Why Choose Between Hold and Control?

Why Choose Between Hold and Control?

by Suzen DuBre

There is a tradeoff baked into upper-limb prosthetic fitting that most clinicians accept without much scrutiny.

Voluntary opening stays closed without effort. Voluntary closing gives the user real grip control. Pick one.

For a long time, that compromise made sense. Now it deserves a harder look.

The research is not ambiguous. Hichert et al. (2017) established that voluntary closing systems provide extended physiological proprioception -- direct physical feedback through the cable about both movement and force. Berning et al. (2014) showed users reported meaningfully better grip control and improved performance in daily activities with VC systems. Hichert and Plettenburg (2019) confirmed that users can reproduce target forces accurately, without visual input, when that feedback loop is present.

The mechanism is clear. Control comes from feedback. VC systems provide it. VO systems do not, not in the same way.

So why does VO remain the default at first fit?

Because sustained VC grip requires sustained cable tension. Over time, that introduces fatigue. And fatigue matters. So the field made a practical decision: sacrifice control for hold.

That decision was reasonable. The question is whether it is still necessary.

If a system preserves the VC feedback loop and maintains grip without continuous cable tension, the tradeoff disappears. Fatigue decreases. Grip consistency improves. Release becomes intentional. Users carry less visual and cognitive load through every task.

The research has already told us what enables control. Clinical experience has already told us why hold matters. The only remaining question is whether we should keep accepting a design constraint the science outgrew.

The ProHensor® was built around this exact premise: voluntary closing feedback preserved, grip hold built in, and the fatigue tradeoff eliminated by design. The science is clear. The fitting standard has room to move.

References

1. Hichert M, Abbink DA, Kyberd PJ, Plettenburg DH. High cable forces deteriorate pinch force control in voluntary-closing body-powered prostheses. PLoS ONE. 2017;12(1):e0169996. doi:10.1371/journal.pone.0169996
2. Berning K, Cohick S, Johnson R, Miller LA, Sensinger JW. Comparison of body-powered voluntary opening and voluntary closing prehensor for activities of daily life. J Rehabil Res Dev. 2014;51(2):253-261. doi:10.1682/JRRD.2013.05.0123
3. Hichert M, Abbink DA, Vardy AN, van der Sluis CK, Janssen WGM, Brouwers MAH, Plettenburg DH. Perception and control of low cable operation forces in voluntary closing body-powered upper-limb prostheses. PLoS ONE. 2019;14(11):e0225263. doi:10.1371/journal.pone.0225263