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Recent publications in the British Journal of Sports Medicine ( BJSM) (mis)represent and (mis)interpret young people’s cardiorespiratory fitness (CRF) and potentially (mis)inform health promotion and clinical practice. 1 2 The papers recognise peak VO2as the criterion measure of CRF but base their estimations of peak VO2 on performances in 20 m shuttle runs (20mSRT). Moreover, and of serious concern to us, estimated peak VO2 is (mis)represented and (mis)interpreted in ratio with body mass (ie, in mL/kg/min). The papers identify a few of the limitations of shuttle running but a recent meta-analysis succinctly summarised the issues. It demonstrated that with children, over half of correlation coefficients between 20mSRT scores and peak VO2 explain less than 50% of the variance in peak VO2. The meta-analysis reported that the criterion-related validity of the 20mSRT with children was only ‘ moderate ’ and concluded, ‘testers must be aware that the performance score of the 20MSR test is simply estimation and not a direct measure of cardiorespiratory fitness’.3 An example of specious interpretation of 20mSRT scores is the assertion that …

The health, fitness and other advantages of youth sports participation are well recognised. However, there are considerable challenges for all stakeholders involved— especially youth athletes—in trying to maintain inclusive, sustainable and enjoyable participation and success for all levels of individual athletic achievement. In an effort to advance a more unified, evidence-informed approach to youth athlete development, the IOC critically evaluated the current state of science and practice of youth athlete development and presented recommendations for developing healthy, resilient and capable youth athletes, while providing opportunities for all levels of sport participation and success. The IOC further challenges all youth and other sport governing bodies to embrace and implement these recommended guiding principles.

Aim To provide an evidence-based review of muscle metabolism changes with sex-, age- and maturation with reference to the development of youth sport performance. Methods A narrative review of data from both invasive and non-invasive studies, from 1970 to 2015, founded on personal databases supported with computer searches of PubMed and Google Scholar. Results Youth sport performance is underpinned by sex-, age- and maturation-related changes in muscle metabolism. Investigations of muscle size, structure and metabolism; substrate utilisation; pulmonary oxygen uptake kinetics; muscle phosphocreatine kinetics; peak anaerobic and aerobic performance; and fatigue resistance; determined using a range of conventional and emerging techniques present a consistent picture. Age-related changes have been consistently documented but specific and independent maturation-related effects on muscle metabolism during exercise have proved elusive to establish. Children are better equipped for exercise supported primarily by oxidative metabolism than by anaerobic metabolism. Sexual dimorphism is apparent in several physiological variables underpinning youth sport performance. As young people mature there is a progressive but asynchronous transition into an adult metabolic profile. Conclusions The application of recent developments in technology to the laboratory study of the exercising child and adolescent has both supplemented existing knowledge and provided novel insights into developmental exercise physiology. A sound foundation of laboratory-based knowledge has been established but the lack of rigorously designed child-specific and sport-specific testing environments has clouded the interpretation of the data in real life situations. The primary challenge remains the translation of laboratory research into the optimisation of youth sports participation and performance.

Objective—To examine short term power output during growth and maturation using a multilevel modelling approach. Methods—Body mass, stature, and triceps and subscapular skinfold thicknesses of boys and girls, aged 12.2 (0.4) years (mean (SD)) at the onset of the study, were measured at age 12, 13, and 17 years. Sexual maturation, classified according to Tanner’s stage of pubic hair development, was assessed on the first two occasions and assumed to be stage 5 at 17 years. Peak power (PP) and mean power (MP) were assessed on each occasion using the Wingate anaerobic test. Results—Initial models, founded on 417 determinations of short term power output, identified body mass, stature, and age as significant explanatory variables of both PP and MP. The values for girls were significantly lower than those for boys, and a significant age by sex interaction described a progressive divergence in the MP of boys and girls. The introduction of sum of two skinfold thicknesses produced a model with an improvement in fit as indicated by a significant change in log likelihood. The stature term was negated and the body mass term increased. The age and sex terms were reduced but remained significant. The age by sex interaction term remained a significant explanatory variable for MP. Maturity eVects were non-significant additional explanatory variables in all models of power output. Conclusion—The values of PP and MP for boys are higher than those for girls, and, for MP, sex diVerences increase with age. Body mass and skinfold thicknesses are significant influences on both PP and MP, but age exerts a positive but non-linear eVect on power output independent of body size and fatness. (Br J Sports Med 2001;35:118‐124)

Objective—To investigate the eVects of two contrasting eight week training programmes on the aerobic performance of 39 prepubescent boys (mean age 10.1 years). Methods—All boys were volunteer subjects from three city schools and the schools were matched by a health related behaviour questionnaire. All of the boys were assessed as Tanner stage one for genitalia and pubic hair development. Criterion laboratory tests included peak V ~O2 as assessed by an incremental discontinuous treadmill test to voluntary exhaustion. Submaximal measurements of heart rate,minute ventilation (V ~E) and V ~O2 were also recorded during the treadmill test. One of the schools provided the control group (n = 14), and boys from the other schools followed two contrasting training programmes. The first was a sprint interval running programme (n = 12) comprising 10 second and 30 second sprints, and the second a continuous cycle ergometer programme (n = 13) maintaining a heart rate in the range 80‐85% of maximum for 20 minutes on a Monark cycle ergometer. After eight weeks training three times a week, the three groups were retested. Results—There were no significant diVerences in peak V ~O2 (p>0.05) with training in either of the groups. Neither were there significant changes in any of the submaximal variables V ~O2 ,V ~ E, or heart rate (p>0.05). Conclusion—The findings of this study indicate that neither eight week sprint interval running nor continuous cycle ergometer training programmes significantly improve maximal or submaximal indicators of the aerobic performance of prepubertal boys. (Br J Sports Med 2000;34:168‐173)

OBJECTIVES: To investigate the physiological effects of two different three times a week, eight week training programmes on the aerobic fitness of nine to ten year old girls. METHODS: Treadmill determined peak VO2, submaximal heart rates, and submaximal blood lactate were the criterion measures. Seventeen girls completed a programme of "aerobics" training where sessions lasted 20-25 minutes. Eighteen girls followed a cycle ergometer training programme which involved pedalling continuously for 20 minutes with the heart rate maintained between 160 and 170 beats/minute. A control group of 16 girls completed the criterion tests but did not train. In the cycle ergometer group and eight control subjects plasma total cholesterol and high density lipoprotein cholesterol were determined before and after training. RESULTS: Peak VO2 did not change significantly with training in either training group, neither were there any significant changes in submaximal heart rates. Blood lactate declined significantly at the two lowest submaximal exercise intensities in the cycle ergometer training group (from 2.3 (1.1) to 1.4 (0.06) mmol/l at stage 1 and from 2.1 (1.2) to 1.6 (0.06) mmol/l at stage 2; means (SD); P < 0.01). Total cholesterol and high density lipoprotein cholesterol remained unchanged with training. CONCLUSIONS: These findings suggest that an eight week structured exercise programme produces minimal changes in either the aerobic fitness or blood lipids of young girls. It may be more beneficial for long term health to promote enjoyment in activity and positive attitudes to exercise rather than attempting to enhance aerobic fitness through strenuous exercise programmes.

The aim of this study was to evaluate whether fixed blood lactate reference values of 2.5 and 4.0 mmol.1(-1) corresponded to the equivalent intensity of exercise in prepubertal and teenage boys, and men. Twenty six prepubertal boys (mean(sd) age) 11.1(0.4) years), 26 teenage boys (mean(sd) age 14.1(0.3) years), and 23 men (mean(sd) age 22.4(2.7) years) gave informed consent to participate in the study. Oxygen consumption (VO2) and heart rates (HR) corresponding to the 2.5 and 4.0 mmol.1(-1) fixed blood lactate reference values were used as the criterion measures during incremental treadmill exercise. At the 2.5 mmol.1(-1) level there were no significant differences (P > 0.05) in % peak VO2 between groups. For both prepubertal and teenage boys the 4.0 mmol.1(-1) lactate level represented a higher mean % peak. VO2 than for the mean (P < 0.05). The prepubertal and teenage values were again not significantly different (P > 0.05). Factors other than maturation during puberty influence blood lactate responses to exercise.

To investigate the reliability of heart rate variability (HRV) measures at rest and during light exercise in children.Short term (five minute) HRV was assessed in 12 children (11-12 years of age). HRV measures were collected at rest with the children supine, breathing at 12 breaths/min, and during exercise on a cycle ergometer while exercising at 25% of peak oxygen uptake. Both resting and exercise data were collected twice from each child.Intraclass correlation coefficients were low to moderate for most measures with wide confidence intervals for each variable in both resting and exercise conditions. Random variation (typical error) within repeated measurements ranged from 31% to 187%.These preliminary findings suggest that HRV measures are unreliable at rest and during light exercise in children aged 11-12 years. Tighter control of extraneous influences is recommended.

This study examined the relationship between daily physical activity and aerobic fitness in 11-16-year-olds. Habitual physical activity was assessed in 28 boys (mean(s.d.) age 13.6(1.3) years) and 45 girls (mean(s.d) age 13.7(1.3) years) from minute-by-minute heart rate monitoring during 3 school days. Aerobic fitness was assessed by determining the percentage peak VO2 at blood lactate reference values of 2.5 and 4.0 mmol l-1 during incremental treadmill running. The 4.0 mmol l-1 level occurred at a mean(s.d.) value of 89(7)% peak VO2 in both boys and girls and mean(s.d.) values at the 2.5 mmol l-1 level were 82(9)% peak VO2 in girls. Mean(s.d.) percentage time with heart rates at or above 140 beats min-1 was 6(3)% in boys and 5(3)% in girls. Corresponding values for percentage time at or above 160 beats min-1 were 3(2) for boys and 2(1) for girls. The number of 10- and 20-min periods of activity with the heart rate sustained above the 140 and 160 beats min-1 thresholds were also totalled over the 3 days. No significant relationships were identified between percentage peak VO2 at the 2.5 or 4.0 mmol l-1 blood lactate reference levels and either percentage time or number of 10- or 20-min periods above 140 or 160 beats min-1 (P > 0.05). These results support the hypothesis that daily physical activity levels in 11-16-year-old children do not stress aerobic metabolism sufficiently to influence aerobic fitness.

This study tested the hypotheses that (1) secondary criteria (respiratory exchange ratio (RER), heart rate, blood [lactate]) traditionally used to verify the determination of maximum oxygen uptake (VO₂(max)) in children can result in the acceptance of a 'submaximal' VO₂(max) or falsely reject a 'true' VO(₂max) and (2) the VO₂(peak) recorded during a ramp test in children is comparable to the VO₂(peak) achieved during supramaximal testing.Thirteen children (9-10 years) completed a ramp cycle test to exhaustion to determine their VO₂(peak). After 15 min of recovery, the participants performed a supramaximal cycle test to exhaustion at 105% of their ramp test peak power.Compared with the VO₂(peak) during the ramp test, a significantly lower VO₂ was recorded at a RER of 1.00 (1.293 litre/min (SD 0.265) vs 1.681 litre/min (SD 0.295), p0.001, n = 12), at a heart rate of 195 beats/min (1.556 litre/min (SD 0.265) vs 1.721 litre/min (SD 0.318), p0.001, n = 10) and at 85% of age-predicted maximum (1.345 litre/min (SD 0.228) vs 1.690 litre/min (SD 0.284), p0.001, n = 13). Supramaximal testing yielded a VO₂(peak) that was not significantly different from the ramp test (1.615 litre/min (SD 0.307) vs 1.690 litre/min (SD 0.284), p = 0.090, respectively).The use of secondary criteria to verify a maximal effort in young people during ramp cycling exercise may result in the acceptance of a submaximal VO₂(max). As supramaximal testing elicits a VO₂(peak) similar to the ramp protocol, thus satisfying the plateau criterion, the use of such tests is recommended as the appropriate method of confirming a 'true' VO₂(max) with children.

Surveys from several countries have identified the presence of risk factors known to be associated with coronary heart disease in children. Data on the distribution of coronary risk factor variables in British children are scarce. This study was therefore designed to test the feasibility of collecting coronary risk factor data from British children and to conduct a preliminary examination of the problem. One hundred and seven children (mean age 12.8 yr) had their height, weight, triceps skinfold and blood pressure checked. Blood samples for cholesterol and HDL-cholesterol analysis were obtained from 93 children. Peak VO2 was determined on 48 children, 76 children had their daily activity monitored and 59 children's stage of sexual maturity was assessed. The boys' peak VO2 was significantly higher than the girls, whether expressed in l.min-1 (p less than 0.05) or ml.kg.-1min-1 (p less than 0.01). No other significant differences (p greater than 0.05) between the sexes were detected. The results indicate that children have relatively high serum cholesterol levels (boys 4.58 +/- 0.79; girls 4.72 +/- 0.80 mmol.l-1). The willingness and enthusiasm of the children, parents and schools to take part in the study clearly demonstrated the feasibility of a large scale study being successfully pursued in the United Kingdom.

Thirteen male competitive swimmers (mean age 14.7 years) were studied during maximal exercise on a treadmill, cycle ergometer and biokinetic swim bench. The mean maximal oxygen uptake values elicited (treadmill = 66.5 ml.kg-1 min.-1; cycle ergometer = 61.0 ml.kg.-1 min.-1; biokinetic swimbench = 44.5 ml.kg.-1 min.-1) were higher than those reported elsewhere for children not engaged in intensive training and even when compared with other groups of similarly aged swimmers the values exhibited were some of the highest recorded. The results were directionally similar to those of other studies comparing treadmill and cycle ergometer exercise with the mean maximal oxygen uptake on the cycle ergometer 9% lower than that on the treadmill. There is no other study with which to compare swim bench values but the majority of maximal values were consistently and significantly lower than those achieved on the other ergometers. The swimmers rank within the group was minimally affected by the type of ergometer on which the measurement was made.

This study examined the relationship between estimates of alactacid anaerobic power, lactacid anaerobic power and aerobic power in a sample of trained swimmers (age 14.4 yr., n = 8) and a sample of untrained boys (age 13.7 yr., n = 13). The anaerobic power outputs were estimated using a modification of the Wingate Anaerobic Test and aerobic power was estimated using a continuous, incremental cycle ergometer test. In addition to leg power outputs the swimmers' arm power using each energy system was estimated and compared with the corresponding leg value. There was no relationship between the estimates of the power of the three energy systems with either the trained or untrained boys. Furthermore with the trained boys there was no relationship between estimates of the power of the same energy system utilised by different limbs. The data support a specificity hypothesis of energy utilisation during exercise with both trained and untrained adolescent boys.