Effects of eccentric exercise on trunk extensor torque and lumbar paraspinal EMG.

PURPOSE: Little is known about the effects of eccentric contractions on the function of the lumbar paraspinal muscles. The purpose of this study was to determine the effects of a single bout of eccentric contractions using the trunk extensor muscles on torque and lumbar paraspinal electromyographic (EMG) parameters. METHODS: Twenty healthy men between the ages of 18 and 49 yr participated in the study. Subjects performed a single bout of 50 maximal voluntary concentric (N = 10) or eccentric (N = 10) trunk extension movements while surface EMG signals were recorded from the multifidus and iliocostalis lumborum muscles. A series of isometric contractions were performed both before the exercise protocol and at five additional time points over the following 7 d. RESULTS: During the exercise protocol, peak torque decreased 30% and 24% in the eccentric and concentric groups, respectively, whereas no change occurred in EMG root-mean-square (RMS). There were no group differences in peak torque generation at any of the postexercise protocol time points. Compared with the preexercise protocol values, multifidus EMG was elevated 27% immediately post and 15 min post in the eccentric group. Similarly, compared with the concentric group, multifidus EMG in the eccentric group was increased 34%, 40%, and 25% immediately post, 15 min post, and 1 d after the exercise protocol, respectively. CONCLUSION: Eccentric contractions using the trunk extensor muscles result in higher levels of multifidus EMG activity to produce a given level of torque. This reduction in neuromuscular efficiency persisted for one day with recovery to baseline levels by the third day. Contrary to studies using other muscle groups, no sustained alteration in muscle function was observed.

Effect of reactive oxygen species on K+ contractures in the rat diaphragm.

Reactive oxygen species (ROS) are postulated to alter low-frequency contractility of the unfatigued and fatigued diaphragm. It has been proposed that ROS affect contractility through changes in membrane excitability and excitation-contraction coupling. If this hypothesis is true, then ROS should alter depolarization-dependent K+ contractures. Xanthine oxidase (0.01 U/ml) + hypoxanthine (1 mM) were used as a source of superoxide anion eliciting oxidative stress on diaphragm fiber bundles in vitro. Diaphragm fiber bundles from 4-mo-old Fischer 344 rats were extracted and immediately placed in Krebs solution bubbled with 95% O2-5% CO2. After 10 min of equilibration, a K+ contracture (Pre; 135 mM KCl) was induced. Fiber bundles were assigned to the following treatment groups: normal Krebs-Ringer (KR; Con) and the xanthine oxidase system (XO) in KR solution. After 15 min of treatment exposure, a second (Post) K+ contracture was elicited. Mean time-to-peak tension for contractures was significantly decreased in Post vs. Pre (16.0 +/- 0.7 vs. 19.8 +/- 1.0 s) with XO; no change was noted with Con. Furthermore, peak contracture tension was significantly higher (31.5%) in the XO group Post compared with Pre; again, no significant change was found with KR. The relaxation phase was also altered with XO but not with KR. Additional experiments were conducted with application of 1 mM hypoxanthine, with results similar to the Con group. We conclude that the application of ROS altered the dynamics of K+ contractures in the rat diaphragm, indicating changes in voltage-dependent excitation-contraction coupling.

The influence of recovery duration on high-intensity exercise performance after oral creatine supplementation.

The purpose of this study was to determine the effects of creatine supplementation on the ability to reproduce and maintain a high percentage of peak power output during the second of two bouts of high-intensity cycle sprinting following four different recovery intervals. Eighty healthy, active male subjects were randomly assigned to one of two groups (creatine or placebo) and one of four recovery intervals (30, 60, 90, or 120 s). Two maximal cycle ergometer sprints, separated by the assigned recovery interval were performed before and after a 5-day supplementation protocol in which 20 g/day of creatine (plus 4 g/day glucose) or 24 g/day glucose placebo were ingested by subjects from creatine and placebo groups, respectively. Maximal peak power output (PP) and the absolute time to fatigue (TTF) were compared pre- versus postsupplementation. No significant group interactions were noted in this study. Specifically, creatine supplementation had no effect on subjects' ability to reproduce or maintain a high percentage of PP during the second bout of exercise.

Measuring fatigue relative to peak power output during high-intensity cycle sprinting.

The purpose of this report was to introduce and validate a method to account for variable fatigue rates during cycle sprinting by incorporating decline from peak power (30%) as a test termination criterion. Fifteen healthy men performed three maximal sprint tests separated by 20 min (Bouts 1 and 2) and 48 hours (Bout 3). Power curves were analyzed for peak power, time to peak, time to fatigue (decline of 30% from peak), total work, total test time, fatigue rate, and the fatigue index. High test-retest reliability was demonstrated for all variables (R = 0.85-0.98). No significant differences were detected between variables (Bouts 1, 2 and 3; p > 0.01). Fatigue rates varied widely among participants (range = 24.7-65.4 W.s-1), but the fatigue index was consistent (31.1 +/- 0.16; mean +/- standard error of measurement, range = 30.1-32.5%). Our data show that variable fatigue responses among participants are normalized to the percentage of decline from peak power by incorporating a relative fatigue cutoff criterion. This approach might inform mechanisms relating to short-term fatigue and recovery during consecutive sprint bouts.

Inter- and intra-observer variation in the reporting of cervical smears: specialist cytopathologists versus histopathologists.

One hundred and ten cervical smears were circulated to five specialist consultant cytopathologists and five consultant histopathologists. Of these smears, 100 were randomized and re-circulated. The cytopathologists reported endocervical cells and wart virus infection more frequently than the histopathologists, although neither group showed good inter-observer agreement for either assessment. Apart from smear adequacy and the presence of endocervical cells, both groups showed good intra-observer agreement in all the parameters measured. This suggests that overall individuals were applying their own personal criteria with consistency over time, although a previous study had shown considerable lack of inter-observer agreement among the histopathologists on the grade of dyskaryosis and the management recommendation. The results indicate that specialist cytopathologists bring a different viewpoint to the reporting of cervical smears than histopathologists. They also show a lack of standardization in the reporting of smears despite the guidelines issued by the British Society for Clinical Cytology.

Interaction between clenbuterol and run training: effects on exercise performance and MLC isoform content.

The purpose of this study was to determine the separate and combined effects of clenbuterol (CB) administration and interval training on running performance and myosin light-chain (MLC) isoform expression in mouse skeletal muscle. Mice were randomly assigned to one of four treatment groups: 1) control (Con), 2) exercise (Ex), 3) drug (CB), or 4) exercise + drug (Ex + CB). CB and Ex + CB mice were given CB (1.6 mg/kg) orally 4 days/wk. Ex and Ex + CB mice were trained 4 days/wk on a motorized treadmill (3 sets of 3 min, 36-40 m/min, 10-17% grade, 30-s recovery). After 8 wk of treatment, exercise conditioning increased total work performed 58% in the Ex group during a run-to-exhaustion treadmill test, whereas CB decreased total work by 25% in the CB group; in combination with exercise training, CB treatment eliminated the Ex-induced increase in work. Polyacrylamide gel electrophoresis indicated that run training, CB treatment, or a combination did not (P > 0.01) promote changes in fast and slow MLC isoforms in the soleus, gastrocnemius, or tibialis anterior muscles. Although not different from each other after 8 wk, CB and Ex + CB treatments produced significantly greater values than Con and Ex for the following variables: muscle mass (17-46%), total protein (22-50%), and myofibrillar protein (19-53%). It was concluded that CB decreases exercise performance and that the combination of Ex and CB have antagonistic effects on running performance; the two treatments do not interact to diminish the anabolic effects of CB on skeletal muscle and do not alter MLC isoform profiles.

Effect of oral creatine supplementation on power output and fatigue during bicycle ergometry.

Our purpose was to determine the effect of oral creatine supplementation on exercise performance during high-intensity short-duration bicycle sprinting. Power output was recorded for 12 healthy untrained males (age 24.08 +/- 0.53 yr, weight 81.22 +/- 1.32 kg) before and after 5 days of creatine (n = 6) or placebo (n = 6) supplementation. A double-blind research design was employed. Subjects performed maximal sprints against a constant load (111.8 N) for 15 s. Each one-half pedal revolution was magnetically counted, and subsequent measurements of peak power, time to peak power, total work, and the fatigue index were digitized and stored on disk. Mean values for peak power, time to peak power, total work, and fatigue index were 958.01 +/- 40.66 W, 4.09 +/- 0.82 s, 11.28 +/- 0.46 kJ, and 32.1 +/- 1.58% decline from peak power, respectively. No significant differences were observed within or between groups before or after supplementation for any of the mechanical parameters measured (P > 0.05). These findings suggest that oral creatine supplementation does not positively affect power output or fatigue during continuous high-intensity bicycle exercise in untrained men.

Glycogen storage in normal and wing-mutant strains of Drosophila melanogaster.

Total body weight, total glycogen content and the percentage of body weight attributable to stored glycogen were measured in wild-type and two wing-mutant strains of 0-2-day-old (immature) and 5-7-day-old (mature) Drosophila melanogaster. Wild-type and wing mutant strains did not differ significantly in any of the measured parameters at 0-2 days of age. By 5-7 days of age, significant increases in glycogen content and glycogen percent had occurred in both wild-type and wing-mutant strains. Likewise, by 5-7 days of age, total body weight had increased significantly in the mature wild-type and vestigial strains but not in apterous flies. Mature wild-type flies displayed significantly greater total body glycogen content and glycogen percent when compared with the mature apterous and vestigial wing-mutant strains.

Interobserver variation in the diagnosis and grading of dyskaryosis in cervical smears: specialist cytopathologists compared with non-specialists.

AIMS: To compare the assessment of dyskaryosis in cervical smears made by specialist consultant cytopathologists and consultant general histopathologists. METHODS: One hundred and ten cervical smears were circulated to 10 observers from five district general hospital histopathology departments and five major departments of cytopathology. Their responses were analysed by five consultant general histopathologists and five consultant specialist cytopathologists. In 54 of the 110 cases, the histology of a corresponding cervical biopsy specimen was compared with the smear assessments. RESULTS: Specialist cytopathologists were more consistent than non-specialists when diagnosing and grading dyskaryosis. They chose the higher grades of dyskaryosis more frequently than the non-specialists. The cytopathologists recommended referral for colposcopy more frequently, but if they asked for a repeat smear, they wanted it done within three months more frequently than the histopathologists. The specialists were more frequently in agreement with the biopsy grade of intra-epithelial neoplasia than the non-specialists, whose smear diagnoses tended to underestimate the severity of the histopathological abnormality. CONCLUSIONS: This study has shown major differences between specialist and non-specialist cytopathologists in the diagnosis and grading of cervical smears and in the recommended management of patients with abnormal smears. These differences may result in uneven clinical management of women with smear abnormalities. It is therefore important to explore possible strategies for standardising the reporting of cervical smears, such as centralisation of screening services, accreditation in cytopathology for non-specialist consultants, and the value of participation in external quality assessment schemes.

Effects of Ca(2+)-channel drugs on K(+)-induced respiration in skeletal muscles.

When skeletal muscles are exposed to elevations in extracellular K+, they experience a significant and long-lasting increase in O2 uptake. The basis for this response is unknown but may be related to an influx in extracellular Ca2+ ions during sarcolemmal depolarization. The purpose of this study was to determine if altering Ca2+ entry, either by removal of Ca2+ from the bathing fluid or by exposing muscles to selective Ca(2+)-channel agonists or antagonists, would affect K(+)-induced respiration. Isolated frog sartorii muscles were incubated in normal Ringer's solution (R) or a modified Ringer's containing 10 or 18 mM KCl. O2 uptake increased 83.7% in R+10 mM KCl and 502.2% in R+18 mM KCl. Incubation in Ca(2+)-free R+18 mM KCl containing Ni2+ in place of Ca2+ depressed the metabolic response to elevated K+. O2 uptake increased 234.5% in R+18 mM KCl containing Ni2+ and 80.6% in R+18 mM KCl containing Mg2+. Similarly, addition of the Ca(2+)-channel antagonists (gallopamil (D600) and diltiazem (DILT)) to R+18 mM KCl also depressed the respiratory response to elevated K+. O2 uptake increased 224.2% and 133.1% in R+18 mM KCL containing D600 and DILT, respectively. Conversely, addition of the Ca(2+)-channel agonists (Bay K 8644 (BAY) or palmitoyl carnitine (PC)) to R+10 mM KCl enhanced the metabolic response to elevated K+. O2 uptake increased 278% and 438.9% in R+10 mM KCl containing BAY and PC, respectively. These results indicate that the stimulatory effects of elevated extracellular K+ on skeletal muscle respiration are at least partially dependent on the availability of extracellular Ca2+ and its subsequent entry during membrane depolarization.

Dexamethasone iontophoresis: effect on delayed muscle soreness and muscle function.

The purpose of this study was to evaluate the pain alleviating effect of dexamethasone iontophoresis on delayed onset muscle soreness (DOMS) produced via an eccentric exercise bout, and to determine the effect on muscle function. Baseline data were collected on 18 female subjects for maximum isometric knee extension contraction (MVC), knee extension peak torque (PT), knee extension work (W), and muscle soreness perception (SP). All values were subsequently reassessed 24 and 48 hours after a 10-min bout of bench stepping. Immediately following the 24-hr reassessment, the experimental (E) (N = 6) and placebo (P) (N = 6) groups received iontophoresis treatment while the control (C) group (N = 6) received no treatment. Percent deviation from baseline of SP was significantly less at 48 hours (p less than 0.05) for the E group compared to P and C groups. However, MCV, PT, and W were no different between the three groups at 48 hours post muscle soreness bout.

Differential effects of temperature on contractile behavior in isolated frog skeletal muscle.

1. The thermal dependence of contractile behavior at different stimulation frequencies was investigated in isolated frog sartorius muscles. 2. Increasing incubation temperature (10-30 degrees C) produced decreases in Pt (43.7%) and P15 (70.3%), and an increase in Po (26.0%). 3. Thermal ratios (R10) calculated for Pt, P15 and Po indicated high thermal dependence at lower temperatures (10-20 degrees C; 0.60, 0.44 and 1.38, respectively) but relative thermal independence at higher temperatures (20-30 degrees C; 0.95, 0.75 and 0.95, respectively). 4. Contractile ratios (Pt/Po and P15/Po) decreased with increased temperature (10-30 degrees C; 56.3% and 76.0%, respectively). 5. Thermal ratios (R20) calculated for peak tension at different stimulation frequencies demonstrated high thermal dependence at the lower frequencies (10-30 pps, 0.46-0.48) and decreasing dependence at higher frequencies (40-50 pps, 0.69-0.82).

2,[3]tert-butyl-4-hydroxyanisole does not reduce SCE induction by benzo(a) pyrene in bone marrow cells of C57BL/6 mice.

Recently, a number of publications have suggested that bone marrow cytogenetics may be used to detect anticarcinogenic or antimutagenic activity. In this work, 0.75% 2,[3]-tert-butyl-4-hydroxyanisole (BHA), fed in the diet for 2 weeks, was tested for its ability to reduce the frequency of benzo(a)pyrene (BP)-induced SCE in mouse bone marrow. C57BL/6 male mice, were injected i.p. with BP at 0, 33, 67, and 100 mg/kg body weight. The mean SCE/chromosome +/- s.e.m. for animals on control diet was 0 mg/kg, 0.108 +/- 0.005; 33 mg/kg, 0.225 +/- 0.011; 67 mg/kg, 0.289 +/- 0.012; 100 mg/kg, 0.311 +/- 0.013. The mean SCE/chromosome +/- s.e.m. for animals on the 0.75% BHA diet was 0 mg/kg, 0.105 +/- 0.006; 33 mg/kg, 0.224 +/- 0.009; 67 mg/kg, 0.262 +/- 0.013; 100 mg/kg, 0.326 +/- 0.012. There are no significant differences between animals on the control and BHA diets. Excretion of BP in urine over a 72 hr time period was significantly increased in animals on the BHA diet, at both low and high doses. Water-soluble metabolites accounted for all of this increase. It appears that bone marrow is not a good model for the gastrointestinal tract, and that short-term assays for anticarcinogens or antimutagens are more likely to be predictive if they are done in the target organs.

Staircase potentiation in isolated frog skeletal muscle: power spectral analysis of the evoked compound muscle action potential.

1. The mechanical and electrophysiological effects of repetitive, low-frequency electrical stimulation on paired sartorii muscles from small male frogs have been investigated, in vitro. 2. Stimulation for 90 sec at 5 Hz resulted in a progressive rise (staircase) than fall (fatigue) in peak twitch tension. 3. The root mean square amplitude, peak-to-peak amplitude, conduction velocity and mean power frequency of evoked compound muscle action potentials (CMAPs) decreased over the stimulation period. 4. Results suggest that alterations in the shape of the CMAP during repetitive stimulation may contribute to the staircase phenomenon.

The positive inotropic effect of epinephrine on skeletal muscle: a brief review.

Chronic and acute administration of epinephrine or related sympathomimetic agents are typically prescribed for the treatment of clinical disorders such as hypotension, anaphylactic and allergic reactions, and bronchial asthma. In addition to its effects on these infirmaties and on carbohydrate metabolism, epinephrine also exerts a positive inotropic effect on fast-contracting skeletal muscle in a variety of animal species. At present, the precise mechanisms responsible for the inotropic effect are not known. This communication reviews the positive inotropic effects of epinephrine on fast-contracting skeletal muscle and discusses possible mechanisms which might mediate this phenomenon. Epinephrine potentiates muscle twitches via the second messenger, cAMP, secondary to hormone binding to membrane-bound beta-receptors. Cyclic AMP then acts to increase carbohydrate metabolism, alter sodium/potassium exchange, phosphorylate myosin isozymes, and/or alter intracellular calcium exchange. Based on theoretical grounds, the first three mechanisms can be excluded. Therefore, it is tentatively hypothesized that the effect is due to cAMP-enhanced calcium exchange within the muscle fiber and/or to increased influx of extracellular calcium. This notion is consistent with the mechanism of the positive inotropic effects of epinephrine on cardiac tissue. If this hypothesis is correct, it would also suggest a role, at least under some conditions, for extracellular calcium in the process of skeletal muscle excitation-contraction coupling.

Extracellular calcium and the inotropic effect of epinephrine on frog skeletal muscle.

The purpose of these experiments was to determine if extracellular calcium plays an important role in mediating the inotropic effect of epinephrine in isolated frog sartorius muscle. Initial experiments indicated that epinephrine potentiated the muscle twitch in a concentration-dependent manner with concentrations of 10 microM to 1 mM, increasing peak tension by approximately 33%. To inhibit the influx of extracellular calcium, muscles were incubated for 20 min in media containing epinephrine in which calcium had been removed and replaced by magnesium or EDTA, or in experimental media containing epinephrine and the calcium channel blockers D-600 or diltiazem (5 microM). Each experimental condition was found to antagonize the effects of epinephrine such that peak twitch tensions were not significantly different from the control. When muscles were returned to normal Ringer's solution containing epinephrine, twitches exhibited progressive potentiation. Muscles were also incubated for 20 min in epinephrine without stimulation. Once stimulation was resumed, twitches were not immediately potentiated but rather gradually increased over time. These results suggest that the inotropic effects of epinephrine are influenced by the influx of extracellular calcium, an event that is dependent on muscle activation.

Caffeine, maximal power output and fatigue.

The purpose of this investigation was to determine the effects of caffeine ingestion on maximal power output and fatigue during short term, high intensity exercise. Nine adult males performed 15 s maximal exercise bouts 60 min after ingestion of caffeine (7 mg.kg-1) or placebo. Exercise bouts were carried out on a modified cycle ergometer which allowed power output to be computed for each one-half pedal stroke via microcomputer. Peak power output under caffeine conditions was not significantly different from that obtained following placebo ingestion. Similarly, time to peak power, total work, power fatigue index and power fatigue rate did not differ significantly between caffeine and placebo conditions. These results suggest that caffeine ingestion does not increase one's maximal ability to generate power. Further, caffeine does not alter the rate or magnitude of fatigue during high intensity, dynamic exercise.

Mechanisms of differential strain sensitivity in gastric carcinogenesis.

The genetically-controlled, distinct sensitivity of different rat strains to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced cancer of the glandular stomach and duodenum was investigated. MNNG is activated through thiols, and the thiol content of the glandular stomach, duodenum, and liver of the BN rat tended to be slightly, but not significantly higher than that of the Wistar, Sprague-Dawley, Lewis, and Buffalo rats. The levels of the DNA repair system, O6-alkylguanine transferase (AGT), in sensitive Wistar strain rats had values similar to those in resistant Buffalo strain rats. Administration of 80 mg/liter of MNNG in the drinking water for six weeks up to the time of tissue collection yielded the same AGT levels. Of all the parameters examined to account for genetically-mediated sensitivity to gastrointestinal cancer induction, namely, N-denitrosation, thiol activation, AGT-related DNA repair, and cell duplication rates, the latter yielded the best association, although these factors acting together may be involved.