INTERSTITIAL LACTATE AND POTASSIUM DYNAMICS IN TRAPEZIUS MUSCLE DURING REPETITIVE LOW-FORCE CONTRACTIONS, MEASURED WITH MICRODIALYSIS

Abstract

Muscle metabolic responses to low-force contractions may not be reflected in systemic blood concentrations. Therefore, local measurements performed with microdialysis might offer an insight into muscle metabolism during e.g. repetitive monotonous work that has been proposed to cause muscle disorders. PURPOSE To test if microdialysis can quantify metabolic changes in the human trapezius muscle during low-force contractions typical for repetitive monotonous work. METHODS A microdialysis catheter was inserted in the upper trapezius muscle in 6 healthy male subjects (28–33 yrs). Microdialysis, electromyography (EMG) and rating of perceived exertion (RPE, 0–9) were recorded from the trapezius muscle and venous blood samples were taken during: 20 min of repetitive low-force contractions (RLC), 60 min of rest (R1), 10 min of static shoulder flexion (SSF) followed by 60 min of rest (R2). RESULTS The average muscle activity was 8 ±2% (%EMGmax) during RLC and 22 ±5% during SSF. RPE increased from 0 to 3 ±1 during RLC and from 0 to 8.5 ±1 during SSF. Plasma lactate was constant at 0.8 ±0.1 mM during RLC and R1, increased to 1.9 ±0.3 during SSF (p < 0.05) and dropped to 0.9 ±0.1 mM during R2. Plasma K+ was unchanged during RLC, R1, SSF and R2. In contrast, interstitial muscle lactate increased during RLC from 2.1 ±0.2 to 2.9 ±0.2 mM (p < 0.05) and returned to 2.2 ±0.2 mM during R1 and K+ increased from 6.3 ±0.8 to 10.4 ±1.4 mM (p < 0.05) and returned to 6.6 ±0.8 mM during R1. During SSF interstitial muscle lactate increased from 2.3 ±0.2 to 6.5 ±1.3 mM (p < 0.05) and decreased to 2.6 ±0.3 mM during R2 while K+ increased from 6.7 ±0.8 to 9.4 ±1.1 mM (p < 0.05) and returned to 6.1 ±1.1 mM during R2. CONCLUSION The microdialysis technique was effective in revealing muscle metabolic events that were not seen systemically. Furthermore, the trapezius muscle showed an anaerobic metabolism during RLC, which could indicate an inhomogeneous muscle activation.