To produce successful and safe walking movements, the locomotor control system must have a detailed awareness of the mechanical properties of the lower limbs. Flexibility of this control comes from an ability to identify and accommodate any changes in limb mechanics by updating its internal representation of the lower limb. To explore the ability of the locomotor control system to tune its representation of the lower limb, eight participants performed three 5 min trials (PRE, WEIGHT and POST) of treadmill walking. During the middle trial the participants wore a 2 kg mass around the leg segment of the left lower limb. Joint kinematics and kinetics were determined to assess changes in the walking movements. The modification of limb inertia by adding mass to the limbs (WEIGHT) required a substantive period of adaptation, which lasted between 45 and 50 strides, before individuals fully adjusted to their new lower limb mechanics to achieve steady-state joint kinematics. These movements were caused in part from an increase in hip flexor and knee extensor activity in early swing followed by an increase in hip extensors and knee flexor activity in late swing. Following the removal of the mass (POST), ankle, knee and hip flexion all increased above the levels that were observed in the PRE condition and returned the baseline levels within 20, 70 and 70 strides, respectively. The removal of the mass appeared to cause a greater disruption to walking than the addition of mass to the limb despite a quick return of the joint moments to the PRE condition. Both the changes following the addition of the mass and its subsequent removal may embody a recalibration of the internal limb representation. These changes were characterized by an integrated response consisting of primary recalibration to the modified mechanical parameters and secondary actions to main the integrity of locomotor objectives such as propulsion, balance, support and safe foot trajectories. These recalibration responses were similar to those demonstrated in upper limb movements in response to altered force environments. Understanding this recalibration process will have implications for the prevention of trips and falls as individuals encounter different movement environments or changes to mechanical properties of their limbs, especially for individuals with decreased proprioception or other neural challenges.
Functional neuroimaging techniques have allowed for investigations into the mechanisms of agerelated deterioration in motor control. This study used functional Magnetic Resonance Imaging (fMRI) to investigate age related differences in the control of grip force magnitude. Using an event-related design, fMRI scans were completed on 13 older adults, and 13 gender matched younger adults, while using their dominant hand to squeeze a rubber bulb for 4s at 10%, 40% or 70% of their maximum voluntary contraction. Both groups were able to match the relative force targets, however the older adults produced significantly lower levels of absolute force. fMRI analysis consisted of a 1) region of interest (ROI) approach to detect differences in selected motor areas within brain and 2) a voxel-wise whole brain comparison to find areas of differential activation that were not defined a priori between the older and younger group. The ROI analysis revealed that despite producing lower levels of absolute force, the older adults showed higher levels of activity predominantly in subcortical structures (putamen, thalamus and cerebellum) when compared to the younger group. The older adults also showed higher levels of activity in the ipsilateral ventral premotor cortex. A total of 19 of the 22 ROIs analyzed showed a significant main effect of the required force-level. In the majority of the ROIs that showed a significant force effect there were no significant differences in the magnitude of the blood-oxygen-level-dependent (BOLD) signal between the 10% and 40% conditions but a significantly higher BOLD signal in the 70% condition, suggesting that the modulation of brain activation with grip force may not be controlled in a linear fashion. It was also found that the older adult group demonstrate higher levels of activation in 7 areas during a force production task at higher force levels using a voxelwise analysis. The 7 clusters that showed significant differences tended to be areas that are involved in visual-spatial and executive processing. The results of this study revealed that older adults require significantly higher activation of several areas to perform the same motor task as younger adults. Higher magnitudes of the BOLD signal in older adults may represent a compensatory pattern to counter age related deterioration in motor control systems.Corresponding Author: Janice J. Eng, PT, OT, Ph.D., Professor, Department of Physical Therapy, University of British Columbia, 212-2177 Wesbrook Mall, Vancouver, BC, Canada V6T 1Z3, Janice.Eng@ubc.ca, Phone: IntroductionThe normal aging process leads to several declines of the motor system that are related to changes within the central nervous system, peripheral nervous system and the musculoskeletal system (Seidler et al., 2010). These changes have the potential to lead to decreased motor performance with aging, which has been observed in the forms of decreased coordination, increased movement variability, slower movements and difficulties with balance and gait (Seidler et al., 2...
Background: The timed-up-and-go test (TUG) is one of the most commonly used tests of physical function in clinical practice and for research outcomes. Inertial sensors have been used to parse the TUG test into its composite phases (rising, walking, turning, etc.), but have not validated this approach against an optoelectronic gold-standard, and to our knowledge no studies have published the minimal detectable change of these measurements. Methods: Eleven adults performed the TUG three times each under normal and slow walking conditions, and 3 m and 5 m walking distances, in a 12-camera motion analysis laboratory. An inertial measurement unit (IMU) with tri-axial accelerometers and gyroscopes was worn on the upper-torso. Motion analysis marker data and IMU signals were analyzed separately to identify the six main TUG phases: sit-to-stand, 1st walk, 1st turn, 2nd walk, 2nd turn, and stand-to-sit, and the absolute agreement between two systems analyzed using intra-class correlation (ICC, model 2) analysis. The minimal detectable change (MDC) within subjects was also calculated for each TUG phase. Results: The overall difference between TUG sub-tasks determined using 3D motion capture data and the IMU sensor data was <0.5 s. For all TUG distances and speeds, the absolute agreement was high for total TUG time and walk times (ICC > 0.90), but less for chair activity (ICC range 0.5–0.9) and typically poor for the turn time (ICC < 0.4). MDC values for total TUG time ranged between 2–4 s or 12–22% of the TUG time measurement. MDC of the sub-task times were higher proportionally, being 20–60% of the sub-task duration. Conclusions: We conclude that a commercial IMU can be used for quantifying the TUG phases with accuracy sufficient for clinical applications; however, the MDC when using inertial sensors is not necessarily improved over less sophisticated measurement tools.
The lower-limb segment elevation angles during human locomotion have been shown to co-vary in a manner such that they approximate a plane when plotted against each other over a gait cycle. This relationship has been described as the Planar Co-Variation Law and has been shown to be consistent across various modes of locomotion on level ground. The goal of this study is to determine whether the Planar Co-Variation Law will hold in situations where the orientation of the walking surface is altered and if aging will have an effect on this intersegmental coordination during these locomotor tasks. Nine healthy young females (mean age = 21.4), and nine older adult females (mean age = 73.3) were asked to complete walking trials on level ground, and walking up ramps with inclines of 3 degrees , 6 degrees , 9 degrees and 12 degrees while the kinematics of their lower limbs were measured. It was found that the Planar Co-Variation Law was held across all ramp incline conditions by both the young adult and older adult groups. It was found that the changes in intersegmental coordination required to walk up the ramp resulted in a unique orientation of the co-variation plane for both groups when walking up a particular incline. The results of this study indicate that the Planar Co-Variation Law will include situations where the walking surface is not level and provides further support to models of motor control that have been proposed where walking patterns for different modes of gait can be predicted based on the orientation of the co-variation plane.
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