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Biomedical subjects

J D Brooke

Publications and source records attributed to J D Brooke.

At least 55 records · Page 3Linked to original sources
PubMed1989

Effect of knee joint angle on a heteronymous Ib reflex in the human lower limb.

Altered efficacy, from change in receptor discharge with different positions of the knee, was investigated in a heteronymous Ib reflex of the human leg. The electrical stimulus was low threshold, to the common peroneal nerve. The divergence of the group I afferents was studied in the electromyograms (EMGs) of ipsilateral and contralateral thigh muscles. The stimulus evoked ipsilateral, short latency, excitation in the three quadriceps muscles studied and inhibition in the knee flexor semitendinosus (ST), with prior contraction of target muscles. This excitation and inhibition did not alter when studied over the range of the knee joint. The stimulus did not evoke responses in contralateral thigh muscles, contracted or relaxed. It is concluded that (1) any change in convergence from discharge of receptors, during extension of the limb, is small and sub-threshold, and (2) this spinal proprioceptive level of neural control appears to be directed primarily to the single limb.

Adult↗
PubMed1988

A technique for electrically induced perturbation of rhythmic leg movement.

The paper describes electrical circuitry which replaces a mechanical brake, for perturbation of the contractile load of the legs during pedalling. The turning flywheel of an ergometer is connected to an alternator, with the electrical load provided by a power resistor connected across the output terminals. A 12-V battery provides the field current. Through variable resistors the field current is altered under microprocessor control, providing different steady-state loads when pedalling and also sudden transient changes of load. The point of change in load in the movement cycle can be accurately selected. The ergometer is instrumented for accurate measurement of pedal crank position, crank angular velocity and reaction force at the foot, to provide a physical description of the evoked steady states and transients, using microprocessor controlled sampling. The results show that the technique has application to the study of the range of reflex responses within a movement cycle and also to the more complex restoration of a movement pattern over a number of cycles. It is applicable to investigation of normal and diseased states.

Electronics↗
PubMed1987

Response synergies over a single leg when it is perturbed during the complex rhythmic movement of pedalling.

Previous studies report that perturbing the posture of humans evokes specific patterns of muscular synergies in the legs. This study investigated the pattern of muscular responses of a whole limb when it was rapidly perturbed in the phase of extending during stationary pedalling. Subjects were instructed to resist. Accordingly, we anticipated increased extensor activity at knee and ankle to overcome the perturbation. This did not occur in the initial responses, appearing at latencies of 85-132 ms (mean = 104 ms). In contrast, there was facilitation in tibialis anterior, and the knee extensors vastus medialis and rectus femoris, together with profound inhibition of the ankle extensors soleus and lateral gastrocnemius. The anticipated extensor response across the limb appeared in the subsequent pattern of electromyogram (EMG) activity, with latencies ranging from 121 to 195 ms (mean = 168 ms), together with a large increase in propulsive force on the pedal. The difference in EMG patterns and latencies between initial and subsequent synergies was used to separate the responses into an earlier 'prevolitional' and a later 'volitional' component.

Adult↗
PubMed1987

A multivariate solution for cyclic data, applied in modelling locomotor forces.

The variability in dependent biological data (measured as forces at the human foot during pedalling) was reduced, by principal components analysis, to two major components which, combined, accounted for 46% of the variability observed in sets of 26 observations per cycle. On the basis of weightings over the cycle, the components were interpreted as due to Power Production and to Phase Switch from power-generation to recovery. Force measurements were made for three frequencies of leg pedalling (1.00, 1.66, and 2.33 Hz at 10 N ergometer resistance). For each principal component, the mean (or summed) deviation over 75 consecutive cycles was found to increase linearly (p less than 0.05) with velocity of leg movement, by 7% and 85% respectively. Analysis of autocorrelations over cycles of movement showed that, in contrast to the strong interconnections of force measures within a cycle of movement, between-cycle dependence was very low. The statistical technique described provides a useful descriptive and inferential method for analyzing dependent cyclic data. The resulting model of the locomotor forces generated at the foot implies that control of power output is substantially for one cycle of a limb and that variability of force increases at the point when the leg switches from power-generation to recovery.

Analysis of Variance↗
PubMed1987

Human group I excitatory projections from ankle dorsiflexors to quadriceps muscle.

A short latency projection of group I afferent fibers from ankle dorsiflexors to knee extensor muscles has been categorized as species specific to humans. However, the effects of the pathway have only been inferred from conditioning homonymous reflexes in relaxed muscle. This study focused directly on the responses evoked in the electromyogram of the heteronymous muscles when active, in two experiments. In the first, preferential activation of group I afferents of ankle dorsiflexors, by electrical stimulation of the common peroneal nerve, excited both vastus medialis (mean latency, 26.3 ms) and rectus femoris (mean latency, 33.5 ms). No excitation or inhibition in either muscle was associated with stimulation of the tibial nerve. The second experiment compared vastus medialis responses with common peroneal nerve stimulation during three different movement conditions in which the muscle was equally contracted: rhythmic isotonic (pedalling); episodic isotonic; isometric contraction. Responses were identified in all three active states, with no significant differences in amplitude or latency. No responses were seen in the relaxed muscle.

Adult↗
PubMed1986

Magnitude of the H reflex of the soleus substantially exceeds the myotatic response from rapid dorsiflexion of the ankle joint.

We compared the magnitude of short-latency EMG responses in the soleus after electrical stimulation and after muscle stretch. The peak to peak amplitudes and areas of such stretch-evoked responses, following initial rotation velocities to 200 degrees/s, did not extend beyond the lower part of the H reflex range (evoked electrically). The disparity suggests caution in the use of electrical stimulation of group 1 afferent fibers when a study is to be made of normal human movement.

Adult↗
PubMed1985

Locomotor limb synergism through short latency afferent links.

Reports of facilitation of lower limb synergists through afferent stimulation in resting humans lead to study of short latency reflex responses during activity of the legs. Four synergistic muscles of the right leg were examined following electrical stimulation of low threshold afferents of the posterior tibial (PTN) and femoral (FN) nerves. Four males cycled on an ergometer with pedals modified to measure the force applied. Movement frequency was 0.8 Hz with 15 N ergometer resistance for two 6 min trials, one involving PTN and the other FN. Collection of EMGs of soleus, lateral gastrocnemius, vastus medialis and rectus femoris lasted for 200 msec after stimulation, which was triggered when the pedal was 56 degrees beyond top-dead-center. Control EMGs were similarly collected during intervening, non-stimulated, pedal cycles within the same work bout. Collection of force on pedals occurred over the same 200 msec period as well as the following two complete pedal revolutions. From PTN stimulation short latency increase occurred not only in homonymous EMGs but also in heteronymous as distant as rectus femoris. FN stimulation similarly resulted in short latency changes in quadriceps and also in triceps surae. Pedal force changes accompanied the EMGs. M response confounding in many cases resulted in only tentative identification of the reflex force evoked. Little change with stimulation was seen in the force in subsequent cycles. The responses represent a net of pathways which could affect within-limb coordination of muscles during human locomotion and extend previous investigations of Ia projections in spinal cats and resting humans.

Adult↗
PubMed1984

A note on stability in force applied to control a repetitive task with the legs.

The forces applied to pedals during cycling were collected every 40 ms from approximately 29,000 movement repetitions. Intra-cycle mean values of force and its variability were significantly correlated, supporting Schmidt's impulse variability theory of within-movement activities of the legs. In addition, as mean forces approached peak values, coefficients of variation decreased. From averages taken minute by minute, intra-cycle forces were seen to rise or fall in concert, implying that the pattern as a whole constituted a significant neuro-muscular unit of control.

Journal Article↗
PubMed1982

Repetitive skill deterioration with fast and exercise-lowered blood glucose.

Using a computerized system for measurement of the variability of force exerted at 26 points in each pedal revolution during the repetitive habituated task of cycling, healthy adult males 6 times performed for 20 minutes, either (a) 3 hours after a meal (fasting) or when so fasted and then fed glucose (b) immediately before, or (c) 30 minutes before performance. Both light and moderate workloads were used. As expected, blood glucose concentrations fell modestly below basal with exercise under (a) or (c) but not under (b). ANOVA of force mean and variability statistics significantly contrasted the 3 treatments, and 2 linear functions from multivariate analysis showed (a) and (c) to be significantly different from (b). These two treatments depressing blood glucose were more variable in force applied, with altered pattern of average forces, especially for points in the task where changes occurred in the force/time relationship. These points may use more immediate feedback correction. Such deterioration of movement control has significant applied implications and invites study of its neural aetiology.

Adult↗
PubMed1982

Between-minute stability in habituated human skill with modestly lowered blood glucose.

Modestly lowered blood glucose (G) occurs with fasting and exercise, increasing variability in forces applied during repetitions of an habituated cycling task. Its effect was studied on stability of the movement cycle pattern of forces from minute to minute. Forces applied at 26 positions in the movement cycle were correlated with each other over 20 one minute samples. Six young men worked (a) 3 hr post-prandial, or as (a) but terminated by feeding 100 g (G) slurry (b) immediately before or (c) 30 minutes before exercise. For each sample, data were averaged over subjects, feet, exercise loads (100 W; 150 W) and 40 movement cycles. Over all conditions together, the movement cycle forces were strongly patterned, implying control by pre-set neural programs. Evoked depressions of blood G below fasting coincided with significant reduction in this patterning. It is suggested that in neural control circuits with modestly depressed blood G, there may be increased sensitivity to feedback over movement cycles.

Adult↗
PubMed1980

Diet, physiological work and accident incidence of forge workers.

Three experiments were made to study the following three factors in forge workers in a hot shop: (a) the metabolic load of daily work, (b) dietary intake, and (c) the effect of supplementing morning dietary intake with glucose syrup ingestion upon accident incidence. High energy output, mean 9.7 MJ (2,300 kcal), complemented high energy intake, mean 15 MJ (3,600 kcal), a shortage of intake in the morning being compensated for after work in the evening. Alcohol intake represented 1 to 2 MJ (240 to 480 kcal) of the evening intake. Glucose syrup ingestion to reverse increased use of fats in the metabolic fuel in the early morning, in a double-blind design, resulted in a significant reduction of accidents. The effect may lie in altered levels of 5-hydroxytryptamine in the central nervous system. Caution in interpreting the effect upon accidents is necessary since the number of subjects was small (57) and the time span limited (18 weeks).

Accidents, Occupational↗
PubMed1979

Bimodal relationship of human tremor and shivering on introduction to cold exposure.

Four subjects were exposed to an environmental challenge of -12 degrees C for 15 min in four conditions of exposure: 1) clothed body and clothed arm, 0.5 clo units: 2) clothed body and exposed arm, 0.4 col; 3) exposed body and exposed arm, 0.1 clo: 4) exposed body and clothed arm, 0.2 clo. Core temperature, surface temperature of the right arm, perceived thermal comfort, EMG indicated onset of shivering, and the frequency of tremor using accelerometry were monitored and data collected every 30 s. The results indicate that tremor frequency significantly increases with cold exposure, but that a significant drop in tremor frequency precedes the onset of shivering. It is suggested that pre-shivering tetany occurs prior to the onset of shivering, acts as a load upon the lever of the hand and reduces the oscillation of the limb.

Adult↗
PubMed1978

Hormonal and cardiac response of autistic children to changes in environmental stimulation.

A study was made of physiological responses of autistic children to variations in environmental load in order to examine the under- versus over-arousal dichotomy. More specifically, measures of urinary mucoprotein excretion and mean heart rate and three measures of heart rate variability were compared with matched controls in conditions of normal, high, and low total environmental load. The results suggest that, although behaviorally unresponsive, the autistic children responded physiologically, were generally in a lower state of arousal than the control group, and were labile in response to changes in stimulation.

Acoustic Stimulation↗