The Electromyographic Threshold in Girls and Women

The electromyographic threshold (EMG_Th) is thought to reflect increased high-threshold/type-II motor-unit (MU) recruitment and was shown higher in boys than in men. Women differ from men in muscular function.

Establish whether females' EMG_Th and girls-women differences are different than males'.

Nineteen women (22.9 ± 3.3yrs) and 20 girls (10.3 ± 1.1yrs) had surface EMG recorded from the right and left vastus lateralis muscles during ramped cycle-ergometry to exhaustion. EMG root-mean-squares were averaged per pedal revolution. EMG_Th was determined as the least residual sum of squares for any two regression-line data divisions, if the trace rose ≥ 3SD above its regression line. EMG_Th was expressed as % final power-output (%Pmax) and %VO₂pk power (%P_VO2pk).

EMG_Th was detected in 13 (68%) of women, but only 9 (45%) of girls (p < .005) and tended to be higher in the girls (%Pmax= 88.6 ± 7.0 vs. 83.0 ± 6.9%, p = .080; %P_VO2pk= (101.6 ± 17.6 vs. 90.6 ± 7.8%, p = .063). When EMG_Th was undetected it was assumed to occur at 100%Pmax or beyond. Consequently, EMG_Th values turned significantly higher in girls than in women (94.8 ± 7.4 vs. 88.4 ± 9.9%Pmax, p = .026; and 103.2 ± 11.7 vs. 95.2 ± 9.9%P_VO2pk, p = .028).

During progressive exercise, girls appear to rely less on higher-threshold/type-II MUs than do women, suggesting differential muscle activation strategy.