Muscle cross‐sectional area and motor unit properties of the medial gastrocnemius and vastus lateralis in normal weight and overfat children

Abstract

This study examined the possible differences in muscle cross-sectional area (mCSA), motor unit action potential amplitudes (MUAP AMPS ) and interspike intervals (ISIs) of the firing instances of the medial gastrocnemius (MG) and vastus lateralis (VL) between normal weight (NW) and overfat (OF) children aged 7-10 years. Fourteen NW (age = 8.6 ± 1.1 years, BMI = 15.8 ± 1.4 kg m −2 ) and 12 OF (age = 8.8 ± 0.9 years, BMI = 21.8 ± 2.4 kg m −2 ) children performed isometric trapezoidal muscle actions at 40% of maximal voluntary contraction of the plantar flexors and knee extensors.Surface electromyography was recorded from the MG and VL and decomposed into the firing events of motor units (MUs). Statistical procedures were performed on the composite recruitment thresholds (RTs), ISIs and MUAP AMPS of recorded MUs collapsed across subjects and the y-intercepts and slopes calculated from each subject's ISI and MUAP AMP vs. RT relationships.Ultrasound was used to assess mCSA, echo intensity (mEI), and subcutaneous fat (sFAT) of the MG and VL. The OF had greater mCSAs, mEI and sFAT (P = 0.004-0.024), but there were no differences in mCSA when accounting for mEI for the MG (P = 0.506) and VL (P = 0.326). The NW children had significantly greater composite MUAP AMPS for the VL and MG (P < 0.001), but only significantly larger MUAP AMPS of the VL remained for the NW (P < 0.001) when subjects were matched for sFAT. There were no differences between groups for the ISI or MUAP AMP vs. RT relationships (P > 0.05). These findings suggest that the OF children did not undergo significant muscle or MU hypertrophy that would be routinely activated during activities of daily living.

Ultrasound method of the USVALID study to measure subcutaneous adipose tissue and muscle thickness on the thigh and upper arm: An illustrated step-by-step guide

“…Some studies scan with an innovative angle of view. For example, panoramic ultrasonography in the transverse plane is done [47,48]. In another study, the ultrasound probe circulates around the limb to make cross-sectional images of the limb on a specially-designed oscilloscope [42] or by the help of a flexible mechanical arm [50,51].Yet this is not feasible in an inpatient setting with limited time and technical resources.…”

Examination of the confounding effect of subcutaneous fat on muscle echo intensity utilizing exogenous fat

“…Echo intensity (EI) of skeletal muscle sonograms has been used as an estimate of muscle quality in individuals with various phenotypes (Blue et al 2018;Herda et al 2020;Mota and Stock 2017;Stock et al 2020), with greater EI scores indicating a greater accumulation of intramuscular connective tissue and/or fat (Pillen et al 2009;Young et al 2015). EI has been proved to be reliable (Caresio et al 2015;Lanferdini et al 2019), thereby encouraging its application in investigating training and aging adaptations (Fukumoto et al 2012a;Mota and Stock 2017).…”

“…Associations between subcutaneous fat thickness and EI estimates of muscle quality in humans are usually discussed from a physiological perspective (Herda et al 2020;Oranchuk et al 2020;Ryan et al 2016;Vakula et al 2019), addressing the damaging effect of obesity on muscle quality that has been confirmed in animal models (Biltz et al 2020;Collins et al 2018). However, the confounding effect that a fat layer may have on EI estimates of muscle quality has not been carefully investigated and is currently not properly taken into account in the literature (Arts et al 2010;Nijboer-Oosterveld et al 2011;Schless et al 2019;Stock et al 2020).…”