Measurement and Interpretation of Maximal Aerobic Power in Children

The assessment of maximal aerobic power (VO2max) in both children and adults is an invaluable tool for the evaluation of exercise performance capacity and general physical fitness in clinical, athletic, public health, and research applications. The complexity of means and considerations, as well as varying specific aims of VO2 max testing, has prevented the formulation of a universally applicable, standard testing protocol, in general, and for children in particular. Numerous tester-controllable factors, such as exercise modality, metabolic measurement system, testing protocol, or data reduction strategies, can affect both the measurement and interpretation of VO2max data. Although the general guiding principles are similar, children differ from adults in several aspects. One notable difference is the frequent absence of a discernible VO2max plateau in children. Thus, the proper choice of equipment and procedures may be different for children than for adults. It is therefore the aim of this article to highlight the general and pediatric-specific considerations that may affect VO2max measurement and interpretation of results

Effects of Plyometric and Resistance Training on Muscle Strength and Neuromuscular Function in Young Adolescent Soccer Players

This study examined the effect of 8-weeks of resistance (RT) and plyometric (PLYO) training on maximal strength, power and jump performance compared with no added training (CON), in young male soccer players. Forty-one 11-13 year-old soccer players were divided into three groups (RT, PLYO, CON). All participants completed 5 isometric knee extensions at 90° and 5 isokinetic knee extensions at 240°/s pre- and post-training. Peak torque (PT), peak rate of torque development (pRTD), electromechanical-day (EMD), rate of muscle activation (Q30), muscle cross-sectional area (mCSA) and jump performance were examined. Both RT and PLYO resulted in significant (p < 0.05) increases in PT, pRTD and jump performance. RT resulted in significantly greater increases in both isometric and isokinetic PT, while PLYO resulted in significantly greater increases in isometric pRTD and jump performance compared with CON (p < 0.05). Q30 increased to a greater extent in PLYO (20%) compared with RT (5%) and CON (-5%) (p = 0.1). In conclusion, 8-weeks of RT and PLYO resulted in significant improvements in muscle strength and jump performance. RT appears to be more effective at eliciting increases in maximal strength while PLYO appears to enhance explosive strength, mediated by possible increases in the rate of muscle activation

Canadian Society for Exercise Physiology Position Paper: Resistance Training in Children and Adolescents

Many position stands and review papers have refuted the myths associated with resistance training (RT) in children and adolescents. With proper training methods, RT for children and adolescents can be relatively safe and improve overall health. The objective of this position paper and review is to highlight research and provide recommendations in aspects of RT that have not been extensively reported in the pediatric literature. In addition to the well-documented increases in muscular strength and endurance, RT has been used to improve function in pediatric patients with cystic fibrosis, cerebral palsy and burn victims. Increases in children’s muscular strength have been attributed primarily to neurological adaptations due to the disproportionately higher increase in muscle strength than in muscle size. Although most studies using anthropometric measures have not shown significant muscle hypertrophy in children, more sensitive measures such as magnetic resonance imaging and ultrasound have suggested hypertrophy may occur. There is no minimum age for RT for children. However the training and instruction must be appropriate for children and adolescents involving a proper warm-up, cool-down and an appropriate choice of exercises. It is recommended that low-to-moderate intensity resistance should be utilized 2-3 times per week on non-consecutive days, with 1-2 sets initially, progressing to 4 sets of 8-15 repetitions for 8-12 exercises. These exercises can include more advanced movements such as Olympic style lifting, plyometrics and balance training, which can enhance strength, power, co-ordination and balance. However specific guidelines for these more advanced techniques need to be established for youth. In conclusion, a RT program that is within a child’s or adolescent’s capacity, involves gradual progression under qualified instruction and supervision with appropriately sized equipment can involve more advanced or intense RT exercises which can lead to functional (i.e. muscular strength, endurance, power, balance and co-ordination) and health benefits

Boys–men mean-power-frequency differences in progressive exercise to exhaustion, confounded by variability and adiposity

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 (%MPFpeak). The resulting curves were compared at 5-% time-to-exhaustion (TTE) intervals, using repeated-measures ANOVA. Raw MPFpeak values were adiposity corrected to 0% fat and used to convert the %MPFpeak data back to absolute MPF values (Hz) for estimating muscle-level MPF. Results: No overall interaction or group effects could be shown between the %MPFpeak 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

Isometric-based EMG threshold in girls and women

Background: The electromyographic threshold (EMGTh) has been suggested to indicate the onset of accelerated higher-threshold (type-II) MU recruitment. Previous research has demonstrated that boys’ EMGTh occurs at higher relative exercise intensities than men’s in both cycling- and isometric-based testing. Girls‒women EMGTh differences were demonstrated only in cycling, but findings were clouded by low EMGTh-detection rates in women (68%) and particularly in girls (45%). Purpose: To examine the EMGTh, in girls and women, using the same males-employed isometric-based test protocol, and compare the females’ findings with those previously obtained in the males. Methods: Seventeen girls and 17 women had their EMGTh determined as well as their one repetition-maximum isometric knee-extension strength (1RM). Vastus-lateralis sEMG root mean square was recorded and the EMGTh was defined as the exercise intensity (%1RM) at the bi-segmental point of the least sum of squares. Results: EMGTh was detected in 88.2% of girls and 94.1% of women, and occurred at higher relative intensities in the girls than in women (56.0±11.1 vs. 47.7±8.0 %1RM). The girls’ 1RM (normalized to lean body mass) was only 69.1% that of the women. Conclusions: Girls’ EMGTh values are higher compared with women’s, possibly reflecting lower ability to activate higher-threshold (type-II) motor units. The females’ EMGTh and detection rate values were similar to the corresponding values previously observed in males. The females’ age-related difference in the recruitment of higher-threshold motor units, as reflected by the EMGTh, appears to be on par with the males.Canadian Network for Research and Innovation in Machining Technology, Natural Sciences and Engineering Research Council of Canad

Comparison of laser speckle contrast imaging and laser-Doppler fluxmetry in boys and men

Objective: We compare microvascular reactivity assessed by laser-Doppler fluxmetry (LDF) and laser speckle contrast imaging (LSCI) of boys and men during rest, post-occlusive reactive hyperaemia (PORH), and cycling exercise. Methods: 19 boys (9±1 y) and 18 men (22±2 y) participated. LDF and LSCI measures were taken of the forearm during rest, PORH, and exercise. Results: For all 3 assessments, the LSCI presented with higher flux values than the LDF for both boys and men (p<0.001). Bland-Altman analyses indicated that there was a positive linear bias between LSCI and LDF measurements in both boys and men. Regression analyses showed that the responses for the two methods were variable, depending on the particular assessment. For instance, at rest in boys there was no relationship between LDF and LSCI (r2=0.002), whilst in men there was a strong relationship (r2=0.86). Conclusions: LSCI presented with higher values than LDF during rest, PORH, and exercise; the disparity between the two measures was larger as blood flow increased. The assessments were generally consistent, both methods appear to provide usable data for the assessment of microvascular reactivity in both boys and men. There are biases to each method and the data are not interchangeable between LDF and LSCI.Collaborative Health Research Projec

Does bracing affect bone health in women with adolescent idiopathic scoliosis?

Purpose: Adolescent idiopathic scoliosis (AIS) is often associated with low bone mineral content and density (BMC, BMD). Bracing, used to manage spine curvature, may interfere with the growth-related BMC accrual, resulting in reduced bone strength into adulthood. The purpose of this study was to assess the effects of brace treatment on BMC in adult women, diagnosed with AIS and braced in early adolescence. Methods: Participants included women with AIS who: (i) underwent brace treatment (AIS-B, n = 15, 25.6 ± 5.8 yrs), (ii) underwent no treatment (AIS, n = 15, 24.0 ± 4.0 yrs), and (iii) a healthy comparison group (CON, n = 19, 23.5 ± 3.8 yrs). BMC and body composition were assessed using dual-energy X-ray absorptiometry. Differences between groups were examined using a oneway ANOVA or ANCOVA, as appropriate. Results: AIS-B underwent brace treatment 27.9 ± 21.6 months, for 18.0 ± 5.4 h/d. Femoral neck BMC was lower (p = 0.06) in AIS-B (4.54 ± 0.10 g) compared with AIS (4.89 ± 0.61 g) and CON (5.07 ± 0.58 g). Controlling for lean body mass, calcium and vitamin D daily intake, and strenuous physical activity, femoral neck BMC was statistically different (p = 0.02) between groups. A similar pattern was observed at other lower extremity sites (p < 0.05), but not in the spine or upper extremities. BMC and BMD did not correlate with duration of brace treatment, duration of daily brace wear, or overall physical activity. Conclusion: Young women with AIS, especially those who were treated with a brace, have significantly lower BMC in their lower limbs compared to women without AIS. However, the lack of a relationship between brace treatment duration during adolescence and BMC during young adulthood, suggests that the brace treatment is not the likely mechanism of the low BMC

Child-Adult differences in antagonist muscle coactivation: A systematic review

Antagonist coactivation is the simultaneous activation of agonist and antagonist muscles during a motor task. Age-related changes in coactivation may contribute to observed differences in muscle performance between children and adults. Our aim was to systematically summarize age-related differences in antagonist muscle coactivation during multi-joint dynamic and single-joint isometric and isokinetic contractions. Electronic databases were searched for peer-reviewed studies comparing coactivation in upper or lower extremity muscles between healthy children and adolescents/young adults. Of the 1083 studies initially identified, 25 met eligibility criteria. Thirteen studies examined multi-joint dynamic movements, 10 single-joint isometric contractions, and 2 single-joint isokinetic contractions. Of the studies investigating multi-joint dynamic contractions, 83% (11/13 studies) reported at least one significant age-related difference: In 84% (9/11 studies) coactivation was higher in children, whereas 16% (2/11 studies) reported higher coactivation in adults. Among single-joint contractions, only 25% (3/12 studies) reported significantly higher coactivation in children. Fifty six percent of studies examined females, with no clear sex-related differences. Child-adult differences in coactivation appear to be more prevalent during multi-joint dynamic contractions, where generally, coactivation is higher in children. When examining child–adult differences in muscle function, it is important to consider potential age-related differences in coactivation, specifically during multi-joint dynamic contractions

Reporting of adverse events in muscle strengthening interventions in youth: A systematic review

To document the extent to which AEs, resulting from intervention studies targeting muscle-strengthening training (MST) in youth, are reported by researchers

The skin blood flow response to exercise in boys and men and the role of nitric oxide

Purpose: Children thermoregulate effectively during exercise despite sweating rate being consistently lower when compared with adults. The skin blood flow (SkBF) response of children to exercise is inconsistent, when compared with adults. We examined the SkBF response to exercise in children and adults, along with the potential contribution of nitric oxide to the SkBF response. Methods: Forearm SkBF during cycling (30 min at 60% O2max) was investigated in 12 boys (10 ± 1 years) and 12 men (22 ± 2 years) using laser-Doppler flowmetry and Nω-nitro-l-arginine methyl ester (L-NAME) iontophoresis to inhibit nitric oxide synthase. Results: The exercise-induced SkBF increase was similar in boys and men (mean ± SD, 540 ± 127 vs. 536 ± 103% baseline, respectively, p = 0.43, d = 0.01 [− 0.8 to 0.8]). However, the total hyperaemic response to exercise (area-under-the-curve, AUC) indicated that boys had a greater vasodilatory response (cutaneous vascular resistance, CVC) (p < 0.01, d = 0.6 [− 1.2 to 2.8] than the men (134,215 ± 29,207 vs. 107,257 ± 20,320 CVC·s−1). L-NAME blunted the SkBF response more in boys than in men (group-by-treatment interaction, p < 0.001) and resulted in smaller AUC in boys (56,411 ± 23,033 CVC·s−1; p < 0.001, d = 1.4 [− 0.4 to 3.2] compared with men (80,556 ± 28,443 CVC·s−1; p = 0.08, d = 0.8 [0.0–1.6]). Boys had a shorter delay from the onset of exercise to onset of SkBF response compared with men (205 ± 48 and 309 ± 71 s, respectively; p < 0.01, d = 1.7 [0.9–2.8]). L-NAME increased the delay in boys and men (to 268 ± 90 and 376 ± 116 s, respectively; p = 0.01, d = 1.0 [0.4–2.1]) but this delay was not significantly different between the groups (p = 0.85). Conclusions: These findings suggest that boys experience greater vasodilation and faster increases in SkBF during exercise compared with men. The contribution of nitric oxide to the SkBF response to exercise appears to be greater in boys than in men.This study was supported by a Collaborative Health Research Project Grant co-sponsored by Canadian Institutes for Health Research and the Natural Science and Engineering Research Counci