List of Controlled Experiments.

Various experiments were conducted to understand the range of achievable performance (i.e., maximum arm rotation speed and energy distribution between the arm and the body) depending on different controlled conditions. Three categories of control parameters are considered.

Tendon control: the pulling velocity of the kevlar string shown in Fig. 1B is regulated by an external motor controller. Multiple experiments were performed at different pulling velocities from 0.5 m s−1 to 2.3 m s−1.

Environment: experiments were conducted with two fluid loading conditions, air and water. In each loading condition, multiple tendon control experiments were performed.

Design: multiple tendon attachment points were considered by changing the joint-to-tendon length, L0 in Fig. 2A, from 19 to 23 mm. Also, different contact angles varying from 0° to 11.4° were tested. In each geometry, multiple tendon control experiments were performed.

Representative videos of striking experiments (L0=23 mm) in air and water are shown in Movies S1–S3: two experiments with different loading, Movies S1 (air) and S2 (water), and one experiment with a different contact angle using a shim to offset the arm, Movie S3 (with a contact angle of 6.4°).