ABSTRACT
This study examined variations in shoulder loading due to differences in the site of stepping foot contact during baseball pitching, while comparing flat ground and mound conditions. Measurement was performed, involving 10 right-handed pitchers who belonged to university baseball clubs, under original flat ground and mound conditions. Pitching movements were classified into 3 categories: [normal], [narrow], and [outside]. Through 3-dimensional motion analysis using a motion capture system, the following results were obtained: 1. The pitching velocity was significantly higher in the [normal] compared with [narrow] and [outside] conditions and under the mound compared with flat ground condition. 2. The peak torque of the shoulder internal rotation was markedly lower in the [narrow] compared with [normal] condition. There were no significant differences between the [normal] and [outside] conditions or between the flat ground and mound conditions. 3. The posterior, superior, and inferior shearing forces, as well as the proximal traction force, which influence the humeral head of the shoulder, were markedly greater in the [normal] compared with [narrow] and [outside] conditions. The anterior and posterior shearing forces and proximal traction force were significantly greater under the mound compared with flat ground conditions. Based on the results, the internal rotation torque of the shoulder, as well as the shearing and traction forces influencing the humeral head of the shoulder, may vary due to differences in the site of stepping foot contact during baseball pitching and between flat ground and mound conditions. The former may also be useful to prevent pitching-related shoulder injuries.
ABSTRACT
In the context of energetics related to a pendular model, the mechanical power (<I>W</I>) and ‘pendular motion efficiency’ (<I>PME</I>) were determined during walking of the subjects who consist of 37 healthy elderly women (65-85 years) and 21 young women (18-25 years) . Using a force plate, the potential and kinetic energies of the body's centre of mass were measured at various constant speeds. Walking speeds were selected and controlled by a newly devised pace-maker. <I>PME</I>, which is equivalent to ‘% recovery’ by Cavagna (1976), indicates a sort of efficiency in transforming potential energy into kinetic energy and vice versa. The external power to accelerate the body (<I>Wext</I> ), which is thought to be supplied by muscles, increased with walking speed, and the rate of increase in <I>Wext</I> tended to be greater in the elderly than in the young subjects. It was noted that the maximal <I>PME</I> values at the optimum speed in both age groups were comparable, but <I>PME</I> values in the elderly decreased more markedly than in the young subjects as walking speed deviated from the optimum. This fact suggests that an adaptability to different walking speeds reduced in the elderly population.
ABSTRACT
The effects of different intensities of muscle training on the force, velocity and power relationship have been examined on human elbow flexor muscles. Twenty male subjects, 18-22 years of age, were divided into 4 different groups ; G<SUB>0</SUB>, G<SUB>30</SUB>, G<SUB>60</SUB>, and G<SUB>100</SUB>. Their training loads were prescribed by a fraction of isometric strength (P<SUB>0</SUB>) measured at right angle of elbow joint : 0% P<SUB>0</SUB> (G<SUB>0</SUB> ; isotonic contraction without load), 30% P<SUB>0</SUB> (G<SUB>30</SUB>), 60% P<SUB>0</SUB> (G<SUB>60</SUB>), and 100% P<SUB>0</SUB> (G<SUB>100</SUB> ; isometric contraction) . The subject contracted his elbow flexors with maximum effort 10 times a day, 3 days a week for 12 weeks. The force-velocity relations and the resultant power output were determined, before and after training period, by a modified Wilkie's apparatus.<BR>The training by maximum isotonic contraction without load (G<SUB>0</SUB>) was found to be most effective for improving maximum velocity (V<SUB>0</SUB>), while the isometric training improved isometric strength (P<SUB>0</SUB>) most. For this, the P-V relations of these groups were specifically modified by greater velocity component (G<SUB>0</SUB>) or greater force component (G<SUB>100</SUB>) . The G<SUB>30</SUB> and G<SUB>60</SUB> groups showed such all-round improvements that the P-V relations shifted in parallel with those of pre-training period. The maximum power (PVmax), which calculated from P-V relationship, increased most in G<SUB>30</SUB>, followed by G<SUB>100</SUB>, G<SUB>60</SUB>, and G<SUB>0</SUB> groups.<BR>From these results it was concluded that the different training loads brought about specific effects on P-V relation, and that the most effective load for improving maximum power was 30% of isometric strength.