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Biomedical subjects

A A Vandervoort

Publications and source records attributed to A A Vandervoort.

At least 37 records · Page 2Linked to original sources
PubMed1996

A 12-year follow-up study of ankle muscle function in older adults.

The purpose of this study was to examine changes in strength over time in a cohort of healthy elderly people who underwent assessments of ankle muscle function 12 years earlier. The isometric strength and contractile characteristics of the dorsiflexors and plantarflexors were studied in 11 male and 11 female subjects, ranging from 73-97 yrs (mean age 84 +/- 7.1 yrs). The same footplate apparatus was used as during the original testing. From 1982 to 1994, plantarflexor strength decreased 2.1% per year in females, and 2.5% per year in males (p < .01). The loss was relatively less in the dorsiflexor muscles; strength decreased 0.3% per year in females, and 0.8% per year in male (p > .05). There were no significant changes in evoked twitch torque in either muscle group, which may be due to the fact that passive tension of the connective tissue increased (p < .01) over the 12-year period. We conclude from this longitudinal assessment of ankle muscle function that the rate of loss of voluntary strength can vary considerably between antagonistic muscle groups. Factors influencing this variable loss warrant further investigation.

Aged↗
PubMed1996

A method of measuring standing isokinetic plantar and dorsiflexion peak torques.

Different methods have been used for concentric (CONC) isokinetic testing of ankle dorsiflexion (DF) and plantar flexion (PF). However, little information is available on either the reliability of these protocols or eccentric (ECC) torque production. As well, previous studies utilized non-weight-bearing test positions. The purpose of this study was to develop a reliable method of testing CONC and ECC DF and PF in a weight-bearing position. One group of adults, including older men and women were tested on two occasions with a standing protocol. Another group of older and younger men and women were compared between the standing method and a supine protocol. For both positions the velocity was 30 degrees.s-1 for the CONC and ECC actions, and the range of motion was 10 degrees DF to 20 degrees PF. Reliability coefficients for peak torque (PT) were acceptable and ranged from 0.65 to 0.90. The two testing positions were significantly related (r = 0.84-0.91), but CONC PT in standing were greater than supine. Therefore, this method of testing isokinetic DF and PF in a standing position has acceptable reliability and produces results consistent with those acquired with the supine protocol. It provides a means of comparing groups and examining intervention strategies while weight-bearing.

Aged↗
PubMed1995

Clinical applicability and test-retest reliability of an external perturbation test of balance in stroke subjects.

We address the test-retest reliability and clinical applicability of an adapted external perturbation balance assessment, ie, the Postural Stress Test (PST). Repeated-measures were designed to assess the clinical features of a component of balance disorder in stroke. Twenty ambulatory stroke patients and 20 age-, gender-, height-, and weight-matched healthy control subjects participated in this study. Stroke patients were tested (using the adapted PST) on 4 separate days; matched control subjects were tested on one occasion. With the subject standing, backward perturbation forces were applied at the level of the center of gravity. Postural reactions to the test were scored in real-time and from videotape, from two different viewing angles, ie, 45 degrees and 90 degrees to the saggital plane. Scores (out of a maximal of 81) were ascertained using a 10-point subjective-observational scale. None of the control subjects fell during testing; four of the hemiplegic subjects fell. Subjects were protected from potential injury by a custom-designed safety harness system. For the hemiplegic subjects, intraclass correlation coefficients (ICCs), calculated as the reliability of any one occasion, ranged from 0.71 to 0.77, whereas those calculated as the reliability of the mean of the first two occasions ranged from 0.83 to 0.93. Although scores on the fourth occasion were significantly greater than those on the third occasion, both being significantly greater than those on the first and second test occasions (p < .05), differences were less than 5 points on the 81-point scale.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1995

Comparison of passive stiffness variables and range of motion in uninvolved and involved ankle joints of patients following ankle fractures.

BACKGROUND AND PURPOSE: The purpose of this study was to quantify several variables of ankle stiffness and dorsiflexion (DF) range of motion (ROM) in the casted (fractured) and noncasted ankles of humans after cast removal. SUBJECTS: Thirty subjects (mean age = 32.4 years, SD = 15.8) with malleolar ankle fractures were tested within 4 days of cast removal but before they began physical therapy. METHODS: A torque motor system generated torque-versus-displacement graphs by recording angular displacement and resistive torque during a 6 0/s passive cycling of the ankle from 10 degrees of plantar flexion to the limit of DF ROM: Maximum passive DF ROM, passive torque, and passive elastic stiffness at the neutral position and energy loss were measured. Testing was performed in the absence of triceps surae muscle electromyographic activity. For analysis, subjects were separated into two groups based on fracture severity. RESULTS: There was no difference in passive torque between the fractured ankles and the matched noncasted ankles. There was a small difference in passive elastic stiffness between the more severely fractured ankles and the matched noncasted ankles. The fractured ankles were different in terms of energy loss from the matched noncasted ankles. For maximum passive DF ROM, there was a large difference between the fractured ankles (more severe: mean = 4.4 degrees; less severe: mean = 6.8 degrees) and the matched noncasted ankles (more severe: mean = 15.1 degrees; less severe: mean = 19.1 degrees). CONCLUSION AND DISCUSSION: Altered length-tension relationships and neuromuscular mechanisms have been suggested to produce postimmobilization joint contractures. The results of this study on humans are consistent with both possibilities and support the theory that changes that occur during immobilization result in protection from overstretching of the fragile calf musculature after a period of ankle fixation. The time course of normalization of stretch reflexes warrants investigation.

Adolescent↗
PubMed1995

Aging of human muscle: structure, function and adaptability.

With increasing age, human skeletal muscles gradually decrease in volume, mainly due to a reduced number of motor units and muscle fibers, and a reduced size of type 2 fibers. As a result, progressive weakening and impaired mobility occur. High-resistance strength training is beneficial, even in the very old, and could possibly reverse some of the detrimental effects of age-related weakness. The importance of exercise for older people affords an excellent opportunity for the medicine community as a major source of information and promotion of physical activity for this rapidly growing segment of the population. In this review, we summarize the current knowledge of the effects of aging on the human neuromuscular system, describe some of the major underlying mechanisms of the aging atrophy and focus on the importance of strength training to improve muscle function in older people.

Adaptation, Physiological↗
PubMed1995

Concentric and eccentric knee extension strength in older and younger men and women.

Decrements in isometric and concentric (Conc) muscular strength with increased age are well documented. However, little information is available on the effects of aging on eccentric (Ecc) strength, even though Ecc or lengthening muscle actions are used in most physical activities. This study examined Conc and Ecc peak torques (PT) during knee extension at 90 degrees/sec in healthy older (62 to 89 yrs) and younger (20 to 29 yrs) men and women. Conc PT decreased more with age than did Ecc (p < 0.01), for both men and women. PT values for the older men and women as a percentage of those of the younger ones were 58.3 and 46.6% for Conc, and 75.1 and 61.7% for Ecc, respectively. These age differences need to be considered during isokinetic evaluations of Conc versus Ecc strength. Other muscle groups should be investigated, and mechanisms remain to be determined.

Adult↗
PubMed1993

Effects of ageing on the motor unit: a brief review.

This review briefly summarizes the current state of knowledge regarding age related changes in skeletal muscle, followed by a more in-depth review of ageing effects on animal and human motor units (MUs). Ageing in humans is generally associated with reductions in muscle mass (atrophy), leading to reduced voluntary and electrically evoked contractile strength by the 7th decade for most muscle groups studied. As well, contraction and one-half relaxation times are typically prolonged in muscles of the elderly. Evidence from animal and human studies points toward age associated MU loss as the primary mechanism for muscle atrophy, and such losses may be greatest among the largest and fastest MUs. However, based on studies in animals and humans, it appears that at least some of the surviving MUs are able to partially compensate for MU losses, as indicated by an increase in the average MU size with age. The fact that muscles in the elderly have fewer, but on average larger and slower, MUs has important implications for motor control and function in this population.

Aging↗
PubMed1993

Effects of motor unit losses on strength in older men and women.

The influence of age-associated motor unit loss on contractile strength was investigated in a representative sample of healthy, active young and older men and women. In 24 younger subjects (22-38 yr) and 20 older subjects (60-81 yr) spike-triggered averaging was employed to extract a sample of surface-recorded single motor unit action potentials (S-MUAPs) from the biceps brachii and brachialis muscles. The amplitude of the maximum compound muscle action potential of the biceps brachii and brachialis muscles was divided by the mean S-MUAP amplitude to estimate the numbers of motor units present. The maximum isometric twitch contraction (MTC) and maximum voluntary contraction (MVC) of the elbow flexors were also recorded in 18 of the younger subjects and in all older subjects. The estimated numbers of motor units were significantly reduced (47%, P < 0.001) in older subjects with a mean value of 189 +/- 77 compared with a mean of 357 +/- 97 in younger subjects. The sizes of the S-MUAPs, however, were significantly larger in older subjects (23%, P < 0.01). Significant but less marked age-associated reductions in the MTC (33%, P < 0.05) and MVC (33%, P < 0.001) were also found and were similar for both men and women. These results suggest that motor unit losses, even in healthy active individuals, are a primary factor in the age-associated reductions in contractile strength.

Action Potentials↗
PubMed1993

An overhead harness and trolly system for balance and ambulation assessment and training.

Safe assessment of standing balance and gait is often jeopardized by the potential for falls, which may have major physical and legal consequences. This article describes the design and use of a system that enhances the safety of the patient and clinician during balance and gait assessment and training. The system consists of an overhead track and moveable trolly that allows the patient, while secured in a simple body harness, the freedom to ambulate, perform functional types of activities, and fall with minimal risk of injury. As a result, a single therapist can more readily assess balance and ambulation, as well as provide training for these skills. In addition, the therapist is free to observe the patient's movements from any position, without direct physical contact. Practically, the system described may allow ambulation training sooner after injury or surgery, permit training in weight-bearing or partial weight-bearing activities with or without assistive devices, and allow the clinician to focus on assessment and training, rather than on patient safety.

Accidental Falls↗
PubMed1992

Age and sex effects on mobility of the human ankle.

We investigated whether values for passive resistive torque, dorsiflexion strength, and active mobility of the ankle joint varied with age in a randomly selected sample of middle-aged and elderly males and females. The main effects of sex and age group were significant, without an interaction effect, on values for passive resistive torque and voluntary strength. The trends indicated that females had lower values for both variables and that passive torque increased and strength decreased with respect to age. Dorsiflexion range of motion also showed a highly significant trend to decrease across age groups, and more so for females than males. Mean values for middle-aged men vs old men went from 20.0 to 13.5 degrees, while corresponding values for women decreased from 20.7 degrees of dorsiflexion to 10.1. Functional ankle movement thus becomes limited with age, but could be improved by strengthening weak dorsiflexor muscles.

Aged↗
PubMed1992

Eccentric and concentric torques of knee and elbow extension in young and older men.

The purpose of this study was to compare the strength of knee extensors and elbow extensors in young and older men under conditions of eccentric loading and concentric contractions. Twelve men ages 23 to 32 years and 12 ages 60 to 75 years were tested at two angular velocities of movement, 90 and 180 degrees.s-1, on a KinCom isokinetic dynamometer. Compared to young men, older men had lower concentric peak torque values for elbow (31%) and knee (32%) extensors (p less than 0.05). The older group showed lower eccentric peak torques on all elbow comparisons (21% lower), and for knee extension at the slower velocity (20%). At the faster velocity, knee extension eccentric peak torque did not differ from that of younger men. Differences between the age groups were significantly less for the eccentric muscle action than for the concentric one. The observation of maintained eccentric strength in older men, particularly at fast velocity, warrants research in defining the mechanism.

Adult↗
PubMed1992

Effects of ageing on human neuromuscular function: implications for exercise.

This review focuses on the age related declines in muscle mass and strength, including a discussion of the potential for improvement of neuromuscular function following exercise training programmes. In the literature, limb muscles have been compared between groups of men and women throughout the adult age range, showing that decreases in voluntary strength do not become apparent until after the age of about 60. Rate of decline then amounts to 10 to 15% per decade, stemming from age related decreases in the amount of excitable muscle tissue. However, high-resistance exercise training programmes are effective in improving both muscle size and voluntary strength, even in very old and frail men and women. These improvements may yield significant gains in the performance of sports and the activities of daily living, such as walking ability. Maintenance exercise programmes must also be advocated to avoid rapid detraining effects seen in elderly people who become sedentary.

Accidental Falls↗
PubMed1991

Reliability of isometric hip abductor torques during examiner- and belt-resisted tests.

The purposes of this study were to determine the test-retest reliability of isometric hip abductor torques in elderly females, to compare two assessment protocols, and to compare the performances of elderly and young females. Twenty elderly and 20 young women were tested on two occasions. During the examiner-resisted test the examiner provided the resistance, and during the belt-resisted test the subject's contralateral leg provided the resistance while the examiner positioned the dynamometer. A four-way ANOVA indicated no occasion effects (p greater than .05). Within each group, similar torques were produced by both legs (p greater than .05). Test-retest intraclass reliability coefficients were good-to-high, ranging from 0.84 to 0.98 for the eight combinations of group-method-leg. The elderly females produced 61% of the torques produced by young females (p less than .01), and the examiner-resisted method produced 65% of the torques produced using the belt-resisted method (p less than .01). The belt-resisted method required less physical effort on the part of the tester, provided greater stabilization of the pelvis, and was preferred by 95% of the subjects.

Adult↗
PubMed1990

Eccentric knee strength of elderly females.

This study compared the strength of the knee extension and flexion muscles in groups of young and elderly women under two conditions: eccentric exercise in which the muscles were lengthened while subjects tried to resist an external force, versus concentric contractions in which the muscles shortened. Twenty-six females, aged 20 to 29 (Mean 25 +/- 3 SD), and 26 elderly women, aged 66 to 89 (Mean 73 +/- 6 SD), were tested at two angular velocities of movement, 45 degrees and 90 degrees/s, on a KinCom isokinetic dynamometer. Elderly women had significantly lower peak and average torque values in all comparisons with the young female group (25 to 54% lower, p less than .01). However, differences between the age groups were consistently smaller for the eccentric type of muscle action than the concentric, in both knee extensors and flexors.

Adult↗
PubMed1989

Plantarflexor muscle function in young and elderly women.

Contractile properties of the ankle plantarflexor muscles were compared between groups of young (means = 26 y) and elderly (means = 82 y) women. The H-reflex muscle contraction in the elderly group was characterized by a significant slowing of torque generation, as compared to the young women (means for average rate of torque development were young = 0.16 Nm ms-1 +/- 0.02 (SE), elderly = 0.09 Nm ms-1 +/- 0.02, P less than 0.05). However, the proportion of the total motor unit pool activated by the reflex was similar for the young and elderly groups at 63% and 70%, respectively. Maximal voluntary isometric torques were significantly lower (71%) in the elderly (young means = 135.3 Nm +/- 9.3, elderly means = 39.2 Nm +/- 2.9, P less than 0.01). These results are consistent with, and extend, previous reports showing decreased strength and speed of contraction in elderly muscle. Given that the average body weight was similar for the young and elderly groups, it was concluded that the aged plantarflexor muscles exhibited considerable impairment in ability to generate stabilizing torques about the ankle joint.

Adult↗
PubMed1989

Comparison of twitch potentiation in the gastrocnemius of young and elderly men.

The capacity for twitch potentiation in the gastrocnemius muscle was determined following maximal voluntary contractions (MVC) in 11 elderly (means +/- SD; 66.9 +/- 5.3 years) and 12 young (25.7 +/- 3.8 years) men. Potentiation was observed by applying selective stimulation to the muscle belly, 2 s after a 5 s MVC. With this procedure, both groups showed significant (P less than 0.05) increases in twitch tension in the gastrocnemius (ratios of potentiated twitch to baseline were means = 1.68 +/- 0.40 for young vs means = 1.40 +/- 0.20 for the elderly, P less than 0.001). Time to peak tension of the twitch decreased from means = 101.5 +/- 17.9 ms to means = 88.0 +/- 15.8 ms in the young men following potentiation; the respective values for the older men were 136.7 +/- 17.9 ms and 133.1 +/- 28.6 ms. These changes resulted in a greater rate of tension development in the potentiated state. The elderly gastrocnemius thus showed qualitatively similar changes in the isometric twitch following potentiation, but reduced and prolonged responses in comparison to young adults. Slowed muscle contraction and reduced capacity for potentiation may be physiological correlates of the reported morphological changes in aged skeletal muscle.

Adult↗
PubMed1989

Age and passive ankle stiffness in healthy women.

The purpose of the study was to evaluate passive joint stiffness in ankles of young (aged 21-40 years; n = 15), middle-aged (aged 41-60 years; n = 15), and young elderly (aged 61-80 years; n = 15) women. The effect of knee position on passive joint stiffness was also evaluated by testing the subjects with the knee flexed (90 degrees) and with the knee extended (0 degrees). A torque motor system was used to record angular displacement and resistive torque during a 6 degrees/sec ankle rotation from 10 degrees of plantar flexion to 10 degrees of dorsiflexion (DF). Passive torque and passive elastic stiffness were measured at 0, 5, and 10 degrees of DF. Both measures increased nonlinearly as the ankle was rotated into DF, but showed no significant differences between the three age groups tested. There was also no significant difference in the passive stiffness measurements when the knee was flexed or extended. We concluded that within the range of motion tested, the factors of age and knee position do not affect the passive stiffness observed in the ankle joints of healthy women. We have now established baseline values of passive ankle joint stiffness for healthy women during DF within a functional ROM, which will be useful in the clinical evaluation of passive ankle joint stiffness and in studies where treatment efficacy is being investigated.

Adult↗