The influence of the muscle length on the distribution of muscle fiber conduction velocity (MFCV) was estimated at 3 different elbow angles (90°, 120°and 150°) during the contraction of 30% of isometric maximtm voluntary contraction (MVC). Surface electromyogram was recorded in the distal region of m. biceps brachii using a surface array electrode. MFCVs at the different locations from the end-plate to the distal tendon of the muscle were measured directly using the averaging method. MFCVs near the end-plate and the distal tendon of the muscle showed the high values, while MFCVs in the middle region between the end-plate and the distal tendon of the muscle had low values at the same elbow angles. The mean MFCVs in the middle region decreased when the muscle length increased during the contraction of 30% MVC. The middle region length changed when the elbow joint was extended from the elbow angle of 90° to that of 150°. Although previous studies showed the influence of muscle length on MFCV for special regions (like end-plate, tendon, and middle region), MFCV for whole regions, that is, the distribution of MFCV has not been studied for various muscle length. The MFCV for the some region in the some muscle length could not be estimated. In the study, the distribution of MFCV in various musele length for the contraction of 30% MVC was obtained, and the model with the function including muscle length for the estimation of MFCV was presented.
The purpose of this study was: 1) to investigate the responses of heart rate (HR), blood lactate and ratings of perceived exertion (RPE) to 1, 000 punches and 1, 000 kicks in collegiate highly skilled (BB Group) and novice (WB Group) karate practitioners; and, 2) to compare RPE obtained from the subjects to RPE expected by their coaches. The mean values of HR, percent of maximal HR (%HRmax), percent of maximal HR reserve (%MHRR), blood lactate and RPE in 1, 000 punches for the BB Group were 102.5 ± 14.8 beats·min-1, 53.1 ± 8.5%, 27.1 ± 12.7%, 0.8 ± 0.2 mmol·l-1 and 12.2 ± 1.2, respectively, and for the WB Group were 116.1 ± 17.9 beats·min-1, 58.1 ± 7.7%, 35.2 ± 13.3%, 1.2 ± 0.6mmol·l-1 and 12.8 ± 1.2, respectively. Likewise, the mean values in 1, 000 kicks for the BB Group were 127.4 ± 12.4 beats·min-1, 66.0 ± 8.0%, 47.0 ± 12.5%, 1.3 ± 0.4 mmol·l-1 and 14.2 ± 1.2, respectively, and for the WB Group were 137.0 ± 14.4 beats·min-1, 70.1 ± 7.4%, 52.0 ± 12.8%, 2.4 ± 0.8 mmol·1-1 and 16.3 ± 1.5, respectively. These responses to 1, 000 punches and 1, 000 kicks were moderate, and the RPE for 1, 000 punches in both BB and WB Groups and for 1, 000 kicks in the BB Group were significantly lower than the RPE expected by their coaches.
The purpose of the present study was to examine the kinetics of mixed venous CO2 pressure (Pvco2) in incremental-load exercise. Pvco2 Seemed to indicate a linear increase after a somewhat slow increase. CO2 store phase appearing in expiration of CO2 (stored CO2) was calculated from the data of O2 uptake (Vo2), CO2 output (Vco2) and work rate. The stored CO2 indicated a linear increase after a time delay. The stored CO2 also significantly related to Pvco2. When kinetics of Pvco2 at light exercise intensity was supposed from stored CO2, Pvco2 seemed to indicate a linear increase with a time delay. Excessive expired CO2 (excess CO2) was calculated from the data of Vo2 and work rate. The excess CO2 significantly related to the increase of blood lactate. The blood lactate seemed to start to increase at around 1080 kpm/min. In spite of this change, a linear increase of Pvco2 was unchanged. This result was considered to be related to the excessive CO2 expiration corresponding to the increase of blood lactate. Thus, within the present results and assumptions, it seemed that Pvco2 indicated a linear increase with a time delay without the effect of lactate increase in incremental-load exercise.
Relations between surface electromyogram (EMG) and fatigue sensation was compared between the first fatiguing contraction and the following contractions with insufficient rests. Six male subjects performed static contractions of the elbow flexors at 8 and 13%MVC with the forearm semipronated and at 13%MVC with the forearm supinated. Contractions were repeated 6 (13%MVC) or 5 (8%MVC) times (C1, C2, C3, C4, C5, C6) with rests of 5 min (13%MVC) or 10 min (8%MVC). During the contractions the subjects reported values of rated fatigue sensation (VRFS) whose scale was from 0.0 (no fatigue sensation) to 4.0 (apparent pain and moderate severity) at every 30 sec. C1 ended between 3.5 and 4.O of VRFS or at 18 min (13%MVC) or 20 min (8%MVC) of contracting time. C2-C5 ended when fatigue sensation became that at the end of C1 or 5 min had passed. Bipolar and monopolar surface EMG was recorded from 6 synergists of elbow flexors. Mean amplitude (AEMG) and relative power below 22Hz (RPWL20) were calculated. Though AEMGs were positively correlated with VRFSs in C1, the correlations were often obscure in C2-C6. Most AEMGs at the same VRFS were larger in C2-C6 than in C1. AEMGs at the start of C2-C6 were sometimes larger than those at the end of C1. RPWL20s of monopolar EMG positively correlated with VRFSs. The RPWL20 correlations were often reserved in all contractions. The increases of AEMGs in C2-C6 at the same VRFS cannot be explained by the migration of the activities among synergists, since the increases in AEMGs were seen in most synergists simultaneously. The compensation of the failure of muscle contractibility were not the only cause of the increases in the AEMGs during fatiguing contractions. The compression of EMG spectrum towards lower frequencies was usable to estimate the change of fatigue sensation.
The present study aimed at investigating an inverted-U relationship between contingent negative variation (CNV) and arousal level by examining the effects on CNV of gradually reduced arousal level by long-lasting task. The subjects conducted a simple reaction time task consisting of warning stimuli (S1) and imperative stimuli (S2). This task consisted of 200 trials and lasted about 40 minutes. During this task, spontaneous EEG before S1 and SPL (skin potential level) were measured as indicators for arousal level. The 200 CNV, EEG and SPL data were classified into 5 blocks each of which included 40 trials of data. Analysis was made in seven subjects in whom reduction in the arousal level in long-lasting task was shown by increase in the relative power values of α waves before S1 and decrease in the SPL. As a result, the amplitude of early CNV at Fz was observed to increase from the earlier half phase (block 1) to the middle phase (block 3) and to decrease from the middle phase (block 3) to the latter half (block 5). In the middle phase, the amplitude was the greatest. The low amplitude of early CNV in the early half of the task (block 1) was inferred to have been induced by excessive arousal state because of the low relative power values of α waves and the high SPL at this time. On the other hand, the low amplitude in the later phase (block 5) was inferred to have been induced by reduction in arousal level because of the high relative power values of α waves and the low SPL. These results suggested that CNV amplitude and arousal level was in an inverted-U relationship.
Head-out Water immersion (HOI) induces various renal functional changes, such as diuresis, natriuresis, and kaliuresis. The present study was undertaken 1) to characterize the renal response to HOI in Koreans who routinely ingest high salt diet and 2) to evaluate the impact of exercise on the renal response to HOI. Six healthy male subjects (average Na+ intake of 232 mEq·day-1) were immersed upto the neck in 34.5°C water and rested in a seated position or exercised on a bicycle ergometer for 3 hours. In resting subjects, we observed a reversible increase in urine flow and a decrease in urine osmolality, with no changes in creatinine clearance. The peak urine flow observed during the second hour of immersion was 4-fold greater than the pre-immersion level. The excretion of total osmotic substances rose progressively during the 3-hour immersion, which was accompanied by a similar change in Na+ excretion. The K+ excretion was slightly elevated. The major component of the immersion diuresis was a water diuresis in the early phase and an osmotic diuresis in the late phase of immersion. In exercising subjects, the diuretic and natriuretic responses, to HOI were attenuated and the kaliuretic response was potentiated. Blood hemoglobin concentration and plasma levels of renin, ADH, and aldosterone decreased during immersionrest, but they remained unchanged or increased during immersion-exercise. These results suggest that 1) the cardiac mechanoreceptor-mediated renal responses to HOI are not changed by chronic high salt diet, and 2) excessive urinary sodium and water losses are prevented by exercise during immersion.
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