This study was designed to analyze physiologically recreational synchronized swimming and speed swimming. Two types of recreational synchronized swimming (Long face-in time performance : LFIP and Short face-in time performance : SFIP) and maximum exertion in the 200-m free style swimming (200 mFR) were measured in six recreational middle-aged female swimmers. LFIP and SFIP were conducted in shallow water. The percentage of face-in time for LFIP was about 10% longer than that of SFIP. Heart rate (HR) during each exercise was measured continuously. Blood lactate concentration (La), the rate of perceived exertion (RPE) and systolic and diastolic blood pressure (SBP, DBP) were measured after each exercise. Average HR during the LFIP, SFIP and 200 mFR were 133±12, 132±13 and 153±12 beats·min^-1 (mean ± SD), respectively. La was 2.4±0.7 mmol·1^-1for LFIP, 2.2±0.6 mmol·1^-1for SFIP and 5.7 ± 2.4 mmol·1^-1for 200 mFR, respectively. SBP was 181±32 mmHg for LFIP, 166±22 mmHg for SFIP and 185±30 mmHg for 200 mFR, respectively. No significant differences were observed in blood pressure among the three exercises. SBP of 200 mmHg or higher after LFIP and 200 mFR was observed in some subjects. HR, La and RPE for LFIP and SFIP showed no significant differences, but were significantly lower than those of 200 mFR. These results show that the exercise intensity of LFIP was moderate and was similar to that of SFIP. LFIP, however, caused a marked rise in SBP. Thus, SFIP may be more recommended for health promotion to recreational middle-aged swimmers than LFIP.

View full abstract

The purpose of this study was to examine the relationship between balancing ability during abrupt acceleration and the habitual physical activity level of elderly females. Thirty-one elderly females, aged 65-75 years, volunteered for this study. Changes in the center of foot pressure (CFP) were measured during postural sway following platform acceleration, and the response time and CFP displacement were evaluated. The scores of their daily physical activities (TS) -consisting of house-hold activities (HS), leisure time activities (LS) and sports activities (SS) -were estimated by the modified Voorrips's questionaire method. Response time and CFP displacement correlated significantly with age (p<0.001) . Response time also correlated significantly with the SS, LS and TS scores (p<0.05) . CFP displacement also correlated significantly with the SS and TS scores (p<0.05) . These results suggest that postural balancing ability during abrupt acceleration correlates signifi-cantly with the habitual physical activity levels, especially sports activities in elderly females.

View full abstract

The effects of endurance training and detraining on cardiac autonomic nervous system activity were studied by using the power spectral analysis of heart rate (HR) variability. Twenty-one sedentary male subjects were trained for 8 weeks using cycle ergometer exercise [70% of maximal oxygen uptake (VO₂max), 60 min, 3.4 times/wk] . Resting HR for 5 min was recorded before the training, after the 8-week training period, and after the 2-week and 4-week detraining period. The indices of cardiac parasympathetic and sympathetic nervous system activity were determined by Mem-Calc method, as the high frequency power (HF : 0.15-0.50 Hz) and the ratio of the low frequency power (LF : 0.04-0.15 Hz) to the HF (LF/HF), respectively. The VO₂max after the training and 4 weeks detraining period were significantly higher than the initial value (before training : 41 ± 1 ml/kg/min ; after training: 48±2, P<0.0001; after detraining: 46±2, P<0.001) . The HF was significantly in-creased by the training (P<0.05), and maintained the increased level for the 2-week detraining period (before training : 6.4±0.3 In ms²; after training: 7.0±0.2, P<0.01; after 2-week detrain-ing: 7.0±0.2, P<0.05) . The increase in the HF, however, disappeared after the 4-week detraining period (6.8±0.31n ms²) . The LF/HF did not show any significant changes during the training and detraining period. These results suggest that an endurance exercise with moderate intensity enhan-ces cardiac parasympathetic nervous system activity, but not cardiac sympathetic nervous system activity. The enhanced cardiac parasympathetic nervous system activity, however, may regress rapidly during detraining period.

View full abstract

The purpose of this study was to confirm both the reproducibility of indices (NIRS slope, NT2, %NIRS fall) and the specificity obtained by analyzing the muscle oxygenation curve measured by near-infrared spectroscopy (NIRS) during ramp exercise. Ten healthy men participated in this study. The NIRS probe was placed on the vastus lateralis muscle. An increase in oxygenation was observed from rest to warm-up at 0 watts (Δ NIRS) . Oxygenation began to decrease lineally as the workload increased (NIRS slope) . In the latter phase of exercise, the oxygenation curve flattened out despite an increasing workload, and as a result, an inflection point was formed (NT2) . The minimum value of oxygenation during ramp exercise was indicated as“%NIRS fall.”
Protocol 1. After a warm-up period of 3 min at 0 watts, a ramp exercise (20 watt/min) test was performed until volitional fatigue. The test was performed for each subject twice (test-1, test-2) with a 1-week interval. Protocol 2. A test was performed with three consecutive ramp exercises (lOwatt/min·20watt/min·30watt/min) up to120watt each with sufficient rest between the exercises.
NT2 was observed in 7 of 10 subjects. Test-1 and test-2 mean values of ANIRS, NIRS slope, watts at NT2 (NT2) and %NIRS fall were not significantly different, and the correlations between test-1 and test-2 were highly significant (r=0.94, P<0.0001: ANIRS, r=0.99, P<0.0001: NIRS slope, r=0.91, P<0.002: NT2 and r=0.78, P<0.005 : %NIRS fall) . The regression lines obtained for correlations of results of test-1 and test-2 were y=-5.89+1.38X (Δ NIRS), y=0.02+ 1.03X (NIRS slope), y=31.52+0.83X (NT2), and y=19.91+0.61X (%NIRS fall) . No significant differences in both intercept and coefficient between the regression line and identity line were found in the NIRS slope and NT2. The rate of decrease in the oxygenation curve became steeper with an increase in work-load from 10 watts/min to 20 watts/min and to 30 watts/min. However, the mean values of the NIRS slope, modified by watts, were 0.29±0.06%/watt, 0.29±0.07%/watt and 0.29±0.07%/watt, respectively. There were no significant differences of the NIRS slopes among these exercises. The results indicate constancy of the rate of decrease in oxygenation per workload.
In conclusion, these findings demonstrate the reproducibility of the NIRS slope and the appearance of NT2 during ramp exercise, and the specific way in which the decrease in muscle oxygenation reflects workload. They suggest that analysis of the muscle oxygenation curve can be used to estimate muscular metabolism and indices of training effects.

View full abstract

This study examined the impact of acute high-intensity exercise on the rate of Ca²⁺uptake and release and Ca²⁺-stimulated adenosine triphosphatase (ATPase) activity of the sarcoplasmic reticulum (SR) in the soleus muscle (SOL) and the superficial region of the vastus lateralis muscle (VS) of rats. The animals were run on a 10% grade at 50 m/min of a motorized treadmill until fatigued (The average time to exhaustion was 306 sec.) . At exhaustion, glycogen concentrations were 65% and 85% less in the SOL and VS, respectively. The rate of Ca²⁺release induced by 4-chloro-m-cresol was un-changed in fatigued SOL and VS. The rate of Ca²⁺uptake stimulated by adenosine triphosphate (ATP) was significantly lower following exercise in VS but not in SOL. This lower rate observed in VS was paralleled by decreased catalytic activity of SR Ca²⁺-ATPase. The rate of Ca2+ uptake measured using adenosine diphosphate and phosphocreatine, as substrate was lower than that of ATP in fatigued VS. These findings suggest that, in fast-twitch muscles, high-intensity exercise not only reduces SR Ca²⁺-ATPase activity but also elicits a decrease in creatine kinase activity, probably resulting from nitric oxide that is produced during exercise.

View full abstract

A study was conducted to investigate the effects of the beta-2 receptor agonist, clenbuterol, on the slow-twitch soleus (SOL) and the fast-twitch extensor digitorum longus (EDL) muscles. Twelve male 5-wk-old mice (ddY ) were divided into two groups ; control ( CANT, n=6 ) and clenbuterol-treated (CLEB, n=6) . Clenbuterol was given in the drinking water (0.02 mg/mL) for 5 weeks. Post-treatment body weights were approximately 10% greater in the CLEB group compared to CANT (P<0.05) . In the SQL muscles of the CLEB group the wet weight and the ratio of muscle weight to body weight was significantly higher than the CANT (P<0.01), but not in the EDL. In the SOL muscles of the CLEB group the muscle type LDH isozyme distribution and enzymatic activity was significantly increased (P<0.01) . However, there was no metabolic change in the EDL muscles. Polyacrylamide gel electrophoresis (SDS-PAGE) of myosin heavy chain (Myosin-HC) indicated a clenbuterol-induced decrease (P<0.05) in the relative percentage of type I Myosin-HC with a concomitant increase (P<0.05) in Type II Myosin-HC in the SQL of the CLEB group. The Myosin-HC composition in the EDL was not altered. These findings suggest that clenbuterol may have induced selectively changes of muscle hypertrophy, the predominant anerobic glycolysis, and the transition of Myosin-HC in the SOL. The differences in the two muscles can be explained by the higher number of beta-2 receptors in slow-twitch muscles.

View full abstract

In the present study, we attempted to reconstruct the surface myo-electric signals from monopolarly recorded motor unit action potentials (MUAPs), and to construct a method of analysis for extracting information from surface ME signals on the recruitment behavior among motor units.
1) The waveform of a single MUAP of a surface electrode recorded monopolarly consisted of three phases : first, a positive, second, a negative transient and, third, a positive phase except for the end-plate region. The appearance of each phase could be interpreted from the field potential in the volume conductor produced by conduction of action potentials from the end-plate to the myotendinous junction.
2) Waveforms of MUAPs indicated that the positive phase and the negative phase are the same in area. In surface ME signals, coincidence of the phase areas was observed. Therefore, it was inferred that all the motor units producing the interfered surface ME signal showed a tendency to coincide with respect to the area between the two phases.
3) The fact that MUAPs consisted of three phases during conduction means that the contribution potential for a recorded electrode changes according to the position of the action potential on the muscle fiber (s) . Therefore, the potential of a surface myoelectric signal represents the sum of the contributed potentials from activated motor units.
4) The amplitude of surface ME potentials tended to be other than 0V as tension increased.
5) Considering the reconstruction of a surface ME signal involving many activated motor units from the contribution potential, the surface ME potential depends on the number of recruited motor units with a different waveform, in addition to the magnitude of synchronization and grouping discharge among motor units.

View full abstract

When monopolarly-recorded surface myoelectric signals from the vastus medialis muscle were analyzed by FFT (Fast Fourier Transform) to obtain an amplitude spectrum, we found a“dip”in amplitude of around 80 Hz. Using the frequency at the“dip” (Turning Frequency : TF) as a cut-off point, the raw myo-electric signals were divided into high frequency components (HFC) and low frequency components (LFC) .
1) TF appeared in the amplitude spectrum from all recording electrodes when the tension reached 60%MVC.
2) TFs shifted to higher frequencies with increased tension.
3) Using cross-correlation analysis, LFCs showed conductivity along muscle fibers. In contrast, a pair of HFCs from nearly fastened electrodes appeared in phase, but a pair of HFCs from distant electrodes showed no relation.
HFCs and LFCs, derived by using TFs from surface myoelectric signals, showed different characteristics in conductivity. This suggests that TF can be a useful analyzing method extracting new information from surface myoelectric signals. Further study is needed to pursue the relation between HFCs and LFCs, and physiological parameters.

View full abstract

The purpose of this study was to compare changes in oxygenation in the Vastus Lateralis (VL) and Rectus Femoris (RF) muscles during a ramp-loaded bicycle exercise. Twelve healthy males participated in the experiment. The test consisted of a leg arterial occlusion at rest and a ramp-loaded exercise (20 watts/min) using a bicycle ergometer until exhaustion. The changes in deoxygenation in each muscle was measured by near infrared spectrometer (NIRS) . The probes of NIRS were placed on VL and RF approximately 12 cm above the right knee. Oxy-Hb/Mb signals from NIRS were calculated as 100% at rest, with 0 % being the lowest value during the leg arterial occlusion. Pulmonary gas exchanges (VE, VO₂, VCO₂) were measured with an expiratory gas analyzer. In 10 subjects, muscle oxygenation level in VL decreased linearly until the deoxygenation limiting point (DOLP) -the point in exercise at which the deoxygenation rate decreases noticeably. However, in 2 subjects, the DOLP was not detected, and the muscle oxygenation level decreased linearly until exhaustion. The muscle oxygenation level in RF also decreased linearly until 70%VO₂max, although the deoxygenation rate was smaller than that in VL. Thereafter, the muscle oxygenation level in RF continued to decrease until exhaustion. No DOLP was found in any subjects in RF. Compared with the muscle oxygenation level in RF at any points during the exercise, those in VL were lower until 90%VO₂max (P<0.001) . However, the difference in muscle oxygenation levels between VL and RF at exhaustion was not noted. This study indicated that the patterns of deoxygenation in VL and RF during a ramploaded bicycle exercise were different.

View full abstract

The purpose of this study was to examine the relationship between isometric cervical extension strength and the cross-sectional area (CSA) of neck extensor muscles in order to obtain fundamental data for conducting neck muscle training to prevent neck injuries. Subjects were 8 males belonging to the judo or American football club in N University. Isometric cervical extension strength was measured at eight positions (0°, 18°, 36°, 54°, 72°, 90°, 108°, maximum flexion) using a cervical extension machine (Medx Inc., USA) . A transaxial magnetic resonance imaging (MRI) image of neck muscles was obtained at the intervertebral disk between C4 and C5 (using an MRI machine made by Hitachi medical Corp., JAPAN) . The findings were as follows.
1. The correlation between isometric cervical extension strength at 36°, 54°and 72°in a neutral position (60.8±1.4°) and the CSA of neck extensor muscles were higher than at other degrees (0°, 18°, 90°, 108°, maximum flexion) . In particular, there was a significant linear relationship at 54° (slightly extended position) .
2. A significant linear relationship was observed between the neck girth and CSA of neck extensor muscles.
In conclusion, there was a closer relationship between isometric cervical extension strengths at certain angles in a neutral position and the CSA of neck extensor muscles. Therefore, it was shown that isometric cervical extension strengths at certain angles in a neutral position mainly represented the CSA of neck extensor muscles.

View full abstract

This study investigated the relationship between the intensity of muscle contraction and muscle oxygenation during dynamic knee extension. Six healthy male subjects (age 24.6±1.2 years) performed knee extension (concentric : 1 s/eccentric : 1 s) to exhaustion at 3 different intensities, 30%, 20% and 10% of maximum voluntary contractile strength (MVC) . A near-infrared spectroscopy (NIRS) probe and surface electrodes of the electromyogram were fixed on the m. rectus femoris. The muscle oxygenation and integral electromyogram (IEMG) were recorded both during and after dynamic knee extension.
The summary of the results was as follows.
1) Continuous time of knee extension decreased with increasing intensity of muscle contraction. There were significant differences between 10%MVC and 20%MVC (p<0.001), and 10%MVC and 30%MVC (p<0.001) .
2) The oxy-hemoglobin level during knee extension decreased with increasing intensity of muscle contraction. There were significant differences between 10%MVC and 30%MVC (p<0.001), 20%MVC and 30%MVC (p<0.001), and 10%MVC and 20%MVC (p<0.05) .
3) Recovery time after knee extension increased with increasing intensity of muscle contraction. There were significant differences between 10%MVC and 30%MVC (p<0.01), and 20%MVC and 30%MVC (p<0.01) .
4) The IEMG increased with increasing time of knee extension. The maximum value was observed just before completing the knee extension on the IEMG. The rate of increase in the IEMG increased with decreasing intensity of muscle contraction.
These results suggest that muscle oxygenation during dynamic knee extension decreases with increasing intensity of muscle contraction, and influences continuous time of muscle contraction.

View full abstract