Isometric-based test improves EMG-threshold determination in boys vs. men
Children have been hypothesized to utilize higher-threshold (type-II) motor units (MUs) to a lesser extent than adults. Two recent studies, using a cycling-based EMG-threshold (EMGTh) protocol, supported the hypothesis, showing children’s EMGTh intensities to be higher than adults’. Conclusions, however, were hampered by children’s low EMGTh detection rates. Insufficiently high contractile forces at exhaustion were postulated as the reason for non-detection, predominantly in children. An intermittent isometric contraction test (IICT) protocol facilitates higher contractile forces prior to exhaustion and was shown effective in EMGTh testing of adults.
Determine whether an IICT protocol would enhance EMGTh detection in children, and consequently increase the magnitude of the previously observed child–adult EMGTh differences.
18 boys and 21 men completed one-repetition-maximum (1RM) isometric knee-extension test. The IICT protocol followed, commencing at 25%1RM and comprising five isometric contractions per load, incremented by ~ 3%1RM to exhaustion. Vastus lateralis surface EMG was recorded and EMGTh, expressed as %1RM, was defined as the onset of the EMG-response’s steeper segment.
EMGTh was detected in 88.9% of boys and 95.2% of men, and occurred at higher relative intensities in boys (56.4 ± 9.2%1RM) than in men (46.0 ± 6.8%1RM). This 10.4% difference was 57% greater than the corresponding, previously reported cycling-based age-related difference.
With the boys’ detection rate nearly on par with the men’s, the IICT protocol appears to overcome much of the intensity limitation of cycling-based protocols and provide a more sensitive EMGTh detection tool, thus extending the previously observed boys‒men difference. This difference adds supports to the notion of children’s more limited type-II MU recruitment capacity.
KeywordsChild Exercise Fatigue Force Electromyography Maturation Muscle Neuromotor Torque
Root mean square of each contraction’s EMG signal
Average of EMGRMS values for each load
Intermittent isometric contraction test
Lean body mass
Least sum of squares
Maximal volitional contraction
Root mean square
The authors wish to thank all participants for their hard work and dedication and to the parents or guardians for bringing the boys and making it all possible.
SW, RD and BF conceived and designed research. SW, NJ, RD and JM conducted the experiments. RD designed and built the custom-made ergometer. SW and RD analyzed the data. SW, RD and BF wrote the manuscript. DG and CT contributed to the design of the experiments and the analysis approach. All the authors read and approved the manuscript.
The study was funded by a Brock University internal grant.
Compliance with ethical standards
Conflict of interest
The authors have no competing interests to declare.
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