To the best of our knowledge, this was the first comparative study to analyze the training outcomes of BMLT for the throwers` shoulder than popular thrower’s ten program. The principal findings of the present study were that this BMLT yielded a greater range of motion, supraspinatus recruitment in the shoulder cocking motion, and improved the throwing velocity for the baseball players. Hence, the results implied that BMLT is an applicable training alternative for the baseball throwers or overhead activities.
The results of the present study showed that BMLT produced a greater static ROM than conventional training in shoulder saggital extension and external/internal rotation, which is an effect of the most critical feature of BMLT, the three-dimensional training plane. This involves greater scapular movement in the cyclic motion from shoulder elevation to horizontal abduction. In the Thrower’s ten program, most of the resistance or muscular training is carried out on a single plane of motion. Combining the reciprocal “dodge movement” on a stable-handled platform, the characteristics of open and closed kinetic chain exercise are merged, and BMLT increases safety and results in less training-related delayed-onset muscle soreness. Previous studies have demonstrated enhancement of training actions and functional activities by BMLT exercise with a greater range of motion[10, 13]. The results of the present study also revealed that a greater range of motion was obtained using this novel weight training modality.
Synchronization of the middle deltoid and supraspinatus is believed to be critical during shoulder abduction[14, 15] especially in cocking phase. In general, the deltoid muscle plays a major role in shoulder abduction, rather than the supraspinatus. However, the supraspinatus lesion is a much more common injury than the deltoid and the conventional training is difficult in changing rotator cuff activation. BMLT offered the superior supraspinatus MVICs (Fig. 4) than conventional training in cocking motion 6 weeks after training. The superior supraspinatus contractions were believed to be positive in improving rotation range of motion and performance in the overhead activity.
The middle deltoid contributes most to movement, while the shoulder abduct in internal rotation and abducts horizontally with external rotation[17–19]. The co-operative mechanism contributes most greatly in the cocking phase[17–19]. The supraspinatus works synchronously with the middle deltoid for shoulder abduction. It has been reported that the supraspinatus is the common injured tendon in the throwing athletes, in particular, partial-thickness tears[7, 8]. Most of the strategies employed for the prevention of supraspinatus injury aim to enhance training or conditioning, introduce a proper throwing mechanism[22, 23], and specify an adequate throwing interval program with appropriate rest. As compared with conventional training, the contribution of the supraspinatus increased after 6 weeks of training which indicated that BMLT improved the supraspinatus contribution in the cocking motion over that resulting from conventional training. From the aspects of injury prevention and performance promotion, we postulated that BMLT is an alternative training to provide better supraspinatus training effect for the throwers. Meanwhile, the improvement of throwing velocity were observed in this study although the velocity improvement is multifactorial[24, 25], but it cannot be denied that the flexibility of the joint and rotator cuff strength posed the essential roles.
Limitations of the present study exist. First, the infraspinatus muscle, which is involved in shoulder external rotation, was not analyzed in the present study owing to the avoidance of EMG signal interference. Second, EMG analysis should also address muscles that facilitate scapular motion, such as the trapezius, rhomboids, levator scapulae and serratus anterior. Third, a longer training interval and recruitment of a greater number of athletes are required to demonstrate and corroborate the training outcomes.