LAUSR

Background The electromyographic threshold (EMG Th ) has been suggested to indicate the onset of accelerated higher-threshold (type-II) MU recruitment. Previous research has demonstrated that boys’ EMG Th occurs at higher relative exercise intensities than men’s in both cycling- and isometric-based testing. Girls‒women EMG Th differences were demonstrated only in cycling, but findings were clouded by low EMG Th -detection rates in women (68%) and particularly in girls (45%) Purpose To examine the EMG Th , in girls and women, using the same males-employed isometric-based test protocol, and compare the females’ findings with those previously obtained in the males. Methods Seventeen girls and 17 women had their EMG Th determined as well as their one-repetition-maximum isometric knee-extension strength (1RM). Vastus-lateralis sEMG root mean square was recorded and the EMG Th was defined as the exercise intensity (%1RM) at the bi-segmental point of the least sum of squares. Results EMG Th was detected in 88.2% of girls and 94.1% of women and occurred at higher relative intensities in the girls than in women (56.0 ± 11.1 vs. 47.7 ± 8.0% 1RM). The girls’ 1RM (normalized to lean body mass) was only 69.1% that of the women. Conclusions Girls’ EMG Th values are higher compared with women’s, possibly reflecting lower ability to activate higher-threshold (type-II) motor units. The females’ EMG Th and detection-rate values were similar to the corresponding values previously observed in males. The females’ age-related difference in the recruitment of higher-threshold motor units, as reflected by the EMG Th , appears to be on par with the males.