[Show abstract][Hide abstract] ABSTRACT: Background
To evaluate if multi-muscle synergies are comprised of flexible combinations of a small number of postural muscles to stabilize the center of pressure (COP) shift during preparation to making a step in the elderly (self-paced level stepping vs. obstacle crossing stepping).Methods
Electromyography (EMG) signals of leg and trunk muscles were recorded. Linear combination of integrated indices of muscle activity (M-modes) and their relationship to changes in the COP shift in the anterior-posterior (AP) direction were first determined. Uncontrolled manifold (UCM) analysis was performed to determine the extent to which variance of the M-modes acted to produce a consistent change in the COP displacement.ResultsThe elderly were capable of stabilizing the COPAP coordinate based on co-varied involvement of the M-modes. The synergy index (¿V) changes in the elderly emerged later (100 ms prior to t0) and its magnitude was smaller as compared to that reported in younger persons.Conclusions
Our study reveals that aging is associated with a preserved ability to explore the flexibility of the M-mode compositions but a decrease ability to use multi-M-mode synergies following a predictable perturbation.
Journal of NeuroEngineering and Rehabilitation 02/2015; 12(1):10. DOI:10.1186/s12984-015-0005-9 · 2.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The aim of this article was to explore age-related differences in the muscle modes (M-modes) during voluntary body sway (VS). M-modes were defined as trunk and leg muscles organized into groups with parallel scaling of muscle activation level within a group. We hypothesized that, in comparison with young performers, older adults would show changes in the compositions of M-modes stabilizing the anterior-posterior (AP) center of pressure (COP) displacement. Young (27.5 ± 7.3 yr, 164.6 ± 9.7 cm and 58.4 ± 10.6 kg) and older (69.4 ± 6.4 yr, 160.0 ± 7.0 cm and 58.9 ± 7.5 kg) subjects performed the VS task in the AP direction while trying to minimize sway in the medio-lateral direction. EMG signals of 10 postural muscles were recorded and analyzed. Principal component analysis (PCA) was used to identify three M-modes within the space of integrated indices of muscle activity. The main findings were (1) that there were no age-related differences in magnitude of the COP displacement or amount of variance explained by the principal components (m-modes), and (2) that the number of times co-contraction and mixed m-modes were used were significantly higher for older adults, and the number of times reciprocal m-modes were used were significantly higher for young adults. These observations suggest that aging is associated with a reduced ability to unite dorsal and ventral muscles of the body, which may be reflective of the CNS developing a useful strategy when faced with self-triggered perturbations.
Research in Sports Medicine 01/2015; 23(1):88-101. DOI:10.1080/15438627.2014.975808 · 1.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Purpose:
To study multi-muscle synergies during preparation in making a step (self-paced level stepping vs. obstacle crossing stepping).
The uncontrolled manifold hypothesis was used to explore the organization of leg and trunk muscles into groups (M-modes) and co-variation of M-mode involvement (M-mode synergies) during stepping tasks. Subjects performed two tasks: (1) making a comfortable step from quiet stance (STCS), (2) stepping over an obstacle of 15% body height from quiet stance, STOS. Electromyographic (EMG) signals of 10 postural muscles were recorded and analyzed. Principal component analysis was used to identify M-modes within the space of integrated indices of muscle activity. Variance in the M-mode space across stepping trials was partitioned into two components, one that did not affect the average value of center of pressure (COP) shift and the other that did. An index (ΔV) corresponding to the normalized difference between two components of variance was computed.
Under the two tasks, strong multi-M-mode synergies stabilizing trajectories of the COP in the anterior-posterior direction were found. Despite the significant differences in the COP shifts and EMG patterns of postural adjustments, the synergies showed only minor differences across the conditions.
These findings demonstrate the robustness of multi-M-mode synergies across different manners of making a step.
[Show abstract][Hide abstract] ABSTRACT: [Purpose] This study investigated the characteristics of postural control following postural disturbance in elite athletes. [Subjects] Ten elite ski jumpers and ten control subjects participated in this study. [Methods] Subjects were required to maintain balance without stepping following unexpected horizontal surface perturbation in a forward or backward direction. [Results] A lower and reproducible peak magnitude of the center of mass velocity was shown in the athlete group compared to the control group. Cross-correlation analyses showed longer time lags at the moment of peak correlation coefficient between trunk flexor and extensor muscle activities, and shorter time lags and higher correlations between ankle flexor and extensor muscle activities were shown in the athlete group than in the control group. [Conclusion] The elite ski jumpers showed superior balance performance following surface perturbations, more reciprocal patterns in agonist-antagonist pairs of proximal postural muscles, and more co-contraction patterns in distal postural muscles during automatic postural responses than control individuals. This strategy may be useful in sports requiring effective balance recovery in environments with a dynamically changing surface, as well as in rehabilitation.
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study is to examine the differences in plantar force associated with changes in backpack load and gait speed during walking. The F-scan tethered system was used to collect plantar pressure data. Subjects were asked to walk on a treadmill with varied levels of backpack load (0%, 10%, 20%, and 30% of body mass) and gait speed (4, 5, and 6 km/h). We found that an increase in gait speed and backpack load lead to increase in the magnitude of the first vertical ground reaction force (vGRF) peak. Greater magnitudes of the second vGRF peak were only associated with an increase when gait speeds were 4 km/h and 5 km/h. There was no speed-related change in the magnitudes of the second vGRF peak at the speed of 6 km/h. The results of this study may be important for the purpose of constituting a load-bearing walking program for protecting against osteoporosis.
Research in Sports Medicine An International Journal 10/2013; 21(4):395-401. DOI:10.1080/15438627.2013.825802 · 1.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We studied multi-muscle synergies of healthy elderly persons during preparation to making a step (self-paced vs. reaction time). The uncontrolled manifold hypothesis was used to explore the organization of leg and trunk muscles into groups (M-modes) and co-variation of M-mode involvement (M-mode synergies) during stepping tasks. We hypothesized that aging accounts for changes in the structure of M-modes, as well as in M-mode synergies. Subjects performed two tasks: (1) a cyclic COP shift over a range corresponding to the maximal amplitude of voluntary COP shift at 1 Hz, (2) stepping tasks under 3 instructions, "comfortably, self-paced," "very quick, self-paced," and "as fast as possible to a visual signal." Electromyographic signals of 10 postural muscles were recorded and analyzed. Principal component analysis was used to identify M-modes within the space of integrated indices of muscle activity in the cyclic sway task. Variance in the M-mode space across stepping trials was partitioned into two components, one that did not affect the average value of COP shift and the other that did. An index (ΔV) corresponding to the normalized difference between two components of variance was computed. The elderly subjects showed more "co-contraction M-mode" and "mixed M-mode" than that of the young subjects. During stepping tasks, both subject groups showed M-mode synergies stabilizing COP shifts in the stepping and supporting legs. The synergies of elderly subjects showed a smaller and delayed value than that of the young subjects. These results suggest that aging is associated with diminished control in multi-muscle synergies in the anticipatory postural adjustments during gait initiation.
Experimental Brain Research 04/2013; 226(4). DOI:10.1007/s00221-013-3449-9 · 2.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The notion of limb dominance has been commonly used in the upper extremity, yet the two lower extremities are often treated as equal for analytical purposes. Attempts to determine the effects of limb laterality on gait have produced conflicting results. The purpose of this study was to determine if limb dominance affects the vertical ground reaction force and center of pressure (COP) during able-bodied gait. The Parotec system (Paromed GmbH, Germany) was used to collect plantar foot pressure data. Fifteen subjects volunteered to participate in this study. The coefficient of variation of the COP displacement in the mediolateral direction and the variability of peak force beneath the lateral forefoot in the nondominant foot were significant greater than in the dominant foot. Moreover, COP velocity in the anterior-posterior direction during the terminal stance phase showed greater value in the dominant foot. Our study provides support for limb laterality by showing limb dominance affected the vertical ground reaction force and center of pressure during walking gait. This finding suggests it is an important issue in movement science for clinicians and would assist in improving sports performance and rehabilitation program.
Journal of applied biomechanics 08/2012; 28(4):473-8. · 0.98 Impact Factor