Myosin heavy chain isoforms influence surface EMG parameters: a study of the trapezius muscle in cleaners with and without myalgia and in healthy teachers

Abstract

The present study had two aims: (1) to investigate potential differences in proportion of myosin heavy chain isoforms in the trapezius muscle between female cleaners with and without trapezius myalgia and healthy teachers, and (2) to elucidate if myosin heavy chain composition and surface electromyogram (EMG) during an isokinetic endurance test of shoulder flexors are significantly related. The subjects were divided into three groups: (1) 25 female cleaners with diagnosed work-related trapezius myalgia; (2) 25 female cleaners without work-related trapezius myalgia; (3) a control group of 21 healthy female teachers who were not exposed to repetitive or static muscle work. All subjects performed a test involving150 forward flexions using an isokinetic dynamometer. During the test surface EMG was recorded from the trapezius muscle. Muscle samples were obtained from the descending part of the trapezius muscle. The fibre type area percentage based on ATPase staining and the proportions of different MHC isoforms as determined by gel electrophoresis. The trapezius was dominated by MHC I (71%), followed by MHC IIA (22-24%), and MHC IIX (5-7%); no significant differences between the three groups of subjects were found. The proportion of MHC I correlated negatively with MHC IIA ( r=-0.78; P<0.001) and MHC IIX ( r=-0.53; P<0.001). Significant correlations existed between the proportion of the MHC isoforms and the corresponding proportion of the fibre type area; 27-45% of the variance was explained. The multivariate analysis of the three groups of subjects revealed that MHC variables showed intercorrelations with EMG (both amplitude and frequency variables). However, the directions of the relationships differed among the three groups; the cleaners with myalgia and the teachers showed the greatest similarities in patterns. Intrinsic muscle properties appear to influence the frequency content of the EMG, which is in contrast to some of the theoretical models of the EMG. Our data could suggest that monotonous work such as professional cleaning can change the relationships between muscle structure and the frequency content of the EMG.

Surface electromyography and peak torque of repetitive maximum isokinetic plantar flexions in relation to aspects of muscle morphology

“…However, the directions of the relationships between proportions of MyHC isoforms and MNF variables differed between the groups. Thus, in the cleaners with myalgia and the healthy teachers MNF correlated positively with the proportion of MyHC type I while in the healthy cleaners the proportion of MyHC IIA correlated positively with the two MNF variables [33]. We have no clear explanation for our finding nor to the disparity in the literature in this respect.…”

“…Based on earlier results in the literature [10,21,43], it would have been reasonable to expect a negative relationship; however, in this study and in our recent study of the vastus lateralis [17] we have found a positive relationship between MNF and type I fibre type proportion. In a recent study of the trapezius of healthy cleaners, cleaners with trapezius myalgia and healthy teachers we have reported that the MyHC isoform proportions influenced the frequency content of the EMG [33]. However, the directions of the relationships between proportions of MyHC isoforms and MNF variables differed between the groups.…”

“…As new studies have indicated that the type IIX is the fastest contracting muscle fibre type in humans [12] and as the majority of recent studies use the term IIX to describe the fastest myosin isoform in humans [28,33] we have used the term IIX and not IIB.…”

Clinical Implications of Muscle-Tendon & -Force Interplay: Surface Electromyography Recordings of m. vastus lateralis in Renal Failure Patients Undergoing Dialysis and of m. gastrocnemius in Individuals with Achilles Tendon Damage

“…In spite of the large number of variables that influence the sEMG signal (De Luca,1997;Farina et al, 2004;Hogrel, 2005), studies on correlations between intrinsic muscle parameters and recorded signals are becoming more numerous (Gerdle et al, 1997;Karlsson & Gerdle, 2001;Kupa et al,1995;Larsson et al, 2002Larsson et al, & 2006Tygesen & Harrison, 2005). In rats, EMG parameters have been shown to be a useful tool to predict muscle excitability (Harrison & Flatman, 1999), and in sheep the technique has been used to follow postnatal muscle development (Tygesen & Harrison, 2005).…”

“…In rats, EMG parameters have been shown to be a useful tool to predict muscle excitability (Harrison & Flatman, 1999), and in sheep the technique has been used to follow postnatal muscle development (Tygesen & Harrison, 2005). sEMG recordings have also been related to the morphological state of muscles, for example i) muscle fibre composition (identified using MHC isoforms or mATPase activity)in humans (Gerdle et al, 1997;Larsson et al, 2002Larsson et al, & 2006 and in rats (Kupa et al, 1995) and, ii) muscle fibre diameter in humans (Gerdle et al, 1997;Larsson et al, 2006) and in rats (Kupa et al, 1995).…”