Kinematische und dynamische Charakteristiken der maximalen Geschwindigkeit bei jungen Sprintern

Sprinting speed is a complex ability whose physiological basis is mostly genetically defined. Top competition results are therefore as a rile attainable only for a small, select number of individuals. The purpose of this study was to find the most important kinematic and dynamic parameters, their developmental trend and their influence on the efficiency in maximal sprinting speed for young sprinters of both sexes, from eleven to eighteen years of age. We recorded kinematic and dynamic parameters with locomometer. The vertical pressure on the surface was calculated by biomechanical modelling of running steps. We calculated correlation between maximal sprinting speed and Kinematic and dynamic parameters. The results show, for both sexes, that the structure of the sprint stride changes drastically in connection to the stride length and frequency, the ratio between the contact and the flight phases and the vertical pressure on the surface. The correlation coefficients show that the duration of contact (R=0.71), the relative stride frequency (R=0.52) and the vertical pressure on the surface (R=0.89) are good indicators of the sprinting potential of young runners.Brzina sprinta je kompleksna sposobnost čija se osnova većinom definira genetički. Vrhunske natjecateljske rezultati sloga u pravilu može postići samo mali broj odabranih pojedinaca. Svrha ovog istraživanja bila je naći najvažnije kinematičke i dinamičke parametre, njihov trend razvoja, te njihov utjecaj na efikasnost maksimalne brzine sprinta kod mladih sprintera oba spola, a ad 11 do 18 godina starosti. Kinematički i dinamički parametri snimani su lokomometrom. Okomiti pritisak na površinu izračunat je biomehaničkim modeliranjem trkaćih koraka. Izračunali smo korelaciju između maksimalne brzine sprinta, te kinematičkih j dinamičkih parametara. Rezultati pokazuju, za oba spola, da se struktura sprinterskog koraka drastično mijenja s obzirom na duljinu koraka i frekvenciju, omjer između faze kontakta i faze leta, te okomitog pritiska na površinu. Korelacijski koeficijenti pokazuju da su trajanje kontakta (R=0.71), relativna frekvencija koraka (R=0.52), te okomiti pritisak na površinu dobri (R=0.89) indikatori sprinterskog potencijala mladih sprintera.Die Geschwindigkeit des Sprints ist eine komplexe Fähigkeit, deren physiologische Basis meistens genetisch definiert wird. Spitzenwettkampfresultate sind deswegen in der Regel nur für eine geringe Anzahl von Sportlern erreichbar. Die Absicht dieser Forschung war die wichtigsten kinematischen und dynamischen Parameter zu finden, ihre Entwicklungstendenzen und ihr Einfluss auf die Effizienz bei der maximalen Geschwindigkeit des Sprints bei den jungen Sprintern beider Geschlechter im Alter von 11 bis 18 Jahre festzustellen. Wir haben die kinematischen und dynamischen Parameter mittels des Lokomometers aufgenommen. Der senkrechte Druck auf die Fläche wurde mittels der biomechanischen Modellierung von Laufschritten berechnet. Wir haben auch die Korrelation zwischen der maximalen Geschwindigkeit des Sprints und den kinematischen und dynamischen Parametern berechnet. Die Resultate zeigen, dass, für beide Geschlechter, die Struktur des Sprintschrittes bedeutend geändert wird in Bezug auf die Länge des Schrittes und die Frequenz, in Bezug auf das Verhältnis zwischen den Kontakt- und den Flugphasen als auch in Bezug auf den senkrechten Druck auf die Fläche. Die Korrelationskoeffiziente zeigen, dass die Dauer der Kontakt (R=0.71), die relative Schrittfrequenz (R=0.52) und der senkrechte Druck auf die Flache gute (R=0.89) Indikatoren des Sprintpotentials bei den jungen Läufern sind

Circulating MicroRNAs as Potential Biomarkers of Exercise Response

Systematic physical activity increases physical fitness and exercise capacity that lead to the improvement of health status and athletic performance. Considerable effort is devoted to identifying new biomarkers capable of evaluating exercise performance capacity and progress in training, early detection of overtraining, and monitoring health-related adaptation changes. Recent advances in OMICS technologies have opened new opportunities in the detection of genetic, epigenetic and transcriptomic biomarkers. Very promising are mainly small non-coding microRNAs (miRNAs). miRNAs post-transcriptionally regulate gene expression by binding to mRNA and causing its degradation or inhibiting translation. A growing body of evidence suggests that miRNAs affect many processes and play a crucial role not only in cell differentiation, proliferation and apoptosis, but also affect extracellular matrix composition and maintaining processes of homeostasis. A number of studies have shown changes in distribution profiles of circulating miRNAs (c-miRNAs) associated with various diseases and disorders as well as in samples taken under physiological conditions such as pregnancy or physical exercise. This overview aims to summarize the current knowledge related to the response of blood c-miRNAs profiles to different modes of exercise and to highlight their potential application as a novel class of biomarkers of physical performance capacity and training adaptation

Morphological, molecular and hormonal adaptations to early morning versus afternoon resistance training

It has been clearly established that maximal force and power is lower in the morning compared to noon or afternoon hours. This morning neuromuscular deficit can be diminished by regularly training in the morning hours. However, there is limited and contradictory information upon hypertrophic adaptations to time-of-day-specific resistance training. Moreover, no cellular or molecular mechanisms related to muscle hypertrophy adaptation have been studied with this respect. Therefore, the present study examined effects of the time-of-day-specific resistance training on muscle hypertrophy, phosphorylation of selected proteins, hormonal concentrations and neuromuscular performance. Twenty five previously untrained males were randomly divided into a morning group (n = 11, age 23 ± 2 yrs), afternoon group (n = 7, 24 ± 4 yrs) and control group (n = 7, 24 ± 3 yrs). Both the morning and afternoon group underwent hypertrophy-type of resistance training with 22 training sessions over an 11-week period performed between 07:30–08:30 h and 16:00–17:00 h, respectively. Isometric MVC was tested before and immediately after an acute loading exclusively during their training times before and after the training period. Before acute loadings, resting blood samples were drawn and analysed for plasma testosterone and cortisol. At each testing occasion, muscle biopsies from m. vastus lateralis were obtained before and 60 min after the acute loading. Muscle specimens were analysed for muscle fibre cross-sectional areas (CSA) and for phosphorylated p70S6K, rpS6, p38MAPK, Erk1/2, and eEF2. In addition, the right quadriceps femoris was scanned with MRI before and after the training period. The control group underwent the same testing, except for MRI, between 11:00 h and 13:00 h but did not train. Voluntary muscle strength increased significantly in both the morning and afternoon training group by 16.9% and 15.2 %, respectively. Also muscle hypertrophy occurred by 8.8% and 11.9% (MRI, p < 0.001) and at muscle fibre CSA level by 21% and 18% (p < 0.01) in the morning and afternoon group, respectively. No significant changes were found in controls within these parameters. Both pre- and post-training acute loadings induced a significant (p < 0.001) reduction in muscle strength in all groups, not affected by time of day or training. The post-loading phosphorylation of p70S6Thr421/Ser424 increased independent of the time of day in the pre-training condition, whereas it was significantly increased in the morning group only after the training period (p < 0.05). Phosphorylation of rpS6 and p38MAPK increased acutely both before and after training in a time-of-day independent manner (p < 0.05 at all occasions). Phosphorylation of p70S6Thr389, eEF2 and Erk1/2 did not change at any time point. No statistically significant correlations were found between changes in muscle fibre CSA, MRI and cell signalling data. Resting testosterone was not statistically different among groups at any time point. Resting cortisol declined significantly from pre- to post-training in all three groups (p < 0.05). In conclusion, similar levels of muscle strength and hypertrophy could be achieved regardless of time of the day in previously untrained men. However, at the level of skeletal muscle signalling, the extent of adaptation in some parameters may be time of day dependent.peerReviewe