Darl W. Vander Linden

Variant and invariant characteristics of the sit-to-stand task in healthy elderly adults

The purpose of this study was to identify kinetic, kinematic, and electromyographic (EMG) characteristics during sit-to-stand (STS) in healthy elderly subjects that were affected by changes in movement speed or initial starting position. Eight healthy elderly adults performed the STS movement at natural and fast speeds. Their ankles were placed in either 5 degrees or 18 degrees of dorsiflexion prior to the movement. A motion analysis system, single force plate, and EMG equipment were used to collect data on ankle, knee, and hip movement, vertical ground reaction forces, vertical and horizontal velocity of the head, and EMG activity from selected muscles. The data were further described according to three specific phases of the STS movement. Two-way analyses of variance for repeated measures were used to determine which of the kinematic, kinetic, and timing variables were affected by changing the speed of the movement or the initial ankle position. When asked to stand as fast as possible, muscle onsets and movement phases were shortened. However, when expressed as a percent of total movement time, normalized extensor muscle onsets were found to be earlier during fast movement of the task, whereas the other variables were not different. Changing the initial ankle position affected muscle onsets, duration of movement phases, and joint excursion. We conclude from these data that many of the characteristics of the sit-to-stand movement are speed invariant and therefore the STS movement is for the most part programmed.(ABSTRACT TRUNCATED AT 250 WORDS)

The relation between limb loading and control parameters of gait initiation in persons with stroke

OBJECTIVE This study investigated the relation between limb loading and selected characteristics of gait initiation in patients after stroke. SUBJECTS AND SETTING Thirteen patients attending a rehabilitation clinic volunteered for the study. DESIGN For the description of clinical features, patients were divided into two groups dependent on the amount of body weight shared by the involved limb during stance before gait initiation. MAIN OUTCOME MEASURES Patients performed six trials of gait initiation with either their involved or noninvolved limb on a force platform. Peak ground reaction forces and bilateral tibialis anterior and gastrocnemius electromyographic (EMG) activity were used for group comparison. RESULTS All patients showed the correct loading and unloading characteristics in the vertical and medial-lateral direction during gait initiation. Strong correlations were noted between initial limb loading and ground reaction forces during gait initiation (r = .79 to .95). Changes in ground reaction forces were significantly less (p < .001) for those patients who demonstrated decreased weight bearing on their involved limb before gait initiation. These patients were also unable to generate forward momentum, as evidenced by the fore-aft ground reaction force, with the involved limb. For all patients, increased gastrocnemius activity was noted in the stance (noninvolved) limb. The data are further discussed in regard to the relationship of the interaction of bilateral EMG activity and ground reaction forces. CONCLUSION This study suggests that there is a correlation between symmetrical weight bearing and the ability to provide those forces that generate forward momentum in the initiation of gait.

Influence of age on concentric isokinetic torque and passive extensibility variables of the calf muscles of women

The purpose of this study was to investigate the influence of age on concentric isokinetic torque (CIT) and passive extensibility (PE) variables of the calf muscles of healthy women. Ten younger women [31.9 (SD 6.1) years] and ten older women [71.1 (SD 6.6) years] were tested using a KIN-COM 500H dynamometer. The PE was tested by stretching the muscles from relaxed plantarflexion to the maximal dorsiflexion (DF) angle at 5°·s−1 without raw electromyogram (EMG) activity exceeding 0.05 mV. The maximal CIT was tested from the maximal DF angle 60° into plantarflexion at four randomly ordered velocities of 30, 60, 120, and 180°·s−1. Separate analysis of variance (ANOVA) tests showed that the standardized (% body mass) concentric peak and mean torques were lower for the older women for all isokinetic velocities (p < 0.001). The “angular delay” from the onset of concentric activation to peak torque was smaller for the older women at 120 and 180°·s−1 (p < 0.05). Age showed negative relationships (Pearson r) with all standardized peak torques (p ⩽ 0.001) and mean torques (p < 0.001), and the “angular delay” at 120 and 180°·s−1 (p ⩽ 0.05). Independent t-tests showed that the maximal DF angle and the change in the PE angle from an initial angle (defined at 10% of the maximal passive torque) to the maximal DF angle were less for the older women (p < 0.05). Age was negatively related to the maximal DF angle and the change in the PE angle (p < 0.01). The results suggest an age-related decrease in calf muscle CIT, muscle length and PE. The smaller “angular delay” for the older women at 120 and 180°·s−1 indicates that CIT testing at rapid velocities can be used to examine age-related changes in calf muscle contractile properties in relation to rapid velocities of movement.

Effect of Bench Height on Sit-to-Stand in Children Without Disabilities and Children With Cerebral Palsy

OBJECTIVE To evaluate the effect of seat height on sit-to-stand (STS) in children with cerebral palsy (CP) and in children without disabilities. DESIGN A mixed design (subject type by seat height) with repeated measures for seat height. SETTING Motion analysis laboratory. PARTICIPANTS Ten children with mild CP (mean age, 10.9+/-2.7 y) and 10 children without disabilities (mean age, 8.7+/-2.4 y). INTERVENTIONS Kinematic and force measurements of STS were completed with 6 infrared cameras and 2 forceplates. MAIN OUTCOME MEASURES Phase duration of the STS movement, amplitude and timing of ground reaction forces, and maximum head velocity during the movement. RESULTS Children with CP took significantly longer to rise to standing (1.71 s) than children without disabilities (1.24 s) (F(1,18)=16.97). The extension phase of STS was also significantly longer for children with CP (.85 s) than for children without disabilities (.45 s) (F(1,18)=18.73). Seat height did not affect time to stand for either children with CP or children without disabilities (F(1,18)=2.82, P>.05). The duration of the extension phase, maximum horizontal and vertical velocity of the head, and maximum vertical ground reaction force were all significantly greater when children stood from the low bench height than from the higher bench height, although we found no significant differences by subject type for maximum horizontal and vertical head velocity or for maximum vertical ground reaction force. CONCLUSIONS Although children with CP were able to modify their motor programs for STS to accommodate changes in seat height as readily as nondisabled children, the speed with which they extended against gravity was slower; therefore, the total STS movement took longer for them to complete than for children without disabilities. Because the time to complete STS from the low and high bench did not differ, it would appear that time to ascend from sitting may be invariant and therefore be a motor control parameter for the STS movement.