Worsening of neck and shoulder complaints in humans are correlated with frequency parameters of electromyogram recorded 1-year earlier

Abstract

The aim was to investigate whether output and electromyogram (EMG) variables obtained from an isokinetic endurance test of the shoulder flexor muscles of 23 women with neck and shoulder problems in a car and truck industry correlated with improvement or worsening of complaints 1 year later. Each subject performed 100 maximal isokinetic shoulder forward flexions at 60 degrees x s(-1). Surface EMG of the trapezius, deltoid, biceps brachii and infraspinatus muscles and mechanical output (peak torque) were determined for each contraction. The EMG was used to determine mean frequency fmean and the ratio between the signal amplitudes of the EMG of the passive relaxation and active flexion parts of each contraction cycle (SAR). The subjects also rated the degree of fatigue they experienced throughout the test. The magnitude of the shift in fmean was correlated with whether improvement or worsening occurred for complaints in the neck and or shoulders; a significant relationship (r2 = 0.44; P = 0.001) existed between the total frequency shift of the four muscles and the variables measuring improvement in complaints. In the multivariate predictions other fmean variables and perception of fatigue were also of significance. The present study would indicate that a high degree of fmean shift correlates with improvement in neck and shoulder complaints 1 year later. One possible reason could be that fmean reflects the muscle morphology and/or a pathological situation for the type-1 muscle fibres.

The influences of muscle fibre proportions and areas upon EMG during maximal dynamic knee extensions

“…This assumption was con®rmed in the present study; subjects with a high proportion of type 1 muscle ®bres had more diculty in relaxing during the passive parts of the contraction cycle than subjects with a high proportion of type 2 muscle ®bres. In agreement with the present ®ndings and interpretations, we have recently found that a high SAR in the shoulder muscles was correlated with worsening in complaints from the neck and shoulders 1 year later (Lundblad et al 1998). The present observation of a correlation between SAR and the proportion of type 1 muscle ®bres is also interesting since studies of the trapezius muscle in clinically healthy subjects and subjects with work-related myalgia indicate that it is mainly the type 1 ®bres that are aected in work-related myalgia (i.e.…”

“…An initial steep decrease (during the initial 40±60 contractions) in force output and mean frequency (MNF) of the EMG (the fatigue phase) followed by a plateau (the endurance level) with no further decrease occurs during repetitive maximum dynamic (isokinetic) contractions (for references see LindstroÈ m et al 1997;Lundblad et al 1998). The reported behaviour of the signal amplitude [root mean square, RMS or integrated (i) EMG] of the EMG during the fatigue phase are heterogeneous (both increases and decreases have been reported), according to the literature.…”

Impaired neck motor function and pronounced pain-related fear in helicopter pilots with neck pain – A clinical approach

“…Shifts towards lower spectral frequencies during a sustained contraction -an indirect indicator of changes in membrane properties -may reflect local muscle fatigue (Merletti et al, 1990;De Luca, 1997). However, little is known about the effects of muscle pain on local EMG frequency shift, and existing results are not clear: increased shift (Gogia and Sabbahi, 1994;Falla et al, 2003) and less frequency shift have both been reported (Lundblad et al, 1998;Kallenberg et al, 2006). Less neck-flexor frequency shift has also been indicated in helicopter pilots with frequent neck pain (Ang et al, 2005).…”

Fibre type proportion and fibre size in trapezius muscle biopsies from cleaners with and without myalgia and its correlation with ragged red fibres, cytochrome- c -oxidase-negative fibres, biomechanical output, perception of fatigue, and surface electromyography during repetitive forward flexions

“…The ®rst component of Table 5 shows that the prevalence of RR ®bres correlated positively with MNFer of the trapezius, infraspinatus, and deltoid muscles (and with SARe of the deltoid muscle). The shift of MNF has been reported to indicate peripheral muscle fatigue during sustained static contractions (Basmajian and DeLuca 1985) and in some studies prominent shifts have been suggested to re¯ect an increased risk of work-related myalgia (for references see Lundblad et al 1998). In contrast to this suggestion, a prospective study of female workers reported that small MNF shifts (high MNFer) of the shoulder¯exor muscles were associated with an increased risk of worsening the complaints of pain in the neck and shoulders 1 year later (Lundblad et al1998).…”