The impact of environmental uncertainty on locomotor adaptation remains unclear. Environmental uncertainty could either aid locomotor adaptation by prompting protective control strategies that ...stabilize movements to assist learning or impede adaptation by reducing error sensitivity and fostering hesitance to pursue corrective movements. To explore this, we investigated participants' adaptation to a consistent force field after experiencing environmental uncertainty in the form of unpredictable balance perturbations. We compared the performance of this group (Perturbation) to the adaptive performance of a group that did not experience any unpredictable perturbations (Non-Perturbation). Perturbations were delivered using a cable-driven robotic device applying lateral forces to the pelvis. We assessed whole-body center of mass (COM) trajectory (COM signed deviation), anticipatory postural adjustments (COM lateral offset), and first step width. The Perturbation group exhibited larger disruptions in COM trajectory (greater COM signed deviations) than the Non-Perturbation group when first walking in the force field. While the COM signed deviations of both groups decreased towards baseline values, only the Non-Perturbation group returned to baseline levels. The Perturbation groups COM signed deviations remained higher, indicating they failed to fully adapt to the force field before the end. The Perturbation group also did not adapt their COM lateral offset to counter the predictable effects of the force field as the Non-Perturbation group did, and their first step width increased more slowly. Our findings suggest that exposure to unpredictable perturbations impeded future sensorimotor adaptations to consistent perturbations.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Humans continuously modulate their control strategies during walking based on their ability to anticipate disturbances. However, how people adapt and use motor plans to create stable walking in ...unpredictable environments is not well understood. Our purpose was to investigate how people adapt motor plans when walking in a novel and unpredictable environment. We evaluated the whole-body center of mass (COM) trajectory of participants as they performed repetitions of a discrete goal-directed walking task during which a laterally-directed force field was applied to the COM. The force field was proportional in magnitude to forward walking velocity and randomly directed towards either the right or left each trial. We hypothesized that people would adapt a control strategy to reduce the COM lateral deviations created by the unpredictable force field. In support of our hypothesis, we found that with practice the magnitude of COM lateral deviation was reduced by 28% (force field left) and 44% (force field right). Participants adapted two distinct unilateral strategies, implemented regardless of if the force field was applied to the right or to the left, that collectively created a bilateral resistance to the unpredictable force field. These strategies included an anticipatory postural adjustment to resist against forces applied to the left, and a more lateral first step to resist against forces applied to the right. In addition, during catch trials when the force field was unexpectedly removed, participants exhibited trajectories similar to baseline trials. These findings were consistent with an impedance control strategy that provides a robust resistance to unpredictable perturbations. However, we also found evidence that participants made predictive adaptations in response to their immediate experience that persisted for three trials. Due to the unpredictable nature of the force field, this predictive strategy would sometimes result in greater lateral deviations when the prediction was incorrect. The presence of these competing control strategies may have long term benefits by allowing the nervous system to identify the best overall control strategy to use in a novel environment.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The primary objectives of this study were to evaluate contractile and non-contractile content of lower leg muscles of boys with Duchenne muscular dystrophy (DMD) and determine the relationships ...between non-contractile content and functional abilities.
Lower leg muscles of thirty-two boys with DMD and sixteen age matched unaffected controls were imaged. Non-contractile content, contractile cross sectional area and non-contractile cross sectional area of lower leg muscles (tibialis anterior, extensor digitorum longus, peroneal, medial gastrocnemius and soleus) were assessed by magnetic resonance imaging (MRI). Muscle strength, timed functional tests and the Brooke lower extremity score were also assessed.
Non-contractile content of lower leg muscles (peroneal, medial gastrocnemius, and soleus) was significantly greater than control group (p<0.05). Non-contractile content of lower leg muscles correlated with Brooke score (rs = 0.64-0.84) and 30 feet walk (rs = 0.66-0.80). Dorsiflexor (DF) and plantarflexor (PF) specific torque was significantly different between the groups.
Overall, non-contractile content of the lower leg muscles was greater in DMD than controls. Furthermore, there was an age dependent increase in contractile content in the medial gastrocnemius of boys with DMD. The findings of this study suggest that T1 weighted MR images can be used to monitor disease progression and provide a quantitative estimate of contractile and non-contractile content of tissue in children with DMD.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
OBJECTIVEThe main objective of this study were to examine the effect of disease on strength in two functionally important lower limb muscles over a period of two-years in children with Duchene ...Muscular Dystrophy (DMD).
DESIGNSeventy-Seven DMD children participated in this study. Plantar flexors (PF), knee extensors (KE) strength and performance on timed tests (Six-min walk, 4-stairs, 10m-walk, supine-up) was assessed yearly over two-years. Multivariate normal regression was used to assess changes in strength over time in the DMD group. Spearman correlations were computed to examine relationship between strength and function.
RESULTSNormalized PF and KE strength, showed a significant decrease (p<0.05) over 2 years, with larger declines in KE. At baseline, KE strongly correlated with performance on timed tests. However, PF strength was found to be a stronger predictor of loss in ambulatory function. Modest correlations (r=0.19-0.34) were found between the decline in strength and functional performance over two-years.
CONCLUSIONSThis study describes the loss of lower limb strength in a large cohort of DMD children over two years. The findings support that lower limb strength alone can not account for the decline in performance on functional tests and the role of other contributing factors, such as compensatory strategies, should be considered.
Abstract The purpose of this study was to assess the contractile and non-contractile content in thigh muscles of patients with Duchenne muscular dystrophy (DMD) and determine the relationship with ...functional abilities. Magnetic resonance images of the thigh were acquired in 28 boys with DMD and 10 unaffected boys. Muscle strength, timed functional tests, and the Brookes Lower Extremity scale were also assessed. Non-contractile content in the DMD group was significantly greater than in the control group for six muscles, including rectus femoris, biceps femoris-long head and adductor magnus. Non-contractile content in the total thigh musculature assessed by MRI correlated with the Brookes scale ( rs = 0.75) and supine-up test ( rs = 0.68), as well as other functional measures. An age-related specific torque increase was observed in the control group ( rs = 0.96), but not the DMD ( rs = 0.06). These findings demonstrate that MRI measures of contractile and non-contractile content can provide important information about disease progression in DMD.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
Duchenne muscular dystrophy (DMD) causes progressive pathologic changes to muscle secondary to a cascade of inflammation, lipid deposition, and fibrosis. Clinically, this manifests as progressive ...weakness, functional loss, and premature mortality. Though insult to whole muscle groups is well established, less is known about the relationship between intramuscular pathology and function.
Differences of intramuscular heterogeneity across muscle length were assessed using an ordinal MRI grading scale in lower leg muscles of boys with DMD and correlated to patient's functional status.
Cross sectional T
weighted MRI images with fat suppression were obtained from ambulatory boys with DMD. Six muscles (tibialis anterior, extensor digitorum longus, peroneus, soleus, medial and lateral gastrocnemii) were graded using an ordinal grading scale over 5 slice sections along the lower leg length. The scores from each slice were combined and results were compared to global motor function and age.
Statistically greater differences of involvement were observed at the proximal ends of muscle compared to the midbellies. Multi-slice assessment correlated significantly to age and the Vignos functional scale, whereas single-slice assessment correlated to the Vignos functional scale only. Lastly, differential disease involvement of whole muscle groups and intramuscular heterogeneity were observed amongst similar age subjects.
A multi-slice ordinal MRI grading scale revealed that muscles are not uniformly affected, with more advanced disease visible near the tendons in a primarily ambulatory population with DMD. A geographically comprehensive evaluation of the heterogeneously affected muscle in boys with DMD may more accurately assess disease involvement.
This project consisted of two studies: Study 1 and Study 2. STUDY 1: Background/Objectives: Mobility problems progressively worsen with advancing stages of dementia. Cognitive decline, along with ...age-associated impairments in muscle weakness and balance, present significant challenges in the performance of everyday tasks which contribute to the incidence of falls. The aim of the study was to determine whether spatiotemporal parameters of turning and transitions differ between older adults with dementia compared to those without dementia, using portable inertial sensor technology in the home environment. Participants: Older adults with dementia n=37 (Instrumented Timed-Up-and-Go), 29 (360° turns) and caregivers n=38 (Instrumented Timed-Up-and-Go), n=40 (360° turns). Outcomes Measures: Performance-based tests: Instrumented Timed-Up-and-Go (iTUG), and 360° turns clockwise (CW) and counterclockwise (CCW) and spatiotemporal measures of sit-to-stand, stand-to-sit, and turning were derived from the Ambulatory Parkinson’s Disease Monitoring (APDM) inertial sensors. Results: Participants with dementia took a significantly longer time to complete the sit-to-stand and stand-to-sit transitions compared to the caregivers (p < 0.05). However, there was no significant difference between the groups in trunk lean angle, average velocity or trunk displacement for either of the transitions between sitting and standing. Participants with dementia demonstrated a slower peak turning velocity and longer turning duration to complete the iTUG turn and 360° turns CW and CCW, compared to the older caregivers (p < 0.001). The mean turning angle was less (wider) in participants with dementia. Conclusion: Participants with dementia were slower while turning and transitioning between sitting and standing compared to the older caregivers. In addition, participants with dementia had a wider turning angle, suggesting differences in movement strategy. STUDY 2: Background/Objectives: With a surge in the number of studies utilizing the Ambulatory Parkinson’s Disease Monitoring (APDM) portable sensor system for investigation of movement in older adults, an investigation of concurrent validity between the laboratory-based motion analysis system (Qualisys, the criterion measure) and the APDM inertial sensor system (proposed alternative) is warranted. The aim of the study was to examine concurrent validity between measures of turning performance obtained from the APDM portable inertial sensor system and the laboratory-based motion analysis system, in people with mild cognitive impairment, in the laboratory setting. Participants: Older adults with mild cognitive impairment (MCI) n=10. Performance based tests: 360° turn counterclockwise (CCW) and spatiotemporal measures of turning derived from the APDM inertial sensors and the laboratory-based Qualisys motion analysis system. Results: Measures of turn duration and peak velocity demonstrated good to excellent positive correlations, r = 0.952, p?0.001 and r = 0.976, p < 0.001, respectively. There was no correlation between the measure of turn angle obtained from the two motion analysis systems ( rs = -0.139). Conclusions: Turn duration and peak velocity measures of APDM system demonstrate excellent correlation with Qualisys measures on the 360° turn, in older adults with MCI, in the laboratory. Further statistical analysis is needed to examine the absolute agreement on the turn angle measures.
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