Exploring the human grip force system: a preliminary study

It has been postulated that cutaneo-receptors from the digits contribute to the control of manipulatory functions of the hand. However, few studies have examined the dynamics of the human grip force system (HGFS) in terms of the dynamic relationship between the vertical loads, taken as an input and the resulting grip force, taken as the output. This paper describes the experimental procedures we have developed to explore the HGFS and presents some initial experimental results. These demonstrate that the step response of the HGFS is biphasic. The first, short latency phase, likely involves only passive and intrinsic components. The second, longer latency phase is likely related to reflex mechanisms since it is preceded by a strong burst of EMG. Moreover, the HGFS response depended nonlinearly on the amplitude and direction of the load applied. These results indicate that further investigation of HGFS dynamics will require the use of nonlinear identification methods.