Biomedical subjects

R R Roy

Publications and source records attributed to R R Roy.

At least 181 records · Page 10Linked to original sources

PubMed1990

Enzyme profiles of single muscle fibers never exposed to normal neuromuscular activity.

Do muscle fiber properties commonly associated with fiber types in adult animals and the population distribution of these properties require normal activation patterns to develop? To address this issue, the activity of an oxidative [succinic dehydrogenase (SDH)] and a glycolytic [alpha-glycerophosphate dehydrogenase (GPD)] marker enzyme, the characteristics of myosin adenosinetriphosphatase (myosin ATPase, alkaline preincubation), and the cross-sectional area of single fibers were studied. The soleus and medial gastrocnemius of normal adult cats were compared with cats that 6 mo earlier had been spinally transected at T12-T13 at 2 wk of age. In control cats, SDH activity was higher in dark than light ATPase fibers in the soleus and higher in light than dark ATPase fibers in the medial gastrocnemius. After transection, SDH activity was similar to control in both muscles. GPD activity appeared to be elevated in some fibers in each fiber type in both muscles after transection. The cross-sectional areas most affected by spinal transection were light ATPase fibers of the soleus and dark ATPase fibers of the medial gastrocnemius, the predominant fiber type in each muscle. These data demonstrate that although the muscle fibers of cats spinalized at 2 wk of age presumably were never exposed to normal levels of activation, the activity of an oxidative marker enzyme was maintained or elevated 6 mo after spinal transection. Furthermore, although the absolute enzyme activities in some fibers were elevated by transection, three functional protein systems commonly associated with fiber types, i.e., hydrolysis of ATP by myosin ATPase and glycolytic (GPD) and oxidative (SHD) metabolism, developed in a coordinated manner typical of normal adult muscles.

Animals↗

PubMed1990

Influence of 7 days of hindlimb suspension and intermittent weight support on rat muscle mechanical properties.

Unloading the rat hindlimb results in a decrease in mass, especially in those muscles that normally have a load-bearing function. The present study was designed to evaluate the effect of intermittent periods of weight support in ameliorating this atrophic response. Adult male Sprague-Dawley rats were assigned to either a control (CON), a hindlimb suspended (HS), or a hindlimb suspended plus intermittent weight support (HS-WS) group. HS-WS rats were walked slowly on a treadmill at 0.2 m/s and a 19% incline for 10 min, every 6 h. After 7 d, the in situ mechanical properties of the soleus (Sol) and medial gastrocnemius (MG) were studied. Body weights of HS and HS-WS rats were 9 and 13% lower than CON. The SOl weight relative to body weight was 21 and 9% lower in HS and HS-WS than CON. Maximum tetanic tension relative to muscle mass was significantly lower in HS than CON, whereas HS-WS had values similar to CON. The MG weight relative to body weight was significantly lower in both suspended groups. The maximum tetanic tension relative to muscle weight was significantly elevated in HS-WS compared to CON, suggesting that weight support may have preferentially maintained the contractile protein component of the muscle. Contraction times were 25% faster (p less than 0.05) in the Sol and unchanged in teh MG of HS rats. For each muscle, the fatigue properties were similar in all groups. These data indicate that a low-force, short-duration exercise regime results in a significant functional recovery in the "slow" Sol, whereas the "fast" MG is less affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Specific tension of human elbow flexor muscles.

Human muscle has a specific tension that is similar to that of other mammalian skeletal muscle. Further, it appears that with the appropriate application of present imaging capabilities, the specific tension of human muscle can be defined more precisely.

Elbow Joint↗

PubMed1989

EMG amplitude relationships between the rat soleus and medial gastrocnemius during various motor tasks.

The amplitude and temporal interrelationships of the EMG signals from the rat soleus (Sol) and medial gastrocnemius (MG) muscles during standing, locomoting on a treadmill at various speeds and inclines and swimming were studied. Joint probability density distributions demonstrated a high level of excitation of the Sol relative to the MG during standing. With increasing treadmill speed and/or incline, there was a greater probability of an enhancement in amplitude of the MG than the Sol. Further, there was a greater probability of higher EMG amplitudes of the deep, mixed fiber type region than the superficial, homogeneously fast fiber type region of the MG as speed and incline of locomotion increased. Based on the plotting of sequential points for the joint probability density distributions of EMG amplitudes of the two synergists, the data demonstrated a much greater amplitude modulation of the Sol than the MG during the initial phases of extensor activity. These plots also showed that the Sol activity terminated earlier than that of the MG. Consequently, the recruitment and derecruitment patterns of these two synergists showed a hysteresis effect, indicating that the motor pools of these two muscles do not function as a single entity. Further, differences in the EMG amplitude relationships of these synergists during a non-weight-bearing activity, i.e. swimming, in comparison to weight-supporting treadmill locomotion suggest that there is a strong peripheral influence on the neural control mechanisms involved.

Animals↗

PubMed1989

Co-contractions in antagonistic hindlimb muscles during simulated step cycle rates.

To determine whether the step cycle rate during locomotion may be limited by mechanical interactions of antagonistic muscles about the ankle, muscle activation patterns were simulated through electrical stimulation and muscle forces monitored in the rat lateral gastrocnemius-soleus (LGS) and tibialis anterior (TA) muscles. Simulations were made in acute experiments on Nembutal-anesthetized rats. Based on EMG data recorded from free-moving rats at 3 treadmill speeds, SOL mean cycle durations, cycles per second (eps), burst durations, and TA onset times following SOL EMG onset were determined. With muscle nerve stimulation based on these temporal patterns, muscle force was monitored from the detached tendons or directly at the approximate insertion sites. To investigate mechanical interactions attributed to the slow-twitch SOL muscle, forces were measured with the LGS intact, and after the SOL was denervated or the tendon was cut. With tendons detached, TA contraction force temporally overlapped with LGS or LG contraction force over periods ranging between 20 and 50 ms at 3.4 cps, 0-10 ms at 4.1 cps, and 0-10 ms at 4.6 cps. LGS force-time traces were asymmetrical, i.e. return time toward baseline force was more prolonged than the time to reach peak force. Without contributions to force from SOL activation, LG rate of relaxation was consistently increased and rate of rise and fall in force-time patterns were more symmetrical. Co-contractions were not observed when LGS contractions followed TA activation. At all cycle rates, forces remained above baseline (range 0.5-4.0 N) between contractions in LGS.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Electromyographic activity of cat hindlimb flexors and extensors during locomotion at varying speeds and inclines.

Electromyographic activity (EMG) was used to determine how hindlimb muscle activation patterns are modified as speed and incline of locomotion are varied in treadmill-trained cats. EMG was recorded using chronically implanted i.m. electrodes from the soleus, medial gastrocnemius, gluteus medius, and tibialis anterior muscles of adult cats during treadmill locomotion at a range of speeds and inclines. The patterns of changes in EMG activity at varying speeds and inclines were similar in all cats. Across speeds, the integrated EMG per step decreased for the soleus but remained constant for the other muscles. The integrated EMG per step was elevated in all muscles at higher inclines. Generally, with increased speed or incline the mean EMG per step was elevated in the medial gastrocnemius, gluteus medius, and tibialis anterior, the largest increase seen in the medial gastrocnemius. Soleus mean EMG per step remained unchanged with increased speed, but showed an absolute increase at the higher inclines. The integrated EMG per minute was always highest for the soleus followed by the medial gastrocnemius, and always lowest for the tibialis anterior. At the faster speeds, the 'on-time' increased in the tibialis anterior and decreased in the other muscles. These data suggest that the number of motor units activated and/or their firing frequencies increased in the medial gastrocnemius and the gluteus medius during locomotion at faster speeds or larger inclines, while relatively little change occurred in the soleus and tibialis anterior. These data also suggest that while there is considerable modulation of the level and duration of excitation of the extensor motor pools there is relatively little modulation of the flexor motor pools to adjust for both the speed and the incline of locomotion.

Acceleration↗

PubMed1989

Electromyographic (EMG) amplitude patterns in the proximal and distal compartments of the cat semitendinosus during various motor tasks.

The electromyographic (EMG) signals recorded from the proximal (STp) and distal (STd) compartments of the cat semitendinosus muscle (ST) during treadmill running at various speeds, jumping and paw-shaking were quantified to assess the degree of independence of neural control of the two portions of the muscle. Five adult cats were implanted with intramuscular electrodes in the STp and STd. Raw EMG signals were sampled, rectified and a modified form of their running average was used to calculate the mean EMG every 20 ms. EMG amplitudes of each portion of the muscle were plotted and their relative density distributions were generated. The relative density distribution was used to represent a measure of the probability of any two amplitudes occurring simultaneously (i.e. joint probability density distribution). Based on the probability density distributions of the EMG signals from different movements, the patterns of recruitment from the STp and STd were similar. However, during jumping and paw shaking, two relatively vigorous tasks, some deviations in the pattern were apparent. These data, therefore, suggest that the two ends of the ST are subjected to similar, but not identical, control mechanisms during the motor tasks studied.

Animals↗

PubMed1989

Effects of periodic weight support on medial gastrocnemius fibers of suspended rat.

Based on the current view that muscle fiber types reflect, at least to some degree, the probability of excitation of motor units in most normal movements, it was hypothesized that brief moderate periods of weight support would have little effect on a muscle that consists predominantly of high-threshold motor units. To test this hypothesis, the effects of 7 days of hindlimb suspension (HS) and HS plus intermittent weight support activity on the size and metabolic properties of individual fibers in the medial gastrocnemius (MG) were studied. HS resulted in a 40% decrease in the mean cross-sectional area of fibers that stain either dark or light for myosin adenosinetriphosphatase (ATPase) at an alkaline preincubation and are located in the deep region (i.e., close to the bone) of the MG. Dark ATPase fibers located in the superficial region were 17% smaller than controls (P greater than 0.05). Although the mean succinate and alpha-glycerophosphate dehydrogenase activities (optical density/min) per muscle fiber were not significantly (P greater than 0.05) affected by HS, it appeared that selected fibers of the deep MG region of HS rats had elevated enzyme activities. HS plus walking on a treadmill for 10 min every 6 h at 5 m/min and at a 19 degrees incline (total of 40 min/day) resulted in mean fiber cross-sectional area and enzyme activities nearer to control than the HS values. All adaptations were much less obvious in the fibers in a superficial (i.e., away from the bone) MG region.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗

PubMed1989

Exercise effects on the size and metabolic properties of soleus fibers in hindlimb-suspended rats.

The soleus atrophies rapidly when a rat is subjected to hindlimb suspension (HS), probably as a result of a decrease in the force encountered by the muscle. To test this premise, adult female rats were HS and half the rats were exercised (HS-EX) on a treadmill for 1.5 h.d-1 at 20 m.min-1 and a 30% grade. After 4 weeks, the midbelly of the soleus was prepared for histochemical analysis. Fibers were typed as dark or light staining for myosin ATPase, alkaline preincubation. Fiber size and quantitative histochemical enzyme activities of succinate dehydrogenase (SDH) were determined using a computer enhanced image processing system. In comparison to age-matched controls, the soleus wet weight was 69 and 30% smaller in HS and HS-EX rats. The mean cross sectional area of the dark ATPase fibers was reduced by 46 and 18% and light ATPase fibers by 69 and 48% in the HS and HS-EX, respectively. The percent dark ATPase fibers increased from 10% in the control rats to 19 and 17% in the HS and HS-EX. In both suspended groups, SDH activities in light ATPase fibers were 40% higher than control. The SDH activity of the dark ATPase fibers of HS-EX was 20% higher than control, while the dark ATPase fibers of HS were similar to control. To determine the degree to which these increases in SDH could be related to reductions in fiber size rather than increases in the actual amount of protein, integrated activity (activity/min x area) was calculated per fiber.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Influence of one-week hindlimb suspension and intermittent high load exercise on rat muscles.

Hindlimb suspension (HS) is a ground-based simulation model for spaceflight commonly used to study the effects of unloading on skeletal muscle. The purpose of the present study was to determine the effects of a daily short-duration, high-load exercise training program in ameliorating the atrophic response and associated adaptations in the mechanical properties of the soleus (SOL) and medial gastrocnemius (MG) muscles to HS. Male Sprague-Dawley rats (mean body weight, approximately 250 g) were assigned randomly to one of three groups: control (CON, n = 7), HS, (n = 7), and HS plus exercise (HS-EX, n = 8). The exercise consisted of rats climbing up a 1-m grid inclined at approximately 85 degrees for eight repetitions with a load equal to 75% body weight attached to their tails repeated four times daily during their active period. Following 7 days, soleus wet weights in the HS and HS-EX rats were 42 and 23% lower than those in the CON rats. The SOL muscle weight to body weight ratio in the HS group was 32% smaller than that in the CON group, whereas it was similar to that of CON in the HS-EX. Maximum tetanic tensions in the HS and HS-EX groups were 44 and 27% less than that in CON, with that in HS-EX being significantly greater than that in HS.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗

PubMed1988

Coexistent Hoffmann reflexes in human leg muscles are commonly due to volume conduction.

The existence of "concomitant" (coexistent) electromyographic reflex responses in soleus and tibialis anterior muscles, produced by posterior tibial nerve stimulation, has been cited as evidence for "reciprocal excitation" between these antagonistic muscles normally reflexly linked by reciprocal inhibition. Using the Hoffmann reflex procedure and posterior tibial nerve stimulation, the existence of true reciprocal excitation was tested in six subjects with no neuromuscular impairment. Coexistent EMG responses were observed in all subjects. In no instance, however, could the tibialis anterior EMG volley to posterior tibial nerve stimulation of the soleus muscle be antidromically blocked by common peroneal nerve stimulation applied at 10 to 20 ms offset latencies. A second stimulation pulse applied to the common peroneal nerve at similar offset latencies did antidromically block a tibialis anterior reflex response to common peroneal nerve stimulation. Therefore, volume conduction of reflex activity from the posterior tibial compartment to the anterior tibial compartment was a common observance. We suggest that coexistent EMG reflex responses, presumed to reflect reciprocal excitation, should be tested by the procedure described to reject the possibility of EMG cross-talk as a confounding variable or as the actual variable under investigation.

Adult↗

PubMed1988

Differential kinetics of fast and slow ankle extensors during the paw-shake in the cat.

Force, length, and EMG were assessed in the medial gastrocnemius and soleus muscles of two cats during the paw-shake response. The medial gastrocnemius produced high forces and significant electrical activity while force production and electrical activity were negligible in the soleus. This observation is significant as it provides evidence, through the direct measurement of muscle force, of selective recruitment of a fast muscle when a slow synergist is not activated. Additionally, the relationship among force, length, and neural activation indicates that the role of the medial gastrocnemius during the paw-shake response is to decelerate muscle lengthening and begin muscle shortening.

Animals↗

PubMed1988

Mechanical output of the cat soleus during treadmill locomotion: in vivo vs in situ characteristics.

To study the mechanical output of skeletal muscle, four adult cats were trained to run on a treadmill and then implanted under sterile conditions and anesthesia with a force transducer on the soleus tendon and EMG electrodes in the muscle belly. After a two-week recovery period, five consecutive step cycles were filmed at treadmill speeds of 0.8, 1.3 and 2.2 m s-1. Locomotion data in vivo included individual muscle force, length and velocity changes and EMG during each step cycle. Data for an average step cycle at each speed were compared to the force-velocity properties obtained on the same muscle under maximal nerve stimulation and isotonic loading conditions in situ. Results indicate that the force and power generated at a given velocity of shortening during late stance in vivo were greater at the higher speeds of locomotion than the force and power generated at the same shortening velocity in situ. Strain energy stored in the muscle-tendon unit during the yield phase in early stance is felt to be a major contributor to the muscle's enhanced mechanical output during muscle shortening in late stance.

Animals↗

PubMed1988

Fiber type composition of the plantarflexors of giraffes (Giraffa camelopardalis) at different postnatal stages of development.

1. A sample of fibers from deep (close to the bone) and superficial (away from the bone) regions of the plantaris (PLT) and medial (MG) and lateral (LG) gastrocnemius muscles of a neonatal, a 17-day-old and an adult giraffe were typed qualitatively as dark or light based on alkaline preincubation myosin ATPase staining properties and then sized. 2. Each muscle at all ages showed a higher percentage and a larger cross-sectional area (CSA) or light ATPase fibers in the deep than the superficial region. This relationship was qualitatively, although not quantitatively, similar to that reported in hindlimb muscles of other mammals. 3. At all ages, the PLT, the deepest muscle in the synergistic group, had the highest relative total CSA of light ATPase fibers among the muscles sampled. 4. At birth, the PLT had an unusually high percentage of light ATPase fibers in comparison to that found in the same muscle of other mammals. With age, the total CSA of light ATPase fibers increased dramatically in the PLT and decreased slightly in the MG and LG. 5. These data suggest that the PLT, especially the deep portion, may functionally replace the soleus muscle which is absent in the giraffe. In addition, the fiber type results demonstrate that the changes in the fiber type composition of individual muscles observed at different postnatal ages in the giraffe are relatively similar to that reported in smaller mammals, suggesting the existence of similar regulatory mechanisms.

Age Factors↗

PubMed1988

Metabolic and fiber size properties of cat tibialis anterior motor units.

The variability among single muscle fiber enzymatic activities and fiber size within a motor unit was studied in the cat tibialis anterior (TA) muscle. Fourteen units were isolated for physiological testing using standard ventral root filament stimulation techniques, and the muscle fibers of these units were identified by glycogen depletion. The cross-sectional areas, succinate dehydrogenase (SDH) and alpha-glycerolphosphate dehydrogenase (GPD) activities, and the relative alkaline myofibrillar adenosine triphosphate staining densities of a sample of glycogen-depleted and -nondepleted muscle fibers were determined using quantitative histochemical techniques. Each of the unit types previously identified to be present in the TA, based on physiological criteria, were represented by the sample population. The variability among the fibers of a unit was significantly more than the variability among repeated measures on a single fiber for cross-sectional area and SDH and GPD activities. The mean coefficients of variation for SDH and GPD activity within motor unit fibers were 29 and 56%, respectively, whereas the variability between fibers of different units within a muscle was significantly greater (53 and 69%, respectively). Additionally, the mean coefficient of variation for cross-sectional area among motor unit fibers was less than that among fibers not depleted of glycogen (25 vs. 46%). These data suggest that although there is clear evidence for some level of neural control of the properties of a muscle unit (variation within a unit was less than the variation across units), this control is not complete, since the variability among fibers of a single unit was significantly more than the variability found between repeated measurements on a single fiber.

Animals↗

PubMed1988

Adaptation of bone and tendon to prolonged hindlimb suspension in rats.

The rat hindlimb suspension model was used to ascertain the importance of ground reaction forces in maintaining bone and tendon homeostasis. Young female Sprague-Dawley rats were randomly assigned to either a suspended or a nonsuspended group. After 28 days, femur bones and patellar tendons were obtained for morphological and biochemical analyses. Prolonged suspension induced a significant change in the geometric configuration of the femur middiaphysis by increasing the minimum diameter (12%) without any significant alterations in cortical area, density, mineral, and collagen concentrations. Femur wet weight, length, DNA, and uronic acid concentrations of suspended animals were not significantly different from bones of nonsuspended rats. However, the collagen and proteoglycan concentrations in patellar tendons of suspended rats were 28% lower than the concentrations of matrix proteins in tissues obtained from nonsuspended animals. These data suggest that elimination of ground reaction forces induces alterations in tendon composition and femur diaphyseal shape by changing regional rates in bone remodeling and localized tendon strain. Therefore it appears that ground reaction forces are an important factor in the maintenance of cortical bone and patellar tendon homeostasis during weight-bearing conditions.

Adaptation, Physiological↗

PubMed1988

Periodic weight support effects on rat soleus fibers after hindlimb suspension.

The morphological and histochemical properties of the rat soleus were studied after 1 wk of hindlimb suspension, one model that removes the weight-bearing function of the hindlimbs. To examine the effectiveness of weight support activity in maintaining soleus mass, fiber size, and succinate dehydrogenase (SDH) activity, the hindlimbs of adult male Sprague-Dawley rats were suspended (HS) and half of these rats were walked on a treadmill for 40 min/day (10 min every 6 h) at 5 m/min and a 19 degree grade (HS-WS). Significant reductions in soleus mass and fiber size were found after 1 wk of HS. Weight support activity decreased the atrophic response by approximately 50%. In the alkaline myofibrillar adenosine triphosphatase (ATPase) dark-staining fibers, SDH activity was higher in the HS than control rats, whereas it was similar to control in the HS-WS rats. Total SDH activity (SDH activity X cross-sectional area) in fibers staining lightly for ATPase in HS and HS-WS rats was lower than in control rats, whereas in the darkly stained ATPase fibers it was similar among the three groups. No changes were observed in fiber type percentages after 1 wk of HS or HS-WS. The results suggest that short-duration, daily weight support activity can ameliorate, but not prevent, soleus atrophy induced by HS. Furthermore, fiber cross-sectional area is more responsive to periodic weight support in dark than light ATPase fibers. These results also demonstrate that muscle fiber atrophy need not be associated with a loss in SDH activity.

Adaptation, Physiological↗

PubMed1988

Spatial distribution of motor unit fibers in the cat soleus and tibialis anterior muscles: local interactions.

The spatial distribution of muscle fibers belonging to a motor unit was studied in the soleus and tibialis anterior muscles of adult cats. Motor unit fibers were depleted of their glycogen through repetitive stimulation of the motoneuron or of the functionally isolated motor axon. Subsequently, the position of depleted muscle fibers was mapped on serial cross sections taken along the length of the muscle. A subset of fibers was selected from the cross section containing the largest number of motor unit fibers and 4 spatial analyses were performed. These analyses were designed to determine whether the muscle fibers belonging to a single unit were distributed in a random manner. To test whether the actual distribution was other than random, Monte Carlo techniques were used to simulate the random innervation of a muscle. From these simulations, a test statistic was calculated for comparison with the observed data. Adjacency and nearest-neighbor analyses revealed no tendency for grouping or dispersion of fibers belonging to a motor unit. However, measurement of the distances between all motor unit fibers revealed a greater tendency for grouping than spreading, suggesting the existence of some mechanism that restricts the absolute distribution and territory of a motor unit.

Animals↗