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. 2024 Oct;124(10):2965-2979.
doi: 10.1007/s00421-024-05500-8. Epub 2024 May 19.

Motor unit firing rates during slow and fast contractions in boys and men

Stacey Woods  1 , Andrew McKiel  1 , Trent Herda  2 , Panagiota Klentrou  1   3 , Michael Holmes  1   3 , David Gabriel  1 , Bareket Falk  4   5
Affiliations

Motor unit firing rates during slow and fast contractions in boys and men

Stacey Woods et al. Eur J Appl Physiol. 2024 Oct.

Abstract

Background: Motor unit (MU) activation during maximal contractions is lower in children compared with adults. Among adults, discrete MU activation differs, depending on the rate of contraction. We investigated the effect of contraction rate on discrete MU activation in boys and men.

Methods: Following a habituation session, 14 boys and 20 men completed two experimental sessions for knee extension and wrist flexion, in random order. Maximal voluntary isometric torque (MVIC) was determined before completing trapezoidal isometric contractions (70%MVIC) at low (10%MVIC/s) and high (35%MVIC/s) contraction rates. Surface electromyography was captured from the vastus lateralis (VL) and flexor carpi radialis (FCR) and decomposed into individual MU action potential (MUAP) trains.

Results: In both groups and muscles, the initial MU firing rate (MUFR) was greater (p < 0.05) at high compared with low contraction rates. The increase in initial MUFR at the fast contraction in the VL was greater in men than boys (p < 0.05). Mean MUFR was significantly lower during fast contractions only in the FCR (p < 0.05). In both groups and muscles, the rate of decay of MUFR with increasing MUAP amplitude was less steep (p < 0.05) during fast compared with slow contractions.

Conclusion: In both groups and muscles, initial MUFRs, as well as MUFRs of large MUs were higher during fast compared with slow contractions. However, in the VL, the increase in initial MUFR was greater in men compared with boys. This suggests that in large muscles, men may rely more on increasing MUFR to generate torque at faster rates compared with boys.

Keywords: Children; Contraction ate; EMG decomposition; Muscle activation.

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References

    1. Aeles J, Bellett M, Lichtwark G, Cresswell A (2022) The effect of small changes in rate of force development on muscle fascicle velocity and motor unit discharge behaviour. Eur J Appl Physiol 122:1035–1044. https://doi.org/10.1007/s00421-022-04905-7 - DOI
    1. Barnes WS (1980) The relationship of motor-unit activation to isokinetic muscular contraction at different contractile velocities. Phys Ther 60:1152–1158. https://doi.org/10.1093/ptj/60.9.1152 - DOI
    1. Bigland-Ritchie B (1981) EMG/force relations and fatigue of human voluntary contractions. Exerc Sport Sci Rev 9:75–118 - DOI
    1. Chalchat E, Piponnier E, Bontemps B et al (2019) Characteristics of motor unit recruitment in boys and men at maximal and submaximal force levels. Exp Brain Res 237:1289–1302. https://doi.org/10.1007/s00221-019-05508-z - DOI
    1. Cohen J (1988) Statistical power analysis for the behavioral sciences. Routledge Academic, New York, NY

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