Children Exhibit a More Comparable Neuromuscular Fatigue Profile to Endurance Athletes Than Untrained Adults.

Bastien Bontemps,Enzo Piponnier,Sébastien Ratel,Martine Duclos,Emeric Chalchat,Vincent Martin,Valérie Julian,Olivia Bocock,Anthony J. Blazevich

doi:10.3389/fphys.2019.00119

Abstract

The present study compared neuromuscular fatigue profiles between children, untrained adults and adult endurance athletes during repeated maximal muscle contractions. Eighteen prepubertal boys, 19 untrained men and 13 endurance male athletes performed 5-s maximal voluntary isometric knee extensor contractions (MVICs) interspersed with 5-s recovery until MVIC reached 60% of its initial value. Single and doublet magnetic stimulations were delivered to the femoral nerve to quantify the time course of potentiated twitch amplitude (Ttw,pot), high-frequency torque (T100 Hz) and the low-to-high frequency torque ratio (T10 Hz/T100 Hz), i.e., indicators of peripheral fatigue. M-wave-normalized EMG amplitudes (EMG/M) and the maximal voluntary activation level (VA) were calculated to quantify central fatigue. Adults (15.9 ± 3.9 repetitions) performed fewer MVICs than children (40.4 ± 19.7) and endurance athletes (51.7 ± 19.6), however, no difference was observed between children and athletes (P = 0.13). Ttw,pot (∼52%, P < 0.001), T100 Hz (∼39%, P < 0.001) and T10 Hz/T100 Hz (∼23%, P < 0.001) decreased only in adults. Similar decrements in vastus medialis and vastus lateralis EMG/M were observed in children and endurance athletes (range: 40–50%), and these were greater than in adults (∼15%). Whilst VA decreased more in children (-38.4 ± 22.5%, P < 0.001) than endurance athletes (-20.3 ± 10.1%, P < 0.001), it did not change in adults. Thus, children fatigued more slowly than adults and as much as endurance athletes. They developed less peripheral and more central fatigue than adults and, although central fatigue appeared somewhat higher in children than endurance athletes, both children and endurance athletes experienced greater decrements than adults. Therefore, children exhibit a more comparable neuromuscular fatigue profile to endurance athletes than adults.

Highlights

It has been recently shown that prepubertal children fatigue much less than untrained young adults but as much as welltrained adult endurance athletes in a brief (30-s) bout of maximal cycling exercise (Wingate test) (Birat et al, 2018)
Prepubertal children are characterized by markedly higher muscle oxidative potential than young adults (Ratel et al, 2008; Tonson et al, 2010), and the same has been shown to be true for well-trained adult endurance athletes compared with untrained adults (Hug et al, 2005)
Children showed significantly lower values for age, height, body mass and Body mass index (BMI) compared to adults and endurance athletes (P < 0.001)

Summary

Introduction

It has been recently shown that prepubertal children fatigue much less than untrained young adults but as much as welltrained adult endurance athletes in a brief (30-s) bout of maximal cycling exercise (Wingate test) (Birat et al, 2018). It was suggested that prepubertal children and endurance athletes experience similar peripheral (i.e., muscular) fatigue during high-intensity exercise but lower peripheral fatigue than untrained adults (Ratel and Blazevich, 2017). This is consistent with reports of prepubertal children fatiguing less at the peripheral level than untrained adults at least during sustained or repeated maximal voluntary isometric contractions (MVICs) (Streckis et al, 2007; Ratel et al, 2015). Scientific evidence for the relative rates of peripheral fatigue development during repeated maximal muscle contractions in prepubertal children and endurance athletes remains to be presented

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