Biomedical subjects

A A Vandervoort

Publications and source records attributed to A A Vandervoort.

At least 19 recordsLinked to original sources

PubMed2001

Association among neuromuscular and anatomic measures for patients with knee osteoarthritis.

OBJECTIVE: To investigate neuromuscular and anatomic factors involved in varus gonarthrosis by identifying measures associated with degenerative changes. DESIGN: Descriptive study. Individual measures that explained substantial portions of the variability in ratings of knee joint-degenerative changes in patients with knee medial compartment osteoarthritis. SETTING: Outpatient orthopedic clinic and biomechanics and muscular assessment laboratory. PATIENTS: Volunteer sample of 20 subjects (age range, 59 +/- 9 yr) with no history of neurologic disease. INTERVENTION: Not applicable. MAIN OUTCOME MEASURES: We assessed degenerative changes, varus alignment, standing balance, and knee proprioception. Weight-bearing radiographs were used to assess the extent of degenerative changes and the degree of varus alignment. Single-limb standing balance control was assessed through tests performed on a force platform. Knee proprioception was assessed with an isokinetic dynamometer, using a joint angle replication test. RESULTS: Forward-stepwise multiple linear regression indicated that the extent of degenerative changes could be best predicted from a linear combination of the independent variables, varus alignment, and standing balance (R =.80, F(2,17) = 14.81, p =.0002). Sixty-four percent of the variability in ratings of degenerative changes was explained by alignment and standing balance measures (37% by varus alignment, 27% by standing balance). Alignment and balance measures were poorly correlated (r =.12, p =.63), further suggesting that they provided different information about gonarthrosis. CONCLUSIONS: Although varus alignment is widely accepted as a clinically important factor in gonarthrosis, and is the focus of many treatment efforts, our results suggest that objective measures of standing balance are also important. As a result, the potential impact of rehabilitation to improve the control of standing balance should be further evaluated in this patient population.

Biomechanical Phenomena↗

PubMed2001

Knee bracing for medial compartment osteoarthritis: effects on proprioception and postural control.

OBJECTIVE: To evaluate the effects of a functional knee brace specifically designed for patients with varus gonarthrosis on measures of proprioception and postural control. SUBJECTS: Fourteen men and six women (aged 59+/-9 yr) with measurable varus alignment and osteoarthritis of the knee medial compartment. METHODS: Proprioception was assessed in the sitting position using an isokinetic dynamometer and was quantified as the ability to replicate target knee-joint angles. Postural control was assessed with a force platform using tests of single-limb standing balance performed, while the patient was standing on a stable surface and standing on foam, and was quantified as the total length of the path of the centre of pressure. All tests were performed with and without the patient's own custom-fit valgus brace. RESULTS: Proprioception was significantly improved following application of the brace [mean difference=0.7 degrees, 95% confidence interval (CI)=0.2 to 1.1 degrees ). Postural control was not significantly affected by the use of the brace during the stable surface test (mean difference=2.6 cm, 95% CI=-4.3 to 9.5 cm) or the foam surface test (mean difference=0.9 cm, 95% CI=-7.5 to 9.4 cm). CONCLUSION: Although enhanced proprioception may be partially responsible for reported improvements with the use of a brace, the present findings call into question the functional importance of the small changes observed.

Braces↗

PubMed2001

Knee bracing after ACL reconstruction: effects on postural control and proprioception.

PURPOSE: To evaluate the effects an anterior cruciate ligament (ACL) brace has on various measures of knee proprioception and postural control. METHODS: Thirty subjects (mean age 27 +/- 11 yr) having undergone unilateral ACL reconstruction were tested with and without wearing their own custom-fit brace on their involved limb. Proprioception was assessed using joint angle replication tests completed on an isokinetic dynamometer. Postural control was assessed using a series of single-limb standing balance tests completed on a force platform. The balance tests included: 1) standing on the stable platform with eyes open, 2) standing on a foam mat placed over the platform with eyes open, 3) standing on the platform with eyes closed, and 4) standing on the platform after landing from a maximal single-limb forward hop. RESULTS: The brace provided a small but statistically significant improvement in proprioception (mean reduction in error scores between target and reproduced angles = 0.64 +/- 1.4 degrees, P = 0.02). For the postural control tests, there was a significant brace condition by test situation interaction (P = 0.02), with the brace providing a small but statistically significant improvement during the test completed on the stable platform with eyes open (mean reduction in center of pressure path length = 4.2 +/- 8.4 cm, P = 0.02) but not during the other more challenging test situations. Additional post hoc analyses indicated that the relationship between knee proprioception and postural control measures were low and not significant (r = 0.003 to 0.19, P > 0.32), consistent with the suggestion that changes in knee proprioception can occur in the absence of substantial changes in postural control. Also, standing balance tests that challenged the somatosensory contribution to postural control (i.e., those completed on foam, or with eyes closed) were significantly related to single-limb forward hop distances (r = -0.4, P < 0.05), whereas performance during the proprioception test was not (r = 0.1, P > 0.50). CONCLUSIONS: In general, bracing appears to improve performance during tasks characterized by relatively limited somatosensory input but not during tasks characterized by increased somatosenory input. The small magnitude of the improvements, coupled with their apparent lack of carry over to more difficult and functionally relevant tasks, questions the clinical benefit of the present effects of bracing.

Adult↗

PubMed2000

Effects of isokinetic strength training on concentric and eccentric torque development in the ankle dorsiflexors of older adults.

This study quantifies concentric and eccentric dorsiflexor muscle torque at various movement velocities and determines the neuromuscular effects from short-term practice of repeated maximal voluntary contractions using an isokinetic resisted exercise program in older adults. Twenty-eight subjects (76.3+/-4.6 years) trained concentric and eccentric dorsiflexion 3 days per week for 2 weeks at 30 degrees, 90 degrees, and 180 degrees/s through 40 degrees of dorsiflexion range of motion. Peak torque, rate of torque development, surface electromyography, and strength curves at each velocity were compared before and after training. Increases were found for concentric (27%) and eccentric (20%) dorsiflexor peak torque and concentric rate of torque production (20%-53%) across all movement velocities (p < .01). Training also significantly increased dorsiflexor concentric (64%) and eccentric (55%) surface electromyography; taken together, this is evidence of apparent adaptation of neural factors in older adults with short-term training. These findings support that eccentric and concentric strength training enhances the control and production of ankle muscle dorsiflexor torque in older adults, with implications for improving functional mobility of the ankle joint.

Aged↗

PubMed2000

Cardiovascular stress associated with concentric and eccentric isokinetic exercise in young and older adults.

Heart rate (HR), mean arterial blood pressure (MAP), and rate-pressure product (RPP) responses to submaximal isokinetic concentric (CON) and eccentric (ECC) knee extension exercise were compared at the same absolute torque output in 20 young (mean+/-SD=23.2+/-1.7 years) and 20 older (mean+/-SD=75.2+/-4.6 years) adults. After determination of peak CON and ECC torques, subjects performed separate, randomly ordered, 2-minute bouts of isokinetic CON and ECC exercise (90 degrees/s, exercise intensity: 50% of CON peak torque). CON exercise elicited greater changes in HR, MAP, and RPP than ECC exercise (p<.001) for both age groups. There were no age-related differences in HR, MAP, or RPP responses for either CON or ECC exercise. At the same absolute torque output, isokinetic CON knee extension exercise elicited significantly greater increases in cardiovascular stress than ECC exercise in both young and older adults. This result has implications for determining appropriate fitness and rehabilitation programs.

Adult↗

PubMed2000

Effect of a neoprene sleeve on knee joint kinesthesis: influence of different testing procedures.

PURPOSE: Objectives of this study were to examine the perceived sense of knee joint position during selected test situations, and to evaluate the proposed kinesthetic effect of a neoprene knee sleeve during these test situations. METHODS: Fifty-nine young healthy subjects (39 females and 20 males) attempted to replicate target knee joint angles using active and passive knee extension movements completed in sitting (nonaxially loaded) situations, and during active knee extension movements completed in supine while applying a load of 15% body weight through the long axis of the tibia (axially loaded). The criterion measure used was the absolute difference between target and reproduced angles, averaged over five attempts (Average absolute difference: AAD). RESULTS: A three-way ANOVA (two genders by three test situations by two sleeve conditions), with repeated measures on the last two factors, indicated a significant main effect for test situation and sleeve condition (P < 0.05), but not for gender. There was also a significant test situation by sleeve condition interaction (P < 0.05). Post-hoc analysis indicated that the AAD score during the active nonaxially loaded test situation without the sleeve was significantly greater than AAD scores for all other tests (P < 0.01). CONCLUSIONS: Pre-existing differences in knee joint kinesthesis observed during different contexts of limb movement must be recognized before various interventions, including the effect of knee supports, can be adequately interpreted. Because knee joint position sense was attenuated during voluntary active movement, and because this attenuation was ameliorated by the use of a sleeve, future studies evaluating the kinesthetic effects of knee bracing may benefit from using active movements. However, since the sleeve did not affect performance during the axially loaded test situation, future studies should also evaluate the relationship between tests of knee joint kinesthesis and other more functional tests of neuromuscular performance.

Adult↗

PubMed2000

A review of injury characteristics, aging factors and prevention programmes for the older golfer.

Participation in the sport of golf has risen considerably, particularly amongst senior players whose age is categorised as 50 years or more. However, golf presents both potential health benefits and risks for this older group of players. The health risks are compounded by the fact that the musculoskeletal and cardiovascular systems of senior players may not be as efficient at withstanding the strains and stress of this type of repetitive exercise. It was the purpose of this review paper to investigate the age-related health issues facing senior golfers and to discuss appropriate intervention strategies to help minimise these detrimental effects. The literature search identified only a minimal amount of epidemiological information pertaining specifically to the older golfer. A number of case reports were found which described a variety of musculoskeletal and cardiovascular incidents involving senior players. There was evidence from the literature that many of the age-related changes affecting older players' risk profiles were preventable or treatable through exercise. It was the conclusion of the authors of this review that conditioning programmes were highly recommended for all older players irrespective of their level of participation. Not only could the programmes prevent injury, they also had the potential to improve performance. Such programmes should incorporate flexibility, strength, endurance, speed and balance exercises specifically tailored to the demands of golf in order to be effective. Exercise equipment did not need to be elaborate and home-based programmes incorporating bodyweight, weighted clubs or elastic tubing resistance could be utilised. Future research needs to focus more specifically on injury incidence and mechanisms amongst groups of senior golfers whose participation rates vary. Randomised controlled trials are also recommended to investigate the efficacy of specific golf-related exercise regimens in this segment of the older population.

Aged↗

PubMed1999

Quadriceps muscle strength, contractile properties, and motor unit firing rates in young and old men.

Changes with age in the voluntary static and dynamic strength of the quadriceps muscle group have been well characterized, and the importance of the muscle group for locomotion and independent living have been highlighted in both normal human aging and in clinical studies. Surprisingly few studies of this muscle group have described age-related changes in voluntary activation ability using twitch interpolation and changes in stimulated contractile properties, and none have assessed the influence of old age on motor unit firing rates. We compared in 13 young (mean age 26 years) and 12 old (mean age 80 years) men the voluntary isometric strength, stimulated contractile properties, and average steady state motor unit firing rates in the quadriceps muscle. Maximum voluntary contraction (MVC) force and twitch tension were approximately 50% lower in the old men, but contractile speed was only approximately 10% slower than in the young men. There was no difference in the ability of either group to activate the quadriceps to a high degree (94-96%). At all isometric force levels tested (10%, 25%, 50%, 75%, and 100% MVC), there were no differences in mean motor unit firing rates. In both groups, the range of firing rates was similar and not large ( approximately 8 Hz at 10% MVC and 26 Hz at MVC). Thus, the substantial age-related weakness in this muscle does not seem to be related to changes in neural drive.

Adult↗

PubMed1999

Motor unit firing rates and contractile properties in tibialis anterior of young and old men.

The effects of aging on motoneuron firing rates and muscle contractile properties were studied in tibialis anterior muscle by comparing results from six young (20.8 +/- 0.8 yr) and six old men (82.0 +/- 1.7 yr). For each subject, data were collected from repeated tests over a 2-wk period. Contractile tests included maximal voluntary contraction (MVC) with twitch interpolation and stimulated twitch contractions. The old men had 26% lower MVC torque (P < 0.01) than did the young men, but percent activation was not different (99.1 and 99.3%, respectively). Twitch contraction durations were 23% longer (P < 0.01) in the old compared with the young men. During a series of repeated brief steady-state contractions at 10, 25, 50, 75, and 100% MVC, motor unit firing rates were recorded. Results from approximately 950 motor unit trains in each subject group indicated that at all relative torque levels mean firing rates were 30-35% lower (P < 0.01) in the old subjects. Comparisons between young and old subjects' mean firing rates at each of 10%, 50%, and MVC torques and their corresponding mean twitch contraction duration yielded a range of moderate-to-high correlations (r = -0.67 to -0.84). That lower firing rates were matched to longer twitch contraction durations in the muscle of old men, and relatively higher firing rates were matched with shorter contraction times from the young men, indirectly supports the neuromuscular age-related remodeling principle.

Action Potentials↗

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↗