Biomedical subjects

A A Vandervoort

Publications and source records attributed to A A Vandervoort.

47 records · Page 3Linked to original sources

PubMed1987

Strength-velocity relationship and fatiguability of unilateral versus bilateral arm extension.

Strength-velocity relations and fatigue resistance in an arm bench press manoeuvre were compared between conditions of bilateral (BL, both arms acting together) and unilateral muscle contraction in 9 young men. BL and UL (sum of the 2 arms acting singly) strength was similar for isometric and slow isokinetic maximal voluntary contractions (MVC); at high velocities BL MVC declined more than UL. In both types of contractions a curvilinear relation was observed between strength and velocity, with significantly higher peak torques (PT) being produced under isometric conditions than for slow velocity efforts (p less than 0.01). Mean declines in PT during 100 repetitive MVCs of approximately 70s were to 25% of initial values for the BL fatigue test and to 37% for UL (p less than 0.01). In contrast to results of a similar investigation of leg extension in the same subjects, the arms showed no BL deficit of strength in the initial part of the strength-velocity curve and approximately twice as much fatigue in repetitive contractions. These physiological differences may stem from the varying habitual activity patterns of the arms and legs.

Adult↗

PubMed1987

Postural stability and Colles' fracture.

We have tested the hypothesis that the Colles' fracture is due, not simply to bone loss at the menopause, but to postural instability in a subset of postmenopausal women such that they are rendered more liable to fall. We have measured bone mass by dual photon spinal densitometry and single photon wrist densitometry and measured postural sway in 19 postmenopausal women with a history of Colles' fracture. Our results show that not only do Colles' fracture subjects have a small reduction in bone mass but they have a significantly increased degree of postural sway, a finding which has previously been recognized to characterize older subjects with recurrent falls.

Accidental Falls↗

PubMed1986

Contractile changes in opposing muscles of the human ankle joint with aging.

The effects of aging on maximal voluntary strength and on the isometric twitch were determined in the ankle dorsiflexor and plantarflexor muscles of 111 healthy men and women aged 20-100 yr. Men were found to be stronger than women at all ages. In both sexes, the average values for maximum voluntary strength of the dorsiflexors and plantarflexors began to decline in the 6th decade. Although the absolute loss of strength was greater for the plantarflexor muscles, the relative losses were similar in the two muscle groups. During maximum voluntary effort, stimulation of motor nerves produced no additional torque in the majority of elderly men and women, indicating that these subjects remained able to utilize their descending motor pathways for optimal muscle activation. Comparisons of muscle compound action potentials, twitch torques, and muscle cross-sectional areas suggested that a decrease in excitable muscle mass was entirely responsible for the lower strength of the elderly. An additional effect of aging was the gradual prolongation of twitch contraction and half-relaxation times throughout the adult life-span.

Adult↗

PubMed1984

Comparison of motor unit activation during unilateral and bilateral leg extension.

Possible differences between the extent of muscle utilization during leg extensions performed bilaterally (BL, both legs acting together) and unilaterally were investigated in young males in college. Significantly less integrated electromyographic activity was recorded from the quadriceps muscles of the dominant leg during BL compared with UL maximal voluntary contractions (MVC). BL strength was significantly lower than the summed (UL; sum of 2 legs acting singly) UL value under isometric conditions [BL = 91 +/- 2.5% (mean +/- SE) of UL; P less than 0.01, n = 9]. By use of a modified isokinetic dynamometer, it was also shown that the effect of increasing the velocity of concentric contraction was significantly greater (P less than 0.001) on BL than UL force development; thus at 424 degrees/s mean BL MVC was only 51 +/- 3.5% of UL. Greater resistance to fatigue was shown in the BL condition in repeated concentric contractions (% decline over 100 MVC at 105 degrees/s was 28 +/- 2.7% for BL vs. 38 +/- 2.9% for UL, P less than 0.001). Results indicated that the extent of motor unit activation appeared to be reduced in BL relative to UL MVC. Compatible evidence from the strength-velocity and fatigability comparisons suggested that this reduction was due to a lesser utilization of the fast-twitch fatigable type of motor unit.

Adult↗

PubMed1983

A comparison of the contractile properties of the human gastrocnemius and soleus muscles.

Twitch speeds and potentiating capacities have been determined for human medial and lateral gastrocnemius and soleus muscles. The experiments involved and application of submaximal stimuli to the respective muscle bellies, with monitoring of the evoked compound action potentials (M-waves) during repetitive stimulation. Contrary to an earlier report, the lateral gastrocnemius was found to have a significantly shorter mean contraction time (100.0 +/- 10.8 ms) than the soleus (156.5 +/- 14.7 ms) and this value was also significantly different from that of the medial gastrocnemius (113.7 +/- 19.6 ms). The mean half-relaxation time for each muscle also differed significantly from those for the other two muscles. A further contrast between the muscles was that potentiation of the twitch, following a 3-s tetanus at 50 Hz, was significantly greater in the lateral gastrocnemius than in soleus (mean values 60.4 +/- 43.1% and 2.6 +/- 3.3% respectively.

Action Potentials↗

PubMed1983

Twitch potentiation after voluntary contraction.

Twitch potentiation was studied in human tibialis anterior (TA) and plantarflexor (PF) muscles after maximal voluntary contractions (MVCs). Potentiation was greater in TA and other dorsiflexor (DF) muscles than in PF and was dependent on the intensity of the voluntary effect. It was also observed that potentiation was maximal after MVCs of approximately 10-s duration; after longer voluntary contractions, the potentiation was partially suppressed by fatigue, especially in the TA. Potentiation was significantly larger when muscles were tested in a shortened position regardless of the position at which the preceding MVCs had been performed.

Adult↗

PubMedDate not supplied

Motor skill learning of concentric and eccentric isokinetic movements in older adults.

Neuromuscular adaptation at the onset of resisted exercise can be observed as increases in torque and surface electromyography. The effect of learning the motor task has been hypothesized to contribute to these early increases, especially for older people. Thus, the purpose of this study was to investigate the facilitatory effects of practice on motor performance in older adults during short-term isokinetic training of the ankle dorsiflexors (DF). Twenty-eight men and women (M = 76.3 +/- 4.6 years) volunteered for a 2-week, 3-days/week strength training program. They were tested in a sitting position on a KinCom isokinetic dynamometer at 30, 90, and 180 degrees s-1 through 40 degrees of DF movement (concentric and eccentric contractions). Criterion curves of lever arm angle patterns were cross-correlated with subject-generated angle patterns, showing significantly better correlations on posttest versus baseline. Smoothness and proficiency of muscle contraction improved with practice by fewer hesitations in movement and increased ability to change between concentric and eccentric muscle contractions. Increased agonist electromyography and torque were hypothesized to be secondary to greater neural drive and/or synchronization of motor unit firing rate and/or recruitment during maximal voluntary contraction, improved coordination, and adapted neural control of concentric and eccentric muscle contraction.

Aged↗

PubMedDate not supplied

The influence of aging and target motion on the control of prehension.

The purpose of this study was to examine age-related differences in reaching behavior when younger (mean age = 26.0 years) and older (mean age = 70.1 years) individuals were required to reach toward and grasp both small and large targets that were either stationary or moving. The older subjects had shorter movement times, and smaller within-subject movement time variability than younger subjects. Also, the deceleration of the reach was shorter for older subjects, indicating that they were not making extensive use of on-line feedback, and were instead utilizing anticipatory control strategies. There were no age differences in the size of the maximum grasp around the target, but the timing of the grasp was influenced by target motion for the younger subjects, suggesting on-line control for the younger subjects only.

Adult↗

PubMedDate not supplied

An outcome measure to quantify passive stiffness of the ankle.

The primary aim of this research project was to develop a method to quantify a specific variable of neuromuscular function, passive stiffness of the ankle. It was then used to determine if values for the outcome measure varied with age and sex in a sample of elderly men and women between 55 and 85 years old. Subjects were screened for medical conditions contraindicative to testing, e.g. severe arthritis, other history of bone or muscle disorders, ankle fracture, neural disorder causing spasticity or contracture. A rotatable footplate which recorded position and resistive torque with a potentiometer and strain gauge, respectively, was linked to an electric, computer-controlled torque motor. Passive elastic stiffness, defined as the slope of the passive resistance curve at 10 degrees dorsiflexion (in N.m/degree), was greater in males, (p < .001), and increased with age (p = .002). There was a significant effect of age group on passive range of motion (ROM) values for ankle dorsiflexion (p < .001), but also a significant sex by age interaction (p = .001). Females showed a large drop from a mean of 19.3 degrees +/- 3.2 in the youngest group (55-60 yr) to 12.1 degrees +/- 5.5 in the 81 to 85 yr olds. Corresponding mean values for the middle-aged males were 15.4 degrees +/- 4.3 versus 13.1 degrees +/- 3.5 of dorsiflexion in the group of 81 to 85 yr old men. It was concluded that passive ROM of the ankle into dorsiflexion showed decreases in the elderly, which seemed to reflect less complaint tissue structures.

Aged↗

PubMedDate not supplied

Spasticity measurement in stroke: a pilot study.

The ability to objectively measure spasticity, related to cerebral stroke, is important in the rehabilitation therapies since many therapeutic modalities have been developed over the years to reduce spasticity. The unproven clinical expectation is that function would be improved were spasticity to be reduced. Unfortunately, the ability to measure spasticity to conduct efficacy studies of spasticity-reducing therapies is not possible. This relates to the multi-variable nature of the spastic syndrome with the result that no clinical measurement technique has been proven to be sensitive, valid and reliable. Therefore, it is important to develop a research-oriented spasticity measurement system to meet this need. We describe the current development of such a system. Details of our pilot study of a reflex excitability technique, designed to measure certain components of cerebral spasticity, are presented. The technique combined biomechanical and electrophysiological measures to investigate a homogenous stroke sample (n = 6); it incorporated the H-reflex in soleus, during passive ankle movements, as a measure of faulty neural inhibition. This component significantly (p < .05) differentiated the stroke sample from a matched, healthy control group (n = 6). Evocation of a cutaneous reflex in soleus was a condition that was problematic and it had to be dropped from the protocol. Joint stiffness, which is thought to affect measures of spasticity during passive movement, did not contaminate the measures. Further research in this direction is required to delineate and measure other neural components of spasticity while taking into account related non-neural variables. The final objective in this line of research is to develop a valid, reliable and sensitive spasticity measurement system that could be used to judge the efficacy of physical neurorehabilitation treatments currently employed to reduce spasticity following stroke.

Aged↗

PubMedDate not supplied

A reflex technique to measure presynaptic inhibition in cerebral stroke.

The purpose of this study was to evaluate the feasibility of reflex excitability measurement techniques in the partial measurement of spasticity related to cerebral stroke. Techniques involved the testing of the soleus H-reflex at specific ankle positions during passive dorsiflexing movements with and without background plantarflexing contractions; conditions attempted to simulate the terminal stance phase of gait. Testing of 12 stroke subjects, having cerebrovascular lesions related only to occlusion of the middle cerebral artery, demonstrated significantly (p < 0.01) less inhibition of the H-reflex during passive ankle dorsiflexion compared to 12 matched, healthy controls. However, evocation of the H-reflex during a low-level, voluntary plantarflexing contraction concomitant with passive dorsiflexion, did not reflect a statistical difference between the two groups. The two conditions were thought to each represent measures of faulty presynaptic inhibition as indicators of cerebral spasticity. A Chi-square calculation of sensitivity for the passive ankle movement without background plantarflexing contraction condition, was shown to significantly differentiate (p < 0.05) between the stroke and normal groups. A positive, but weak, correlation was found for stroke subjects between this reflex measure and the Ashworth clinical measure of spasticity (r = 0.49). Although stroke subjects exhibited increased joint stiffness when the full range of passive ankle dorsiflexion movement was considered, in comparison to the matched healthy control subjects, no significant increase in passive stiffness was found at the joint position of the reflex evocation. Size of the cerebral lesion, as determined from CT or MRI scan, was not related to the spasticity measures. Therefore, in a homogeneous stroke sample, a component of cerebral spasticity i.e., faculty Ia presynaptic inhibition, has been measured during a simulated functional movement in the lower extremity and was shown to differentiate this group from a matched, healthy, control sample. Joint stiffness did not contaminate the measures.

Aged↗