Valter Di Salvo

Match-to-Match Variability of High-Speed Activities in Premier League Soccer

The aim of the present investigation was to determine the between-match variability of high-speed running activities completed by a large sample of elite players over an extended period of time. A further aim of the study was to determine the influence of playing position on the magnitude of this variability. Observations on individual match performance measures were undertaken on 485 outfield players (median of 10 games per player; range=2-57) competing in the English Premier League from 2003/2004 to 2005/2006 using a computerised tracking system (Prozone, Leeds, England). High-speed activities selected for analysis included total high-speed running distance (THSR), high-speed running (HSR), total sprint distance (TSD) and the total number of sprints undertaken. Total high-speed running distance in possession and without possession of the ball was also analysed. Match-to-match variability was generally high across all variables with a mean CV of 16.2+/-6.4% (95% CI=15.6-16.7%) and 30.8+/-11.2% (95% CI=29.9-31.7%) reported for HSR and TSD covered during a game. This variability was generally higher for central players (midfielders and defenders) and lower for wide midfielders and attackers. Greater variability was also noted when the team were in possession of the ball (approximately 30%) than when they did not have possession (approximately 23%). The findings of the present study indicate that match-to-match variability in performance characteristics of elite soccer players is high. This inherent variability means that research requires large sample sizes in order to detect real systematic changes in performance characteristics.

The effects of a whole-body vibration program on muscle performance and flexibility in female athletes

Fagnani F, Giombini A, Di Cesare A, Pigozzi F, Di Salvo V: The effects of a whole-body vibration program on muscle performance and flexibility in female athletes. Am J Phys Med Rehabil 2006;85:956–962. Objective:This randomized controlled study was designed to investigate the short-term effects of an 8-wk whole-body vibration protocol on muscle performance and flexibility in female competitive athletes. Design:Twenty-six young volunteer female athletes (ages 21–27 yrs) were randomized to either the vibration group or control group. The vibration intervention consisted of an 8-wk whole-body vibration 3 times a week employed by standing on a vertical vibration platform. As outcome measures, three performance tests (counter-movement jump, extension strength of lower extremities with an isokinetic horizontal leg press, and a sit-and-reach test for flexibility) were performed initially and after 8 wks. Results:A total of 24 athletes completed the study properly. In the vibration group (n = 13) whole-body vibration induced significant improvement of bilateral knee extensor strength (P < 0.001), counter-movements jump (P < 0.001), and flexibility (P < 0.001) after 8 wks of training. No significant changes were found for all the outcome measures for the control group (n = 11). Conclusions:Whole-body vibration is a suitable training method to improve knee extension maximal strength, counter-movement jump, and flexibility in a young female athlete if it is properly designed. Not only do the optimal frequency, amplitude, and g-forces need to be identified but also the level of muscle activation that would benefit more from vibration stimulation. The improvement of flexibility is important not only for performance but also for the prevention of muscle-tendon injury.

Sprinting analysis of elite soccer players during European Champions League and UEFA Cup matches

Abstract It has been suggested that assessment of high-intensity activities during a match is a valid measure of physical performance in elite soccer. Recently, sprinting activities have been analysed in more depth. The aim of this study was to develop a detailed analysis of the sprinting activities of different playing positions during European Champions League and UEFA Cup competitions. Altogether, 717 elite outfield soccer players were evaluated throughout 2002–2006 using ProZone® (Leeds, UK). Sprinting (explosive and leading) was analysed for each playing position. To compare positional differences, a Kruskal-Wallis analysis was performed. Differences were found among positions for total number of sprints and total sprint distance covered: wide midfielders > (attackers = wide defenders) > central midfielders > central defenders (P < 0.001), as well as for explosive sprints: (wide midfielders = attackers = wide defenders) > central defenders, wide midfielders > central midfielders > central defenders and attackers = wide defenders = central midfielders (P < 0.001), and leading sprints: wide midfielders > (attackers = wide defenders) > central midfielders > central defenders (P < 0.001). For each group, there were no differences in ratio of explosive to leading sprints. Wide midfielders performed a higher number of sprints in all five distance categories than all other positions. This study showed that sprinting characteristics are influenced by position. Wide midfielders have to complete additional high-intensity activities during training sessions compared with the other positions to achieve the performance level required during the match.

Monitoring Accelerations With GPS in Football: Time to Slow Down?

The aims of the current study were to examine the magnitude of between-GPS-models differences in commonly reported running-based measures in football, examine between-units variability, and assess the effect of software updates on these measures. Fifty identical-brand GPS units (15 SPI-proX and 35 SPIproX2, 15 Hz, GPSports, Canberra, Australia) were attached to a custom-made plastic sled towed by a player performing simulated match running activities. GPS data collected during training sessions over 4 wk from 4 professional football players (N = 53 files) were also analyzed before and after 2 manufacturer-supplied software updates. There were substantial differences between the different models (eg, standardized difference for the number of acceleration >4 m/s2 = 2.1; 90% confidence limits [1.4, 2.7], with 100% chance of a true difference). Between-units variations ranged from 1% (maximal speed) to 56% (number of deceleration >4 m/s2). Some GPS units measured 2-6 times more acceleration/deceleration occurrences than others. Software updates did not substantially affect the distance covered at different speeds or peak speed reached, but 1 of the updates led to large and small decreases in the occurrence of accelerations (-1.24; -1.32, -1.15) and decelerations (-0.45; -0.48, -0.41), respectively. Practitioners are advised to apply care when comparing data collected with different models or units or when updating their software. The metrics of accelerations and decelerations show the most variability in GPS monitoring and must be interpreted cautiously.

Integrating different tracking systems in football: multiple camera semi-automatic system, local position measurement and GPS technologies

Abstract During the past decade substantial development of computer-aided tracking technology has occurred. Therefore, we aimed to provide calibration equations to allow the interchangeability of different tracking technologies used in soccer. Eighty-two highly trained soccer players (U14–U17) were monitored during training and one match. Player activity was collected simultaneously with a semi-automatic multiple-camera (Prozone), local position measurement (LPM) technology (Inmotio) and two global positioning systems (GPSports and VX). Data were analysed with respect to three different field dimensions (small, <30 m2 to full-pitch, match). Variables provided by the systems were compared, and calibration equations (linear regression models) between each system were calculated for each field dimension. Most metrics differed between the 4 systems with the magnitude of the differences dependant on both pitch size and the variable of interest. Trivial-to-small between-system differences in total distance were noted. However, high-intensity running distance (>14.4 km · h−1) was slightly-to-moderately greater when tracked with Prozone, and accelerations, small-to-very largely greater with LPM. For most of the equations, the typical error of the estimate was of a moderate magnitude. Interchangeability of the different tracking systems is possible with the provided equations, but care is required given their moderate typical error of the estimate.

Peak Match Speed and Maximal Sprinting Speed in Young Soccer Players: Effect of Age and Playing Position

This study assessed the relationship between peak match speed (PMS) and maximal sprinting speed (MSS) in regard to age and playing positions. MSS and absolute PMS (PMSAbs) were collected from 180 male youth soccer players (U13-U17, 15.0 ± 1.2 y, 161.5 ± 9.2 cm, and 48.3 ± 8.7 kg). The fastest 10-m split over a 40-m sprint was used to determine MSS. PMSAbs was recorded using a global positioning system and was also expressed as a percentage of MSS (PMSRel). Sprint data were compared between age groups and between playing positions. Results showed that regardless of age and playing positions, faster players were likely to reach higher PMSAbs and possibly lower PMSRel. Despite a lower PMSAbs than in older groups (eg, 23.4 ± 1.8 vs 26.8 ± 1.9 km/h for U13 and U17, respectively, ES = 1.9 90%, confidence limits [1.6;2.1]), younger players reached a greater PMSRel (92.0% ± 6.3% vs. 87.2% ± 5.7% for U13 and U17, respectively, ES = -0.8 90% CL [-1.0;-0.5]). Playing position also affected PMSAbs and PMSRel, as strikers were likely to reach higher PMSAbs (eg, 27.0 ± 2.7 vs 23.6 ± 2.2 km/h for strikers and central midfielders, respectively, ES = 2.0 [1.7;2.2]) and PMSRel (eg, 93.6% ± 5.2% vs 85.3% ± 6.5% for strikers and central midfielders, respectively, ES = 1.0 [0.7;1.3]) than all other positions. The findings confirm that age and playing position affect the absolute and relative intensity of speed-related actions during matches.

MRI-Based Regional Muscle Use during Hamstring Strengthening Exercises in Elite Soccer Players.

The present study examined site-specific hamstring muscles use with functional magnetic resonance imaging (MRI) in elite soccer players during strength training. Thirty-six players were randomized into four groups, each performing either Nordic hamstring, flywheel leg-curl, Russian belt or the hip-extension conic-pulley exercise. The transverse relaxation time (T2) shift from pre- to post-MRI were calculated for the biceps femoris long (BFl) and short (BFs) heads, semitendinosus (ST) and semimembranosus (SM) muscles at proximal, middle and distal areas of the muscle length. T2 values increased substantially after flywheel leg-curl in all regions of the BFl (from 9±8 to 16±8%), BFs (41±6–71±11%), and ST (60±1–69±7%). Nordic hamstring induced a substantial T2 increase in all regions of the BFs (13±8–16±5%) and ST (15±7–17±5%). T2 values after the Russian belt deadlift substantially increased in all regions of the BFl (6±4–7±5%), ST (8±3–11±2%), SM (6±4–10±4%), and proximal and distal regions of BFs (6±6–8±5%). T2 values substantially increased after hip-extension conic-pulley only in proximal and middle regions of BFl (11±5–7±5%) and ST (7±3–12±4%). The relevance of such MRI-based inter- and intra-muscle use in designing more effective resistance training for improving hamstring function and preventing hamstring injuries in elite soccer players should be explored with more mechanistic studies.

Effects of tapering on physical match activities in professional soccer players

ABSTRACT This study aimed to examine: (i) the effect of decreasing training load (TL) during taper weeks on physical match activities in professional soccer players, and (ii) to disclose the relationship between weekly TL and physical match activities. Rating of perceived exertion was collected after each training session and match to quantify the TL in 19 professional players over 17 standard and 7 taper weeks during the season. Physical match activities were quantified by a computerised match analysis system and compared between standard training and taper weeks. Compared to standard weeks, the duration and frequency of training sessions during the taper weeks decreased (−21.7% and −18.8%, respectively; P < 0.01) with no change in intensity (−4.8%; P = 0.09). Consequently, the weekly TL decreased during the taper weeks (−25.5%; P < 0.01). Increases in distance covered by intense running (+15.1%; P < 0.05), high-intensity running (HIR) (+15.7%; P < 0.01), number of sprints (+17.8%; P < 0.05) and number of high-speed runs (+15.7%; P < 0.05) were observed during the seven matches played after the taper weeks. High relationships were observed between TL and HIR distance covered, number of HIR and number of sprints (r = −0.53; r = −0.55; r = −0.65, respectively; P < 0.01). Decreasing TL during taper weeks by reducing training duration and frequency but maintaining intensity was associated with an increase in physical activities during matches. However, it needs to be determined whether tapering or other match factors led to the changes in match activity.

Physical and technical performance of elite youth soccer players during international tournaments: influence of playing position and team success and opponent quality

ABSTRACT This study investigated the positional differences in physical performance of elite youth footballers in a tournament scenario and the influence of team success and opponent quality on team physical and technical performance. Match performance observations were collected using a semi-automated multi-camera tracking system across 2 elite under-17 international club tournaments from all players and teams (n = 1,457 individual cases). Teams were classified based on their final tournament ranking as top (1–4 ranking), middle (5–8 ranking) and bottom (9–12 ranking). Technical performance measures were expressed in absolute terms and relative to the time the team was in ball possession. Positional differences in physical performance and the influence of team success and opponent quality on team match performance were identified using a generalised linear mixed model. Positional differences were similar to that observed in elite senior players. Top ranking teams performed a greater number of absolute and relative shots and shots on target than bottom teams (effect size = 0.67–0.82). Top ranking teams performed a greater number of relative tackles than bottom and middle teams (ES; 0.44 –0.70). When playing against top ranking opponents the number of absolute shots and shots on target, shot conversion and passing accuracy were lowest compared with playing against middle and bottom opponents (ES; −0.86 to −0.31). In an elite youth tournament setting, opponent quality and team success can influence match performance. These contextual factors should be considered when analysing match performance and used to inform team tactics, selection and substitution strategies.

Body fat assessment in elite soccer players: cross-validation of different field methods

ABSTRACT Objective: In soccer players, body fat mass (FM) is commonly estimated by assessment methods such as skinfolds, bioelectrical impedance analysis (BIA) and dual-energy X-ray absorptiometry (DXA). The main aim was to cross-validate the 3 field methods for quantifying body fat against a recent model of DXA. Methods: This study involved a group of 18 international-level, elite male soccer players belonging to the squad of a Serie A club in Italy. Results: All skinfold equations (with the exception of Deuremberg) showed large-to-very large positive correlations (r from 0.61 to 0.82, p ≤ 0.01) with DXA, however, BIA %FM data showed unclear relationship. All the sum of skinfolds showed moderate-to-very large positive correlations with DXA (r from 0.46 to 0.79, p values from 0.061 to 0.000). The combination of triceps and iliac crest skinfolds selected by the stepwise procedure explained 78.6% variance in DXA total %FM. Conclusion: All different methods employed in the present study are likely to differ, which prevent their use interchangeably. Almost all the equations showed positive correlations, but with different values in comparison with a recent model of DXA. Finally, the sum of skinfolds appears to be a good alternative when limited time and budged is available.