The aim of this study was to investigate the effects of duration of low-load repetitive work on intramuscular lactate, pyruvate, glutamate and prostaglandin E2 (PGE2), and oxygen saturation in the trapezius muscle. Twenty healthy females were studied during baseline rest, during low-load repetitive work for either 30 (REP 30) or 60 (REP 60) minutes, and 60 minutes recovery. Intramuscular microdialysate (IMMD) samples were obtained, and local muscle tissue oxygenation (StO2 %) assessed with near infrared spectroscopy (NIRS). Subjects rated their perceived exertion (Borg CR-10 scale) and capillary blood was sampled for lactate analysis. The results showed a significant increase in IMMD lactate in response to both REP 30 and REP 60 (P<0.05 and P<0.01 respectively) and glutamate (P<0.0001), but no progressive increase with increasing work duration. Both IMMD pyruvate and lactate tended to be significantly increased during the recovery period. No corresponding increase in blood-lactate was found. Local muscle StO2 % did not change significantly in response to work and was not correlated to the IMMD lactate concentration. The ratings of perceived exertion increased in response to work, and remained increased after recovery for REP 60.

In conclusion, the results of this study show significantly increased IMMD lactate and, glutamate concentrations in the trapezius muscle of healthy females in response to low-load work, but no progressive increase with increased work duration. Further, they do not indicate that the increased IMMD lactate concentration was caused by a locally decreased or insufficient muscle tissue oxygenation.