62,040 research outputs found
Postural control during quiet standing following cervical muscular fatigue: effects of changes in sensory inputs
The purpose of the present experiment was to investigate the effects of
cervical muscular fatigue on postural control during quiet standing under
different conditions of reliability and/or availability of somatosensory inputs
from the plantar soles and the ankles and visual information. To this aim, 14
young healthy adults were asked to sway as little as possible in three sensory
conditions (No vision, No vision-Foam support and Vision) executed in two
conditions of No fatigue and Fatigue of the scapula elevator muscles. Centre of
foot pressure (CoP) displacements were recorded using a force platform. Results
showed that (1) the cervical muscular fatigue yielded increased CoP
displacements in the absence of vision, (2) this effect was more accentuated
when somatosensation was degraded by standing on a foam surface and (3) the
availability of vision allowed the individuals to suppress this destabilising
effect. On the whole, these findings not only stress the importance of intact
cervical neuromuscular function on postural control during quiet standing, but
also suggest a reweigthing of sensory cues in balance control following
cervical muscular fatigue by increasing the reliance on the somatosensory
inputs from the plantar soles and the ankles and visual information
Can Attention Focus Instructions Reduce the Effects of Fatigue on Balance Control?
Localized muscular fatigue has been identified to have detrimental effects on balance control, an important skill for everyday life. Manipulation of attention focus instructions has been shown to benefit performance of various motor skills including balance and has been found to facilitate endurance during fatiguing tasks. The purpose of this thesis was to determine if the use of attention focus instructions could attenuate the effects of muscular fatigue on balance control. Twenty-four participants performed a balance task (two-legged stance on an unstable platform) before and after a fatigue protocol. Trunk sway, platform excursions, and lower limb muscle activity was measured. Results suggest that use of either internal or external attention focus instructions can reduce the immediate effects of muscular fatigue of the lower limb on balance control as shown through reduced trunk sway and platform excursions. These results have relevance for individuals performing balance tasks in a fatigued state
The influence of stress and muscle fatigue on implicitly and explicitly learned motor skills
According to Beek (2000), disturbing causes at the upper level of action (i.e. stress) and at the lower level of control (i.e. muscular fatigue) might result in different effects on performance when comparing implicit and explicit learning. In the present experiment an errorless/errorfull learning paradigm was used to enable the implicit/explicit acquisition of a dart throwing skill. After a pretest, the errorfull group (N=23) throwed from a progressively decreasing distance (from 317 to 257 cm), while the inverse procedure was used for the errorless group (N=21) (from 157 to 217 cm). One week after the four-day learning period (400 trials) both groups performed a transfer test, a fatigue test and a stress test (all from 237 cm). The fatigue test was preceded by a double Wingate protocol on an arm crank ergometer. At the beginning of the stress test participants were told they could win a significant financial reward in case of a good performance. Retrospective self-report of nervousness was administered under stressed and unstressed conditions. Hitting accuracy of the errorfull group improved from M=5.29 (maximum=15) in the first learning block to M=7.81 in the final learning block, while the errorless group evolved from M=9.67 to M=8.74, which is typical for an errorless/errorfull learning paradigm. In comparison to the scores at the pre-test both groups performed equally (performance increase of 22%) at the transfer test. Performance of both groups decreased at the fatigue test, but this decrease was much less in the explicit group (5%, ns) as compared to the implicit group (18%, p<.005). Stress manipulation resulted in an increase of self-reported nervousness; however stress did not have a differential impact on performance in both groups. Our results of the fatigue test confirmed the hypothesis of robustness of explicit motor learning to physiological fatigue, meaning that success depends on the personâs ability to circumvent the (temporary) impairment induced by muscular fatigue, and thus develop alternative strategies based upon explicit knowledge. The contradiction with the findings of Poolton et al. (2006) may be due to task specificity and the sort of fatigue induced (local vs. global), which calls for further research on this topic. Our results of the stress test do not show the superiority of implicit or explicit learning when performing under stress
Fatigue-induced changes of impedance and performance in target tracking
Kinematic variability is caused, in part, by force fluctuations. It has been shown empirically and numerically that the effects of force fluctuations on kinematics can be suppressed by increasing joint impedance. Given that force variability increases with muscular fatigue, we hypothesized that joint impedance would increase with fatigue to retain a prescribed accuracy level. To test this hypothesis, subjects tracked a target by elbow flexion and extension both with fatigued and unfatigued elbow flexor and extensor muscles. Joint impedance was estimated from controlled perturbations to the elbow. Contrary to the hypothesis, elbow impedance decreased, whereas performance, expressed as the time-on-target, was unaffected by fatigue. Further analysis of the data revealed that subjects changed their control strategy with increasing fatigue. Although their overall kinematic variability increased, task performance was retained by staying closer to the center of the target when fatigued. In conclusion, the present study reveals a limitation of impedance modulation in the control of movement variability
The magnitude of the effect of calf muscles fatigue on postural control during bipedal quiet standing with vision depends on the eye-visual target distance
The purpose of the present experiment was to investigate whether, with
vision, the magnitude of the effect of calf muscles fatigue on postural control
during bipedal quiet standing depends on the eye-visual target distance. Twelve
young university students were asked to stand upright as immobile as possible
in three visual conditions (No vision, Vision 1m and Vision 4m) executed in two
conditions of No fatigue and Fatigue of the calf muscles. Centre of foot
pressure displacements were recorded using a force platform. Similar increased
variances of the centre of foot pressure displacements were observed in the
fatigue relative to the No fatigue condition for both the No vision and Vision
4m conditions. Interestingly, in the vision 1m condition, fatigue yielded: (1)
a similar increased variance of the centre of foot pressure displacements to
those observed in the No vision and Vision 4m conditions along the
medio-lateral axis and (2) a weaker destabilising effect relative to the No
vision and Vision 4m conditions along the antero-posterior axis. These results
evidence that the ability to use visual information for postural control during
bipedal quiet standing following calf muscles fatigue is dependent on the
eye-visual target distance. More largely, in the context of the multisensory
control of balance, the present findings suggest that the efficiency of the
sensory reweighting of visual sensory cues as the neuro-muscular constraints
acting on the subject change is critically linked with the quality of the
information the visual system obtains
THE RELATIONSHIP BETWEEN MUSCULOSKELETAL STRENGTH, PHYSIOLOGICAL CHARACTERISTICS, AND KNEE KINESTHESIA FOLLOWING FATIGUING EXERCISE
Fatiguing exercise may result in impaired functional joint stability and increased risk of unintentional injury. While there are several musculoskeletal and physiological characteristics related to fatigue onset, their relationship with proprioceptive changes following fatigue has not been examined. The purpose of this study was to establish the relationship between musculoskeletal and physiological characteristics and changes in proprioception, measured by threshold to detect passive motion (TTDPM), following fatiguing exercise. Twenty, physically active females participated (age: 28.65 ± 5.6 years, height: 165.6 ± 4.3 cm, weight: 61.8 ± 8.0 kg, BMI: 22.5± 2.3 kg/m2, BF: 23.3 ± 5.4%). During Visit 1, subjects completed an exercise history and 24-hour dietary questionnaire, and body composition, TTDPM familiarization, isokinetic knee strength, and maximal oxygen uptake/lactate threshold assessments. During Visit 2, subjects completed TTDPM and isometric knee strength testing prior to and following a fatiguing exercise protocol. Wilcoxon signed rank tests determined TTDPM and isometric knee strength changes from pre- to post- fatigue. Spearmanâs rho correlation coefficients determined the relationship between strength and physiological variables with pre- to post-fatigue changes in TTDPM and with pre-fatigue and post-fatigue TTDPM in extension and flexion (α=0.05). No significant differences were demonstrated from pre-fatigue to post-fatigue TTDPM despite a significant decrease in isometric knee flexion strength (P<0.01) and flexion/extension ratio (P<0.05) following fatigue. No significant correlations were observed between strength or physiological variables and changes in TTDPM from pre- to post-fatigue in extension or flexion. Flexion/extension ratio was significantly correlated with pre-fatigue TTDPM in extension (r=-0.231, P<0.05). Peak oxygen uptake was significantly correlated with pre-fatigue (r=-0.500, P<0.01) and post-fatigue (r=-0.520, P<0.05) TTDPM in extension. No significant relationships were demonstrated between musculoskeletal and physiological characteristics and changes in TTDPM following fatigue. The results suggest that highly trained individuals may have better proprioception, and that the high fitness level of subjects in this investigation may have contributed to absence of TTDPM deficits following fatigue despite reaching a high level of perceptual and physiological fatigue. Future studies should consider various subject populations, other musculoskeletal strength characteristics, and different modalities of proprioception to determine the most important contributions to proprioceptive changes following fatigue
Re-weighting of somatosensory inputs from the foot and the ankle for controlling posture during quiet standing following trunk extensor muscles fatigue
The present study focused on the effects of trunk extensor muscles fatigue on
postural control during quiet standing under different somatosensory conditions
from the foot and the ankle. With this aim, 20 young healthy adults were asked
to stand as immobile as possible in two conditions of No fatigue and Fatigue of
trunk extensor muscles. In Experiment 1 (n = 10), somatosensation from the foot
and the ankle was degraded by standing on a foam surface. In Experiment 2 (n =
10), somatosensation from the foot and ankle was facilitated through the
increased cutaneous feedback at the foot and ankle provided by strips of
athletic tape applied across both ankle joints. The centre of foot pressure
displacements (CoP) were recorded using a force platform. The results showed
that (1) trunk extensor muscles fatigue increased CoP displacements under
normal somatosensatory conditions (Experiment 1 and Experiment 2), (2) this
destabilizing effect was exacerbated when somatosensation from the foot and the
ankle was degraded (Experiment 1), and (3) this destabilizing effect was
mitigated when somatosensation from the foot and the ankle was facilitated
(Experiment 2). Altogether, the present findings evidenced re-weighting of
sensory cues for controlling posture during quiet standing following trunk
extensor muscles fatigue by increasing the reliance on the somatosensory inputs
from the foot and the ankle. This could have implications in clinical and
rehabilitative areas
Tongue-placed tactile biofeedback suppresses the deleterious effects of muscle fatigue on joint position sense at the ankle
Whereas the acuity of the position sense at the ankle can be disturbed by
muscle fatigue, it recently also has been shown to be improved, under normal
ankle neuromuscular state, through the use of an artificial tongue-placed
tactile biofeedback. The underlying principle of this biofeedback consisted of
supplying individuals with supplementary information about the position of
their matching ankle position relative to their reference ankle position
through electrotactile stimulation of the tongue. Within this context, the
purpose of the present experiment was to investigate whether this biofeedback
could mitigate the deleterious effect of muscle fatigue on joint position sense
at the ankle. To address this objective, sixteen young healthy university
students were asked to perform an active ankle-matching task in two conditions
of No-fatigue and Fatigue of the ankle muscles and two conditions of
No-biofeedback and Biofeedback. Measures of the overall accuracy and the
variability of the positioning were determined using the absolute error and the
variable error, respectively. Results showed that the availability of the
biofeedback allowed the subjects to suppress the deleterious effects of muscle
fatigue on joint position sense at the ankle. In the context of sensory
re-weighting process, these findings suggested that the central nervous system
was able to integrate and increase the relative contribution of the artificial
tongue-placed tactile biofeedback to compensate for a proprioceptive
degradation at the ankle
Superpulsed low-level laser therapy protects skeletal muscle of mdx mice against damage, inflammation and morphological changes delaying dystrophy progression.
Aim: To evaluate the effects of preventive treatment with low-level laser therapy (LLLT) on progression of dystrophy in mdx mice. Methods: Ten animals were randomly divided into 2 experimental groups treated with superpulsed LLLT (904 nm, 15 mW, 700 Hz, 1 J) or placebo-LLLT at one point overlying the tibialis anterior muscle (bilaterally) 5 times per week for 14 weeks (from 6th to 20th week of age). Morphological changes, creatine kinase (CK) activity and mRNA gene expression were assessed in animals at 20th week of age. Results: Animals treated with LLLT showed very few morphological changes in skeletal muscle, with less atrophy and fibrosis than animals treated with placebo-LLLT. CK was significantly lower (p = 0.0203) in animals treated with LLLT (864.70 U.lâ1, SEM 226.10) than placebo (1708.00 U.lâ1, SEM 184.60). mRNA gene expression of inflammatory markers was significantly decreased by treatment with LLLT (p<0.05): TNF-α (placebo-control = 0.51 ”g/”l [SEM 0.12], - LLLT = 0.048 ”g/”l [SEM 0.01]), IL-1ÎČ (placebo-control = 2.292 ”g/”l [SEM 0.74], - LLLT = 0.12 ”g/”l [SEM 0.03]), IL-6 (placebo-control = 3.946 ”g/”l [SEM 0.98], - LLLT = 0.854 ”g/”l [SEM 0.33]), IL-10 (placebo-control = 1.116 ”g/”l [SEM 0.22], - LLLT = 0.352 ”g/”l [SEM 0.15]), and COX-2 (placebo-control = 4.984 ”g/”l [SEM 1.18], LLLT = 1.470 ”g/”l [SEM 0.73]). Conclusion: Irradiation of superpulsed LLLT on successive days five times per week for 14 weeks decreased morphological changes, skeletal muscle damage and inflammation in mdx mice. This indicates that LLLT has potential to decrease progression of Duchenne muscular dystrophy
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