ABSTRACT
OBJECTIVE: Motor impairments related to hand function are common symptoms in patients with movement disorders, such as Parkinson’s disease (PD) and focal hand dystonia (FHD). However, hand dysfunction has not been quantitatively assessed as a clinical tool for screening patient groups from healthy controls (HCs). The aim of our study was 1) to quantitatively assess hand dysfunction in patients with PD and FHD and its usefulness as a screening tool 2) to grade disease severity in PD and FHD based on hand dysfunction. METHODS: The current case-control study included HCs (n = 50) and patients with known history of PD (n = 25) or FHD (n = 16). Hand function was assessed by a precision grip task while participants lifted objects of 1.3 N and 1.7 N under dry skin conditions, followed by very wet skin conditions (VWSCs). Receiver operating characteristic and summative scoring analyses were performed. RESULTS: In PD, the combination of loading phase duration and lifting phase duration at quantitative cutoffs of 0.36 and 0.74 seconds identified 21/25 patients as diseased and 49/50 subjects as HCs with 1.7 N under VWSCs. In PD, 5/21 was graded as “mild” and 16/21 as “moderate cases.” In FHD, slip force at a cutoff of 1.2 N identified 13/16 patients as diseased and 41/50 subjects as HC with 1.7 N under VWSCs, but disease severity could not be graded. CONCLUSION: Our results demonstrate the use of precision grip task as an important clinical tool in assessment of hand dysfunction in movement disorder patients. Use of quantitative cutoffs may improve diagnostic accuracy and serve as a valuable adjunct to existing clinical assessment methods.
Subject(s)
Humans , Case-Control Studies , Dystonia , Hand Strength , Hand , Lifting , Mass Screening , Movement Disorders , Parkinson Disease , ROC Curve , SkinABSTRACT
The effects of visual information about object size on grip force programming were investigated. Fifteen subjects (26.1±7.6 yrs) repeated lifts of a cube-like grip apparatus (30×30×30 mm, 30g) using a thumb and index finger, while three boxes of different sizes but equal weight (small : 10×10×60 mm, medium : 30×30×60 mm, large : 60×60×60 mm, 25g) were pseudorandomly presented by attaching beneath the grip apparatus. Lifting tasks were performed in two visual conditions. In the full-vision condition, subjects could perceive the box size prior to the lift-off of the grip apparatus, similar to normal everyday conditions. In the obstructed-vision condition, subjects could not perceive the box size due to the placement of a screen during the initial lifting phase, and only the grip apparatus were visible over the screen. The grip apparatus measured grip and load forces during the trial and we found that the grip and load force applied to the grip apparatus in the full-vision condition significantly increased with box size regardless of equal weight. In contrast, when the size information was removed in the obstructed-vision condition, the force applied for a given box of any size was always that adequate for the largest box, suggesting that the scaling of fingertip force by utilizing size information may be achieved by reducing forces for the smaller boxes on the basis of the force output applied for the largest box, but not by increasing forces on the basis of the force output applied for the smallest box.
ABSTRACT
The effects of aging on adaptive force control of precision grip while manipulating a small object were compared between older (84.2±8.9 yrs, n=33) and young adults (19.1±0.24 yrs, n=18) from the following perspectives: (1) adaptation to an unfamiliar object with uncertain physical properties during 16 consecutive lifts ; (2) adaptation to an object with a non-slippery (sandpaper) surface during 12 consecutive lifts, followed by 12 consecutive lifts with a slippery (silk) surface ; and (3) adaptation to objects with different weights (0.49, 0.98, 1.96 and 2.94 N) during 24 lifts (6 consecutive lifts for each weight) .During each trial, grip and load forces were monitored. Safety margin force and slip force were evaluated from the data obtained.<BR>The majority of older adults employed a considerably greater safety margin for an unfamiliar object in the initial trials than did young adults, while the minority of the older adults were able to adapt their safety margin force with a few trials, like the young adults. The older adults who overestimated the safety margin force, however, successfully adjusted their grip force to more optimal levels with repeated lifts, suggesting that the adaptive capability of grip force remained even at 90 years of age. The adaptation of older adults, however, was found to be slower (i. e., required more trials) than that of young adults. Upon encountering surface friction change, the safety margin forces in older adults were more strongly affected by the previous surface condition than those in the young adults. In addition, adaptation to a non-slippery surface seemed more difficult than that to a slippery surface with aging. Upon encountering weight change, older adults showed more difficulties in scaling their safety margin forces according to object weights.<BR>Slower adaptation and difficulty in adaptation to the friction or weight change in older adults may reflect the agerelated decline of tactile sensitivity which impaired the signaling of frictional conditions and various discrete events in the hand. In addition, the lift repetition for force adaptation may possibly reflect the age-related deficit or slowing of central processing capacities related to grip force production.
ABSTRACT
The effects of the surface friction of a grasped object on the regulation of grip force during holding tasks using a precision grip were investigated. Using a force transducer-equipped grip apparatus, the grip force and load force acting on the object were measured continuously while surface materials (silk, wood, suede and sandpaper) and load weights (0.98N, 1.96N, 2.94N, 4.90N and 9.81N) were varied. From the recorded data, the average static grip force, slip force, safety margin force and static friction coefficient were evaluated.<BR>It was found that both the slip force and safety margin force increased as the slipperiness of the object surface increased. Significant interactions between surface type and weight were observed in the slip force and static friction coefficient. The interaction effect resulted from the fact that the frictional relationships with the fingers changed according to both weight and surface conditions. This was considered due to the viscoelastic nature of finger skin. An increase in the safety margin force with surface slipperiness was considered due to psychological reaction, probably fear of dropping the object. Unexpected changes in surface conditions caused a greater safety margin force than trials without a surface change, which might also have been associated with psychological reaction to uncertainty of the new surface condition. A relatively large inter-subject variation was found in the slip force and safety margin force relative to slippery surfaces.
ABSTRACT
The effects of“lifting height (2 cm, 6 cm, and 10 cm) ”and“lifting velocity (natural and fast) ”, and influence of reaching action on timing and manipulative forces of the precision grip were examined while lifting a test object. Five adult males volunteered as subjects for the study. Grip forces, load force (the vertical lifting force) and vertical position of the test object were measured and time derivatives of them were computed using laboratory software. It was found that lifting height and velocity exerted significant interaction effects in movement time of the object during lifting phase (T3), peak load force (PLF) and peak velocity (PVel) . Significant main effects of height and velocity were as follows. The higher the lifting height (2 cm, 6 cm, 10 cm) was, the longer T 3 as well as larger PGF, PLF, PdGF/dt, and PVeI were. For the fast velocity trials, T 2 and T 3 were shorter, and PGF, PLF, PdGF/dt, PdLF/dt, and PVeI were larger than the natural velocity condition. The influence of the lifting velocity was stronger in the height of 6, 10 cm than in the height of 2 cm. For all trials with different heights and different velocity, the force rate profiles (dGF/dt and dLF/dt) were continuous, bell-shaped and single-peaked during the loading phase. There was a parallel increase of grip force in relation to an increase of load force. To reveal the height effect further, the target height was unexpectedly changed in some trials at the moment of finger contact with the grip surface. It was found that both timing and force actions were similar to the initial target height condition followed by an apparent correction of gripping and lifting actions to reach the secondary target height.<BR>Results of this study suggest that both lifting height and velocity were important factors to determine the force actions when manipulating an object. Both grip force and load force seem to be well-programmed according to intended height and velocity conditions.<BR>When the lifting action was made following the reaching action, T 3 became shorter, PGF became less, and PVeI became longer than those without the reaching action. The reaching action thus seems to facilitate the force coordination during the lifting action.