The electromyographic threshold in boys and men
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Children have been shown to have higher lactate (LaTh) and ventilatory (VeTh) thresholds than adults, which might be explained by lower levels of type-II motor-unit (MU) recruitment. However, the electromyographic threshold (EMGTh), regarded as indicating the onset of accelerated type-II MU recruitment, has been investigated only in adults.
To compare the relative exercise intensity at which the EMGTh occurs in boys versus men.
Participants were 21 men (23.4 ± 4.1 years) and 23 boys (11.1 ± 1.1 years), with similar habitual physical activity and peak oxygen consumption (VO2pk) (49.7 ± 5.5 vs. 50.1 ± 7.4 ml kg−1 min−1, respectively). Ramped cycle ergometry was conducted to volitional exhaustion with surface EMG recorded from the right and left vastus lateralis muscles throughout the test (~10 min). The composite right–left EMG root mean square (EMGRMS) was then calculated per pedal revolution. The EMGTh was then determined as the exercise intensity at the point of least residual sum of squares for any two regression line divisions of the EMGRMS plot.
EMGTh was detected in 20/21 of the men (95.2 %) and only in 18/23 of the boys (78.3 %). The boys’ EMGTh was significantly higher than the men’s (86.4 ± 9.6 vs. 79.7 ± 10.0 % of peak power output at exhaustion; p < 0.05). The pattern was similar when EMGTh was expressed as percentage of VO2pk.
The boys’ higher EMGTh suggests delayed and hence lesser utilization of type-II MUs in progressive exercise, compared with men. The boys–men EMGTh differences were of similar magnitude as those shown for LaTh and VeTh, further suggesting a common underlying factor.
KeywordsChildren Exercise Motor unit activation
Motor unit/motor units
Maximal voluntary contraction
Onset of blood lactate accumulation
Peak height velocity
Maximal power attained at end of the EMGTh test
Peak aerobic power (mechanical power output corresponding to VO2pk)
Respiratory exchange ratio
Root mean square
Peak oxygen consumption
The authors wish to thank all participants for the hard work and dedication they invested in this study. We are also indebted to the boys’ parents or guardians for consenting, bringing the boys, and making it all possible. Special gratitude and appreciation is reserved for Mr. James Desjardins for developing the necessary software in a most proficient manner and with the utmost patience for the whims and wishes of the researchers. Funding: The study was funded by the Canadian Institutes of Health Research, Grant No199944.
Conflict of interest
The authors have no competing interests to declare.
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