Single finger movements in the aging hand: changes in finger independence, muscle activation patterns and tendon displacement in older adults
With aging, hand mobility and manual dexterity decline, even under healthy circumstances. To assess how aging affects finger movement control, we compared elderly and young subjects with respect to (1) finger movement independence, (2) neural control of extrinsic finger muscles and (3) finger tendon displacements during single finger flexion. In twelve healthy older (age 68–84) and nine young (age 22–29) subjects, finger kinematics were measured to assess finger movement enslaving and the range of independent finger movement. Muscle activation was assessed using a multi-channel electrode grid placed over the flexor digitorum superficialis (FDS) and the extensor digitorum (ED). FDS tendon displacements of the index, middle and ring fingers were measured using ultrasound. In older subjects compared to the younger subjects, we found: (1) increased enslaving of the middle finger during index finger flexion (young: 25.6 ± 12.4%, elderly: 47.0 ± 25.1%; p = 0.018), (2) a lower range of independent movement of the index finger (youngmiddle = 74.0%, elderlymiddle: 45.9%; p < 0.001), (3) a more evenly distributed muscle activation pattern over the finger-specific FDS and ED muscle regions and (4) a lower slope at the beginning of the finger movement to tendon displacement relationship, presenting a distinct period with little to no tendon displacement. Our study indicates that primarily the movement independence of the index finger is affected by aging. This can partly be attributed to a muscle activation pattern that is more evenly distributed over the finger-specific FDS and ED muscle regions in the elderly.
KeywordsFinger enslaving Tendon interconnections Motor control Muscle coactivation Multi-channel EMG Ultrasound
The authors thank the subjects for participating in the study, Barry Hes for assisting in the measurements, the department of Medical Ultrasound Imaging Center (MUSIC), especially Rik Hansen and Kaj Gijsbertse for their help with the ultrasound software, Henk Kortier, Josien van den Noort and Ed Droog from the University of Twente for their help with the PowerGlove and Bert Clairbois, Hans Agricola and Leon Schutte of the department of Human Movement Sciences for technical assistance. This research is funded by the European Commission through MOVE-AGE, an Erasmus Mundus Joint Doctorate program (2011-0015).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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