Search PubMed⌕ Search

Biomedical subjects

R D Herbert

Publications and source records attributed to R D Herbert.

At least 19 recordsLinked to original sources
PubMed2002

Change in length of relaxed muscle fascicles and tendons with knee and ankle movement in humans.

Ultrasonography was used to measure changes in length of muscle fascicles in relaxed human tibialis anterior and gastrocnemius during passively imposed changes in joint angle. Changes in the length of muscle fascicles were compared to changes in the length of the whole muscle-tendon units calculated from joint angles and anthropometric data. Relaxed muscle fascicles underwent much smaller changes in length than their muscle-tendon units. On average, muscle fascicles in tibialis anterior 'saw' 55 +/- 13 % (mean +/- S.D.) of the total change in muscle-tendon length. This indicates nearly half of the total change in muscle-tendon length was taken up by stretch of tendon. In gastrocnemius, which has relatively long tendons, only 27 +/- 9 % of the total change in muscle-tendon length was transmitted to muscle fascicles. Thus, the tendency for passive movement to be taken up by the tendon was greater for gastrocnemius than tibialis anterior (P = 0.002). For these muscles, the relatively large changes in tendon length across much of the physiological range of muscle-tendon lengths could not wholly be explained by tendon slackness, changes in fibre pennation, or stretch or contraction history of the muscle. Our data confirm that when joints are moved passively, length changes 'seen' by muscle fascicles can be much less than changes in the distance between muscle origin and insertion. This occurs because tendons undergo significant changes in length, even at very low forces.

Adult↗
PubMed2002

Muscle stretching for treatment and prevention of contracture in people with spinal cord injury.

Contracture, or reduced joint mobility, is a common and disabling sequel of spinal cord injury. The primary intervention for the treatment and prevention of contracture is regular stretch to soft tissues. While the rationale for this intervention appears sound, the effectiveness of stretching has not been verified with well designed clinical trials. One recent randomised trial suggests there is no clinically worthwhile effect from a typical stretch protocol applied to spinal cord injured patients. Despite the negative results of this first trial, we argue that therapists should continue administering stretch for the treatment and prevention of contracture until the results of further studies emerge. To maximise the probability of attaining a clinically worthwhile effect, we suggest that therapists stretch soft tissues for long periods (at least 20 min, and perhaps for as long as 12 h a day). Practical suggestions are given on how to readily provide spinal cord injured patients with sustained stretch to key joints and muscle groups. Stretch is most likely to be effective if started before the onset of contracture. Soft tissues most at risk should be targeted, particularly if contracture is likely to impose functionally important limitations.

Contracture↗
PubMed2001

Time course of stress relaxation and recovery in human ankles.

OBJECTIVE: To characterise the time course of stress relaxation and recovery from stress relaxation in human ankles. DESIGN: Two experiments were conducted. The first used a randomised within-subjects design, and the second used a randomised between-subjects regression design. BACKGROUND: Several studies have described the time course of stress relaxation in human joints, but most have looked only at the effects of short durations of stretch. The time course of recovery from stretch in human ankles has not been documented. METHODS: In the first experiment, one ankle of each of eight subjects was stretched to a fixed dorsiflexion angle for 20 min. The ankle was then released for 2 min (during which time subjects either remained relaxed or performed isometric contractions), then stretched again. In a second experiment, on 24 subjects, the ankle was stretched for 20 min, then released between 0 and 20 min, then stretched again. In both experiments, subjects remain relaxed and ankle torque was measured continuously. RESULTS: When a constant-angle stretch was applied to the ankle, torque declined bi-exponentially towards an asymptote that was 58% of the initial torque. Nearly 5 min of stretch were required to obtain half of the maximal possible stress relaxation. Torque had recovered by 43% within 2 min of the release of stretch, but the degree of recovery did not appear to depend on whether subjects remained relaxed or performed isometric contractions. The time course of recovery was similar to the time course of stress relaxation. CONCLUSIONS: Long duration stretches are required to produce a large proportion of the maximal possible stress relaxation. Recovery is initially rapid when the stretch is released. RELEVANCE: These data provide a description of the time course of the effects of stretch, and of the subsequent relief of stretch, on mechanical properties of human ankles.

Adult↗
PubMed2000

A randomized trial assessing the effects of 4 weeks of daily stretching on ankle mobility in patients with spinal cord injuries.

OBJECTIVE: To determine the effect of 4 weeks of 30 minutes of daily stretching on ankle mobility in patients with recent spinal cord injuries (SCIs). DESIGN: Assessor-blinded randomized controlled trial. SETTING: Two spinal injury units in Sydney, Australia. PATIENTS: Consecutive sample of 14 recently injured patients with paraplegia and quadriplegia. INTERVENTION: Treated ankles were stretched continuously into dorsiflexion with a torque of 7.5 N x m for 30 minutes each weekday for 4 weeks. Contralateral ankles received no stretches. MAIN OUTCOME MEASURES: Passive torque-angle curves for both ankles were obtained at study commencement, then at weeks 2, 4, and 5 (ie, during, at the end of, and 1 week after the stretching program). Torque-angle measurements were obtained with the knee extended and flexed. Mean values for parameters (baseline angle, angle at 10 N x m, slope) describing the characteristics of the torque-angle curves were derived for each knee position. Changes from pretest to each subsequent test were calculated, as well as 95% confidence intervals (CIs) for differences in these changes between stretched and controlled ankles. RESULTS: The stretching intervention did not significantly change any of the 3 parameters describing the torque-angle curves of the ankle in either knee position. At the beginning of the study, the mean (+/-SD) angles obtained with the application of a standardized torque with the knee extended for the control and stretch ankles were 105 degrees (+/- 10.4 degrees) and 106 degrees (+/- 9.8 degrees), respectively. After 4 weeks, these values were 106 degrees (+/- 10.6 degrees) and 107 degrees (+/- 10.6 degrees) (mean difference in change of angle = 0 degrees; 95% CI, -3.3 degrees to 3.3 degrees). CONCLUSION: Thirty minutes of daily stretching for 4 weeks does not significantly change ankle mobility in recently injured patients with SCIs.

Adult↗
PubMed2000

PEDro. A database of randomized trials and systematic reviews in physiotherapy.

This paper describes PEDro, the Physiotherapy Evidence Database. PEDro is a web-based database of randomized controlled trials and systematic reviews in physiotherapy. It can be accessed free of charge at http://ptwww.cchs.usyd.edu.au/pedro. The database contains bibliographic details and abstracts of most English-language randomized trials and systematic reviews in physiotherapy, and of many trials and reviews in other languages. Trials on the database are rated on the basis of their methodological quality so that users of the database can quickly identify trials of high quality. Trials and systematic reviews are extensively indexed to facilitate searching. PEDro provides an important information resource to support evidence-based clinical practice.

Databases, Bibliographic↗
PubMed2000

A randomized trial of preexercise stretching for prevention of lower-limb injury.

PURPOSE: This study investigated the effect of muscle stretching during warm-up on the risk of exercise-related injury. METHODS: 1538 male army recruits were randomly allocated to stretch or control groups. During the ensuing 12 wk of training, both groups performed active warm-up exercises before physical training sessions. In addition, the stretch group performed one 20-s static stretch under supervision for each of six major leg muscle groups during every warm-up. The control group did not stretch. RESULTS: 333 lower-limb injuries were recorded during the training period, including 214 soft-tissue injuries. There were 158 injuries in the stretch group and 175 in the control group. There was no significant effect of preexercise stretching on all-injuries risk (hazard ratio [HR] = 0.95, 95% CI 0.77-1.18), soft-tissue injury risk (HR = 0.83, 95% CI 0.63-1.09), or bone injury risk (HR = 1.22, 95% CI 0.86-1.76). Fitness (20-m progressive shuttle run test score), age, and enlistment date all significantly predicted injury risk (P < 0.01 for each), but height, weight, and body mass index did not. CONCLUSION: A typical muscle stretching protocol performed during preexercise warm-ups does not produce clinically meaningful reductions in risk of exercise-related injury in army recruits. Fitness may be an important, modifiable risk factor.

Adolescent↗
PubMed1999

Twitch interpolation in human muscles: mechanisms and implications for measurement of voluntary activation.

An electrical stimulus delivered to a muscle nerve during a maximal voluntary contraction usually produces a twitchlike increment in force. The amplitude of this "interpolated twitch" is widely used to measure voluntary "activation" of muscles. In the present study, a computer model of the human adductor pollicis motoneuron pool was used to investigate factors that affect the interpolated twitch. Antidromic occlusion of naturally occurring orthodromic potentials was modeled, but reflex effects of the stimulus were not. In simulations, antidromic collisions occurred with probabilities of between approximately 16% (in early recruited motoneurons) and nearly 100% (in late recruited motoneurons). The model closely predicted experimental data on the amplitude and time course of the rising phase of interpolated twitches over the full range of voluntary forces, except that the amplitude of interpolated twitches was slightly overestimated at intermediate contraction intensities. Small interpolated twitches (4.7% of the resting twitch) were evident in simulated maximal voluntary contractions, but were nearly completely occluded when mean peak firing rate was increased to approximately 60 Hz. Simulated interpolated twitches did not show the marked force drop that follows the peak of the twitch, and when antidromic collisions were excluded from the model interpolated twitch amplitude was slightly increased and time-to-peak force was prolonged. These findings suggest that both antidromic and reflex effects reduce the amplitude of the interpolated twitch and contribute to the force drop that follows the twitch. The amplitude of the interpolated twitch was related to "excitation" of the motoneuron pool in a nonlinear way, so that at near-maximal contraction intensities (>90% maximal voluntary force) increases in excitation produced only small changes in interpolated twitch amplitude. Thus twitch interpolation may not provide a sensitive measure of motoneuronal excitation at near-maximal forces. Increases in the amplitude of interpolated twitches such as have been observed in fatigue and various pathologies may reflect large reductions in excitation of the motoneuron pool.

Adult↗
PubMed1998

Voluntary activation of human elbow flexor muscles during maximal concentric contractions.

1. To measure voluntary activation of human elbow flexor muscles during maximal concentric contractions, the twitch interpolation method was modified to enable detection of torque increments evoked by single stimuli during contractions of up to 300 deg s-1. Subjects flexed the elbow to rotate a loaded beam 'as fast as possible' (load typically 23-58 N m) from 70 deg below to 70 deg above the horizontal. Electrical stimuli were delivered to biceps brachii when the beam passed through the horizontal. Voluntary activation was estimated from the amplitude of the interpolated twitch, which was expressed as a percentage of the twitch produced by relaxed muscles shortening at the same velocity. 2. In eleven subjects, the level of voluntary activation during repeated maximal concentric contractions (median 99.4%) did not differ significantly from that during maximal isometric contractions (98.0%). Voluntary activation during maximal contractions did not depend on shortening velocity and was the same when tested at two angles 30 deg apart. 3. To induce fatigue, five subjects repeatedly lifted and lowered a heavy load at about 30 deg s-1, and continued for ten to twelve contractions after they needed assistance to continue lifting. All maintained the capacity to attain maximal levels of activation. 4. It is concluded that voluntary drive to elbow flexor muscles during maximal concentric contractions is usually maximal or near-maximal, and that this level of drive can be maintained during development of peripheral fatigue.

Adult↗
PubMed1998

Effects of real and imagined training on voluntary muscle activation during maximal isometric contractions.

In this study we directly tested the hypothesis that isometric strength training increases voluntary drive to muscles. In addition, it was attempted to replicate the findings of an earlier study that showed imagined training increases voluntary strength as much as actual training, as this finding provides key support for the hypothesis that training increases voluntary drive (Yue & Cole 1992). Fifty-four subjects were randomly allocated to groups that performed 8 weeks of isometric training of the elbow flexor muscles, imagined isometric training, or a control task involving the lower limbs. Voluntary isometric strength and activation of the elbow flexor muscles were measured before and after training. Voluntary activation was measured with a sensitive form of twitch interpolation. Training, imagined training and control groups increased voluntary isometric elbow flexor strength by means of 17.8% (+/- 3.1 SEM), 6.8% (+/- 2.6) and 6.5% (+/- 3.0), respectively. The training group increased in strength significantly more than imagined training and control groups (P = 0.01 for both comparisons), but the small difference between imagined training and control groups was not significant (P = 0.31). Prior to training, voluntary activation of all subjects was high (96.2 +/- 0.5%). This did not change significantly with training and there were no significant differences between groups. These data challenge the hypothesis that training of the elbow flexor muscles increases isometric strength by inducing adaptations of the central nervous system, because they show that training does not increase voluntary activation and imagined training does not increase strength.

Adult↗
PubMed1997

Rest length and compliance of non-immobilised and immobilised rabbit soleus muscle and tendon.

The first aim of this study was to measure the contributions of muscle and tendon to the total compliance of resting muscle-tendon units. A second aim was to determine whether the decrease in muscle-tendon unit rest length produced by prolonged immobilisation in a shortened position is mediated primarily by adaptations of the muscle or tendon. One ankle joint from each of five rabbits was immobilised in a plantarflexed position for 14 days. The passive length-tension properties of soleus muscle fascicles and tendons from both hindlimbs were measured using a video-based tensile-testing system. In non-immobilised muscles, muscle fascicle strains exceeded tendon strains by up to four times. However, because the rest length of tendon was much greater than that of muscle fascicles, changes in tendon length accounted for nearly half of the total change in muscle-tendon unit length. The rest length of immobilised muscle-tendon units was less than that of non-immobilised muscle-tendon units from contralateral limbs. Most of this difference was attributable to a change in the rest length of the tendon; there was little change in the rest length of muscle fascicles. It is concluded that the tendon is responsible for a large part of the compliance of rabbit soleus muscle-tendon units at physiological resting tensions, and that adaptation of tendon rest length is the primary mechanism by which the rabbit soleus shortens in response to immobilisation at short lengths.

Animals↗
PubMed1997

Intersegmental dynamics of standing from sitting.

OBJECTIVE: To compare the magnitude of muscle moments acting on either end of body segments with other motion-dependent and gravitational moments during the task of standing up. DESIGN: A mathematical model which partitions moment components was developed and applied and descriptive analysis of the resultant data conducted. BACKGROUND: It has been hypothesized that segmental interactions may be exploited during the task of standing up from sitting to lessen demands for the production of large muscle forces. There has been no investigation of the relative sizes of these interactions nor of their impact on the task. METHOD: Kinematic data obtained from six healthy male subjects were used as inputs to a 'top-down' dynamic model. Each total segmental moment was partitioned into a net muscle component as well as gravitational and motion-dependent components. RESULTS: The model successfully predicted both muscle moments determined by the 'ground-up' inverse dynamics approach and also ground reaction forces measured with a force platform. Motion-dependent moments were consistently small compared with muscle and gravitational moments. CONCLUSION: Segmental motion during standing up is controlled almost entirely by gravitational moments and the direct action of muscles which span either end of the segment. Motion-dependent moments do not significantly reduce the muscle moments required to stand up. RELEVANCE: Knowledge and understanding of the mechanical demands on the body during rising from sitting to standing are important in identifying critical elements for successful performance. Such information may also provide a basis for the development or refinement of strategies to retrain the movement following injury or disease.

Journal Article↗
PubMed1997

A randomized, controlled clinical trial of a treatment for shoulder pain.

BACKGROUND AND PURPOSE: The aim of this study was to evaluate the efficacy of a physical therapy approach to the treatment of shoulder pain. Subjects. Sixty-six volunteers with shoulder pain believed to be of local mechanical origin were randomly allocated to either a treatment group or a control group. METHODS: Subjects in the treatment group received 1 month of physical therapy aimed at restoring function of their shoulder muscles. Subjects in the control group received no treatment. Outcome measurements of pain intensity, range of motion (ROM), isometric muscle force, functional impairment, and self-perception of improvement were obtained by blinded assessment. RESULTS: Subjects in the treatment group showed improvement in pain-free abduction and flexion ROM, functional impairment, and self-perception of improvement. The control group deteriorated slightly over the experimental period in ROM and functional impairment measures. CONCLUSION AND DISCUSSION: These results suggest that the physical therapy approach used in this study is effective in improving shoulder function in subjects experiencing pain of mechanical origin. The results also provide little evidence of spontaneous recovery over a 1-month period.

Activities of Daily Living↗
PubMed1996

Muscle activation in unilateral and bilateral efforts assessed by motor nerve and cortical stimulation.

Voluntary muscle activation was measured with twitch interpolation in 11 subjects during attempted maximal voluntary contractions of the right thumb adductor muscles either in isolation ("thumb alone") or as the subjects simultaneously performed maximal voluntary contractions of the left thumb adductors or left elbow flexors ("both thumbs" or "thumb and elbow", respectively). During thumb alone contractions, median voluntary activation of the right thumb adductors was 90.3%, and subjects fully activated the thumb adductors on 22% of all contractions. Transcranial magnetic stimulation of the cortex during maximal voluntary efforts produced small twitchlike force increases, suggesting that at least part of the voluntary activation failure was attributable to suboptimal corticospinal drive. Maximal voluntary force produced by the right thumb adductors in the three conditions differed by < 2% (P = 0.21), and the ability to activate the thumb adductors in the both thumbs condition was only marginally less than during thumb alone contractions (median 88.6%; P = 0.004). Thus subjects are usually unable to fully activate their thumb adductors with maximal voluntary efforts, and simultaneous maximal contractions of contralateral muscle groups have little effect on this ability.

Adult↗
PubMed1995

Changes in pennation with joint angle and muscle torque: in vivo measurements in human brachialis muscle.

1. Estimates of pennation in human muscles are usually obtained from cadavers. In this study, pennation of human brachialis was measured in vivo using sonography. Effects of static and dynamic changes in elbow angle and torque were investigated. 2. Pennation was measured in eight subjects using an 80 mm, 5 MHz, linear-array ultrasound transducer to generate sagittal images of the brachialis during maximal and submaximal isometric contractions at various elbow angles. It was shown that estimates of pennation were reproducible, representative of measurements made throughout the belly of the muscle and not distorted by compression of the muscle with the transducer or rotation of the muscle out of the plane of the transducer. 3. Mean resting pennation was 9.0 +/- 2.0 deg (S.D., range 6.5-12.9 deg). When the muscle was relaxed there was no effect of elbow angle on pennation. However, during a maximal isometric contraction (MVC), with the elbow flexed to 90 deg, pennation increased non-linearly with elbow torque to between 22 and 30 deg (mean 24.7 +/- 2.4 deg). The effect of increasing torque was small when the elbow was fully extended. The relationship between elbow angle, elbow torque and brachialis pennation suggests that the relaxed brachialis muscle is slack over much of its physiological range of lengths. 4. There was no hysteresis in the relationship between torque and pennation during slow isometric contractions (0.2 MVC s-1), and the relationship between elbow angle and pennation was similar during slow shortening and lengthening contractions. 5. Two consequences follow from these findings. Firstly, intramuscular mechanics are complex and simple planar models of muscles underestimate the increases in pennation which occur during muscle contraction. Second, spindle afferents from relaxed muscles may not encode joint angle over the full range of movement.

Adult↗
PubMed1994

Fatigue contributes to the strength training stimulus.

To investigate the role of fatigue in strength training, strength increases produced by a training protocol in which subjects rested between contractions were compared with those produced when subjects did not rest. Forty-two healthy subjects were randomly allocated to either a no-rest group, a rest group, or a control group. Subjects in the two training groups trained their elbow flexor muscles by lifting a 6RM weight 6-10 times on 3 d each week for 6 wk. Subjects in the no-rest group performed repeated lifts without resting, whereas subjects in the rest group rested for 30 s between lifts. Both training groups performed the same number of lifts at the same relative intensity. The control group did not train. Subjects who trained without rests experienced significantly greater mean increases in dynamic strength (56.3% +/- 6.8% (SD)) than subjects who trained with rests (41.2% +/- 6.6%), and both training groups experienced significantly greater mean increases in dynamic strength than the control group (19.7% +/- 6.6%). It was concluded that greater short-term strength increases are achieved when subjects are required to lift training weights without resting. These findings suggest that processes associated with fatigue contribute to the strength training stimulus.

Adolescent↗
PubMed1993

The effect of position of immobilisation on resting length, resting stiffness, and weight of the soleus muscle of the rabbit.

The extent of immobilisation-induced adaptations of muscle length and muscle weight is known to be profoundly influenced by the position (or length) at which the muscle is immobilised. However, the effect of the full range of positions of immobilisation on subsequent adaptations of muscle length and weight has not yet been investigated. To examine further the effect of position of immobilisation, we used cast-immobilisation of the hind limbs of 23 rabbits, in various positions between full plantar flexion and full dorsiflexion. Six muscles from non-immobilised rabbits were used as the controls. After 10 days of immobilisation, the wet weight of the soleus muscle and the resting length and resting stiffness of the soleus muscle-tendon unit were determined. Immobilisation in a shortened position was associated with a significantly greater decrease in length and weight than was immobilisation in a lengthened position. In addition, immobilisation produced significant increases in the resting stiffness of muscle-tendon units, although there was no evidence of a position-dependent increase in stiffness. Muscle weight was influenced by the position of immobilisation in a nonlinear way. The data support the views that the pre-immobilisation resting length of the muscle represents a threshold length and that immobilisation at lengths longer than this retards immobilisation-induced atrophy.

Animals↗