Authors: M L Gorelick J M M Brown
Publish Date: 2007/02/03
Volume: 100, Issue: 1, Pages: 35-44
Abstract
The aim of this study was to determine by a noninvasive whole muscle mechanomyographic technique wMMG how muscle segment contractile properties varied within the segments of the multifunctional deltoid muscle and how such variations in contractile properties may reflect the muscle segment’s function and fibre type composition We hypothesised that muscle segment contractile properties consistent with slower twitch muscle fibre populations would be associated with the deltoid’s prime mover abductor muscle segment middle head rather than the prime mover flexor and extensor muscle segments anterior and posterior heads Eighteen healthy and athletic University students nine males and nine females mean age 20–24 years volunteered for this study Each subject’s right upper limb was secured with the forearm flexed to 30° and the shoulder in 45° of abduction The wMMG laser sensor was positioned perpendicular to the middle of each muscle segment to record the involuntary lateral displacement of the muscle belly following a maximal single twitch percutaneous neuromuscular stimulation PNS 180 V max 80 mA max 50 μs Ten trials were recorded from each of the seven deltoid segments for a total of 70 trials per subject From each segment eight variables were analysed from the recorded wMMG waveforms maximal displacement D max delay time T d contraction time T c sustain time T s relaxation time T r and half relaxation time ½T r average rate of contraction ARC and the average rate of relaxation ARR The results indicated that the contractile properties of the seven segments of the deltoid muscle showed significant P 005 variation in a medial to lateral direction Medially the straplike segments of the anterior S1 S2 and posterior heads S4–S7 with larger moment arms for shoulder flexion and extension respectively had the fastest contractile properties In contrast the multipennate segment 3 with the largest moment arm for shoulder abduction had the slowest contractile properties P 005 Muscle segment contractile properties were matched to the biomechanical and architectural characteristics of the individual muscle segmentsThe authors wish to thank Mr Darryl McAndrew and the UoW students of BMS303 for assistance during the collection of the data Mr Mario Solitro for technical assistance Mrs Bevin Arnason and Mr Benjamin Musker for assistance with the illustrations and the University of Wollongong for a Doctoral scholarship to MG and a study leave assistance grant to MB
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