Passive Stiffness of Coupled Wrist and Forearm Rotations

Abstract

Coordinated movement requires that the neuromuscular system account and compensate for movement dynamics. One particularly complex aspect of movement dynamics is the interaction that occurs between degrees of freedom (DOF), which may be caused by inertia, damping, and/or stiffness. During wrist rotations, the two DOF of the wrist (flexion-extension and radial-ulnar deviation, FE and RUD) are coupled through interaction torques arising from passive joint stiffness. One important unanswered question is whether the DOF of the forearm (pronation-supination, PS) is coupled to the two DOF of the wrist. Answering this question, and understanding the dynamics of wrist and forearm rotations in general, requires knowledge of the stiffness encountered during rotations involving all three DOF (PS, FE, and RUD). Here we present the first-ever measurement of the passive stiffness encountered during simultaneous wrist and forearm rotations. Using a wrist and forearm robot, we measured coupled wrist and forearm stiffness in 10 subjects and present it as a 3-by-3 stiffness matrix. This measurement of passive wrist and forearm stiffness will enable future studies investigating the dynamics of wrist and forearm rotations, exposing the dynamics for which the neuromuscular system must plan and compensate during movements involving the wrist and forearm.

The Impact of Aging and Hand Dominance on the Passive Wrist Stiffness of Squash Players: Pilot Study (Preprint)

“…The experiment commenced randomly with the left or right upper limb (using the MATLAB randi X function (MathWorks, Natick, 2016, MA)) [26]. The reference position for the upper limb was in keeping with the set-up of Durand et al [17] and Drake & Charles [14] to allow accurate analysis and comparison of study results; the elbow was flexed to 30-degrees, the third metacarpal was aligned with the forearm, and the wrist was positioned in 0-degrees wrist extension and 7° of ulnar deviation (UD). Although previous studies have used an almost neutral RUD wrist position (0° along wrist UD), this study and Durand et al [17] deliberately selected 7° of wrist UD as this initial wrist position was more comfortable, allowing subjects to remain in a passive muscle state and avoid unwanted muscle activity.…”

“…The inclusion criteria were as follows; i) male, ii) 18 years or older, iii) no prior wrist surgery or injury, iv) English speaking, and v) a minimum of five years playing experience. Only male subjects were recruited to reduce the risk of data variability, as previous work had demonstrated a difference in the magnitude and direction of wrist quasistiffness between the male and female sex [14][15][16][17]. Subjects were asked not to participate in any upper-limb exercise in the 24-hours preceding their evaluation session to decrease the risk of reduced wrist range of motion (ROM) due to muscle swelling [11] and muscle thixotropic behavior [23] associated with eccentric wrist exercise.…”

“…The increased mechanical loading of the wrist associated with squash play may also explain the significant difference in the orientation of wrist quasi-stiffness between the unskilled and young squash playing groups. Nonetheless, as there is inconsistency in the orientation of wrist quasi-stiffness reported in the literature, it is possible that both differences in study subject's physical activities and study methodology contribute to the variance seen [14][15][16][17].…”

“…Extensive research has been conducted on passive joint quasi-stiffness of the lower limb and the impact on gait [6,7], with less research focusing on the upper limb and the equally important impact on activities of daily living, leisure activities, and sports. Of the joints within the upper limb, the neuromuscular control of the wrist has been identified as being dominated by joint stiffness [13,14]. It is, therefore, of paramount importance that we develop our understanding of the properties and variables of passive wrist stiffness in different populations to better comprehend how stiffness impacts the planning and coordination of wrist movements by the neuromuscular system during functional and sporting activities.…”

“…Previous studies have investigated the impact of study methodology [15][16][17], sex [14][15][16][17], and hand dominance [17]. A recent study [17] demonstrated that there was increased passive wrist quasi-stiffness in the dominant compared to the non-dominant upper-limb of healthy young men and women.…”