On the Precision Grip in Manual Transport
The aim of the present study was to investigate the grip and load force relations in the precision grip (between thumb and index finger) in static and dynamic situations, and to develop automatic procedures for the analysis of position and force data from tests involving the precision grip. The goal of the work was to create physiologically based methods for identification and quantitative determination of disturbances in the nervous control of hand motor function.
In the static case, the excess grip force used in order to maintain a certain safety margin, lifting a 600 g object using the precision grip, was explored. Special algorithms were developed to automatically determine this safety margin. In the dynamic case, the grip-lift synergy was investigated using a manual transport task. Algorithms were developed to determine and analyze the different phases of the transport. The effect of movement speed on the manual transport task was investigated. Special parameters were defined to examine the significance of this effect.
The static and dynamic precision grip methods were used on patients with movement disorders as well as on healthy persons. A safety margin analysis was performed in Rheumatoid Arthritis patients and in healthy persons. Differences were found in motor behavior between the two groups but no correlation was found for the safety margin and a simple timed test (GAT).
The correlation coefficient between GF and LF was determined in manual transport phases in movements both in the forward and the backward direction. Parkinson patients in medicated and non-medicated state as well as healthy persons participated. There were higher correlation coefficients between the grip and load forces in the initial phases, before the lift was completely established, as compared to the ballistic phases of the transport. This was evident both in PD patients and healthy persons. Precision grip parameters were calculated for healthy subjects. All of the parameters had a significant relation to the movement speed, which indicates that movement speed can be a regulatory variable for the generation of the grip and load forces.
Force-movement analysis is well suited for the study of hand motor function. Dividing the task into appropriate phases opens possibilities to select specific indicators for different CNS disturbances.