Isometric force vectors for 2D forearm (flexion/extension & pronation/supination) produced by 13 optimally recruited muscles (Supinator, SUP; the short and long heads of Biceps Brachii, BIC sh and ln; Brachialis, BRS; Brachioradialis, BRD; Pronator Teres, PT; Pronator Quadratus, PQ; the long, medial, and lateral heads of Triceps, TRI ln, m, and lt; Extensor Carpi Radialis longus and brevis, ECRl and ECRb; flexor carpi radialis, FCR). A. Pulling directions in 2D space for the 8 muscles typically recordable with surface EMG electrodes. B. Force vectors (red + symbols) toward 16 targets computed according to 1-8 synergies extracted (using multiple initializations) from the 8 somewhat redundant muscles recordable with surface EMG electrodes. C and D. Pulling directions for the 8 less-redundant muscles that better reflect the 2D task and simulated force vectors for synergies extracted for those muscles. E and F. Synergy performance as in Fig. 3. From (Aymar de Rugy et al., 2013) with permission of the publishers.