Interstitial muscle lactate, pyruvate and potassium dynamics in the trapezius muscle during repetitive low-force arm...

Local muscle metabolic responses to repetitive low-force contractions and to intense static contractions were studied by microdialysis in humans.

Microdialysate and electromyography (EMG) were sampled from the trapezius muscle, mixed venous blood samples were taken and perceived exertion was rated (0-9) before and during 20 min of standardized repetitive arm movement (REP), 60 min recovery (R1), and 10 min 90 degrees sustained arm position (SUS) at 20% maximum voluntary contraction, followed by 60 min recovery (R2) in six healthy male participants (28-33 years).

Average muscle activity was 8 +/- 2% of EMGmax-RMS (mean +/-SEM) during REP and 22 +/- 5% of EMGmax-RMS during SUS. Perceived exertion increased from 0 to 3.2 +/- 0.5 during REP and from 0 to 8.5 +/- 0.3 during SUS. During REP interstitial muscle lactate increased from 2.1 +/- 0.2 to 2.9 +/- 0.2 mmol L(-1) (P < 0.001) and returned to the baseline level during R1, while dialysate [K+] increased from 3.8 +/- 0.2 to 4.7 +/- 0.2 mmol L(-1) (P < 0.002) and returned to 3.8 +/- 0.2 mmol L(-1) during R1. In contrast, plasma lactate and [K+] remained unchanged. During SUS interstitial muscle lactate increased from 2.3 +/- 0.2 to 3.3 +/- 0.3 mmol L(-1) (P < 0.003), increased further to 6.5 +/- 1.3 mmol L(-1) post-exercise (P < 0.001) and returned to baseline levels during R2. Dialysate [K+] increased from 3.9 +/- 0.2 to 4.6 +/- 0.2 mmol L(-1) (P < 0.05) and returned to baseline level during R2. Plasma lactate increased significantly during SUS whereas plasma [K+] was unchanged. During REP and SUS interstitial pyruvate was unchanged but increased in the post-exercise period proportional to the exercise intensity.

The microdialysis technique was effective in revealing muscle metabolic events that were not found systemically. Furthermore, the trapezius muscle showed an anaerobic metabolism during low-force contraction, which could indicate inhomogeneous muscle activation.