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Background: Increases in high-intensity locomotor activity of match play have been recorded in elite soccer. This places an onus on academy practitioners to develop players for the future demands of the game. At an academy level, locomotor data are not available for analysis over a longitudinal period, and thus changes can only be assessed with physical attribute assessment. The aim of the present study is to establish if changes in physical capacity were observed in a professional Scottish soccer academy over a ten-year period. Methods: A retrospective analysis was completed where linear mixed effect (LME) models were individually fitted to explain variation across each measure of physical capacity. Model selection was undertaken with likelihood ratio tests where the initial complex models were compared to simpler nested models to arrive at the final model by maximum likelihood. Results: The main findings were that most recent players' sprint test data revealed a significant improvement in 5m, 10m and 20m sprint performance, greater increases in CMJ performance in older age groups, and greater increases in YYIR1 performance at U13 and U14. Most physical results showed increased performance with greater relative height and weight. Conclusion: Players recruited more recently to academies are fitter than they were previously. Reference values within clubs that establish first team requirements will contribute to appropriate planning and implementation of training.

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ABSTRACT: Hall, AJ, Aspe, RR, Craig, TP, Kavaliauskas, M, Babraj, J, and Swinton, PA. The effects of sprint interval training on physical performance: a systematic review and meta-analysis. J Strength Cond Res 37(2): 457-481, 2023-The present study aimed to synthesize findings from published research and through meta-analysis quantify the effect of sprint interval training (SIT) and potential moderators on physical performance outcomes (categorized as aerobic, anaerobic, mixed aerobic-anaerobic, or muscular force) with healthy adults, in addition to assessing the methodological quality of included studies and the existence of small study effects. Fifty-five studies were included (50% moderate methodological quality, 42% low methodological quality), with 58% comprising an intervention duration of ≤4 weeks and an array of different training protocols. Bayesian's meta-analysis of standardized mean differences (SMD) identified a medium effect of improved physical performance with SIT (ES 0.5 = 0.52; 95% credible intervals [CrI]: 0.42-0.62). Moderator analyses identified overlap between outcome types with the largest effects estimated for anaerobic outcomes (ES 0.5 = 0.61; 95% CrI: 0.48-0.75). Moderator effects were identified for intervention duration, sprint length, and number of sprints performed per session, with larger effects obtained for greater values of each moderator. A substantive number of very large effect sizes (41 SMDs > 2) were identified with additional evidence of extensive small study effects. This meta-analysis demonstrates that short-term SIT interventions are effective for developing moderate improvements in physical performance outcomes. However, extensive small study effects, likely influenced by researchers analyzing many outcomes, suggest potential overestimation of reported effects. Future research should analyze fewer a priori selected outcomes and investigate models to progress SIT interventions for longer-term performance improvements.

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AbstractThe purpose of this long-term retrospective analysis was to determine whether anthropometric and physical performance data could predict success in elite youth Scottish soccer players. Stature, body mass, sprint, jump and aerobic performance were collected from 512 players (U10 to U17) across a 10-year period. Players participated in an average of four profiling sessions (range: 1-14) and up to a maximum of three per year (August, December, and May) with standardisation applied to the surface, test order, time and protocols. One hundred players were awarded professional contracts. Associations between variables were quantified with mixed-effects linear models. Prediction was assessed with least absolute shrinkage and selection operator (LASSO) regression developed on a training set (2/3 data) and tested with proportion of error on a leave-out (1/3 data) test set. Confidence intervals were obtained through bootstrap LASSO samples. A strong relative age bias was identified with 50% of successful players born in the first quarter of the year. Successful players were on average taller and performed better in sprint and jump tests (p < 0.05). However, effects were small and even when variables were combined, proportion of errors identified were similar to random guessing (0.45[95%CI:0.41-0.49]). The results indicate that whilst successful players as youths demonstrate on average distinct anthropometric and physical profiles, these differences are unlikely to provide a reliable source to predict success within an already talented group. Practitioners should use data collected to guide exercise prescription but be aware of its substantive limitations in predicting success in isolation.

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Infusion of carnitine has been observed to increase non-oxidative glucose disposal in several studies, but the effect of oral carnitine on glucose disposal in non-diabetic lean versus overweight/obese humans has not been examined. This study examined the effects of 14 days of L-carnitine L-tartrate oral supplementation (LC) on blood glucose, insulin, NEFA and GLP-1 responses to an oral glucose tolerance test (OGTT). Sixteen male participants were recruited [lean (n = 8) and overweight/obese (n = 8)]. After completing a submaximal predictive exercise test, participants were asked to attend three experimental sessions. These three visits were conducted in the morning to obtain fasting blood samples and to conduct 2 h OGTTs. The first visit was a familiarisation trial and the final two visits were conducted 2 weeks apart following 14 days of ingestion of placebo (PL, 3 g glucose/day) and then LC (3 g LC/day) ingested as two capsules 3×/day with meals. On each visit, blood was drawn at rest, at intervals during the OGTT for analysis of glucose, insulin, non-esterified fatty acids (NEFA) and total glucagon-like peptide-1 (GLP-1). Data obtained were used for determination of usual insulin sensitivity indices (HOMA-IR, AUC glucose, AUC insulin, 1st phase and 2nd phase ß-cell function, estimated insulin sensitivity index and estimated metabolic clearance rate). Data were analysed using RMANOVA and post hoc comparisons where appropriate. There was a significant difference between groups for body mass, % fat and BMI with no significant difference in age and height. Mean (SEM) plasma glucose concentration at 30 min was significantly lower (p < 0.05) in the lean group on the LC trial compared with PL [8.71(0.70) PL; 7.32(0.36) LC; mmol/L]. Conversely, plasma glucose concentration was not different at 30 min, but was significantly higher at 90 min (p < 0.05) in the overweight/obese group on the LC trial [5.09(0.41) PL; 7.11(0.59) LC; mmol/L]. Estimated first phase and second phase ß-cell function both tended to be greater following LC in the lean group only. No effects of LC were observed on NEFA or total GLP-1 response to OGTT. It is concluded that LC supplementation induces changes in blood glucose handling/disposal during an OGTT, which is not influenced by GLP-1. The glucose handling/disposal response to oral LC is different between lean and overweight/obese suggesting that further investigation is required. LC effects on gastric emptying and/or direct 'insulin-like' actions on tissues should be examined in larger samples of overweight/obese and lean participants, respectively.

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