Decomposition of leg movements during overground walking in individuals with traumatic brain injury.

OBJECTIVE: Walking requires precise coordination of bilateral lower extremity motions at all joints. This ability can be affected by traumatic brain injury (TBI). The study investigated inter-joint coordination of lower extremities during overground walking after TBI. METHODS: Ten individuals with post-injury ataxia, postural stability and gait abnormalities, as well as 10 sex- and age-matched control subjects were involved in the study. Participants walked at self-selected speed in three experimental conditions: normal walking without any additional task; walking with a narrow base of support, and walking while holding a cup full of water. Inter-joint coordination was analysed as the percentage of gait cycle during which the leg movement was decomposed with 0% indicating simultaneous motion of the two joints (i.e. hip-knee, knee-ankle, and hip-ankle) through the entire gait cycle or 100% indicating motion of only one joint. Decomposition was calculated for each pair of joints and for the left and right leg separately. RESULTS: Participants with TBI showed greater decomposition indices and poorer inter-joint coordination respectively than control individuals for all joint pairs (p < 0.01). Walking with the narrower base of support or with a cup, increased movement decomposition in the TBI group, but not in the control group. CONCLUSION: The results revealed post-injury gait impairment that manifests as decomposition of multi-joint motions of the lower extremities during overground walking.

The effect of actual and imaginary handgrip on postural stability during different balance conditions.

The stabilizing effect of holding an object on upright posture has been demonstrated in a variety of settings. The mechanism of this effect is unknown but could be attributed to either additional sensorimotor activity triggered by a hand contact or cognitive efforts related to performance of a supra-postural task. A potential mechanism was investigated by comparing postural stability in young healthy individuals while gripping a custom instrumented wooden stick with a 5N force and while imagining holding the same stick in the hand. Twenty subjects were tested during three standing balance conditions: on a stationary surface, on a freely moving rockerboard, and with an unexpected perturbation of 10° forward rockerboard tipping. Postural stability was evaluated as velocity of the center of mass (COM) and center of pressure (COP) compared across all experimental conditions. COM and COP velocities were equally reduced when subjects gripped the stick and imagined gripping while standing stationary and on the rockerboard. When perturbed, subjects failed to show any postural stability improvements regardless of handgrip task. Results indicate a stabilizing effect of focusing attention on motor task performance. This cognitive strategy does not appear to contribute any additional stabilization when subjects are perturbed. This study adds to the current understanding of postural stabilization strategies.

Fiber type composition and maximum shortening velocity of muscles crossing the human shoulder.

A study of the fiber type composition of fourteen muscles spanning the human glenohumeral joint was carried out with the purpose of determining the contribution of fiber types to overall muscle cross-sectional area (CSA) and to estimate the maximum shortening velocity (V(max)) of those muscles. Muscle biopsies were procured from 4 male cadavers (mean age 50) within 24 hr of death, snap frozen, mounted, and transversely sectioned (10 microm). Slides were stained for myofibrillar ATPase after alkaline preincubation. Photoimages were taken of defined areas (100 fibers) using the Bioquant system, and fiber type and CSA were measured from these images. Staining for mATPase produced three different fiber types: slow-oxidative (SO), fast-oxidative-glycolytic (FOG), and fast-glycolytic (FG). On average, the muscle fiber type composition ranged from 22 to 40% of FG, from 17 to 51% of FOG, and from 23 to 56% of SO. Twelve out of the 14 muscles had average SO proportions ranging from 35 to 50%. V(max) was calculated from the fiber type contribution relative to CSA and shortening velocity values taken from the literature. The maximum velocities of shortening presented here provide a physiological basis for the development of human shoulder musculoskeletal models suitable for predicting muscle forces for functionally relevant tasks encompassing conditions of muscle shortening and lengthening.