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Biomedical subjects

G Kamen

Publications and source records attributed to G Kamen.

At least 37 records · Page 2Linked to original sources
PubMed1992

Contralateral influences on triceps surae motoneuron excitability.

In an effort to more fully investigate spinal reflex pathways in humans, we measured the isometric force-time curve of the tibial nerve H-reflex in 12 college age subjects. We also conditioned the reflex with a contralateral H-reflex stimulus or a contralateral tendon-tap, to ascertain the effects of crossed spinal segmental inputs on alpha motoneuron excitability. The conditioning stimulus preceded the test reflex by 10, 25, 40, 55, 70, 85, 100, 115, 130 or 145 msec. The results demonstrate that a conditioning tibial nerve H-reflex produced marked facilitation onto the contralateral triceps surae motoneurons, predominantly at longer-latency intervals. Conversely, a conditioning Achilles tendon-tap produced long-latency inhibition to the triceps surae. These results demonstrate that differential motoneuron excitability changes can be produced by electrical and mechanical conditioning stimuli. Moreover, these excitability changes may be long lasting and only appear after a relatively long latency. Several neurophysiological mechanisms are proposed to contribute to these changes.

Adult↗
PubMed1992

Segmental reflex organization in endurance-trained athletes and untrained subjects.

In an effort to investigate the effects of training on spinal reflex pathways in humans, we measured the isometric force-time curve of the patellar (PTR) and Achilles (ATR) tendon-tap reflex in 12 endurance-trained (ET) athletes and 12 control (C) subjects. We also conditioned the tendon jerk with a contralateral or ipsilateral tendon-tap stimulus, to ascertain the effects of segmental inputs on crossed-spinal reflex activity. The conditioning stimulus preceded the test reflex by 25, 40, 55, 70, 85, 100, 115, 130, or 145 ms. The results demonstrated significant differences in control reflexes and conditioned reflexes between the two groups. A contralateral patellar tendon-tap produced a significantly greater excitatory effect to the contralateral quadriceps motoneurons for the ET group, whereas a contra- or ipsilateral conditioning caused a significantly greater inhibitory effect to the triceps surae motoneurons for the ET athletes. These results demonstrate that motoneuron excitability changes can be produced as a result of ipsi- and contralateral segmental inputs, and raise the possibility that trained athletes demonstrate different reflex recovery profiles. Several neurophysiological mechanisms are proposed to contribute to these changes.

Achilles Tendon↗
PubMed1991

Effects of percutaneous stimulation on motor unit firing behavior in man.

Motor unit firing behavior in human first dorsal interosseous (FDI) muscle was studied during controlled constant force isometric contractions. The threshold at which motor units were recruited and the mean firing rate at 50% of maximal voluntary contraction (MVC) were evaluated following stimulation of the skin area over the second digit. Stimulation of cutaneous receptors tended to increase the recruitment threshold of most of the motor units recruited under 20% MVC, while high-threshold motor units (those recruited over 30% MVC) generally exhibited a decrease in recruitment threshold. Less dramatic changes in motor unit firing rates were observed, but those motor units recruited over 30% MVC exhibited some increase in firing rate. The relationship between the change in recruitment threshold and change in motor unit firing rate is not rigid and seems to be susceptible to considerable synaptic noise.

Action Potentials↗
PubMed1991

Interactions in human quadriceps-triceps surae motoneuron pathways.

In an effort to more fully investigate spinal reflex pathways in humans, we measured the isometric force-time curve of the patellar (PTR) and Achilles (ATR) tendon-tap reflex in 12 college age subjects. We also conditioned the tendon jerk with a contralateral or ipsilateral tendon-tap stimulus, to ascertain the effects of segmental inputs on crossed-spinal reflex activity. The conditioning stimulus preceded the test reflex by 25, 40, 55, 70, 85, 100, 115, 130 or 145 ms. The results demonstrate that a tap to the contralateral patellar tendon produced long-latency excitation of quadriceps motoneurons, but a tap to the contralateral Achilles tendon produced short-latency facilitation and long-latency inhibition of the triceps surae motoneurons. Also, a conditioning tap to the contra- or ipsilateral patellar tendon produced a brief short-latency facilitation that was followed by a distinct, long-latency inhibition of triceps surae motoneurons. These results demonstrate that motoneuron excitability changes can be produced as a result of ispi- and contralateral segmental inputs. Moreover, these excitability changes may be long-lasting and only appear after a relatively long-latency. Several neurophysiological mechanisms are proposed to contribute to these changes.

Achilles Tendon↗
PubMed1991

Organization of segmental reflexes in trained dancers.

Unilateral and conditioned Achilles tendontap reflex (ATR) characteristics were examined in a group of skilled dancers and a group of sedentary, untrained subjects (n = 7/group). For the conditioned reflex, the right ATR was conditioned by a tap to the left Achilles tendon using intervals of 10, 40, 70, 100, 130, 160 and 190 ms. Peak isometric force, contraction time and half-relaxation time were examined on each trial. The results indicated that the trained dancers exhibited less unilateral isometric force and longer half-relaxation times (p less than 0.05) than the untrained subjects. Moreover, the contralateral conditioning stimulus caused a more marked short-latency facilitation as well as a long-latency inhibition in the reflex force characteristics for the trained dancers when compared with the untrained subjects. These differences in both simple and conditioned reflexes in individuals trained for dance activities may reflect differences in muscle stiffness, tissue compliance or neural organization.

Achilles Tendon↗
PubMed1991

Stimulus intensity and experimental design effects on motor response processing.

Experimental design effects and range effects may have influenced previous studies on motor response processing (Grice & Hunter, 1964; Grice, Nullmeyer, & Schnizlein, 1979; Poulton, 1973). This investigation was conducted concurrently with two experiments. First, Erlebacher's (1977) more powerful analysis of variance (ANOVA) model, which allows for the testing of the independent variable (stimulus intensity effect), the experimental design effect (between-subjects [BS] vs. within-subjects [WS]), and the important interaction between independent variable and experimental design was utilized to clarify if the nature of the experimental design (BS, WS) biases motor response processing. Second, Erlebacher's (1977) ANOVA model was used to determine if motor response processing was affected by stimulus intensity and experimental design when different ranges of auditory stimuli were compared. Results indicate motor response processing was inversely affected by increasing stimulus intensity. Experimental design effects and range effects did not appear to bias motor response processing. We conclude stimulus intensity effects on motor response processing appear to be the result of true neuromotor functioning and not artifacts of experimental design or of range effects.

Acoustic Stimulation↗
PubMed1990

Quadriceps excitability is enhanced by a conditioning tap to the Achilles tendon.

In an effort to more fully investigate spinal reflex pathways in humans, we measured the isometric force-time characteristics of the patellar tendon-tap reflex in ten college-age subjects. We also conditioned the tendon jerk with a tap to the contralateral Achilles tendon or the ipsilateral Achilles tendon. The results clearly demonstrated that a conditioning tap to the Achilles tendon produced a marked (greater than 200 percent) excitatory effect onto the quadriceps muscle. Also, this effect occurred sooner when the quadriceps was conditioned by an ipsilateral stimulus rather than a contralateral stimulus. It is concluded that in accord with other conditioning studies to date, the quadriceps muscle is characterized by a predominantly excitatory effect caused by a conditioning stimulus, and that this arousal is independent of the origin of the conditioning stimulus.

Achilles Tendon↗
PubMed1989

Unusual motor unit firing behavior in older adults.

Motor unit firing behavior was studied in the first dorsal interosseus (FDI) and tibialis anterior (TA) muscles of 10 aged subjects during slow, isometric contractions. Previous study in younger individuals had shown that motor units are recruited and derecruited in an orderly manner whereby the early-recruited units are the last to be derecruited. However, there were several examples in the old subjects in which some high-threshold motor units were derecruited at much lower levels of force. Concurrent antagonist firing in an effort to maintain the required precision is considered a likely candidate for such prolonged motor unit activation.

Action Potentials↗
PubMed1989

Long-latency enhancement of quadriceps excitability from stimulation of skin afferents in young and old adults.

This study examined the role of cutaneous input on spinal excitability in young and old adults. Patellar tendon reflexes were elicited in 15 old adults (M = 75 yrs) and 25 young adults (M = 26 yrs) at intervals ranging from 15 to 175 ms following cutaneous stimulation to one of four skin sites: (a) ipsilateral calf, (b) contralateral calf (old adults only), (c) ipsilateral anterior thigh, and (d) contralateral anterior thigh. The younger adults had a more vigorous reflex response than the older adults, as indicated by peak force. Force latencies were also faster for the younger adults than the older adults. However, both age groups showed a long-latency facilitation of quadriceps excitability regardless of cutaneous stimulation site. Thus, it seems that low threshold cutaneous afferents contribute an excitatory input to the extensor motoneuron pool that is maintained with age.

Adult↗
PubMed1988

Conditioned patellar tendon reflexes in sprint- and endurance-trained athletes.

Tendon reflex characteristics were examined in endurance-trained, sprint-trained, and control subjects (10 SS/group) using a conditioned patellar tendon reflex (PTR) paradigm. Paired PTRs were administered using inter-tap intervals of 0, 25, 50, 75, 150, and 300 ms, with the left leg reflex elicited first, followed by a right leg PTR. A force transducer secured at the ankle was used to measure peak force, time to peak force, and reflex latency. In the unilateral condition, significant differences (P less than 0.05) existed between athletic groups, with the sprint-trained athletes exhibiting greater peak force, faster time to peak force, and faster reflex latency than the endurance athletes. Significant differences (P less than 0.05) also existed for the conditioned reflex. There was a slight depression in reflex parameters in the untrained and sprint-trained groups up to an interval of 50 ms. At later intervals (greater than 50 ms), a marked enhancement occurred in all groups for all dependent measures studied. This longer latency excitatory effect persisted until the 150 ms interval. These differences in both simple and conditioned reflexes in individuals trained for endurance and sprint activities may reflect inherent differences in muscle-tendon stiffness or neural organization.

Adult↗
PubMed1986

Effects of exercise and anabolic steroids on total and lipoprotein cholesterol concentrations in male and female rats.

Forty male and 40 female rats were randomly assigned to 1 of 4 experimental groups. Half of the animals of each gender were exercised by jumping (weighted by a vest with up to 70% body weight) to a height of 16 cm 20 times X d-1 (30 s between jumps) 5 d X wk-1 for 8 wk. Half of the exercised animals and half of the sedentary animals were injected with the anabolic steroid durabolin (0.2 mg in 0.1 ml sesame seed oil) 6 d X wk-1 for the last 3 wk of the 8-wk exercise program. The other animals were injected with 0.1 ml of sesame seed oil (as a placebo) on the same schedule. At the end of the 8-wk program, blood was drawn from the right atria of the anesthetized animals. Plasmas were analyzed for total cholesterol (TC) and high density lipoprotein cholesterol (HDL-C) concentrations. Low density lipoprotein cholesterol (LDL-C) concentration was estimated as the difference between these two parameters (TC - HDL-C). A three-factor analysis of variance (2 X 2 X 2) demonstrated that there was a significant (P less than 0.05) gender effect (males greater than females), but no steroid or exercise main effects for TC. There were significant (P less than 0.05) steroid and exercise main effects for both HDL-C and estimated LDL-C, as well as a significant gender main effect for estimated LDL-C (but not HDL-C).(ABSTRACT TRUNCATED AT 250 WORDS)

Anabolic Agents↗
PubMed1984

Ulnar and posterior tibial nerve conduction velocity in athletes.

Ulnar and posterior tibial motor nerve conduction velocity (NCV) was assessed in 91 athletes and nonathletes. The athletes included male weight lifters, swimmers, jumpers and male and female track sprinters and distance runners. NCV of the weight lifters was significantly faster than that of the other groups for both motor nerves. The male marathoners had the slowest posterior tibial NCV of all subject groups. A discriminant function analysis was successful in classifying 50.6% of the subjects into power-type, endurance-type, or untrained categories, based on ulnar and posterior tibial nerve conduction velocities. These results suggest that both genetic and environmental factors are important determinants of motor nerve conduction velocity.

Body Height↗
PubMed1984

Strength recovery patterns following exercise with an imposed myotatic stretch.

An investigation was conducted to determine the effects of isometric exercise with an imposed myotatic stretch on the resultant pattern of strength recovery in trained and untrained subjects. Thirty 5-second maximal isometric contractions were administered to 12 trained and 12 untrained men with an intertrial interval of 10 seconds. On one day a 1-second stretch was delivered during each 5-second trial, while on another day, only isometric exercise was performed. Results showed that the pattern of strength recovery over the 10-minute recovery period was similar for both groups and both exercise conditions. However, during the first minute of the recovery period, the imposed stretch exercise resulted in a much faster rate of strength recovery than isometric exercise. It is concluded that the recovery of maximal isometric strength can be altered with the type of muscle contraction involved in the exercise task.

Adult↗
PubMed1983

The acquisition of maximal isometric plantar flexor strength: a force-time curve analysis.

A paradigm involving the static force-time curve was used to study the mechanisms through which gains in maximal isometric strength are achieved during repeated testing. Twelve males performed three maximal contractions of the plantar flexors on each of six test days. Each contraction was executed as rapidly as possible, with the force recorded on a rapidly moving pen recorder. Although highly significant increases in maximal plantar flexor strength occurred over the six days, no changes were seen in the maximal rate of tension development. However, assessment of the amount of force reached at absolute time intervals revealed that more force was attained at the early time intervals on the first few days of testing than on the later days, indicating a distinct change in the shape of the static force-time curve. Several neural mechanisms are suggested to explain the alteration in shape of the static force-time curve which accompanies the acquisition of maximal strength.

Journal Article↗
PubMed1981

Fractioned reaction time in power-trained and endurance-trained athletes under conditions of fatiguing isometric exercise.

Fractionated knee extensor and plantar flexor reaction time (RT) components were assessed in a group of eight weightlifters and eight long distance runners. Following a 4-day period of baseline stabilization for each muscle group, a 50% maximal voluntary contraction (MVC) holding-time exercise was administered. Results showed that the runners had longer premotor times (PMT) than the weightlifters in the knee extensors, but had much faster PMTs than the lifters in the plantar flexor condition. Compared to previously reported investigations using non-athletes, the data for the present sample of athletes indicated faster total reaction times(TRT) in both the knee extensors and the plantar flexors. A resistance of 15% MVC applied during the RT task resulted in a lengthening of the motor time (MT) component in both groups prior to exercise. However, while knee extensor resisted motor time was lengthened by the exercise task, no such lengthening occurred in plantar flexor resisted RT. It is concluded that power-trained and endurance-trained athletes exhibit difference in response to a fractionated RT task, under both baseline and fatiguing exercise conditions.

Journal Article↗
PubMed1981

Exercise effects upon reflex time components in weight lifters and distance runners.

In an effort to identify neuromuscular parameters which differentiate between power-type and endurance-type athletes, an investigation was conducted to determine the effects of an isometric exercise task upon patellar and Achilles fractionated reflex time components in a group of weight lifters and long-distance runners. A reflex hammer was used to deliver a tendon tap stimulus to the patellar tendon (sitting position) and the Achilles tendon (prone position). Under resting conditions, no differences in Achilles reflex components existed between the two subject groups. However, patellar reflex latency was significantly shorter in the weight lifters than in the distance runners. Following knee extensor exercise consisting of three bouts of a 50% MVC holding-time task, the power group manifested a marked lengthening in total reflex time and reflex motor time. In the endurance group, reflex time lengthened after the first bout, but became shorter after the last two bouts. A similar Achilles reflex pattern was seen in both groups after plantar flexor exercise--an initial elongation of the peripheral components of reflex time, followed by a trend towards shorter reflex components in the later bouts. It was suggested that several factors may be competing to produce the bi-directional results observed in reflex time components following isometric exercise.

Achilles Tendon↗