Fatigue-free operation of most body-powered prostheses not feasible for majority of users with trans-radial deficiency.

The study measured only 23 adults, so the estimates may be imprecise and may not fit every trans-radial prosthesis user. Participants varied widely in age, congenital or acquired defect, affected side, current prosthesis type, body-powered experience and daily use, which likely contributed to the wide force range. Maximum cable force may depend on motivation and the experimenter's encouragement, so some participants may not have produced their true maximum. The test disabled cable excursion and asked for a 3-second maximum effort, so it does not show what happens during normal prosthesis use over the day. The 20% fatigue-free boundary came from prior isometric work, not from repeated prosthesis use measured in this sample. Discomfort was summarised from body maps by the experimenter and did not measure each person's discomfort threshold or pain severity. Anthropometric prediction worked only for females; other measures did not predict maximum force, so upper-arm circumference is not a general substitute for force measurement.

The authors declared no potential conflicts of interest. The research was funded by Fonds NutsOhra, grant 1101-049.

Do not conclude that body-powered prostheses are unsuitable for everyone or that they cause pain in ordinary daily use. This study tested short maximum cable efforts, and the authors note that daily activities may use lower forces, and that duration and frequency also affect discomfort.