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Biomedical subjects

R D Herbert

Publications and source records attributed to R D Herbert.

27 records · Page 2Linked to original sources
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↗
PubMed1980

A computerized alert program for acutely ill patients.

An integrated computer system with a central data-base and decision-making capabilities is the basis of an investigation of a computerized alerting program that rapidly detects, analyzes, and generates diagnostic interpretations and treatment protocols for life-threatening laboratory abnormalities. Preliminary study data suggests that use of the alerting program to promptly notify physicians of abnormal laboratory values results in more prompt and correct treatment of patients.

Acute Disease↗