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Zong-Ming Li, Shouchen Dun, Daniel A. Harkness and Teresa L. Brininger

The purpose of the current study was to examine motion enslaving characteristics of multiple fingers during isolated flexion of the distal interphalangeal joints. Because the distal interphalangeal joints are flexed by multiple tendons of the single flexor digitorum profundus, the current experimental design provided a unique advantage to understand inter-finger enslaving effects due to the flexor digitorum profundus. Eight subjects were instructed to flex the distal inter-phalangeal joint of each individual finger from the fully extended position to the fully flexed position as quickly as possible. Maximal angular displacements, velocities, or accelerations of individual fingers were used to calculate the enslaving effects. An independence index, defined as the ratio of the maximal displacement of a master finger to the sum of the maximal displacements of the master and slave fingers, was used to quantify relative independence of each finger. The angular displacements of the index, middle, ring, and little fingers were 68.6° (±7.7), 68.1° (±10.1), 68.1° (±9.7), and 74.7° (±13.3), respectively. The motion of a master finger was invariably accompanied by motion of 1 or 2 slave fingers. Angular displacements of master and slave fingers increased to maximum values with time monotonically. Velocity curves demonstrated bell-shaped profile, and the acceleration curves were sinusoidal. Enslaving effects were generated mainly on the neighboring fingers. The amount of enslaving on the middle and ring fingers exceeded more than 60% of their own maximum angular displacements when a single adjacent finger moved. The index finger had the highest level of independence as indicated by the lowest enslaving effects on other fingers or by other fingers. The independence indices of the index, middle, ring, and little fingers were 0.812 (±0.070), 0.530 (±0.051), 0.479 (±0.099), and 0.606 (±0.148), respectively. In all tasks, motion of slave fingers always lagged with respect to the master finger. Time delays, on average, ranged from 7.8 (±5.0) to 35.9 (±22.1) ms. Our results suggest that there exist relatively large enslaving effects among the compartments of the flexor digitorum profundus, and functional independence of fingers in daily activities is likely enhanced through synergistic activities of multiple muscles, including flexors and extensors.

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Tomoko Aoki, Shinichi Furuya and Hiroshi Kinoshita

Using fast tapping tasks with each of the four fingers (single-finger tapping) and with two of the fingers used alternately (double-finger tapping), the ability to make rapid tapping movement by the individual fingers was compared between expert pianists and nonmusician controls in both genders. Maximal pinch and grasp forces were also measured to assess strength of individual fingers and whole hand, respectively. Movement of the ring and little fingers was slower than that of the index and middle fingers in both the pianists and controls. The slowness of the ring and little fingers was, however, much less evident in the pianists than the controls in both tapping tasks. The pianists also had smaller intertap interval variability for the index and middle fingers. No pianist–control difference was found for the pinch and grasp forces. Piano training, therefore, effectively changed the ability to move individual fingers rapidly, but not their flexor strength. No gender difference was found in any of the tapping tasks though males had greater strength. Gender thus does not appear to be a factor differentiating the ability to move individual fingers rapidly.

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Sheng Li, Frederic Danion, Mark L. Latash, Zong-Ming Li and Vladimir M. Zatsiorsky

One purpose of the present study was to compare indices of finger coordination during force production by the fingers of the right hand and of the left hand. The other purpose was to study the relation between the phenomena of force deficit during multifinger one-hand tasks and of bilateral force deficit during two-hand tasks. Thirteen healthy right-handed subjects performed maximal voluntary force production tasks with different finger combinations involving fingers of one hand or of both hands together. Fingers of the left hand demonstrated lower peak forces, higher indices of finger enslaving, and similar indices of force deficit. Significant bilateral effects during force production by fingers of both hands acting in parallel were seen only during tasks involving different fingers or finger groups in the two hands (asymmetrical tasks). The bilateral deficit effects were more pronounced in the hand whose fingers generated higher forces. These findings suggest a generalization of an earlier introduced principle of minimization of secondary moments. They also may be interpreted as suggesting that bilateral force deficit is task-specific and may reflect certain optimization principles.

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Sheng Li

This study investigated the possible role of the corticospinal system during force generation and force relaxation. Nine young and healthy subjects were instructed to produce a total force with four fingers within a hand following a preset force generation and relaxation ramp template closely. Excitability of corticospinal (CS) projections was assessed by single- and paired-pulse TMS. Errors introduced by a finger force were partially compensated by other finger forces during force generation, but were amplified during force relaxation. The CS excitability was greater during force generation than maintenance or relaxation. No difference in intracortical inhibition or facilitation was found. Nonnormalized finger extensor EMG responses remained unchanged. The findings suggest that force relaxation is not just a withdrawal from activation, and multifinger interactions are likely controlled beyond the primary motor cortex.

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Niranjan Chakrabhavi and Varadhan SKM

The hand is considered to be the most dexterous part of the human body, yet it comes with its limitations. A task involving a movement of an instructed finger often involves a movement of noninstructed fingers. This phenomenon is known as finger interdependence 1 or enslavement effect. 2 The

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Shohei Shibata, Yuki Inaba, Shinsuke Yoshioka and Senshi Fukashiro

An overarm throw is a complex multijoint limb movement. Of arm segments, fingers are the only and final segments that contact the ball. Some previous studies have investigated finger kinematics ( Hore & Watts, 2011 ; Hore, Watts, & Tweed, 1996 ). Hore, Watts, and Tweed ( 1996 ) reported that

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Mark Holten Mora-Jensen, Pascal Madeleine and Ernst Albin Hansen

Index finger tapping is a relatively simple motor task that is related to various everyday activities such as computer work and playing musical instruments. Furthermore, the task is widely applied in studies of both healthy individuals ( Hammond & Gunasekera, 2008 ; Hansen & Ohnstad, 2008

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Tomoko Aoki, Hayato Tsuda and Hiroshi Kinoshita

Finger function is essential for our daily activities. The fingers are used both to grasp various objects and to perform skilled and sophisticated movements, such as handwriting, sewing, and playing a musical instrument. Deterioration of the finger function due to aging or illness limits

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David Giles, Joel B. Chidley, Nicola Taylor, Ollie Torr, Josh Hadley, Tom Randall and Simon Fryer

Rock climbing requires repeated isometric contractions of the finger flexors, which are responsible for flexion of the metacarpophalangeal and interphalangeal joints. 1 These contractions cause regular periods of ischemia in the forearms; the extent of this ischemia and the subsequent recovery

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Elizabeth L. Stegemöller, Joshua R. Tatz, Alison Warnecke, Paul Hibbing, Brandon Bates and Andrew Zaman

influence movement performance in persons with neurological disorders remain limited. Recent research has demonstrated that cued repetitive finger movement performance deteriorates in persons with PD at rates near to and above 120 beats per minute (bpm; Stegemöller, Allen, Simuni, & MacKinnon, 2010