Change of direction asymmetry across different age categories in youth soccer

Background In youth, the development of change of direction (COD) and sprint performance is a key component for successfully competing in soccer across age. During a COD, the presence of directional asymmetries may be detrimental due to the unpredictable nature of the sport. Therefore, the aims of the study were to investigate asymmetries in COD ability and to examine the differences in COD and sprint performance across age in young soccer players. Methods Sixty-eight sub-elite soccer players of different age categories (U18, U17, U16, U15) were tested on a 10-m linear sprint test and 90°COD (5-m entry and exit) test in both directions. Asymmetric index (AI) of COD deficit was obtained for dominant (fastest) and non-dominant directions (slowest). Results The results showed that U16 were more asymmetrical than U18, U17, and U15 from large to moderate effects. The sprint time improved linearly across age with U18 and U15 displaying the fastest and slowest 10-m sprint performance (p 0.05). Conclusion Given the results of this study, practitioners are encouraged to assess asymmetries between dominant and non-dominant directions rather than solely players’ COD ability in young soccer players

Factors influencing perception of effort (session rating of perceived exertion) during elite soccer training

Purpose: The aim of the current study was to identify the external-training-load markers that are most influential on session rating of perceived exertion (RPE) of training load (RPE-TL) during elite soccer training. Methods: Twenty-two elite players competing in the English Premier League were monitored. Training-load data (RPE and 10-Hz GPS integrated with a 100-Hz accelerometer) were collected during 1892 individual training sessions over an entire in-season competitive period. Expert knowledge and a collinearity r &lt; .5 were used initially to select the external training variables for the final analysis. A multivariate-adjusted within-subjects model was employed to quantify the correlations of RPE and RPE-TL (RPE × duration) with various measures of external training intensity and training load. Results: Total high-speed-running (HSR; &gt;14.4 km/h) distance and number of impacts and accelerations &gt;3 m/s2 remained in the final multivariate model (P &lt; .001). The adjusted correlations with RPE were r = .14, r = .09, and r = .25 for HSR, impacts, and accelerations, respectively. For RPE-TL, the correlations were r = .11, r = .45, and r = .37, respectively. Conclusions: The external-load measures that were found to be moderately predictive of RPE-TL in soccer training were HSR distance and the number of impacts and accelerations. These findings provide new evidence to support the use of RPE-TL as a global measure of training load in elite soccer. Furthermore, understanding the influence of characteristics affecting RPE-TL may help coaches and practitioners enhance training prescription and athlete monitoring.</p

The importance of GPS features to describe elite football training

Aim: The development of valid methods for assessing training-load is essential in football because extreme training responses may result in training maladaptation and injuries (Ehrmann et al., 2016). Thus, the aim of this study was to investigate GPS features importance to describe football training. Methods: Twenty-six elite football players (age=26\ub14yrs; BMI=24.01\ub10.86) competing in the Italian Serie B were monitored (23 weeks, 5 training per week). Training-load data were collected during 2080 individual training sessions using a portable non-differential 10Hz GPS integrated with 100Hz 3-D accelerometer, a 3-D gyroscope, a 3-D digital compass (STATSports Viper, Northern Ireland). Seven training-load indexes were recorded: total distance (m); High Speed Running Distance (distance(m) covered above 19.8Km/h); Metabolic Distance (distance(m) covered above 20W/Kg); High Metabolic Load Distance (distance(m) covered above 25.5W/Kg); Explosive Distance (distance(m) covered above 25.5W/Kg and below 19.8Km/h); Acceleration>2m/s2 (n); Deceleration>2m/s2 (n). The min-max standard scaler was applied in each features to standardize data of each player reducing the intra-individual differences. The feature importance percentage to describe the weekly training was based on extra random classifier (RFC). Precision and recall of the supervised cluster algorithm were provided to assess its ability to classify data correctly in accordance with the labelled training data. Results: RFC algorithm had precision and recall of 63% and 62% to predict weekly training, respectively. The features importance based on RFC algorithm showed the following rank: Metabolic distance (17.9%), Acceleration>2m/s2 (15.2%), total distance (14.7%), Deceleration>2m/s2 (14.4%), Explosive distance (13.6%), High Metabolic Load Distance (13.4%) and High Speed Running Distance (10.8%). Discussion: These results suggest that an index created using features with higher importance (Metabolic distance and Acceleration>2m/s2) could be used to characterize elite football training. Reference Ehrmann FE, Duncan CS, Sindhusake D, Franzsen WN, Greene DA (2016) GPS and Injury Prevention in Professional Soccer. J Strength Cond Res 30:360\u201336

Skeletal muscle and performance adaptations to high-intensity training in elite male soccer players: speed endurance runs versus small-sided game training.

PURPOSE: To examine the skeletal muscle and performance responses across two different exercise training modalities which are highly applied in soccer training. METHODS: Using an RCT design, 39 well-trained male soccer players were randomized into either a speed endurance training (SET; n = 21) or a small-sided game group (SSG; n = 18). Over 4 weeks, thrice weekly, SET performed 6-10 × 30-s all-out runs with 3-min recovery, while SSG completed 2 × 7-9-min small-sided games with 2-min recovery. Muscle biopsies were obtained from m. vastus lateralis pre and post intervention and were subsequently analysed for metabolic enzyme activity and muscle protein expression. Moreover, the Yo-Yo Intermittent Recovery level 2 test (Yo-Yo IR2) was performed. RESULTS: Muscle CS maximal activity increased (P < 0.05) by 18% in SET only, demonstrating larger (P < 0.05) improvement than SSG, while HAD activity increased (P < 0.05) by 24% in both groups. Na(+)-K(+) ATPase α1 subunit protein expression increased (P < 0.05) in SET and SSG (19 and 37%, respectively), while MCT4 protein expression rose (P < 0.05) by 30 and 61% in SET and SSG, respectively. SOD2 protein expression increased (P < 0.05) by 28 and 37% in SET and SSG, respectively, while GLUT-4 protein expression increased (P < 0.05) by 40% in SSG only. Finally, SET displayed 39% greater improvement (P < 0.05) in Yo-Yo IR2 performance than SSG. CONCLUSION: Speed endurance training improved muscle oxidative capacity and exercise performance more pronouncedly than small-sided game training, but comparable responses were in muscle ion transporters and antioxidative capacity in well-trained male soccer players

The Correlation between Running Economy and Maximal Oxygen Uptake: Cross-Sectional and Longitudinal Relationships in Highly Trained Distance Runners

A positive relationship between running economy and maximal oxygen uptake (V̇O2max) has been postulated in trained athletes, but previous evidence is equivocal and could have been confounded by statistical artefacts. Whether this relationship is preserved in response to running training (changes in running economy and V̇O2max) has yet to be explored. This study examined the relationships of (i) running economy and V̇O2max between runners, and (ii) the changes in running economy and V̇O2max that occur within runners in response to habitual training. 168 trained distance runners (males, n = 98, V̇O2max 73.0 ± 6.3 mLkg-1min-1; females, n = 70, V̇O2max 65.2 ± 5.9 mL kg-1min-1) performed a discontinuous submaximal running test to determine running economy (kcalkm-1). A continuous incre-mental treadmill running test to volitional exhaustion was used to determine V̇O2max 54 par-ticipants (males, n = 27; females, n = 27) also completed at least one follow up assessment. Partial correlation analysis revealed small positive relationships between running economy and V̇O2max (males r = 0.26, females r = 0.25; P&lt;0.006), in addition to moderate positive re-lationships between the changes in running economy and V̇O2max in response to habitual training (r = 0.35; P&lt;0.001). In conclusion, the current investigation demonstrates that only a small to moderate relationship exists between running economy and V̇O2max in highly trained distance runners. With&gt;85 % of the variance in these parameters unexplained by this relationship, these findings reaffirm that running economy and V̇O2max are primarily determined independently