The passive stiffness of the wrist and forearm

Abstract

Because wrist rotation dynamics are dominated by stiffness (Charles SK, Hogan N. J Biomech 44: 614 -621, 2011), understanding how humans plan and execute coordinated wrist rotations requires knowledge of the stiffness characteristics of the wrist joint. In the past, the passive stiffness of the wrist joint has been measured in 1 degree of freedom (DOF). Although these 1-DOF measurements inform us of the dynamics the neuromuscular system must overcome to rotate the wrist in pure flexion-extension (FE) or pure radial-ulnar deviation (RUD), the wrist rarely rotates in pure FE or RUD. Instead, understanding natural wrist rotations requires knowledge of wrist stiffness in combinations of FE and RUD. The purpose of this report is to present measurements of passive wrist stiffness throughout the space spanned by FE and RUD. Using a rehabilitation robot designed for the wrist and forearm, we measured the passive stiffness of the wrist joint in 10 subjects in FE, RUD, and combinations. For comparison, we measured the passive stiffness of the forearm (in pronation-supination), as well. Our measurements in pure FE and RUD agreed well with previous 1-DOF measurements. We have linearized the 2-DOF stiffness measurements and present them in the form of stiffness ellipses and as stiffness matrices useful for modeling wrist rotation dynamics. We found that passive wrist stiffness was anisotropic, with greater stiffness in RUD than in FE. We also found that passive wrist stiffness did not align with the anatomical axes of the wrist; the major and minor axes of the stiffness ellipse were rotated with respect to the FE and RUD axes by ϳ20°. The direction of least stiffness was between ulnar flexion and radial extension, a direction used in many natural movements (known as the "dart-thrower's motion"), suggesting that the nervous system may take advantage of the direction of least stiffness for common wrist rotations. wrist stiffness; muscle tone; neuromuscular; motor control; spasticity GRACEFUL MOVEMENT REQUIRES that the neuromuscular system compensate for unwanted dynamics of the body. For example, it is well known that simple reaching movements require complex torques to compensate for the coupled inertial dynamics of the arm (Hollerbach and Flash 1982). Decades of research have shown that the compensation of unwanted limb dynamics is accomplished through a combination of feedback control (through muscles, reflex loops, and adaptation) and predictive control, and much effort has focused specifically on how the brain compensates for the coupled inertial dynamics of the arm during reaching movements (Bastian et al. 1996;Bastian 2006).Recent work has shown that the dynamics of wrist rotations are quite different from reaching movements: wrist rotations are dominated by stiffness, not inertia (Charles and Hogan 2011), suggesting that a major part of wrist control involves compensating for the stiffness of the wrist joint. Several studies have measured wrist stiffness in flexion and/or extension (Axelson and Hagbarth 2001;Cornu et a...

Changes in passive ankle stiffness and its effects on gait function in people with chronic stroke

“…Bressel and McNair used a slow, prolonged static and cyclic calf stretching of 30 min duration in patients with stroke to compare its short-term effects on PAS and reported a decrease in paretic PAS [22]. Generally speaking, the training-induced changes in sagittal plane PAS reported here differed from those published by others ( Finally, it is worthwhile to point out that our success in PAS measurement of the paretic ankle in multiple DOFs parallel those for the upper limb, e.g., wrist [53][54][55] and arm [56], which could ultimately provide us with a clearer understanding of how the nervous system may take advantage of the direction(s) of higher compliance, albeit differently for the two cases.…”

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

“…Data collected before commencing each trial of 36 movements were removed, knowing the time to complete each movement, the number of movements, and the acquisition frequency. The processed data was then applied to two different estimation methods, the fitting ellipse (FE) [16] and the multiple regression method (MR) [28], to obtain wrist stiffness magnitude and orientation among the 4 parameters commonly used (listed below) to characterize a stiffness ellipse [16,28]; ellipse. Previous research indicates that the major weakness of the FE approach is that it only considers the components of torque and angle parallel to the perturbation direction and does not include stiffness effects perpendicular to the perturbation direction.…”

“…Rj is the rotation matrix for the jth direction,  represents angular displacement, and 'K' represents quasi-stiffness.) [16] The multiple regression (MR) method (Equation 2) determines the four elements of the stiffness matrix by multiple linear regression (using MATLAB's regress function [26] …”

“…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.…”

“…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.…”