The Electromyographic Threshold in Girls and Women

in Pediatric Exercise Science
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  • 1 Brock University
  • 2 Liverpool John Moores University
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Background:

The electromyographic threshold (EMGTh) 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.

Purpose:

Establish whether females’ EMGTh and girls–women differences are different than males’.

Methods:

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. EMGTh 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. EMGTh was expressed as % final power-output (%Pmax) and %VO2pk power (%PVO2pk).

Results:

EMGTh 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; %PVO2pk= (101.6 ± 17.6 vs. 90.6 ± 7.8%, p = .063). When EMGTh was undetected it was assumed to occur at 100%Pmax or beyond. Consequently, EMGTh 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%PVO2pk, p = .028).

Conclusions:

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

Long, Dotan, Pitt, McKinlay, Tokuno, and Falk are with the Faculty of Applied Health Sciences, Brock University, St Catharines, ON, Canada. O’Brien is with the Research Institute for Sport & Exercise Science, Faculty of Science, Liverpool John Moores University, UK.

Address author correspondence to Raffy Dotan at rdotan@brocku.ca.