After lateral gastrocnemius-soleus (LGS) nerve section in intact cats, a rapid locomotor compensation involving synergistic muscles occurs and is accompanied by spinal reflex changes. Only some of these changes are maintained after acute spinalization, indicating the involvement of descending pathways in functional recovery. Here, we address whether the development of these adaptive changes is dependent on descending pathways. The left LGS nerve was cut in three chronic spinal cats. Combined kinematics and electromyographic (EMG) recordings were obtained before and for 8 d after the neurectomy. An increased yield at the ankle was present early after neurectomy and, as in nonspinal cats, was gradually reduced within 8 d. Compensation involved transient changes in step cycle structure and a longer term increase in postcontact medial gastrocnemius (MG) EMG activity. Precontact MG EMG only increased in one of three cats. In a terminal experiment, the influence of group I afferents from MG and LGS on stance duration was measured in two cats.LGS effectiveness at increasing stance duration was largely decreased in both cats. MG effectiveness was only slightly changed: increased in one cat and decreased in another. In cat 3, the plantaris nerve was cut after LGS recovery. The recovery time courses from both neurectomies were similar ( p Ͼ 0.8), suggesting that this spinal compensation is likely a generalizable adaptive strategy. From a functional perspective, the spinal cord therefore must be considered capable of adaptive locomotor plasticity after motor nerve lesions. This finding is of prime importance to the understanding of functional plasticity after spinal injury.
Background: Previous studies have assessed the effects of perturbation training on balance after stroke. However, the perturbations were either applied while standing or were small in amplitude during gait, which is not representative of the most common fall conditions. The perturbations were also combined with other challenges such as progressive increases in treadmill speed. Objective: To determine the benefit of treadmill training with intense and unpredictable perturbations compared to treadmill walking-only training for dynamic balance and gait post-stroke. Methods: Twenty-one individuals post-stroke with reduced dynamic balance abilities, with or without a history of fall and ability to walk on a treadmill without external support or a walking aid for at least 1 minute were allocated to either an unpredictable gait perturbation (Perturb) group or a walking-only (NonPerturb) group through covariate adaptive randomization. Nine training sessions were conducted over three weeks. NonPerturb participants only walked on the treadmill but were offered perturbation training after the control intervention. Pre- and post-training evaluations included balance and gait abilities, maximal knee strength, balance confidence and community integration. Six-week phone follow-ups were conducted for balance confidence and community integration. Satisfaction with perturbation training was also assessed. Results: With no baseline differences between groups (p>0.075), perturbation training yielded large improvements in most variables in the Perturb (p<0.05, Effect Size: ES>.46) group (n=10) and the NonPerturb (p≤.089, ES>.45) group (n=7 post-crossing), except for maximal strength (p>.23) in the NonPerturb group. Walking-only training in the NonPerturb group (n=8, pre-crossing) mostly had no effect (p>.292, ES<.26), except on balance confidence (p=.063, ES=.46). The effects of the gait training were still present on balance confidence and community integration at follow-up. Satisfaction with the training program was high. Conclusion: Intense and unpredictable gait perturbations have the potential to be an efficient component of training to improve balance abilities and community integration in individuals with chronic stroke. Retrospective registration: ClinicalTrials.gov. March 18th, 2020. Identifier: NCT04314830 (https://clinicaltrials.gov/ct2/show/NCT04314830?term=NCT04314830&draw=2&rank=1).
BACKGROUND: Work-related musculoskeletal disorders (WRMSDs) remain a challenge despite research aimed at improving their prevention and treatment. Extrinsic feedback has been suggested for the prevention and rehabilitation of WRMSDs to improve sensorimotor control, and ultimately to reduce pain and disability. However, there are few systematic reviews on the effectiveness of extrinsic feedback for WRMSDs. OBJECTIVE: To perform a systematic review investigating the effect of extrinsic feedback for the prevention and rehabilitation of WRMSDs. METHODS: Five databases (CINAHL, Embase, Ergonomics Abstract, PsycInfo, PubMed) were searched. Studies of various designs assessing the effects of extrinsic feedback during work tasks on three outcomes (function, symptoms, sensorimotor control) in the context of prevention and rehabilitation of WRMSDs were included. RESULTS: Forty-nine studies were included, for a total sample of 3387 participants (including 925 injured) who performed work-related tasks in the workplace (27 studies) or in controlled environments (22 studies). The use of extrinsic feedback was shown to be effective in controlled environments for short-term prevention of functional limitations and sensorimotor alterations (very limited to moderate evidence) and for improving, in injured participants, function, symptoms and sensorimotor control (moderate evidence). In the workplace, it was shown to be effective for short-term prevention of functional limitations (limited evidence). There was conflicting evidence regarding its effect for WRMSD rehabilitation in the workplace. CONCLUSION: Extrinsic feedback is an interesting complementary tool for the prevention and rehabilitation of WRMSDs in controlled environments. More evidence is needed regarding its effect for the prevention and rehabilitation of WRMSDs in the workplace.
Following a 30-minute exposure to an unusual motor strategy called “Torso Rotation” (TR), the signs and symptoms of motion sickness appear along with perceptual illusions during movement, gaze and postural instability, and a significantly reduced vestibulo-ocular response (VOR) gain. With repeated exposure to TR, the motion sickness disappears and gaze instability seems to be reduced. Is this apparent improvement in gaze stability associated with a reduction of the transient change in VOR gain? Motion sickness (subjective questionnaire) and VOR gain (passive step rotations in darkness) were measured before and repeatedly after TR on 7 consecutive days. Despite a complete loss of symptoms in 3 to 4 days, the transient, daily change in VOR gain remained unaffected. Furthermore, there was no increase in the use of compensatory saccades. It is concluded that adaptation to TR-induced motion sickness is not the result of a change in VOR's sensitivity to TR.
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