MEDIAN POWER FREQUENCY OF THE SURFACE ELECTROMYOGRAM AND BLOOD LACTATE CONCENTRATION IN INCREMENTAL CYCLE ERGOMETRY

The electromyogram (EMG) median power frequency of the vastus laterali s and flexor digitorum superficialis muscles was measured in 12 subjec ts during cycle ergometry with step-wise increasing exercise intensiti es up to 100% of VO2max. Blood lactate concentration was measured to i nvestigate the relationship between changes in lactate concentration a nd shifts in the EMG median power frequency of exercising vastus later alis and non-exercising flexor digitorum superficialis muscles. The re sults indicated that lactate concentration did not systematically affe ct median frequency: in spite of a considerable increase in blood lact ate concentration, no systematic decrease of the median frequency duri ng exercise was found, either for the vastus lateralis or for the flex or digitorum superficialis muscles. Instead of a decrease of the media n frequency during exercise, as seen in isometrical protocols, an incr ease was seen in most subjects. An interesting finding was a decrease of the median frequency of vastus lateralis muscle during recovery in 8 subjects. The present findings showed that the relationship between EMG frequency decrease, lac tate accumulation and fatigue, as observed in isometric protocols, cannot be simply applied to dynamic exercise.