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Biomedical subjects

A A Vandervoort

Publications and source records attributed to A A Vandervoort.

At least 19 recordsLinked to original sources
PubMed1999

Effect of a static calf-stretching exercise on the resistive torque during passive ankle dorsiflexion in healthy subjects.

STUDY DESIGN: A within-subject experimental design was used with to measure the effect of calf-stretching exercises on the resistive torque during passive ankle dorsiflexion in a group of 20 healthy men (aged 21 to 40). OBJECTIVES: The purpose of this study was to determine if the performance of calf-stretching exercises would produce a decrease in resistive torque during passive ankle dorsiflexion. BACKGROUND: Calf-stretching exercises are widely used in sporting, fitness, and rehabilitation settings yet the effects of stretching on the passive mechanics of the ankle joint are not well understood. METHODS AND MEASURES: A KIN-COM isokinetic dynamometer was used to measure the passive resistive torque of the ankle while the joint complex was moved through return cycles from 10 degrees plantarflexion to 10 degrees dorsiflexion at a constant velocity of 6 degrees/s. Each subject's right or left ankle was randomly assigned to either a control or an experimental condition. The latter underwent a total of 4 static stretches, each lasting 30 seconds. RESULTS: The main findings of the study were that the calf-stretching exercises did not produce a significant reduction in the resistive torque during ankle dorsiflexion, as measured by the peak to peak torque at 10 degrees of ankle dorsiflexion or in the center range of the hysteresis loop at 0 degree dorsiflexion. CONCLUSION: Static calf-stretching exercises of short duration did not reduce the passive resistance of the connective tissue within the surrounding muscle and joint structures in the ankles of healthy young men.

Adult↗
PubMed1997

Age-related changes in motor unit function.

This review focuses on the functional relationship between age-related morphological and physiological changes at the level of the motor unit (MU). It is well established that older humans are weaker than younger people, exhibit reduced force control, and have slower neuromuscular contractile properties. Older people may also exhibit a decrease in MU discharge rate, and an increase in variability of MU discharge at high force levels. The matching of MU discharge and contractile properties may be an age-related neurophysiological strategy adopted to optimize motor control, similar to that observed in acute conditions such as fatigue. Because muscle force output is modulated partially by MU discharge behavior, the study of these properties may offer insights into the physiology of muscular weakness and motor function in older people. In turn, this will allow the implementation of optimal exercise and rehabilitation programs to reduce the degree of dependence associated with aging.

Aging↗
PubMed1997

Standing strength training of the ankle plantar and dorsiflexors in older women, using concentric and eccentric contractions.

Many studies have reported strength gains in older adults following high-intensity resistance training. However, the muscle contraction types examined have been primarily isometric (static) or concentric (CONC; shortening). Less is known about how eccentric (ECC) strength in older adults responds to training or about the efficacy of ECC contractions as training stimuli in these subjects, even though muscle contractions of this type are performed in most training regimens and daily physical activities. In this study, 15 physically active, healthy older women [68 (5) years; mean (SD)] completed an 8-week resistance training program of two sessions per week. Training consisted of three sets of eight repetitions of CONC ankle plantar flexion (PF) and ECC dorsiflexion (DF), at greater than 80% of the initial peak torque, in a standing position only. Subjects were tested in standing and supine positions for: (1) strength over a range of 10 degrees DF to 20 degrees PF for both CONC and ECC; DF and PF (2) passive resistive torque of the plantar flexors at 6 degrees/s; and (3) DF and PF rate of torque development. All strength testing and training was done at 30 degrees/s. Significant increases (P < 0.01) were found for both CONC DF (increases 30%) and ECC DF (increases 17%) peak torque in the standing position. No significant changes occurred for DF strength as measured with the subjects in the supine position, PF strength in either position, passive resistive torque, or rate of torque development. In summary, strength gains occurred only in the dorsiflexors, which were trained using ECC contractions. Improvements in DF strength were specific to the position of training, which has implications for the transferability of strength gains to functional tasks such as maintaining gait.

Aged↗
PubMed1997

Eccentric peak torque of the plantar and dorsiflexors is maintained in older women.

Although a relative preservation of eccentric (ECC) strength with age has been reported previously, this phenomenon has not been studied in lower leg muscles. Concentric (CONC) and ECC plantar (PF) and dorsiflexion (DF) in healthy active older women (OW; n = 16, age = 67 +/- 4 years) and younger women (YW; n = 16, age = 27 +/- 4 years) were studied. Passive resistive torque of the plantar flexors and average rate of torque development (RTD) for both DF and PF were also measured. The OW had CONC peak torques that were 74% and 89% of the YW for PF and DF, whereas ECC peak torques were 97% and 100% of the YW. ECC torque patterns were almost identical for both groups, but there were significant differences for passive resistive torque (OW > YW; p < .01) and CONC RTD (OW < YW; p < .05). While increased passive resistive torque did not prove to be influential in maintaining ECC strength with age, it had a negative effect on CONC DF function.

Adult↗
PubMed1997

An evaluation of the length-tension relationship in elderly human plantarflexor muscles.

The purpose of this study was to determine the effect of aging on the muscle length-tension relationship in the plantarflexor muscles of 10 subjects aged 20-30 yr (Mean = 23; 5 males, 5 females), 10 subjects aged 60-80 yr (Mean = 72.3; 5 males, 5 females), and 10 subjects over 80 yr (Mean = 84.1, 5 males, 5 females). Isometric twitch properties, maximum voluntary strength, passive tension, and range of motion were measured at five different joint angles [20 degrees dorsiflexion (DF), 10 degrees DF, 0 degree, 10 degrees plantarflexion (PF), and 20 degrees PF]. Active (evoked and voluntary) and passive torque production were maximal when the ankle was rotated into the DF positions for all three age groups, whereas the lowest values were recorded when the ankle was rotated into 20 degrees PF. Males were stronger than females at all joint angles (p < .01). Also, young adults were stronger than both elderly adult groups (p < .01). These results illustrate that despite the considerable age-associated loss in both voluntary and evoked strength in the plantarflexors, the optimal angle for torque production remains the same for younger and older adults.

Adult↗
PubMed1997

Peak passive resistive torque at maximum inversion range of motion in subjects with recurrent ankle inversion sprains.

Although a number of mechanical and neuromuscular processes have been identified, the primary mechanisms underlying residual functional instability of the ankle remain unclear. Understanding such mechanisms will help physical therapists identify where to focus treatment efforts, ultimately leading to more effective rehabilitation. In the present investigation, resistive torque at maximum ankle inversion was evaluated to determine if lateral ankle structures demonstrated mechanical laxity. Thirty subjects with a history of unilateral recurrent inversion sprains were tested bilaterally. A custom-made apparatus provided a stress to the lateral ankle in a method that was similar to the inversion stress test. Two measures of laxity were used: maximum passive inversion range of motion and peak passive resistive torque. Differences between the involved and uninvolved ankles were determined using analysis of covariance procedures. There were no significant differences between involved and uninvolved ankles for maximum inversion range of motion and for peak passive resistive torque. Post hoc testing confirmed adequate statistical power. The results support previous investigations, which suggest that functional instability can exist in the absence of mechanical lateral ankle laxity.

Adult↗
PubMed1997

Effects of detraining on knee extensor strength and functional mobility in a group of elderly women.

Long-term detraining results for individuals 75 years and older are needed. The purpose of this study was to assess long-term detraining effects on quadriceps strength and functional mobility in nursing home residents. Ten women (X = 82.8 years) who completed a strength training program were reassessed 1 year later. Clinical methods were used to remeasure dynamic and isometric quadriceps strength and functional mobility. One repetition maximum quadriceps strength declined 68.3% (p < 0.05) from trained values. Isometric strength losses were 29.8% at 90 degrees (p < 0.05), 28.7% at 60 degrees (p < 0.05), and 24.4% at 20 degrees (p < 0.05) of knee flexion 1 year postexercise. Fast-paced walking, self-selected paced walking, and timed up and go speed decreased 28.6% (p < 0.05), 19.5% (p < 0.05), and 54.1% (not significant), respectively, from posttraining. One year vs. baseline, isometric strength decreased 0-14.3%, dynamic strength decreased 48.9%, and functional mobility declined 16.5-20.7% despite an intervening training program. An increased strength loss rate beyond the age of 80 years may be a major factor influencing functional independence.

Activities of Daily Living↗
PubMed1996

Development of a home ankle exerciser.

A portable, lightweight home ankle exerciser was designed and built by the Biomedical Engineering Department of University Hospital in London, Ontario, Canada. The ankle exerciser incorporates several unique features that overcomes the drawbacks of exercise equipment presently available. For optimal muscle strengthening, the resistance offered by the device matches the strength curve of the ankle muscles. The magnitude of the resistance can be widely varied to accommodate any subject. Resistance is generated by a slip clutch rather than by springs or weights which can be cumbersome and potentially dangerous. One of the considerations in the design of the ankle exerciser was to monitor subject compliance with the exercise regimen. This is accomplished with a battery-operated monitoring unit mounted on the device. The exerciser is instrumented with a battery-powered torque transducer and digital display unit that enables the subject and assessor to monitor the exercise resistance level at a glance.

Adult↗
PubMed1996

The influence of summary knowledge of results and aging on motor learning.

This study examined whether older adults (mean age = 75.0 years) use summary knowledge of results (KR) to facilitate learning in a manner similar to that of young adults (mean age = 22.5 years). All subjects were required to learn a computer-key-pressing task in a specified goal time. During acquisition, subjects received either KR after every trial, or summary KR. All subjects then performed no-KR retention trials. In acquisition, KR after every trial facilitated timing accuracy for both the younger and older groups in comparison to the summary KR groups. The young subjects were equally variable in both KR practice groups. For older subjects summary KR facilitated more consistent performance. In retention, the summary groups were more accurate than those subjects who received KR after every trial. There were no accuracy or variability differences between the two age groups during retention. These results suggest that older adults are able to use summary KR to facilitate learning in a manner similar to that of young adults.

Adult↗
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↗