Motor point map of upper body muscles

The purpose of the present study was to systematically investigate the upper body motor point (MP) positions of selected muscles and to create an atlas of the identified MPs.

MPs were searched bilaterally in 15 male and 15 female subjects by scanning the skin with a special pen electrode at low stimulation frequency (3 Hz) and current amplitude (<10 mA). The following muscles were investigated: biceps brachii, triceps brachii, deltoideus, trapezius, latissimus dorsi, erector spinae (lumbar part), pectoralis minor and major, and rectus abdominis.

A total of 1,563 MPs were identified. The MPs could be clustered into 31 distinct positions on each side of the body. However, the number of MPs per muscle varied between subjects: 2 MPs were found for the biceps brachii, 2-3 for the triceps brachii, 4-5 for the deltoideus, 2-3 for the pectoralis major, 1 MP for the pectoralis minor, 4-5 for the trapezius, 3-4 for the latissimus dorsi, 4-5 for the rectus abdominis, and 2-3 for the erector spinae in its lumbar part. Referring to the applied grid, upper limb and lower back muscles presented a low inter-individual variation, whereas MPs of the deltoideus, the pectoralis major, and the rectus abdominis were characterized by a poor homogeneity. All MPs were found to be highly symmetrical between both sides of the body (r = 0.96; p < 0.001).

The presented data and the corresponding map will help physiotherapists, and conditioning specialists improve their neuromuscular electrical stimulation therapy or training, respectively.