Dynamic properties of partially denervated muscle

The mechanical and electrical properties of the partially denervated first dorsal interosseous muscle were measured in 14 patients and 14 normal control subjects. The following variables were studied during isometric contraction: maximum voluntary contraction; maximum rate of rise of tension in a rapid voluntary contraction; amplitude, rate of rise, time to peak, and duration of peak of the compound muscle action potential; twitch force, maximum rate of rise, contraction time, and half-relaxation time; and tetanic (50 Hz) force, rate of rise, and tetanus/twitch ratio. The force produced during repetitive stimulation of the ulnar nerve at 10, 20, 50, and 100 impulses per second was also analyzed. The major findings were: (1) decreased load bearing (voluntary contraction, twitch, and tetanus), (2) prolonged twitch contraction times and half-relaxation times, (3) decreased tetanus/twitch ratio, and (4) preserved rate of rise of tension.     

Influence of vertical posture development on the velocity properties of triceps surae muscle in normal children

Contraction time and half-relaxation time of triceps surae muscle were studied in 9 normal children immediately after they began to stand alone and again 6 weeks later. The velocity properties of the muscle were recorded during isometric twitch induced by supramaximal indirect stimulation. The development of the vertical posture at the end of the first year was found to be associated with prolongation of the contraction time, reaching values observed in 3-year-old children and adults. During the same period the half-relaxation time did not change. Data are reported to show that the influence of the vertical posture on the contraction time is due to changes in the contractile properties of the muscle. It is assumed that the velocity properties of triceps surae are influenced by the long-term activation of the muscle in supporting the vertical posture.     

Alterations in muscle contractile properties and fiber composition after weight-lifting exercise in cats

To determine if weight-lifting exercise alters the contractile properties of muscle, eight cats were trained to lift weights with their right forelimb to receive a food reward. After 10 to 61 weeks of training and lifting (0.45 to 1.52 kg), the palmaris longus (PLM) and flexor carpi radialis (FCR) muscles were prepared for physiological examination for 6 trained and 16 control cats. This report demonstrated that exercise-induced hypertrophy resulted in a significant increase in the isometric twitch (35% FCR, 32% PLM) and tetanic (23% FCR, 41% PLM) tensions for both exercised muscles. In addition, there was a significant increase of the time to peak tension (22% FCR, 34% PLM) and half-relaxation time (45% FCR, 78% PLM) of an isometric twitch and a slowing of the rate of tension development (39% FCR, 32% PLM) of the exercised muscles. Even though the overall effect of weight-lifting exercise was to slow the contractile properties of the muscles for most cats, the histochemical profiles of the trained muscles showed a significant increase in fast-twitch glycolytic fibers (from 45 to 58%) and a decrease in the proportion of fast-twitch oxidative glycolytic fibers (from 29 to 20%) for the PLM. No significant change was observed in the proportion of slow-twitch oxidative fibers in this muscle or in the fiber proportions of the FCR. It appears that light to moderate weight-lifting exercise alters the contractile properties of the muscle independent of the muscle fiber populations demonstrated by histochemistry.     

Voluntary muscle activation, contractile properties, and fatigability in children with and without cerebral palsy

Cerebral palsy (CP) may lead to profound weakness in affected portions of the extremities and trunk. Knowing the mechanisms underlying muscle weakness will help to better design interventions for increasing force production in children with CP. This study quantified voluntary muscle activation, contractile properties, and fatigability of the quadriceps femoris and triceps surae in children with and without CP. Twelve children with CP (7-13 years) and 10 unaffected children (controls, 8-12 years) were assessed for (1) voluntary muscle activation during maximum voluntary isometric contractions (MVICs); (2) antagonist coactivation during agonist MVICs; (3) contractile properties, and (4) fatigability using electrically elicited tests. Children with CP were significantly weaker, had lower agonist voluntary muscle activation, and greater antagonist coactivation. In children with CP, the quadriceps normalized force-frequency relationship (FFR) was shifted upward at low frequencies and was less fatigable than controls. No differences were seen between groups in the normalized FFR and fatigability of the triceps surae. In addition, no differences were seen in the sum of the time to peak tension and half-relaxation times between groups for either muscle. Because children with CP demonstrated large deficits in voluntary muscle activation, using voluntary contractions for strength training may not produce forces sufficient to induce muscle hypertrophy. Techniques such as enhanced feedback and neuromuscular electrical stimulation may be helpful for strengthening muscles that cannot be sufficiently recruited with voluntary effort.     

Isometric contractions of normal and spastic human skeletal muscle

Isometric contractile properties of human elbow flexor muscles were examined in 27 normal subjects (7 females and 20 males). Contractions of elbow flexors were elicited by application of electrical pulses to the biceps motor points. The tension development was recorded at the wrist with the elbow angle fixed at 90°–100°. The data for the time to peak and time to half relaxation of the twitch, the twitch tension-to-tetanus tension ratio, and the posttetanic twitch potentiation are reported. The contractile properties of spastic elbow flexor muscles from 7 subjects who had been hemiparetic for periods ranging from 4 months to 60 months were found to be similar to those of muscles in normal subjects and unaffected muscles in hemiparetic subjects.     

Slowing of fast-twitch muscle in the dystrophic mouse

Isometric twitch tension was measured in fast-twitch and slow-twitch muscles of normal and dystrophic ( ) mice in vivo. In dystrophic mice more than 6 months old the fast-twitch extensor digitorum longus (EDL) showed a prolongation of the time to peak tension as well as the time to relax to one-half peak tension ( ) compared with age-matched controls. In younger dystrophic mice (4 to 6 weeks) the time to peak tension was prolonged but not significantly so. This apparent “slowing” of dystrophic fast-twitch muscle was accompanied by a reduction in both cooling potentiation and post-tetanic potentiation toward values typical of slow-twitch muscle. Slow-twitch soleus muscle (SOL) of old mice was almost unaffected by the dystrophic process with regared to its contractile characteristics. However, there appeared to be a slight, but significant “speeding” of young dystrophic SOL compared with age-matched control muscles. This was apparent in reduced times to peak tension and half-relaxation as well as an enhanced cooling potentiation. We suggest that the altered contractile characteristics result from a change in some intrinsic property of the muscle fibers rather than from extrinsic factors such as the additional perimysial connective tissue seen in these muscles.     

EXCITATION-CONTRACTION LATENCY IN THE MUSCLES OF CHILDREN AND ADULTS

Excitation-contraction latency in the fast flexor carpi ulnaris and in the slow triceps surae muscles was studied in healthy children aged one month, 10 months and three years, and in adults. The tests were carried out during isometric twitch following supramaximal indirect stimulation. Excitation-contraction latency was found to increase with age in both the fast and slow muscles. The latency is longer for the slow than the fast muscle. A positive correlation was found in the children between excitation-contraction latency and contraction time.     

Alterations in contractile properties of extensor digitorum longus muscle from mice following denervation at 1 day of age

Changes in contractile properties of developing fast-twitch skeletal muscle of the C57/BL6J mouse were studied following neonatal denervation. A sciatic neurectomy was performed at 1 day of age and then denervated and control muscles were examined at 7, 14, and 21 days postdenervation. In addition, normal muscles were studied at 1 day of age. The denervated muscles exhibited prolongation of time-to-peak twitch tension and half-relaxation time, a slowing of the maximum velocity of shortening, and a marked increase in resistance to fatigue compared with controls. Isometric tetanus tension was reduced compared to the control muscle both in absolute terms and when expressed relative to body weight at all ages studied. The absolute isometric twitch tension was reduced at 7 and 14 days, but was reduced only at 21 days when expressed as a fraction of the muscle weight. Post-tetanic twitch potentiation failed to appear in the denervated muscle. It would appear that neonatal denervation results in an uncoupling of the developmental pattern of skeletal muscle.     

Comparison of the development of isometric contractile properties of embryonic avian normal and dystrophic skeletal muscle

Embryonic posterior latissimus dorsi (PLD) muscles were isolated at 24-h intervals between days 14 and 20 in ovo from a line of normal chickens (412) and a line afflicted with hereditary muscular dystrophy (413), and their isometric contractile properties were compared. The results demonstrated differences in the isometric contractile responses between normal and dystrophic embryonic PLD muscles. The normalized twitch and tetanic tensions were significantly less for the dystrophic muscle immediately before hatching. Some kinetics of the isometric responses were also different between normal and dystrophic muscles. At embryonic day 16 the times to one-half peak twitch tension, to peak twitch tension, and to one-half peak tetanic tension were significantly longer for the dystrophic muscles. The maximum rate of tetanic force development at days 14, 16, and 18 was lower in the dystrophic muscles. At embryonic day 18 the twitch relaxation of the dystrophic muscle was significantly slower. The results indicated that as early as the final week in ovo, the dystrophic PLD produced less tension and, in some respects, was slower than the normal muscle. Moreover, the differences in the kinetics of the responses were transient, i.e., differences in the kinetics that were observed at day 16 in ovo were not seen closer to hatching.     

Effect of hind-limb suspension on young and adult skeletal muscle. I. Normal mice

The purpose of this study was to determine the effect of hind-limb suspension (HS) on morphometric, histologic, and contractile characteristics of fast extensor digitorum longus (EDL) and slow soleus (SOL) twitch muscles in adult and immature mice. Hind-limb suspension for 2 weeks was used to produce atrophy in two groups of mice, ages 4 and 12 weeks, with nonsuspended animals serving as controls. Young HS mice exhibited marked decreases in SOL weight, length, cross-sectional area (CSA), twitch and tetanic tensions, and rates of tension development and relaxation, with increases in fatigue resistance. HS reduced the diameter of both type I and IIA fibers, increased the percentage of type I fibers, and decreased the percentage of type IIA fibers in both young and adult SOL. Muscle weight, length, CSA, IIA and IIB fiber areas, and maximum rate of tetanic tension development were decreased in EDL of young HS mice; fatigue resistance and EDL half-relaxation times were increased. For most parameters evaluated, slow twitch muscle was more affected than fast twitch. HS affected contractile characteristics less than morphometric or histologic parameters. Rates of tension development and relaxation were the contractile parameters most affected by HS, and the time parameters of contraction were least affected. For all measurements young mice were more affected than adult mice.     

Changes in isometric contractile properties of fast-twitch and slow-twitch skeletal muscle of C57BL/6J dy2J/dy2J dystrophic mice during postnatal development

Our primary aim was to determine if there exists a preferential involvement of the fast-twitch or slow-twitch skeletal muscle fibers in the dy2J/dy2J strain of murine dystrophy. The changes in the contractile properties of the slow-twitch soleus (SOL) and the fast-twitch extensor digitorum longus (EDL) muscles of normal and dystrophic mice were studied at 4, 8, 12, and 32 weeks of age. Isometric twitch and tetanus tension were decreased in the 4- and 8-week-old dystrophic EDL compared with controls, this situation being reversed in the older animals. At 12 weeks, the dystrophic EDL generated 15% more tetanic tension than normal EDL and by 32 weeks no significant difference was seen between normal and dystrophic EDL twitch or tetanus tension. By 8 weeks, dystrophic EDL exhibited a prolonged time-to-peak twitch tension (TTP) and half-relaxation time (1/2RT) of the isometric twitch which continued to 32 weeks. For the dystrophic SOL, decreased twitch and tetanus tension was observed from 4 to 32 weeks. At 8 and 12 weeks, TTP and 1/2RT of dystrophic SOL were prolonged. However, by 32 weeks there was no longer a significant difference seen in TTP or 1/2RT between normal and dystrophic SOL. Our results appear to indicate that a loss of the primary control which is determining the fiber composition of the individual muscles is occurring as the dystrophic process advances.     

Extensor muscle responses to triamcinolone

Triamcinolone acetonide (20 mg/kg) was administered intraperitoneally on each of 4 days to female rats and several mechanical and electrical properties of extensor muscle were analyzed. After 1 day of treatment, the duration of the twitch was increased but neither the twitch nor the tetanic tension was affected by the drug. After 4 days of treatment both twitch and tetanic tensions showed a slight increase. Contraction time, half-relaxation time, and twitch duration were normal after 4 days of treatment. The resting membrane potential was significantly decreased during treatment. The passive properties of the muscle membrane were unaffected. The overshoot, amplitudes, and rate of depolarization of indirectly elicited action potentials were all decreased on Day 1 of triamcinolone acetonide treatment but these parameters returned to normal by Day 4. The arithmetic mean frequency and the log frequency of miniature endplate potentials increased during treatment but the increase was not significant until Day 4. The average miniature endplate potential amplitude significantly increased during treament, but the modal and median amplitudes were unaffected. In high Mg²⁺ solutions (15 mm) quantal content remained essentially the same as control, and the quantal size decreased. In curarized preparations (400 ng/ml) both quantal content and size were the same in controls and treated rats.     

The value of electrophysiological examination of the flexor carpi ulnaris muscle in the diagnosis of ulnar nerve lesions at the elbow

Summary The aim of the present study was to answer the question whether electrophysiological examination of the m. flexor carpi ulnaris, especially of the distal latency (stimulation point 2 cm above the sulcus ulnaris) to this muscle, represents a valid procedure for the localisation of an ulnar nerve lesion at the elbow.In 64 patients, a total of 68 ulnar nerve lesions at the elbow were subjected to conventional clinical and electrophysiological examinations.A pathologically prolonged distal latency to m. flexor carpi ulnaris (>4.0 ms) was found in 82.4% of the patients. In terms of their value in the topo-diagnosis of an ulnar lesion, measurement of the distal latency to m. flexor carpi ulnaris and conventional analysis of trans-sulcal motor conduction velocity of the fibres to the hypothenar muscles yield equivalent information. However, evaluation of the distal latency to m. flexor carpi ulnaris is not only subject to fewer sources of error but is also techniqually much easier to perform. In the localisation of a clinically suspected ulnar nerve lesion at the elbow, we therefore suggest that the electrophysiological investigation should commence with an examination of the distal latency to m. flexor carpi ulnaris.

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Zusammenfassung Die Studie soll die Frage beantworten, ob die elektrophysiologische Untersuchung des M. flexor carpi ulnaris, insbesondere dessen distale motorische Latenz (Reizpunkt 2cm oberhalb Sulcus ulnaris), als brauchbarer Test für die Lokalisation von Läsionen des N. ulnaris am Ellenbogen gelten kann.Bei 64 Patienten wurden insgesamt 68 Ulnarisläsionen am Ellenbogen mit konventioneller klinischer und elektrophysiologischer Methodik untersucht.Eine pathologisch verlängerte distale motorische Latenz zum M. flexor carpi ulnaris (>4,0 ms) wurde in 82,4% der Patienten gefunden. Die Messung der distalen motorischen Latenz zum M. flexor carpi ulnaris und die Bestimmung der motorischen Nervenleitgeschwindigkeit im Bereich des Sulcus ulnaris ergaben hinsichtlich der Topodiagnostik von Läsionen des N. ulnaris gleich gute Ergebnisse. Die Messung der distalen motorischen Latenz zum M. flexor carpi ulnaris ist jedoch mit geringeren Fehlerquellen behaftet und zudem technisch einfacher durchführbar. Bei Verdacht auf eine Schädigung des N. ulnaris im Ellenbogenbereich sollte deshalb die elektrophysiologische Diagnostik mit der Bestimmung der distalen motorischen Latenz zum M. flexor carpi ulnaris beginnen.

     

Effect of time of day on force variation in a human muscle.

The effect of time of day on the neural activation and contractile properties of the human adductor pollicis muscle was investigated in 13 healthy subjects. Two different times of day were chosen, corresponding to the minimum (7 h) and maximum (18 h) levels of strength. The force produced was compared with the associated electromyographic (EMG) activity during voluntary and electrically induced contractions in order to determine whether peripheral or central mechanisms play a dominant role in diurnal force fluctuation. The results indicated that the force produced during a maximum voluntary contraction (MVC) was significantly higher (+8.9%) in the evening than the morning. Since the increase in force of the MVC and the tetanic contraction (100 Hz) were similar, it is suggested that peripheral mechanisms are responsible for diurnal fluctuations in force. This conclusion is supported by the observation that central activation, tested by the interpolated twitch method during an MVC, did not change, and that the EMG was less per unit force in the evening. In addition to the increase in maximum twitch and tetanus force, significant changes in muscle contractile kinetics were also observed. The maximum rate of tension development and the relaxation of the twitch and tetanus increased in the evening, and the twitch contraction time (CT) and the time to half-relaxation (TR(1/2)) were reduced. Because the mean range of variation in skin temperature (2. 6 degrees C) observed over the course of the day was very low, this change cannot entirely explain those observed in muscle contractile properties.     

Isometric contractile properties of fast- and slow-twitch muscles in normal and spastic mice

Isometric contractile properties of the fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus (SOL) muscles of 24 male C57 mice were studied in vitro at 35°C. Ten animals exhibited the hereditary movement disorder known as spasticity. EDL muscles of spastic and normal mice developed similar specific tensions and they had similar twitch tension:tetanic tension ratios. The time-to-peak tension and the time to half relaxation in the twitch of spastic EDL muscles were, on average, slightly longer. SOL muscles of spastic and normal mice also developed similar specific tensions and their twitch contractions had similar times to half-relaxation. The time-to-peak tension in the twitch and the twitch tension: tetanic tension ratio of spastic SOL muscles were, on average, higher than in normal SOL. The significance of our findings remains somewhat uncertain.     

Histochemical and contractile property changes during human muscle development

When the histochemical and contractile properties of infant muscles change postnatally, and what influence muscle function has on these changes, were the focus of this study. Contractile properties were measured in the plantaflexor (PF) and dorsiflexors (DF) of 19 newborns and 36 infants aged 5–16 months. Infants were tested between one and four times at monthly intervals. Measurements included maximal twitch tension (P_t), time to peak tension (TPT), and half-relaxation times (1/2RT). TPT was similar in PF (77 ms) and DF (73 ms) at birth, remained unchanged in DF, and slowed in PF to 110–120 ms between 9 and 12 months. Type I distributions were determined at autopsy in fetal through to adult muscles. Completion of differentiation occurred in soleus at about the age that contractile properties slowed and infants started to use these muscles more. A trend of higher percentages of type I distributions was also noted in children than either newborns or adults in other muscles. The implications of these findings and the clinical use of these methods for evaluating peripheral neuromuscular function is discussed. © 1993 John Wiley & Sons, Inc.     

Contractile properties of rat fast-twitch skeletal muscle during reinnervation: effects of testosterone and castration

The isometric contractile properties of skeletal muscle were examined after nerve crush to establish the temporal sequence of recovery during reinnervation of normal, castrated, and testosterone-treated rats. Extensor digitorum longus muscles of male rats were studied in vivo 8 to 21 days after crushing the peroneal nerve 1 cm from the muscle. The earliest signs of functional reinnervation in normal animals were observed 8 to 9 days after nerve crush when faint muscle twitches with markedly prolonged twitch contraction times were recorded. By days 10 and 11, twitch tension was 9 to 20% of control, twitch contraction time was 149 to 183% of control, and tetanic tension was 4 to 9% of control values. The optimal frequency of stimulation was 58 to 64 Hz, the twitch:tetanus ratio was three times control values, and little or no posttetanic potentiation of twitch tension was observed. During the next 9 days there was a gradual return of all experimentally measured contractile properties toward control values; the relative rate of return was twitch tension greater than twitch contraction time greater than twitch:tetanus ratio greater than tetanic tension greater than optimal frequency of stimulation greater than posttetanic potentiation. Neither testosterone nor castration significantly altered either the rate or extent of functional reinnervation 8 to 21 days after nerve crush (P greater than 0.05). During this period the twitch:tetanus ratio for any given animal was highly correlated (r = 0.83, P less than 0.001) with the extent of functional recovery of neurally evoked muscle tension and was determined to be the most reliable index of the degree of muscle reinnervation. These data provide valuable baseline information for future studies of reinnervation of skeletal muscle.     

Effects of hypokinesia/hypodynamia on contractile and histochemical properties of young and old rat soleus muscle

To determine if the atrophic process was different in the young and in the aged slow-twitch soleus muscle, in which the aging process is clearly apparent, hind limb hypokinesia/hypodynamia was induced. After 3 weeks, we measured speed-related indices, tension indices, and tension producing capacities. Fiber type composition and fiber cross-sectional area were also investigated. After the treatment, body weight and muscle weight decreased, the most important loss being measured in the young group. The ratio of muscle weight to body weight was not altered by hypokinesia/hypodynamia but this ratio was greater in the 3-month-old control group than in the 22-month-old group. Contraction time and half-relaxation time decreased in both groups. In the control group, the old soleus muscle was slower to contract and relax than in the young muscle. Tension indices and tension producing capacities decreased. These included twitch tension, maximally developed tension, force generated per gram muscle, and specific tension. The mean muscle area and muscle weight of the young soleus decreased more than that of the old soleus. The fiber cross-sectional area was reduced in both groups whereas fiber type composition remained the same after hypokinesia/hypodynamia. The suspension atrophy appeared to be independent of age in the soleus at the contractile level whereas atrophy was greater in the young muscle at the morphometric level.     

Effect of neonatal denervation-reinnervation on the functional capacity of a 129ReJ dy/dy murine dystrophic muscle

The sciatic nerves of 14-day-old 129 ReJ normal (++) and dystrophic (dy/dy) mice were transected in the mid-thigh region. The cut ends of the nerves were approximated to facilitate regeneration. One hundred days after denervation, contractile properties of denervated-reinnervated, normal and dystrophic extensor digitorum longus (EDL) muscles were compared to age-matched normal and dystrophic muscles. In dystrophic muscle, in vitro twitch and tetanic tensions were reduced, compared to those of normal muscle. The denervation-reinnervation procedure resulted in an increase in these parameters as compared to unoperated dy muscle. These data correlated with increases in total myofiber cross-sectional areas. Twitch contraction time was not significantly affected by the dystrophic condition or by the denervation-reinnervation protocol. Whereas dystrophic muscle had a longer half-relaxation time than normal muscle, denervation-reinnervation of the dystrophic EDL resulted in a significantly faster half-relaxation time. While fatigue resistance was greater in dystrophic muscles than in normal muscle, there was a significant decrease in fatigue resistance in the denervated-reinnervated dystrophic muscle. Transient neonatal denervation results in modification of both the morphological and physiological characteristics of murine dystrophy.     

Contrasting effects of suspension on hind limb muscles in the hamster

The contractile properties of plantaris and soleus muscles were studied in 46-day-old hamsters after 4 weeks of rear-end suspension; their controls were animals which had not been treated or else had been operated upon but not suspended. In the suspended hamsters the plantaris muscles, of which approximately 90% of fibers are normally type II, maintained the properties of fast-twitch muscles in terms of their contraction and half-relaxation times, maximum rates of rise of tetanic tension, and posttetanic potentiation of the twitch. The small reduction of mean tetanic tension, although not significant statistically, was compatible with relatively mild atrophy of the type II fibers; approximately half of the type I fibers appeared to have converted to type II. In contrast, the soleus muscles, normally slow-twitch with approximately 60% type I fibers, exhibited significant shortening of their contraction and half-relaxation times after suspension and the maximum rates of rise of tetanic tension were increased. These changes, and the greatly reduced twitch and tetanic tensions, were compatible with the finding of much greater atrophy of type I than type II fibers, together with the conversion of approximately 10% of fibers from type I to type II. Unlike other contractile variables, posttetanic depression of the soleus twitch was unaffected by suspension. Our findings have implications in relation to other models of disuse.