Raffy Dotan

A physiologically based method is presented for accuracy assessment of decomposed-motor-unit properties. This contrasts with the statistically based conventional method, which assesses the probability of positive identification of unique motor units. Consequently, little to no congruence was found between the two methods’ outcomes. Unexpectedly, more inaccuracies were identified in nominally “high-accuracy” motor units than among their “low-accuracy” counterparts. These findings question the validity and justification of motor-unit elimination from analysis and call for revisiting the underlying premises.

Background Only scant research has compared children’s mean power frequency (MPF) to adults’, with a clear overview still lacking. A significant obstacle has been MPF’s high variability, which this study aimed to overcome by elucidating the MPF characteristics distinguishing boys from men in progressive exhaustive exercise. Methods Electromyographic (EMG) data of 20 men (23.5 ± 2.5yrs) and 17 boys (10.2 ± 1.0 yrs), who performed progressively exhausting, intermittent isometric knee extensions, were subjected to secondary MPF analysis. Participants’ vastus lateralis MPF data series were transformed to third-order polynomial regressions and expressed as percentages of the peak polynomial MPF values (%MPF_peak). The resulting curves were compared at 5-% time-to-exhaustion (TTE) intervals, using repeated-measures ANOVA. Raw MPF_peak values were adiposity corrected to 0% fat and used to convert the %MPF_peak data back to absolute MPF values (Hz) for estimating muscle-level MPF. Results No overall interaction or group effects could be shown between the %MPF_peak plots, but pairwise comparisons revealed significantly higher men’s values at 50–70%TTE and lower at 100%TTE, i.e. boys’ shallower MPF rise and decline. The adiposity-corrected boys’ and men’s composite MPF values peaked at 125.7 ± 2.5 and 166.0 ± 2.4 Hz, respectively (110.7 ± 1.7 and 122.5 ± 2.1 Hz, uncorrected), with a significant group effect (p < 0.05) and pairwise differences at all %TTE points. Conclusions The boys were lower than the men in both the observed and, more so, in the adiposity-corrected MPF values that presumably estimate muscle-level MPF. The boys’ shallower MPF rise and decline conform to children’s claimed type-II motor-unit activation and/or compositional deficits and their related known advantage in muscular endurance.

Children and adults employ different thermoregulatory strategies. Under heat stress, children rely more on non-evaporative heat exchange, while sweating is adults’ foremost heat-dissipation process. Several anatomical, physiological, and psychological factors can affect differential risk of thermal injury in the child versus the adult athlete. Children have greater surface-area-to-mass ratio, lower sweating rate, higher peripheral blood flow in the heat, and a greater extent of vasoconstriction in the cold. They can acclimatise to a similar extent but do so at a lower rate than adults. Differences in perceived exertion and thermal strain, cumulative experience, cognitive development, and decision-making capacity may negatively affect the youth athlete’s behaviour under competitive and other situations, possibly subjecting him or her to sub-par performance or to greater risk of thermal injury. However, except for limited environmental conditions, children in general, and youth athletes in particular, are physiologically capable of handling environmental challenges as effectively as adults.

Clear definition, identification, and reporting of adverse event (AE) monitoring during training interventions are essential for decision making regarding the safety of training and testing in youths. Purpose: To document the extent to which AEs, resulting from intervention studies targeting muscle strengthening training (MST) in youth, are reported by researchers. Methods: Electronic databases (CINAHL, PubMed, SPORTDiscus, and Web of Science) were searched for English peer-reviewed articles published before April 2018. Inclusion criteria were: (1) average age Results: One hundred and ninety-one full-text articles were screened. One hundred and thirty met all MST criteria, out of which only 44 (33.8%; n = 1278, age = 12.1 [1.1] y) included a statement as to the presence/absence of adverse events. The 86 other studies (66.2%) included no such statement. Of the reporting 44 studies, 18 (40.1%) indicated one or more adverse events. Of the 93 reported adverse events, 55 (59.1%) were linked to training or testing. Conclusions: Most MST studies in youth do not report presence/absence of adverse events, and when reported, adverse events are not well defined.

Scrutinizing functional threshold power via controversial concepts leads to confusion and discreditation of a valuable performance marker. This letter attempts to sort out the controversies.