Mechanical and neural factors have been suggested to limit finger independence. Fingers producing involuntary movement or force production during intended actions of another finger are considered “enslaved” to that finger. The purpose of this thesis was to quantify the contribution of passive mechanical factors to this enslaving effect, in particular, the contributions of the intertendinous connections between extensor tendons. Twenty participants (10 men, 10 women) performed Master and Slave Tasks in three wrist (30° extension, neutral, 30° flexion) and two metacarpophalangeal (MCP) (straight and 90° flexion) postures. During the Master Task, the ring finger was the intended or “master” finger. Three 10 s isometric ring finger extensions were performed at 25% of maximum voluntary contraction. Finger force and surface electromyography of the 4 extensor digitorum (ED) bellies were recorded. In the Slave Tasks, the middle and little fingers (“slave” fingers during the Master Task) each performed three 10 s isometric finger extensions at their mean activation levels during the Master Task. Hypothetical mechanical contribution (HMC) was determined for the middle and little fingers. The HMC was defined as the difference between the involuntary force (from the Master Task) and the voluntary force (from the Slave Task) relative to the involuntary force. A small proportion of the HMC values (Middle: 39%; Little: 15%) were within the expected range of 0 to 100%, suggesting that the equation developed in this study provided a limited representation of the contribution of passive intertendinous structures. Index finger forces increased with MCP flexion, suggesting the importance of juncturae tendineii in finger independence. Higher ED activity during wrist extension, than neutral or flexed postures, with straight MCP supports previous evidence in the literature. The complex phenomenon of enslaving in different wrist and MCP positions warrants further research for quantifying the mechanical contribution in finger independence. / Thesis / Master of Science in Kinesiology

<p>Biomechanical and neural factors have both been suggested to contribute to the limited independence of finger movement and involuntary force production. The purpose of this study was to evaluate the degree of finger independence by examining the activity of the four compartments of extensor digitorum (ED) and flexor digitorum superficialis (FDS) using surface electromyography and involuntary force production in the non-task fingers using methods such as the “enslaving effect” (EE) and the “selectivity index” (SI). Twelve male participants performed a series of 5-second sub-maximal exertions at 5, 25, 50 and 75% of maximum using isometric isotonic and ramp finger flexion and extension exertions. Ramp exertions were performed from 0 to 85% of each finger’s maximum force with ascending and descending phases taking 4.5 seconds each with 0.5 seconds of plateau at 85%. Lower EE and higher SI (more selective force production) was found in flexion exertions compared to extension partially due to the higher activity of the antagonist ED compartments counterbalancing the involuntary activation of the non-task FDS compartments. Minimal FDS activity was seen during extension exertions. At forces up to and including 50%, both EE and muscle activity of the non-task compartments were significantly higher in descending exertions than the isotonic or ascending exertions. The selectivity index was also lower during the descending flexion and extension exertions at 25 and 50% MVC exertions. Up to mid-level forces, both finger proximity and contraction mode affects involuntary force production and muscle activation while at higher forces only finger proximity (and not the exertion mode) contributes to finger independence. The fingers were less selective at higher exertion levels (75% MVC) and all 3 exertion modes resulted in similar SI at 75% MVC in all flexion and extension exertions.</p> / Master of Science in Kinesiology