## 4 Discussion  
This simple rPMS technique produced the same extent of flexion and abduction of the MCP point as active movement. Pain during rPMS was lower. Furthermore, the PIP and DIP joints were extended more in rPMS than in active motion, indicating that the interosseous and lumbrical muscles were stimulated. This technique is unique because it stimulates the intrinsic muscles from the dorsum of the hand to flex the MCP joint. Voluntary MCP joint flexion is usually accompanied by the activities of the extrinsic muscles (flexor digitorum superficialis and flexor digitorum profundus) resulting in PIP and DIP joint flexion. In contrast, MCP joint flexion and PIP and DIP joint extension occur by stimulating intrinsic muscles with rPMS. We can activate the intrinsic muscles of the hand selectively by applying rPMS without compensatory movement of the extrinsic muscles. This technique could be used as a therapeutic procedure for various conditions that cause immobility of the MCP joint secondary to dysfunction of the intrinsic muscles of \begin{table}
\begin{tabular}{c r r r r r r r r} \hline \hline \multirow{2}{*}{**Participant**} & \multicolumn{4}{c}{**Active Flexion**} & \multicolumn{4}{c}{**rPMS**} \\ \cline{2-10}  & **MCP Joint** & **PIP Joint** & **DIP Joint** & **MCP Joint** & **MCP Joint** & **PIP Joint** & **DIP Joint** & **MCP Joint** \\  & **Flexion** & **Flexion** & **Flexion** & **Abduction** & **Flexion** & **Flexion** & **Flexion** & **Abduction** \\ \hline A & \(79\pm 4\) & \(12\pm 1\) & \(9\pm 5\) & \(22\pm 3\) & \(93\pm 8\) & \(7\pm 6\) & \(9\pm 2\) & \(13\pm 4\) \\ B & \(85\pm 4\) & \(-3\pm 5\) & \(8\pm 4\) & \(18\pm 1\) & \(102\pm 6\) & \(-1\pm 11\) & \(3\pm 7\) & \(12\pm 9\) \\ C & \(77\pm 10\) & \(21\pm 8\) & \(6\pm 12\) & \(12\pm 1\) & \(70\pm 9\) & \(-16\pm 3\) & \(-16\pm 6\) & \(17\pm 11\) \\ D & \(79\pm 3\) & \(5\pm 6\) & \(1\pm 4\) & \(14\pm 1\) & \(76\pm 3\) & \(-22\pm 3\) & \(-22\pm 10\) & \(9\pm 5\) \\ E & \(78\pm 4\) & \(12\pm 11\) & \(10\pm 9\) & \(20\pm 2\) & \(87\pm 16\) & \(18\pm 14\) & \(19\pm 8\) & \(13\pm 4\) \\ F & \(80\pm 6\) & \(10\pm 15\) & \(2\pm 2\) & \(8\pm 1\) & \(66\pm 17\) & \(-21\pm 8\) & \(0\pm 4\) & \(14\pm 4\) \\ G & \(75\pm 3\) & \(27\pm 11\) & \(-10\pm 7\) & \(5\pm 3\) & \(78\pm 8\) & \(-8\pm 7\) & \(-12\pm 13\) & \(8\pm 6\) \\ H & \(75\pm 9\) & \(-3\pm 13\) & \(5\pm 10\) & \(16\pm 3\) & \(69\pm 6\) & \(-4\pm 6\) & \(-6\pm 11\) & \(9\pm 4\) \\ I & \(74\pm 4\) & \(3\pm 7\) & \(4\pm 3\) & \(13\pm 2\) & \(88\pm 7\) & \(0\pm 1\) & \(10\pm 7\) & \(3\pm 0\) \\ J & \(81\pm 5\) & \(9\pm 7\) & \(1\pm 1\) & \(9\pm 2\) & \(72\pm 8\) & \(-5\pm 2\) & \(1\pm 9\) & \(6\pm 5\) \\ \hline \hline \end{tabular} MCP—metacarpophalangeal; PIP—proximal interphalangeal; DIP—distal interphalangeal. Data are described as mean \(\pm\) standard deviation.  
\end{table} 
Table 1: Maximum joint angles between active MCP joint flexion and rPMS. Figure 3: The maximum angles of the of MCP, PIP, and DIP joints by active movement and rPMS. There were no significant differences in the maximum angles of flexion and abduction of the MCP joint. rPMS extended the PIP and DIP joints significantly more. the hand. When the intrinsic muscles of the hand are not activated, MCP joint contractors in the extended position tends to occur [2]. rPMS may prevent joint contractors from immobility by repeatedly flexing the MCP joint. Furthermore, this procedure may improve paralysis, increase the flexion strength of the MCP joint, and improve pinching or fine finger movements in patients with hemiplegia due to a stroke or incomplete cervical spinal cord injury. This study has several limitations. We evaluated hand joint movement by stimulating the intrinsic muscles of the hand using rPMS in healthy subjects. The rPMS coil was the same regardless of the participant's hand or muscle size. Therefore, depending on the subject's physical characteristics, the joint movements induced by rPMS vary. In addition, we did not evaluate different age groups nor differences by sex. The sample size was small in this study.