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Biomedical subjects

C L Richards

Publications and source records attributed to C L Richards.

50 records · Page 3Linked to original sources
PubMed1991

Effects of a single session of prolonged plantarflexor stretch on muscle activations during gait in spastic cerebral palsy.

Activations of the triceps surae (TS) and tibialis anterior (TA) muscles during gait were studied in children with spastic cerebral palsy (CP) immediately before and after 30 min of standing on a tilt-table with the ankle dorsiflexed to stretch the TS in the experimental group (n = 8) or after a rest period in the control group (n = 11). The EMG activity from the TS and TA was recorded concomitantly with electronic footswitch signals by a computer. Video records were made of the sagittal gait movements. Effects of PMS were determined by comparing change scores for selected spatiotemporal and muscle activation parameters between the groups. The change scores defined for the muscle activations were: a post-test/pre-test ratio of the EMG activity in specific segments of the gait cycle and a locomotor spasticity index. PMS did not significantly (p greater than 0.05) affect any of the spatiotemporal parameters nor did it alter any of the TS and most of the TA activation parameters or the SI indexes for the TS and TA. Only the TA post/pre activation ratio for the 0-16% segment of the gait cycle was smaller (p less than 0.01), indicating a decrease in TA activation post-PMS.

Adolescent↗
PubMed1991

Strength recovery and muscle activation of the knee extensor and flexor muscles after arthroscopic meniscectomy. A pilot study.

Maximal isokinetic strength and electromyographic activity of the operated leg were measured preoperatively and one, two, three, and eight weeks postoperatively after a partial medial meniscectomy by arthroscopy in a group of ten patients. Strength deficits, measured with a Kin-Com dynamometer using a static preloading protocol, were found in comparison with a group of matched healthy subjects preoperatively and three and eight weeks postoperatively in the knee extensors. These deficits were related to previously unreported modifications in the shape of the moment-angle curves and a tendency to lower activation levels of the vastus medialis (VM) but not the vastus lateralis or rectus femoris muscles. No deficits were found in the knee flexors preoperatively or three and eight weeks postoperatively, but the medial hamstrings activation level was lower for movements at 30 degrees per second. During flexion movements, the percentage of coactivation of the antagonist VM was significantly greater than healthy values at 30 degrees and 180 degrees per second. These results clearly indicate that neuromuscular recovery is not complete when return to work is advocated three to four weeks postoperatively. Such findings suggest the need for a rehabilitation program to promote recovery of the knee muscles in workers with a physically demanding occupation.

Adult↗
PubMed1990

Angle dependency in strength measurements of the ankle plantar flexors.

Muscle strength (or muscular moment) generated during dynamic contractions varies with joint angle. This raises the question about the choice of a representative angle in the evaluation of strength capacity. To assess this angle dependency in strength measurements, dynamic moment-angle curves for plantar flexor muscles were obtained in 43 healthy subjects (28 men and 15 women) with a controlled acceleration dynamometer at 0.52 rad s-1 (30 degrees s-1) and using maximal static preloading before the beginning of movement to attenuate the force development phase. Differences between gender and correlations between strength and anthropometric measures were calculated at each 0.087 rad (5 degrees). The plantar flexion moment was larger in men, in general, but this difference was largest when the ankle was most dorsiflexed. The correlations between moment and anthropometric measures were also higher in the first half of the plantar flexion movement. These results stress the importance of reporting joint angles at which moment of force measures were made. Furthermore, they show that the maximal strength capacity of the plantar flexors is best represented by the moment measured in dorsiflexion angles when the muscles are lengthened.

Ankle Joint↗
PubMed1990

Effects of prolonged muscle stretch on reflex and voluntary muscle activations in children with spastic cerebral palsy.

We studied the short term effects of a single session of prolonged muscle stretch (PMS) on reflex and voluntary muscle activations in 22 children with spastic cerebral palsy (CP) assigned to an experimental (n = 12) and a control group (n = 10). Children of the experimental group underwent PMS of the triceps surae (TS) by standing with the feet dorsiflexed on a tilt-table for 30 min, whereas children of the control group were kept at rest. The effects were determined by measuring the associated changes in torque and in electromyographic (EMG) activity of the TS and tibialis anterior (TA) muscles during both passive ankle movements and maximal static voluntary contractions. The results indicate that PMS led to reduced spasticity in ankle muscles as demonstrated by the significant reductions (p less than 0.05) of the neuromuscular responses (torque and EMG) to passive movement. These inhibitory effects lasted up to 35 min after cessation of PMS. In addition, the capacity to voluntarily activate the plantar flexors was significantly (p less than 0.05) increased post-PMS, but the capacity to activate the dorsiflexors was apparently not affected. These findings suggest that repeated sessions of PMS may have beneficial effects in the management of spasticity in children with CP.

Cerebral Palsy↗
PubMed1988

Influence of contractile tension development on dynamic strength measurements of the plantarflexors in man.

The influence of the contractile tension rise time on isokinetic force-angle records has been inferred from static force-time curves but has not been experimentally determined. The purpose of this study is thus to describe the influence of the contractile rise time on the force-angle curves produced during maximal voluntary, acceleration controlled, isokinetic plantarflexions at 30 degrees/s. Since we could not measure directly the period of force development unbiased by changes in muscle length during the movements, we devised an experimental strategy which allowed the computation of the dynamic force-time curve. Thus in five normal men, we first recorded force-angle curves produced during maximal voluntary plantarflexion movements preceded by maximal static pre-loading (D:-10 degrees Max) in order to eliminate the period of tension development from the force-angle record. Next, we recorded force-angle curves produced during maximal voluntary contractions initiated from two different starting angles without pre-loading (D:-10 degrees Min and D:0 degrees Min) to include the period of tension rise. The dynamic force-time curve was computed by correcting these force-angle curves (D:-10 degrees Min and D:0 degrees Min) for the hypothetical loss in force due to muscle shortening. We compared the relative (to remove the effects of force magnitude) computed dynamic force-time curves with relative static force-time curves measured at three different angles. We found the shape and several other parameters of all three static and both computed dynamic force-time curves to be similar (p greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Study of human muscle contraction using electrically evoked twitch responses during passive shortening and lengthening movements.

Electrically evoked twitch properties of the human plantarflexor muscles were measured with the muscles at a constant length (static) and during passive shortening and lengthening. A Kin-Com dynamometer system was used to passively move the ankle joint at 0.52 rad s-1 (30 degrees s-1), as well as to record the twitch responses which were elicited by supramaximal electric shocks applied over the tibial nerve in the popliteal fossa. In the lengthening and shortening conditions, twitches were evoked by triggering the shocks so that the twitch response occurred at a similar angular position for all three conditions. The lengthening twitch peak torque was about twice as large as that recorded for the shortening condition. There was, however, no statistical difference in the twitch time course in these three testing conditions. This twofold increase in the peak twitch torque during lengthening, compared to shortening, is much greater than the torque increase reported during eccentric, as compared to concentric maximal voluntary contractions. These findings suggest that a deactivation process of the contractile system occurs during muscle shortening, while in contrast, during passive lengthening a potentiation mechanism is acting, and that both these mechanisms are independent of volitional muscle activation. The present study is the first to demonstrate the possibility of electrically evoked contractions of human muscles during passive lengthening and shortening. We believe that the use of such evoked contractions may be promising for the study of contractile behaviour of human skeletal muscles during eccentric and concentric conditions.

Adult↗
PubMed1987

Action of 5-hydroxytryptamine, substance P, thyrotropin-releasing hormone and clonidine on motoneurone excitability.

We have investigated the influence on the excitability of lumbar motoneurons of 5-hydroxytryptamine (5-HT), substance P and thyrotropin releasing hormone (TRH), three substances which coexist in the same bulbospinal descending pathway and end in large part around motoneurons. We have also studied the effect of clonidine, an alpha 2 noradrenergic agonist. This was done in spinalized rats (T5) treated three weeks before with 5-7-dihydroxytryptamine. Under those circumstances 5-HTP (I.P.), 5-HT (intrathecally) TRH (I.P. or I.T.) and substance P (I.T.) all elicited a strong excitation of motoneurons as measured by integrated EMG of the hindlimb muscles. Substance P reduced by almost half the subsequent response to 5-HTP, 1 hour and 24 hours later. TRH given acutely did not modify the response to 5-HTP but given chronically for twenty one days by means of Alzet minipump, markedly increased the response to 5-HTP. Clonidine by itself decreased the excitability of motoneurons and antagonized the excitatory effect of 5-HTP and TRH. In a pilot trial, cyproheptadine, a 5-HT antagonist was shown to decrease the manifestations of spasticity in patients with a partial spinal lesion. Clonidine also appears to be of potential use in the treatment of spasticity.

5-Hydroxytryptophan↗
PubMed1984

Quantitative evaluation of the effects of acetazolamide in Friedreich's ataxia: a pilot study.

We evaluated the effects of acetazolamide in 4 young patients with Friedreich's ataxia by clinical and quantitative laboratory methods. Dynamic muscle function of the lower extremity was measured during isokinetic knee movements and gait. The acetazolamide trial was terminated at 7 to 11 weeks because of reported side effects or increased ataxia in 3 of the patients. The quantitative evaluations revealed lower dynamic strength values and alterations in the gait movement pattern in all patients. These changes, which were interpreted as deterioration, were partially reversible with cessation of acetazolamide. The advantages of such quantitative evaluations of dynamic muscle function in the evaluation of therapy in Friedreich's ataxia are discussed.

Acetazolamide↗
PubMed1983

Quantitative evaluation of the effects of L-dopa in torsion dystonia: a case report.

We used electrophysiologic methods in the diagnosis of torsion dystonia and the evaluation of therapy in a 7-year-old child. Electromyographic (EMG) activity patterns in five leg muscles were recorded during specific voluntary and passive movements as well as during gait. We found patterns of coactivation in leg muscles in walking or isolated movements, and a shortening reaction was seen in the tibialis anterior. These findings in combination with clinical observations led to the diagnosis of torsion dystonia and the choice of L-dopa therapy. Beneficial effects of therapy were assessed by the same methods.

Child↗
PubMed1982

Action of cyproheptadine in spastic paraparetic patients.

The antiserotonergic agent cyproheptadine was evaluated in six patients as a medication for the management of spasticity due either to spinal cord trauma or to multiple sclerosis. Oral doses of cyproheptadine were progressively increased from 6 mg to 24 mg per day. Trial periods extended from 4 to 24 months and included a placebo substitution period. Cyproheptadine was found to decrease significantly the spontaneous and elicited ankle clonus in all six patients and spontaneous spasms in five patients. Cyproheptadine decreased the EMG activity and the dynamic strength produced by the knee extensor and flexor muscles during isokinetic movements in two of the four patients evaluated objectively. Subjectively, however, the patients did not report diminished strength.

Adult↗
PubMedDate not supplied

Results of a triple blind clinical study of myoblast transplantations without immunosuppressive treatment in young boys with Duchenne muscular dystrophy.

The effects of myoblast transplantations without an immunosuppressive treatment on muscle strength, and the formation of dystrophin-positive fibers was studied in five young boys with Duchenne muscular dystrophy (DMD) using a triple blind design. Injections of myoblasts were made into one biceps brachii (BB), and the opposite BB, used as a control, was sham-injected; the experimenters and the patient were blind to the myoblast-injected side. At the same time, myoblasts were also injected in the left tibialis anterior (TA) of these patients. The strength developed during maximal static contractions of the elbow flexor and extensor muscles was measured with a Kin-Com dynamometer. No increase in static elbow flexion torque was measured at any time from 2 mo up to 18 mo after the transplantation. One month after the transplantation, the percentage of dystrophin-positive fibers in the myoblast-injected TA ranged from 0 to 36%, while it ranged from 0 to 4% on the control side. The expression of dystrophin in these fibers, however, was generally low, and most likely less than 10% of the normal level. In the biceps brachii of both sides 6 mo after the transplantation, less than 1.5% of dystrophin-positive fibers were detected. The injections also triggered a humoral immune response of the host. Antibodies were capable of fixing the complement, and of lysing the newly formed myotubes. One of the antigens recognized by this immune response is possibly dystrophin. These results strongly suggest that myoblast transplantations, as well as gene therapy for DMD, cannot be done without immunosuppression.

Biopsy↗
PubMedDate not supplied

Abstinence promotion and the provision of information about contraception in public school district sexuality education policies.

CONTEXT: For more than two decades, abstinence from sexual intercourse has been promoted by some advocates as the central, if not sole, component of public school sexuality education policies in the United States. Little is known, however, about the extent to which policies actually focus on abstinence and about the relationship, at the local district level, between policies on teaching abstinence and policies on providing information about contraception. METHODS: A nationally representative sample of 825 public school district superintendents or their representatives completed a mailed questionnaire on sexuality education policies. Descriptive and multivariate analyses were conducted to identify districts that had sexuality education policies, their policy regarding abstinence education and the factors that influenced it. RESULTS: Among the 69% of public school districts that have a district-wide policy to teach sexuality education, 14% have a comprehensive policy that treats abstinence as one option for adolescents in a broader sexuality education program; 51% teach abstinence as the preferred option for adolescents, but also permit discussion about contraception as an effective means of protecting against unintended pregnancy and disease (an abstinence-plus policy); and 35% (or 23% of all U.S. school districts) teach abstinence as the only option outside of marriage, with discussion of contraception either prohibited entirely or permitted only to emphasize its shortcomings (an abstinence-only policy). Districts in the South were almost five times as likely as those in the Northeast to have an abstinence-only policy. Among districts whose current policy replaced an earlier one, twice as many adopted a more abstinence-focused policy as moved in the opposite direction. Overall, though, there was no net increase among such districts in the number with an abstinence-only policy; instead, the largest change was toward abstinence-plus policies. CONCLUSIONS: While a growing number of U.S. public school districts have made abstinence education a part of their curriculum, two-thirds of districts allow at least some positive discussion of contraception to occur. Nevertheless, one school district in three forbids dissemination of any positive information about contraception, regardless of whether their students are sexually active or at risk of pregnancy or disease.

Adolescent↗