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Effects of muscle fatigue on directional coordination of fingertip forces during precision grip.

ABSTRACT: Object manipulation requires well-coordinated force vectors involving both magnitudes and directions. Despite extensive studies about force magnitudes during manipulation, relatively little is known how the muscle fatigue could affect the directional coordination of fingertip forces. This study aims to examine the effects of muscle fatigue on inter-digit coordination of force directions during precision grip. Sixteen female subjects performed precision grip with their thumb and index finger before and after fatigue tasks, which required subjects to produce continuous submaximal pinch strength on the apparatus for a duration more than 200 s. Both their left and right hands were evaluated using the same testing protocol. The means and standard deviations of the coordination angle and the projection angle were applied to quantify the directional coordination across the digits and the force vector direction of each individual digit. Results showed that fatigue led to significant reduction in the mean values of coordination angle and that of projection angle of the index finger in the ipsilateral hand (p < 0.05). Meanwhile, fatigue induced increases in both the standard deviations of coordination angle and projection angle of both digits in the ipsilateral hand (p < 0.05). These results imply that the muscle fatigue could interfere with the grasping stability by altering the directional coordination of all the involved digits and the control of force directions for each individual digit. These findings provide insights into fatigue-related changes of force directional regulation and coordination in dexterous manipulation.

SUBMITTER: Hu W

PROVIDER: S-EPMC6287841 | biostudies-other | 2018

REPOSITORIES: biostudies-other

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Project description:BackgroundMaximal isometric finger dead-hangs are used in rock climbing to strengthen finger flexors. Although various grip positions are often used when performing finger dead-hangs, little is known regarding how these grip positions can affect forearm muscle activity. Understanding how forearm muscles are recruited during dead-hangs could help foreseeing the potential for training of different grip positions. The aim of the present study was to explore the training applications of the various grip positions by comparing the activity of forearm muscles during maximal dead-hangs in rock climbers.Materials & methodsTwenty-five climbers performed maximal dead-hangs in three climbing-specific grip positions: CRIMP, SLOPE, and SLOPER. We recorded the maximal loads used and the sEMG of the flexor digitorum profundus (FDP), the flexor digitorum superficialis (FDS), the flexor carpi radialis (FCR), and the extensor digitorum communis (EDC). Individual and global (sum of all muscles) root mean square (RMS) and neuromuscular efficiency (NME) values were computed. Repeated measures analysis were performed to assess grip differences (p < 0.05).ResultsSLOPER showed the largest maximal load values among the three grip positions (p < 0.001, d ≥ 2.772). Greater global (p ≤ 0.044, d ≥ 0.268), FDS (p ≤ 0.005, d ≥ 0.277), and FCR (p < 0.001, d ≥ 1.049) activity was observed for the SLOPER compared to CRIMP and SLOPE, while EDC (p ≤ 0.005, d ≥ 0.505) showed lower activity in the SLOPER compared to the other two grip positions. SLOPER presented the highest global (p < 0.001, d ≥ 0.629), FDP (p < 0.001, d ≥ 0.777), FDS (only CRIMP vs SLOPER: p < 0.001, d = 0.140), and EDC NME (p < 0.001, d ≥ 1.194). The CRIMP showed greater FDS activity (p = 0.001, d = 0.386) and lower NME (p = 0.003, d = 0.125) compared to SLOPE.ConclusionsThese results revealed that, under maximum intensity conditions, SLOPER could stimulate the FDS and FCR better than the other grip positions at the expense of using greater loads. Similarly, maximum CRIMP dead-hang could better stimulate the FDS than the SLOPE, even when using similar loads.

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Effects of muscle fatigue on directional coordination of fingertip forces during precision grip.

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