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Paul Ritsche,1 Ralf Roth,1 Thomas Bernhard,2 Lukas Nebiker,1 Eric Lichtenstein,1 Martino Franchi,3 Jörg Spörri,4,5 Oliver Faude1 1Department of Sport, Exercise and Health, University of Basel, Basel, Switzerland; 2FC Basel 1893, Basel, Switzerland; 3Human Neuromuscular Physiology Lab, Department of Biomedical Sciences, University of Padua, Padova, Italy; 4Sports Medical Research Group, Department of Orthopaedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland; 5University Centre for Prevention and Sports Medicine, Department of Orthopaedics, Balgrist University Hospital, University of Zurich, Zurich, SwitzerlandCorrespondence: Paul Ritsche, University of Basel, Department of Sport, Exercise and Health, Grosse Allee 6, Basel, 4052, Switzerland, Email Paul.ritsche@unibas.chPurpose: Adolescent soccer players experience distinct physiological changes due to chronological and biological maturation, impacting their soccer performance. Here, we explored age-related variations and associations between quadriceps geometry and strength in male national-level adolescent soccer players.Patients and Methods: We used ultrasonography to examine the regional architecture and morphology of the rectus femoris (RF) and vastus lateralis (VL) muscles, and we assessed knee extension strength by isometric and isokinetic dynamometry. Players were categorized into four age groups: under (U) 15 (n=18, age=13.7± 0.5 years), U16 (n=15, age=14.7± 0.5), U17 (n=19, age=15.7± 0.5), U18 (n=18, age=16.7± 0.5) and U21 (n=25, age=18.5± 0.5).Results: The absolute and relative strengths were higher in the U16 compared to U15 by 12– 15% and 6– 8%, 11– 12% and 6– 7% in the U17 compared to U16, 5– 7% and − 1– 2% in the U18 compared to U17 and 0– 15% and − 1– 11% in the U21 compared to U18 age groups, respectively. VL architecture did not change relevantly between the age groups. The muscle anatomical cross-sectional area (ACSA) of the VL and RF differed non-uniformly and muscle region-specific by 10– 36%, with highest values in the U21 age group. Moderate correlations between the VL architecture and knee extension strength in both legs were observed only in the U16 age group. The quadriceps ACSA showed age-specific correlations with knee extension strength.Conclusion: Our findings highlight non-uniform differences in quadriceps muscle morphology and absolute and relative strength among male national-level adolescent soccer players in different age groups. The correlations observed between muscle morphology or architecture and strength were muscle, muscle region, leg and age dependent.Keywords: strength, youth, muscle architecture, vastus lateralis, rectus femoris

Resistance exercise with blood flow restriction (BFR) is considered a safe and powerful training tool. Low-load (LL) resistance training with BFR results in comparable hypertrophy compared to conventional heavy-load (HL) resistance training (Centner et al., 2019). Additionally, LL training with BFR (LL-BFR) induces comparable (Grønfeldt et al., 2020) or slightly lower (Centner et al., 2019) effects on muscle strength than HL training. It is generally accepted that increases in maximum strength are mediated by muscular hypertrophy and/or neural adaptations. However, the effect of BFR on neural adaptations is scarcely investigated. The aim of this study was therefore to investigate the effects of BFR on acute neural adaptations following a single bout of resistance training. Fifteen male participants (21-35 years) volunteered to participate in this study. On three separate days, participants performed a strength training session of the right elbow flexors with either LL, LL-BFR or HL. Neuromuscular adaptations were investigated before and after each resistance training session by means of transcranial magnetic stimulation (single- and paired-pulse TMS) and peripheral nerve stimulation (Mmax). Data were acquired during submaximal sustained isometric contractions. During LL-BFR, the cuff was inflated to 50% of the individual arterial occlusion pressure to restrict venous outflow in the working musculature during exercise. The preliminary data analysis with mixed linear models revealed that, compared to baseline values, normalized MEPs (% of Mmax) from the trained biceps brachii were enhanced for HL (Cohen’s d = 0.51) but not LL-BFR (Cohen’s d = 0.03) when compared to LL. None of the groups showed relevant changes in short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF). The size of Mmax decreased slightly for HL (Cohen’s d = -0.18) but not LL-BFR (Cohen’s d = 0.06) when compared to LL. This is the first study that investigated acute neural adaptations in response to resistance training with and without BFR. We observed increased MEP amplitudes after HL but not LL what is in line with previous evidence (Mason et al., 2019). Since training with BFR results in a rapid increase in motoneuronal excitability (Copithorne et al., 2020), the increased MEP are less likely caused by changes at the cortical site. Centner, C., Wiegel, P., Gollhofer, A., & König, D. (2019). Effects of blood flow restriction training on muscular strength and hypertrophy in older individuals: A systematic review and meta-analysis. Sports Medicine, 49, 95-108. https://doi.org/10.1007/s40279-018-0994-1 Copithorne, D. B., Rice, C. L., & McNeil, C. J. (2020). Effect of blood flow occlusion on corticospinal excitability during sustained low-intensity isometric elbow flexion. Journal of Neurophysiology, 123(3), 1113-1119. https://doi.org/10.1152/jn.00644.2019 Grønfeldt, B. M., Lindberg Nielsen, J., Mieritz, R. M., Lund, H., & Aagaard, P. (2020). Effect of blood-flow restricted vs heavy-load strength training on muscle strength: Systematic review and meta-analysis. Scandinavian Journal of Medicine & Science in Sports, 30(5), 837-848. https://doi.org/10.1111/sms.13632 Mason, J., Howatson, G., Frazer, A. K., Pearce, A. J., Jaberzadeh, S., Avela, J., & Kidgell, D. J. (2019). Modulation of intracortical inhibition and excitation in agonist and antagonist muscles following acute strength training. European Journal of Applied Physiology, 119, 2185-2199. https://doi.org/10.1007/s00421-019-04203-9

Retinal vessel alterations have been shown to be associated with cardiovascular risk factors and physical inactivity as early as childhood. In this context, the analysis of physical activity in children has solely been based on questionnaire assessments. The study aimed to examine the association of physical fitness performance and self-reported physical activity with retinal vessel diameters in young children. Three hundred ninety-one primary schoolchildren [7.3 years ( SD 0.4)] were examined in this cross-sectional study. The primary outcome was endurance performance measured with the 20-m shuttle run. The additional tests consisted of a 20-m sprint, jumping sidewards and balancing backwards. Retinal microcirculation was assessed using a static retinal vessel analyzer. Parents completed questionnaires about physical and sedentary activities. Endurance performance was associated with narrower retinal venular diameters [−0.9 (95% CI: −1.8; −0.1) measuring units (mu)/ unit shuttle run, P = 0.04] and a higher arteriolar to venular ratio [0.003 (−0.001; 0.006)/unit shuttle run, P = 0.06]. The sprint performance was associated with narrower retinal arterioles [4.7 (0.8; 8.6) mu/unit sprint, P = 0.02]. Indoor playing activity correlated with narrower retinal venules [−0.04 (−0.07; −0.01) mu/per unit, P = 0.02]. Our data suggest that objectively measured endurance performance relates with better retinal vessel health in early childhood. [ABSTRACT FROM AUTHOR]

Veteran football players above 40 years have rarely been subject to scientific investigations. This is worrisome because their number is considerable and their cardiovascular risk probably increased. Therefore, a cross-sectional study was conducted in 100 football players between 40 and 63 years of age. This included a medical history and physical examination, venous blood sampling, measurement of resting blood pressure, a resting electrocardiogram (ECG), an exhaustive cycle ergometry and a multistage field test. Also, measurements of heart rate and blood lactate concentration were carried out during one typical training session and one match. Participants trained 1.0 ± 0.6 sessions per week and played 27 ± 8 matches per season. Of them, 19% were smokers. Resting blood pressure was 138 ± 15/88 ± 8 mmHg. Hypertension prevalence (WHO definition) was 66%. Total cholesterol averaged 220 ± 41 mg . dl−1, HDL 46 ± 13 mg . dl−1and LDL 134 ± 33 mg . dl−1. The average 10-year risk for cardiovascular events (Framingham score) was 6%. Mean maximal power output on the cycle ergometer was 2.8 ± 0.6 W . kg−1, mean VO2peak40.0 ± 7.3 ml . min−1. kg−1. Comparing training and competition, no significant differences in cardiovascular and metabolic load were found. In summary, their cardiovascular risk was similar to age-adjusted reference values. However, they showed slightly better ergometric performance. More frequent training stimuli might be necessary to reach more favourable risk factor profiles. Training and competition lead to similar cardiocirculatory and metabolic stress which is considerably high and might put players into danger who have pre-existing cardiac disease. [ABSTRACT FROM AUTHOR]

The present study evaluated the effects of a newly developed injury prevention programme for children’s football (“FIFA 11+ Kids”) on motor performance in 7–12-year-old children. We stratified 12 football teams (under-9/-11/-13 age categories) into intervention (INT,N = 56 players) and control groups (CON,N = 67). INT conducted the 15-min warm-up programme “FIFA 11+ Kids” twice a week for 10 weeks. CON followed a standard warm-up (sham treatment). Pre- and post-tests were conducted using: single leg stance; Y-balance test; drop and countermovement jump; standing long jump; 20-m sprint; agility run; slalom dribble; and wall volley test. We used magnitude-based inferences and linear mixed-effects models to analyse performance test results. We observed likely beneficial effects favouring INT in Y-balance (right leg; +3.2%; standardised mean difference (SMD) = 0.34;P = 0.58) and agility run (+3.6%; SMD = 0.45;P = 0.008). Possibly beneficial effects were found in Y-balance, drop jump reactive strength index, drop jump height, countermovement jump, standing long jump, slalom dribble and wall volley test. At least possibly beneficial improvements in favour of “FIFA 11+ Kids” were observed in nearly all parameters. Most effects were small, but slight improvements in motor performance may potentially contribute to a reduction of injury risk. [ABSTRACT FROM AUTHOR]

The study investigated the effects of slackline training (rope balancing) on balance, jump performance and muscle activity in children. Two primary-school classes (intervention, n = 21, INT: age: 10.1 (SD 0.4) y, weight: 33.1 (4.5) kg; control, n = 13, CON: age: 10.0 (SD 0.4) y, weight: 34.7 (7.4) kg) participated. Training was performed within 6 weeks, 5 times per week for 10 min each day. Balance (static and dynamic stance), countermovement jumps, reverse balancing on beams (3, 4.5 and 6 cm width), slackline standing (single- and double-limb) and electromyographic activity (soleus, gastrocnemius, tibialis anterior) were examined. INT significantly improved single- and double-limb slackline standing (double limb: 5.1 (3.4) s–17.2 (14.4) s; right leg: 8.2 (5.8) s–38.3 (36.0) s; left leg: 10.6 (5.8) s–49.0 (56.3) s; p < 0.001; 0.17 < η p ² < 0.22). Reduced left-leg dynamic sway ( − 20.8 %, p = 0.06, η p ² = 0.10), improved 4.5 cm balancing ( + 18.5 %, p = 0.08, η p ² = 0.10) and decreased muscle activity during slackline standing for the mm. soleus ( − 23 %, p = 0.10, η p ² = 0.18) and tibialis anterior ( − 26 %, p = 0.15, η p ² = 0.14) was observed for INT. Jump performance remained unchanged (p = 0.28, η p ² = 0.04). In conclusion, daily slackline training results in large slackline-specific balance improvements. Transfer effects to static and dynamic stance, reverse balancing or jumping performance seemed to be restricted. [ABSTRACT FROM AUTHOR]

This study aimed at determining the reproducibility of pacing profiles (PP) during simulated swimming trials as well as the comparison between simulated and real competitions (RC). Sixteen competitive front crawl swimmers (7 females, 9 males) performed 2 × 200 m, 2 × 400 m and 2 × 800 m tests, each test 7 days apart. All 100 m split (ST) and total times (TT) were recorded (additionally 50 m ST for the 200 m bouts). The PP of one RC within a maximum of 8 weeks before or after data acquisition was used for comparison. No difference was observed between test and retest for TT (p < 0.16). Coefficients of variation (CV) for all ST during 800 m were between 0.9 and 1.8 % (standard error of measurement (SEM) = 0.6–2.1 s), except for the last 2 sections (CV = 2.5 % and 2.9 %). During 400 m and 200 m, CV was below 1.7 % for each section (SEM = 0.4–1.7 s). Mean differences between test and retest ranged from 1.8 s (Cl: 0.1–3.4 s) in the 400 m bouts to 4.1 s (Cl: 1.3–9.5 s) for the 800 m races. Although section times were faster during all sections of RC compared to SC, PP was similar during both trials (p > 0.22). However, swimmers were faster in each section during RC. In conclusion, PP seem stable, at least during the first three quarters of the race. Furthermore, simulated trials seem to be an acceptable model to analyse PP in competitive swimming. [ABSTRACT FROM AUTHOR]

Purpose: Given percentages of VO(2max) are widely used for training and study purposes although they might not result in homogeneous metabolic strain. Therefore, the homogeneity of metabolic responses to prolonged exercise at fixed percentages of VO(2max) should be investigated.Procedures: Twenty-one healthy male subjects (29+/-5 years, 77+/-8 kg, VO(2max): 59.9+/-11.8 ml min(-1)kg(-1)) performed two incremental tests to exhaustion on a cycle ergometer to determine VO(2max). Subsequently, two 60 min tests at 60 and 75% VO(2max) were conducted in randomised order. VO(2) was kept constant by adjusting the work rate. Blood lactate (La) responses as primary outcome variable to quantify metabolic strain were assessed.Findings: Mean La was 2.1+/-1.1 mmol l(-1) (min-max: 0.7-5.6 mmol l(-1)) during the 60% VO(2max) test and 4.6+/-1.9 mmol l(-1) (min-max: 2.2-8.0 mmol l(-1)) during the 75% VO(2max) test. The coefficients of variation of La amounted for 52.4 and 41.3% during the 60 and 75% VO(2max) test, respectively. La responses did not differ significantly between three subgroups of the subjects (N=7 with VO(2max)<55 ml min(-1)kg(-1), N=7 with VO(2max) 55-65 ml min(-1)kg(-1), and N=7 with VO(2 max)>65 ml min(-1)kg(-1); P>or=0.08).Conclusion: Altogether, prolonged exercise at given percentages of VO(2max) leads to inhomogeneous metabolic strain as indicated by the large variability of La responses. This holds true even in subgroups of similar aerobic capacity. Thus, intensity prescription for endurance training and study purposes should not be solely based upon percentages of VO(2max) when a comparable metabolic strain is intended. [ABSTRACT FROM AUTHOR]

Background: Prolonged exercise may induce temporary immunosuppression with a presumed increased susceptibility for infection. However, there are only few data on immune cell function after prolonged cycling at moderate intensities typical for road cycling training sessions. Methods: The present study examined the influence on immune cell function of 4 h of cycling at a constant intensity of 70% of the individual anaerobic threshold. Interleukin-6 (IL-6) and C-reactive protein (CRP), leukocyte and lymphocyte populations, activities of natural killer (NK), neutrophils, and monocytes were examined before and alter exercise, and also on a control day without exercise. Results: Cycling for 4 h induced a moderate acute phase response with increases in IL-6 from 1.0 (SD 0.5) before to 9.6 (5.6) pg/ml 1 h after exercise and CRP from 0.5 (SI) 0.4) before to 1.8 (1.3) mg/l 1 day after exercise. Although absolute numbers of circulating NK cells, monocytes, and neutrophils increased during exercise, on a per cell basis NK cell activity, neutrophil and monocyte phagocytosis, and monocyte oxidative burst did not significantly change after exercise. However, a minor effect over time for neutrophil oxidatuve burst was noted, tending to decrease after exercise. Conclusions: Prolonged cycling at moderate intensities does not seem to seriously alter the function of cells of the first line of defence. Therefore, the influence of a single typical road cycling training session on the immune system is only moderate and appears to be safe from an immunological point of view. [ABSTRACT FROM AUTHOR]