Hidetsugu Nishizono

Muscle fiber conduction velocity related to stimulation rate

Muscle fiber conduction velocity in human biceps brachii muscle, produced by voluntary contraction and by contraction owing to microstimulation of a single motor unit, was measured with surface array electrodes. The conduction velocity of the fibers in the motor unit was calculated from the conduction time of the motor unit action potential along the electrode array and the electrode separation. With voluntary contraction, a conduction velocity of 4.25 +/- 0.43 m/sec (mean +/- S.D., n = 68) was obtained. In recording the surface EMG, the mean firing rate of the motor unit was 15.8 imp/sec (range 6-24 imp/sec). Significantly slower conduction velocity of 3.69 +/- 0.33 m/sec (mean +/- S.D., n = 56) was found after microstimulation (P less than 0.001). The higher the stimulation rate the higher was the conduction velocity. With increasing stimulus rates of 5, 10, 20 and 40 c/sec, the mean and S.D. of the conduction velocity were 3.74 +/- 0.33 m/sec (2.1% increase in the mean value to 1 c/sec stimulus rate), 4.16 +/- 0.37 m/sec (13.6%), 4.35 +/- 0.54 m/sec (18.8%) and 4.80 +/- 0.49 m/sec (31.1%), respectively. The firing rate for voluntary contraction was in the same range of the one obtained with 10-20 c/sec electrical stimulation, conduction velocity was the same in the two conditions. We conclude that measurement of muscle fiber conduction velocity should also be standardized with muscle fiber firing rate.

Muscle fiber conduction velocity and contractile properties estimated from surface electrode arrays

Using an array of surface electrodes set 5 mm apart, we estimated the conduction velocities of muscle fibers during submaximal voluntary isometric contraction of human first dorsal interosseous muscle. The conduction velocity obtained by the averaging method ranged from 3.2 to 5.0 m/sec with a mean of 4.2 m/sec. Twitch tensions in the muscle detected during voluntary isometric contractions ranged from 0.31 to 5.97 g with a mean of 2.75 g based on an averaging method triggered by surface myoelectric signals. Threshold forces of the motor units varied from 120 to 930 g. The rise time of the force developed by isometric adduction ranged from 36.0 to 75.4 msec, with a mean of 55.4 msec. The conduction velocity of the muscle fiber showed a high correlation with the twitch (r = 0.71, n = 50; P less than 0.001) and threshold (r = 0.52, n = 50; P less than 0.001) forces, but a low one with rise time (r = -0.32, n = 50; P less than 0.05). The use of the averaging method with surface electrode arrays, especially for voluntary isometric contractions, shows that motor unit conduction velocity and contractile properties are functionally correlated.

Changes in intra-abdominal pressure and spontaneous breath volume by magnitude of lifting effort: highly trained athletes versus healthy men

Intra-abdominal pressure (IAP) is closely related to breathing behavior during lifting. Abdominal muscles contribute to both IAP development and respiratory function. The purpose of this study was to examine whether spontaneous breath volume and IAP altered with increased isometric lifting effort, and to compare the effect of different abdominal muscle strengths on these parameters. Maximal IAP during the Valsalva maneuver (maxIAP) and maximal isometric trunk flexor strength were measured in 10 highly trained judo athletes (trained) and 11 healthy men (controls). They performed isometric lifting with 0 (rest), 30, 45, 60, 75, 90, and 100% of maximal lifting effort (MLE). Natural inspiratory and expiratory volumes were calculated from air-flow data immediately before and after the start of lifting. IAP, measured using an intra-rectal pressure transducer during lifting, was normalized by maxIAP (%maxIAP). Trained athletes had higher maxIAP and stronger trunk flexor muscles than controls. A significant main effect of lifting effort was found on %maxIAP and respiratory volume. An interaction (lifting effort by group) was found only for %maxIAP. No significant group main effect or interaction was found for respiratory volume. Inspiratory volume increased significantly from tidal volume to above 60 and 45% of MLE in trained athletes and controls, respectively. Expiratory volume decreased significantly from tidal volume at above 30% of MLE in both the groups. These results suggest that spontaneous breath volume and IAP development are coupled with increased lifting effort, and strong abdominal muscles can modify IAP development and inspiratory behavior during lifting.

The relationship between court surface and tactics in tennis using a computerized scorebook.

The purpose of this study was to use a newly developed computerised scorebook for tennis in order to clarify the characteristics of tennis tactics used on specific court surfaces. The authors developed a computerised scorebook for tennis that calculates the time duration of shots, points, and the time between points. Data were collected from matches played by male Japanese intercollegiate players. A total of 97 points were observed. Two observers (A, B) were recruited for recording matches using the scorebook. The mean error of observer A was 0.003±0.05 s, while the mean error of observer B was 0.02±0.10 s. The computerised scorebook for tennis was used to collect data for clarifying the characteristics of tennis tactics used on specific court surfaces. Forty-one matches from the Grand Slam tournaments held in 2003 and 2004 were analyzed. The scorebook recorded the final shot of each point, the result of each point, and the time duration of each shot. The final shots were categorised into the following 5 groups: service, return of serve, ground strokes, attacking strokes, and defending strokes. The time between the impact of the serve and the impact of the return of serve determined the duration of service. The time duration of ground strokes was calculated as the time between the impact of one player and the impact of the other player. A chi-square test was used to compare the distribution of the final shots on each surface. An ANOVA test was conducted in order to compare the time duration on each surface and a Tukey’s HSD test was used for multiple comparisons. For the last shot of each point, significant differences were observed between the court surface and the distribution of the type of stroke. The percentage of ground strokes was high on clay while the percentages for attacking and defending strokes were high on grass. Furthermore, the rate of service strokes was high on hard courts. The shot time duration of the 1st service was 0.91 s on clay, 0.71 s on grass, and 0.73 s on hard courts. The time duration of service on clay was significantly longer than the time durations observed on other surfaces. The time duration of ground strokes was 1.36 s on clay, 1.34 s on grass, and 1.35 s on hard courts. The time duration of ground strokes on clay was significantly longer than time durations observed on grass; however, the difference was only 2/100 of a second. Service and return of service strokes were important to the tactics used on grass and hard courts as players must react more quickly than on clay. Ground strokes were important on clay and hard courts, and the average time duration of ground strokes was equal on these surfaces.

An analysis of time factors in elite male tennis players using the computerised scorebook for tennis

The authors developed the computerized scorebook for tennis to analyze the time duration of shots. The purpose of this study was to analyze the time factors in Grand Slam singles matches using the computerized scorebook for tennis. Eighty-two players’ performances from forty-one matches in Grand Slam tournaments held in 2003 and 2004 were analyzed. The French Open, Wimbledon and the U.S. Open were selected to compare the effect of court surface on timing factors. The time duration of both 1st and 2nd service was longest at the French Open. Players need different service strategy between the French Open and the other tournaments because of the difference of strategy. Time duration of ground strokes showed no significant differences between the three tournaments. Ground strokes and rally play followed similar rhythms at all three tournaments. These results were obtained using the computerized scorebook for tennis. The usefulness of the scorebook for tennis coaching was demonstrated.

An analysis of the time duration of ground strokes in Grand Slam men’s singles using the computerised scorebook for tennis

The purpose of this study was to analyse the time duration of ground strokes in various court surfaces in men’s singles tennis. We used the computerised scorebook for tennis to collect the data from the three Grand Slam men’s singles tennis tournaments (French Open, Wimbledon, U.S. Open) held in 2003 and 2004. The total number of study matches was 41. The time duration of ground strokes was analysed from the data. The factor of the player’s situation showed a significant difference (p<0.01). The time duration of ground strokes on the server was 1.33±0.01 s and on receiver was 1.38±0.01 s. This result was influenced by the difference of tactics in service games and return games. The server has the advantage due to starting the rally by means of the serve. It leads the server to play more aggressively than the receiver.