Kazumi Masuda

Changes in surface EMG parameters during static and dynamic fatiguing contractions.

The effect of contraction types on muscle fiber conduction velocity (MFCV), median frequency (MDF) and mean amplitude (AMP) of surface electromyography was examined in the vastus lateralis of 19 healthy male adults. The subjects performed knee extension both statically and dynamically until they were exhausted. The static contraction was a sustained isometric extension of the knee at a joint angle of 90 degrees with 50% of the maximum voluntary contraction (MVC) load. The dynamic contraction was a repetitive isotonic extension of the knee between the angles of 90 degrees and 180 degrees with the same 50% MVC load at a frequency of 10 times per minute. MFVC during the static contraction significantly decreased during the exercise (p < 0.01). On the other hand, MFVC during the dynamic contraction did not significantly change throughout the exercise. MDF decreased and AMP increased during both types of contractions (p < 0.01). Because the blood flow within the muscle is maintained during the dynamic contraction by enhanced venous return from the contracting muscle, these results suggested that MFVC is affected by the metabolic state in the muscle and the changes in MDF cannot be explained only by that of MFVC.

Endurance training under 2500-m hypoxia does not increase myoglobin content in human skeletal muscle

Abstract. The present study was carried out to determine whether myoglobin (Mb) concentration ([Mb]) in human skeletal muscle is influenced by 8xa0weeks of endurance training under normal conditions, and under hypoxic conditions equivalent to an altitude of 2500xa0m. Fourteen healthy but sedentary male adults who did not participate in any regular exercise program took part in this study. They were divided into two groups according to the training regime to which they were submitted: the N group, who exercised under normobaric conditions, and the H group, who exercised under hypobaric conditions. All subjects performed an incremental cycling exercise at sea level to evaluate their maximal O2 uptake (

Relationships between Fiber Composition and NMR Measurements in Human Skeletal Muscle

dot V{rm O}_{{rm 2max}}

Maintenance of myoglobin concentration in human skeletal muscle after heavy resistance training

n) before and after the 8-week endurance training course period. Muscle tissue samples were obtained by needle biopsy from the vastus lateralis muscle for histochemical and biochemical analysis. Training induced an increase in

Morphological adaptation of capillary network in compensatory hypertrophied rat plantaris muscle

dot V{rm O}_{{rm 2max}}

Oxidative Enzyme Activity and Soma Size in Motoneurons Innervating the Rat Slow-Twitch and Fast-Twitch Muscles After Chronic Activity

n in both the N and H groups (P<0.05), although there was no significant difference in these changes between groups. The 8-week training had no effect on [Mb] in either group. Muscle fiber composition was also unaffected by the training course. In contrast, citrate synthase activity in both groups increased by [mean (SD)] 28.2 (33.3)% (N: P<0.01) and 32.0 (18.2)% (H: P<0.05) after training, and the number of capillaries (capillary:fiber ratio) increased by 47.7 (33.8)% (N: P<0.01) and 32.3 (20.6)% (H: P<0.05). There were no significant differences in these parameters between the N and H groups. These results suggest that significant improvement of aerobic potential as a result of endurance training are not accompanied by increases in [Mb] in human skeletal muscle. In addition, a lower absolute workload may not be sufficient to stimulate Mb synthesis in humans, even where endurance training is carried out under hypoxia.

Effects of Different Intensity Endurance Training on the Capillary Network in Rat Skeletal Muscle

The purpose of this study was to examine the relationships between the relative contents of phosphocreatine (PCr), inorganic phosphate (Pi), β‐adenosine triphosphate (ATP), and transverse relaxation time (T2) with fiber composition, which determined histochemically in the human skeletal muscle. The vastus lateralis muscles of 28 volunteers were subjected to phosphorus nuclear magnetic resonance (31P NMR) spectroscopy, magnetic resonance imaging (MRI) and muscle biopsy. Muscle fibers were divided into typeu2009I and typeu2009II fibers using myosin ATPase stain. A wide range of fiber composition levels were observed in the subjects (27.3–74.6% typeu2009I fibers). The PCr/ATP, Pi/ATP and (PCr+Pi)/ATP ratios were positively related to the percentage of typeu2009II fibers (r=0.695, p<0.001, r=0.429, p<0.05 and r=0.773, p<0.001, respectively). There was no correlation between fiber composition and the PCr/Pi ratio (r 0.127,u2009n.s.) or intracellular pH (r=0.305, n.s.). Moreover, no correlation was found between T2 and fiber type (r=0.144, n.s.). These results suggest that 31P NMR can detect the differences in relative content of phosphates between typeu2009I and typeu2009II fibers, thereby noninvasively evaluating fiber composition in human skeletal muscle.

RELATIONSHIP BETWEEN REDUCTION OF HIP JOINT AND THIGH MUSCLE AND WALKING ABILITY IN ELDERLY PEOPLE

Abstract The aim of this study was to determine the effects of 8 weeks of resistance training (RT) on the myoglobin concentration ([Mb]) in human skeletal muscle, and to compare the change in the [Mb] in two different RT protocols. The two types of protocol used were interval RT (IRT) of moderate to low intensity with a high number of repetitions and a short recovery time, and repetition RT (RRT) of high intensity with a low number of repetitions and a long recovery time. A group of 11 healthy male adults voluntarily participated in this study and were divided into IRT (nu2009=u20096) and RRT (nu2009=u20095) groups. Both training protocols were carried out twice a week for 8 weeks. At the completion of the training period, the one-repetition maximal force values and isometric force were increased significantly in all the subjects, by about 38.8% and 26.0%, respectively (Pu2009<u20090.01). The muscle fibre composition was unchanged by the 8 weeks of training. The muscle fibre cross-sectional areas were increased significantly by both types of training in all fibre types (I, IIa and IIb, mean +16.1%, Pu2009<u20090.05). The [Mb] showed no significant changes at the completion of the training [IRT from 4.63 (SD 0.63) to 4.48 (SD 0.72), RRT from 4.47 (SD 0.75) to 4.24 (SD 0.80)u2009mgu2009·u2009g−1 wet tissue] despite a significant decrease in citrate synthase activity [IRT from 5.27 (SD 1.45) to 4.49 (SD 1.48), RRT from 5.33 (SD 2.09) to 4.85 (SD 1.87)u2009μmolu2009·u2009min−1u2009·u2009g−1 wet tissue; Pu2009<u20090.05] observed after both protocols. These results suggested that myoglobin and mitochondria enzymes were regulated by different mechanisms in response to either type of RT. Moreover, the maintained [Mb] in hypertrophied muscle should preserve oxygen transport from capillaries to mitochondria even when diffusion distance is increased.

ADAPTATIONS OF MYOGLOBIN IN RAT SKELETAL MUSCLES TO ENDURANCE RUNNING TRAINING

The aim of this study was to examine the morphological adaptation of the capillary network in hypertrophied plantaris muscles by examining both capillary numbers and luminal circumferences. Hypertrophy of the plantaris muscle was induced by myectomy of the gastrocnemius muscle. This hypertrophy was characterised by increases in muscle mass and fibre cross-sectional area. All capillary parameters were determined using morphometric methods in perfusion-fixed plantaris muscle. Increased capillary-to-fibre ratio was observed in the overloaded plantaris muscle while no change was observed in the capillary luminal circumference. No differences were observed in the capillary density and the capillary-to-fibre perimeter ratio of the normal and the hypertrophied plantaris muscle. These results indicated that chronic overload-induced neocapillarization, but not enlargement of capillary luminal circumference, contributed to the prevention of decreases in the capillary-to-fibre perimeter ratio in the plantaris muscle in the hypertrophied process.

Adaptation of myoglobin in compensatory hypertrophied rat muscle

The effects of chronic activity induced by running training on the activity of the mitochondrial enzyme succinate dehydrogenase (SDH) and soma size in motoneurons innervating the slow-twitch soleus (SOL) and fast-twitch extensor digitorum longus (EDL) muscles were studied in rats using the retrograde neuronal tracer Nuclear Yellow. Rats were assigned to control and trained groups that were subjected to treadmill running for 10 weeks (2 h/day, 30 m/min, 5 days/week). After training, both SOL and EDL muscles showed clear adaptations (citrate synthase activity in the SOL muscle, and the fast-twitch oxidative-glycolytic fiber area of the EDL muscle increased significantly after training). The SDH activity of the motoneurons innervating both SOL and EDL muscles was unchanged by training. However, SOL motoneurons of trained rats had a significantly larger soma size and a significantly higher total SDH activity [SDH activity x soma size) than those of control. Total SDH activity was calculated to examine the absolute SDH protein content of the motoneurons. On the other hand, there was no difference in both soma size and total SDH activity of EDL motoneurons between the two groups. These data demonstrate that chronic activity has a considerably stronger impact on soma size and total oxidative enzyme activity of motoneurons innervating slow-twitch rather than fast-twitch muscles.