time increased at the end as measured by both SD (P = 0.037) and CV (P = 0.030) but no change was observed for other variables. Left-right symmetry measured using either SI or SA did not differ between sessions. In summary, spatio-temporal gait characteristics and symmetry while wearing firefighting equipment are insensitive to physiological fatigue. Prolonged walking in heat while wearing firefighting equipment may increase gait variability and therefore the likelihood of a fall. Future studies are needed to confirm the potential relationship between fatigue and gait variability and to investigate the possible influence of individual variation.
Gait Posture 2010 Feb
PMID:Effect of fatigue and hypohydration on gait characteristics during treadmill exercise in the heat while wearing firefighter thermal protective clothing. 1996 97

There is growing evidence that aging and muscle fatigue result in impaired postural reflexes in humans. Therefore, the objective of this study was to examine the effects of ankle fatigue on functional reflex activity (FRA) during gait perturbations in young and elderly men. Twenty-eight young (27.0+/-3.1 years, n=14) and old (67.2+/-3.7 years, n=14) healthy active men participated in this study. Fatigue of the plantarflexors and dorsiflexors was induced by isokinetic contractions. Pre and post-fatigue, subjects were tested for their ability to compensate for decelerating gait perturbations while walking on a treadmill. Latency, FRA of lower extremity muscles and angular velocity of the ankle joint complex were analysed by means of surface electromyography and goniometry. After the fatigue protocol, no significant main and interaction effects were detected for the parameter latency in m. tibialis anterior (TA). For both groups, a significant pre to post-test decrease in FRA in TA (p<.001) was observed coming along with increases in antagonist coactivity (p=.013) and maximal angular velocity of the ankle joint (p=.007). However, no significant groupxtest interactions were found for the three parameters. Ankle fatigue has an impact on the ability to compensate for gait perturbations in young and elderly adults. However, no significant differences in all analysed parameters were detected between young and elderly subjects. These results may imply that age-related deteriorations in the postural control system do not specifically affect the ability to compensate for gait perturbations under fatigued condition.
Gait Posture 2010 May
PMID:Effects of ankle fatigue on functional reflex activity during gait perturbations in young and elderly men. 2043 45

This work aims at testing the influence of peripheral and central fatigue, after maximal oxygen uptake test (Test1) and prolonged (Test2) cycle ergometer exercises, respectively, on sway density curve (SDC) parameters of postural control. Sixteen healthy male subjects were submitted to stabilometric tests, before and after the exercises. The Test1 was started at 12.5W, with 12.5W/min increments and 50rpm cadence until exhaustion. From the respiratory gas exchange signals, the first ventilatory threshold was obtained by the v-slope method. After a minimum of 72h, the subjects performed the Test2 for 60min, at a power output corresponding to 70% of such threshold. Before and just after these exercises, a set of 10 stabilometric trials of 50s was performed, alternating the eyes open and closed conditions, intercalated by a 10s resting period. The resulting signals were used to obtain the SDC. The Test1 caused decrease of the mean of peaks duration in SDC (p<0.05), decreasing the stability level, with small changes in the rates of central nervous system (CNS) and muscular torque controls. Conversely, Test2 increased the mean of time intervals between peaks in SDC (p<0.05), thus decreasing the CNS commands rate with minor changes in the stability level. Visual privation had a greater effect on body sway than these exercises, which were applied to muscles that are not the main actuators in body sway control. Concluding, this study allowed discriminating the effects of exercise intensities on body sway control.
Gait Posture 2010 Jun
PMID:Effects of maximal oxygen uptake test and prolonged cycle ergometer exercise on the quiet standing control. 2054 31


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