The purpose of this study was to evaluate the activity of the shoulder muscles with various loads in the external rotational motion of the shoulder and to find the load in which only the inner muscles work mainly and the outer muscles don't work.

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[Purpose]The purpose of this study was to evaluate the activity of shoulder muscles in various shoulder positions in the external rotational motion.
[Materials and methods]We examined the non-dominant side of shoulders of 8 adult males who did not have any shoulder disorder. We pasted surface electrodes for 7 outer muscles and stuck needle electrodes into 3 inner muscles of each subject. Each person performed isometric external rotation motion in various loads (0,3,9,15Nm) in 6 positions (60° internal rotation, neutral,30° external rotation with arm at side, and neutral,45° external rotation,90° external rotation with arm at 90° abduction position) with a Cybex-NORM770. We obtained electromyograms of each muscle. An electromyogram signal during a maximum manual muscle strength test (MMT) was selected as the normalizing value (100%) for each subject.
Each activity (%MMT) was atatistically compared, using Scheffe's test. The statistical significance was set at 0.01.
[Results and conclusion]During isometric external rotation motion, in internal rotation or arm at side position, the activities of the muscles were low and the activities of the inner muscles were higher than those of the outer muscles, so these positions might be appropriate for rotator cuff exercises in the early phase of rehabilitation. While, in the 90° external rotation with arm at 90° abduction positi on, which is similar to the cocking phase of throwing, the activities of all the muscles including the outer muscles were very high. So we must be careful when we do shoulder exercise in such like position not to overload the shoulder muscles.

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    The purpose of this study is to get the basic data for build up the systematic coaching method, to elucidate key coaching points related to movement in baseball hitting, to integrate and assemble these points, to elicit experiential knowledge from expert baseball coaches. Forty guidance books of baseball hitting were published in Japan which were transcribed onto text data, and divided into segments on the basis of meaning unit. We labeled “target parts (posture, axis, head and face, arm, viewpoint, trunk, hip, leg, object, equipment)” and “movement phase (stance, take back, top, step, approach, impact, follow-through and comprehensive)” to these text data. For this process, we conducted triangulation to improve reliability and validity. We extracted 3215 units and analyzed the number of each labels. The most frequent label was “equipment” and the next frequent label was “leg” and “arm” and “trunk”. These results suggest that key coaching points of baseball hitting shift from “leg” to “trunk” to “arm” in progress of movement phase. From the number of “target parts” in “movement phase” suggest that baseball hitting is coached for target both the comprehensive and partial, and it became clear what many baseball coaches were coaching who have common knowledge in the movement phase.

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