The prevalences of cytochrome c oxidase negative and superpositive fibres and ragged-red fibres in the trapezius muscle of female cleaners with and without myalgia and of female healthy controls

The association of cytochrome c oxidase negative fibres (COX-negative) and ragged-red fibres (RR-fibres) with work related trapezius myalgia has been proposed. Hitherto studies have been small or without control groups. The a im of the present study was to investigate the prevalences of RR-fibres and COX-negative fibres in female cleaners with (n = 25) and without (n = 23) trapezius myalgia and in clinically healthy female teachers (n = 21). The c leaners did mainly floor cleaning requiring monotonous loading on the trape zius muscle. A questionnaire covering background data and aspects of pain ( prevalence, duration, intensity and influence on daily living) was answered . Biopsies were obtained from the trapezius muscle by an open surgical tech nique. The three groups did not differ in prevalence of COX-negative or COX -superpositive (i.e. type-I fibres with extremely strong brownish reaction in both the COX and SDH/COX stainings) fibres. The prevalence of COX-negati ve fibres was age dependent. Two subgroups of RR-fibres were present when s tained for COX; COX-negative (73%) and COX-superpositive (26%) fibres. Fort y-two percent of the COX-negative fibres were RR-fibres and 79% of the COX- superpositive were:RR-fibres. A significantly (P = 0.002) higher proportion of the COX-superpositive fibres in the cleaners were RR-fibres compared to the teachers. Multivariate regression analysis revealed that age, occupati on as cleaner and a tender point in the trapezius were significantly associ ated with increased prevalences of RR-fibres; a cleaner with a tender point had a 4.35 higher prevalence of RR-fibres compared to a teacher without a tender point. No correlations between other pain related variables and prev alence of RR-fibres were noted. In conclusion, RR-fibres but not COX-negati ve or COX-superpositive fibres were correlated with cleaning work tasks and with a tender point in the trapezius. (C) 2000 International Association f or the Study of Pain. Published by Elsevier Science B.V.