In this study, we investigated trainees’ adaptation by conducting static balance training in a tandem standing posture. The horizontal tensile force loads in the front, back, left, and right directions were applied using pneumatic artificial muscles. We analyzed the adaptation that occurred during training by changing the direction of the horizontal tensile load on the lumbar region according to the tendency of the trainee. We conducted the experiments using the following protocol. Ten trainees participated in the experiment. In Phase 1, we applied loads in four directions the same number of times in random order to investigate the weak direction in the balance of each trainee. In Phase 2, we measured five trainees in each group: Group 1 was trained in the same way as Phase 1, and Group 2 was intensively trained in two directions in which the balance found in Phase 1 was difficult to maintain. In Phase 3, we performed the same experiment as in Phase 1. We analyzed the adaptation of the trainees using the margin of stability (MoS), a balance evaluation index. We compared the experimental results of Phases 1 and 3. In Group 1, the tendency for improvement in balance was unclear. On the other hand, the balance index in Group 2 improved in four out of five trainees in both the front-back and left-right directions. These results suggest that the training method concentrating on the weak direction could provide a clear directionality to the training effect.

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