• 3D movement and muscle activity patterns in a violin bowing task

      Wales, Jennifer.; Applied Health Sciences Program (Brock University, 2007-06-29)
      Objective: Overuse injuries in violinists are a problem that has been primarily analyzed through the use of questionnaires. Simultaneous 3D motion analysis and EMG to measure muscle activity has been suggested as a quantitative technique to explore this problem by identifying movement patterns and muscular demands which may predispose violinists to overuse injuries. This multi-disciplinary analysis technique has, so far, had limited use in the music world. The purpose of this study was to use it to characterize the demands of a violin bowing task. Subjects: Twelve injury-free violinists volunteered for the study. The subjects were assigned to a novice or expert group based on playing experience, as determined by questionnaire. Design and Settings: Muscle activity and movement patterns were assessed while violinists played five bowing cycles (one bowing cycle = one down-bow + one up-bow) on each string (G, D, A, E), at a pulse of 4 beats per bow and 100 beats per minute. Measurements: An upper extremity model created using coordinate data from markers placed on the right acromion process, lateral epicondyle of the humerus and ulnar styloid was used to determine minimum and maximum joint angles, ranges of motion (ROM) and angular velocities at the shoulder and elbow of the bowing arm. Muscle activity in right anterior deltoid, biceps brachii and triceps brachii was assessed during maximal voluntary contractions (MVC) and during the playing task. Data were analysed for significant differences across the strings and between experience groups. Results: Elbow flexion/extension ROM was similar across strings for both groups. Shoulder flexion/extension ROM increaslarger for the experts. Angular velocity changes mirrored changes in ROM. Deltoid was the most active of the muscles assessed (20% MVC) and displayed a pattern of constant activation to maintain shoulder abduction. Biceps and triceps were less active (4 - 12% MVC) and showed a more periodic 'on and off pattern. Novices' muscle activity was higher in all cases. Experts' muscle activity showed a consistent pattern across strings, whereas the novices were more irregular. The agonist-antagonist roles of biceps and triceps during the bowing motion were clearly defined in the expert group, but not as apparent in the novice group. Conclusions: Bowing movement appears to be controlled by the shoulder rather than the elbow as shoulder ROM changed across strings while elbow ROM remained the same. Shoulder injuries are probably due to repetition as the muscle activity required for the movement is small. Experts require a smaller amount of muscle activity to perform the movement, possibly due to more efficient muscle activation patterns as a result of practice. This quantitative multidisciplinary approach to analysing violinists' movements can contribute to fuller understanding of both playing demands and injury mechanisms .
    • The Effects of β-Adrenergic Stimulation on Post-Tetanic Potentiation of Concentric Force in Fast Skeletal Muscle From Wildtype and skMLCK Devoid Mice.

      Morris, Stephen Roy; Applied Health Sciences Program
      Stimulation induced myosin RLC phosphorylation, catalyzed by the skeletal myosin light chain kinase (skMLCK) is known as the primary mechanism for twitch force potentiation (PTP). We assessed concentric PTP in the absence and presence of epinephrine (1 μM). To this end, extensor digitorum longus (EDL) muscles from wildtype (WT) and skMLCK-/- (KO) mice were incubated for 30-minutes in normal (CON) or epinephrine containing (EPI) Tyrode’s solution (in vitro, 25°C); undergoing a series of twitches before and after a standard conditioning stimulus (CS; 4x100 Hz) to determine PTP (post-CS/pre-CS). Epinephrine initially enhanced PTP compared to the WT and KO control values, respectively; peaking at 19.3 ± 1.6% and 15.7 ± 10.2% by the 8-minute mark (P < 0.0001) without altering myosin phosphorylation (P = 0.503). WT muscles were significantly elevated above KO values at all time points (P < 0.05); with the exception of the final 8-minute value (P = 0.172). However, both genotypes showed similar responses to epinephrine (r2 = 0.895), demonstrating that epinephrine may primarily act on a pathway independent of myosin phosphorylation.
    • Neuromotor Mechanisms Involved in the Recovery from Local Muscular Fatigue

      Green, Lara; Applied Health Sciences Program (Brock University, 2013-01-14)
      The phenomenon of over-recovery consists of a participant’s maximal force levels returning to values above initial levels. The present study examined the presence and causes of over-recovery following local muscular fatigue. Fourteen males completed two fatigue protocols consisting of maximal isometric dorsiflexion contractions. Upon completion of the fatigue protocol participants’ force was monitored over a 15 minute recovery period. Dorsiflexion force and surface electromyography (sEMG) from the tibialis anterior and soleus were monitored concurrently. Following the two fatigue conditions (10 and 20% force decrement) force recovered to 100.5 and 99.5% of initial levels for each condition, respectively. Surface EMG root-mean-square amplitude and MPF exhibited changes consistent with a warm-up effect. It was concluded that over-recovery was not present in the tibialis anterior following a local muscular fatigue. However, the return in force to initial values, rather than a persistent decrement as normally observed, was mediated by the warm-up effect.