William S. Barnes

The relationship between maximum isometric strength and intramuscular circulatory occlusion

Twenty male college students served as subjects for lhe study which investigated the relationship between maximum isometric strength and the isometric tension necessary to produce total occlusion of intramuscular circulation. Subjects performed a scries of progressively increasing static contractions by squeezing a hand dynamometer and the subsequent blood flow responses were measured. Blood flow was occluded at a mean of 63-5% maximum handgrip strength for the total group tested. To determine whether individuals of different maximum strength occlude at different percentages of their MVC, subjects were divided into high and low strength groups. The high strength group was found to occlude at 51-5% of MVC while the low strength group occluded at 75-5% of MVC. A significant negative correlation (r= -0.58) was found between maximum isometric strength and the per cent of maximum strength necessary to produce intra-muscular occlusion. There was no significant difference between the absolute tension producing o...

Storage and mobilization of muscle glycogen in exercising horses fed a fat-supplemented diet*

Summary In a switchback experiment, six mature mares were fed a control and a fat-supplemented diet while being exercised in a galloping regimen. After three weeks adaptation to each diet, horses performed an exercise test (ET) consisting of four, 600-m gallops. Muscle biopsies were obtained before and after the ET, and blood samples were taken before, during and throughout recovery from the ET. Resting glycogen concentration in the biceps femoris muscle increased (P

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 ones maximal ability to generate power. Further, caffeine does not alter the rate or magnitude of fatigue during high intensity, dynamic exercise.

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.

Expression of the pregnancy-specific beta 1-glycoprotein genes in human testis

Northern blot analysis with placental pregnancy-specific beta 1-glycoprotein (SP1) cDNA probe showed the presence of SP1 mRNAs in human testis. Presence of translational products of the mRNAs was demonstrated by Western blot analysis with anti-human SP1 antibodies albeit difference in mobilities between the testis and placental proteins was apparent. Screening of human testis cDNA library with placental SP1 probe yielded 4 groups of positive clones. Two groups were identical to human placental SP1 cDNAs previously reported. The other 2 groups consisted of cDNA of incompletely processed mRNAs. These 2 groups were present in high abundance. Sequence analysis suggested that the cDNAs were products of different genes.

Respiration and lactate production in isolated frog skeletal muscle: Effects of passive stretch

The effects of varying degrees of passive stretch on in vitro oxygen consumption and intracellular lactate efflux have been investigated in paired recti abdomini muscles from small male frogs. Oxygen consumption [mm3 (STP)/mg (dry wt)/hr] was found to be linearly related to load (r = 0.98), increasing from 1.57 +/- 0.11 (SE) at 2 g to 2.30 +/- 0.18 at 10 g, 2.89 +/- 0.16 at 20 g and 3.26 +/- 0.21 at 30 g. Lactate released into the medium [microM/g (dry wt)/hr] was inversely related to load (r = -0.52), increasing initially from 36.84 +/- 3.28 (SE) at 2 g to 108.55 +/- 12.9 at 10 g, then abruptly decreasing with additional loading (18.10 +/- 2.60 at 20 g and 11.71 +/- 2.80 at 30 g). Results suggest that as stretch-related oxidative energy metabolism increases, there is a lessening dependence on anaerobic energy-yielding processes.

Redox modulation of diaphragm contractility: Interaction between DHPR and RyR channels

Previous reports indicate that reactive oxygen species (ROS) may modulate contractility in skeletal muscle. Although Ca(2+)-sensitivity of the contractile apparatus appears to be a primary site of regulation, dihydropyridine receptor (DHPR or L-type Ca(2+) channels) and calcium efflux in isolated sarcoplasmic reticulum (SR) vesicles appear to be redox sensitive as well. However, DHPR as a target is poorly understood in intact muscles at body temperature, particularly in the diaphragm, a muscle more dependent on external Ca(2+) than locomotor muscles. Previously, we reported that oxidant challenge via xanthine oxidase (XO) alters the K(+) contractures in diaphragm fiber bundles, suggestive of a role of L-type Ca(2+) channels. Contractility of isolated rat diaphragm fiber bundles revealed a biphasic response to ROS challenge that was dose and time dependent. Potentiation of twitch and low-frequency diaphragm fiber bundle contractility with 0.02 U•ml(-1) XO was reversible or partially preventable with washout, dithiothreitol, and the SOD/catalase mimetic EUK-134. The RyR antagonist ruthenium red inhibited xanthine oxidase-induced potentiation, while the RyR agonist caffeine elevated diaphragm twitch and low-frequency tension in a non-additive manner by 55% when introduced simultaneously with ROS challenge. The DHPR antagonist nitrendipine (15 μM) inhibited elevation in low-frequency diaphragm tension produced by ROS challenge. Caffeine threshold tension curves were shifted to the left with 0.02 U•ml(-1) XO, but this effect was partially reversed with 15 μM nitrendipine. These results are consistent with the hypothesis that DHPR redox state and RyR function are modulated in an interactive manner, affecting contractility in intact diaphragm fiber bundles.

Glycogen utilization in isolated frog muscle: An effect of passive mechanical stretch

The effect of passive mechanical stretch on glycogen utilization and total protein maintenance in paired sartorii muscles from small male frogs has been investigated, in vitro. Glycogen content of stretched muscles decreased 72.6% over a 24-hr incubation period, compared to a 23.1% decline in unstretched control muscles. Stretched muscles retained 54.7% of their total protein content over a 24-hr period, compared to 38.4% in the unstretched control muscles. Unstretched muscles demonstrated a significant (11.1%) increase in wet weight following 24 hr of incubation, presumably due to increased water retention. There were no significant changes in the wet wts of stretched muscles.

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).

Respiratory capacity of developing chick red and white skeletal muscle

Oxygen consumption, cytochrome oxidase and succinoxidase activity was measured in samples of leg and breast muscle from chick embryos ranging in age from 11 to 19 days. Respiratory parameters increased significantly in both muscle groups during embryonic life. By the later stages of incubation, leg and breast muscles differed significantly in cytochrome and succinoxidase activity. Oxygen uptake between leg and breast muscles did not differ significantly during later development. The results suggest at least a partial pre-natal differentiation of skeletal muscle in the domestic fowl.