Purpose: To investigate the strengths and limitations of different indicators to measure physical load. Furthermore, indicators were evaluated for discrimination between performance levels and playing positions. Methods: Ninety positional match files from 70 elite players and 91 match files from 69 sub-elite players were collected during 14 official under-18 matches using a local position measurement system. Indicators are calculated from either speed, absolute acceleration (acc-abs), or percentage acceleration (acc-%). The acc-% describes the level of acceleration depending on the maximal voluntary acceleration (amax) for each initial running speed. Effect sizes (ES) were used to determine discriminative ability. Results: The number of high accelerations largely depended on the method (absolute threshold [>3 m·s−2 and >4 m·s−2]: 120 and 59 efforts; high percentage threshold [>75% amax]: 84 efforts). Only a small number of highly accelerated efforts reached speeds considered as high-speed running (>19.8 km·h−1: 32.6%). More high acc-% exist from initial running speed >2 m·s−1 (23.0) compared with acc-abs (>3 m·s−2: 14.4; >4m·s−2: 5.9). Elite players achieve higher values in most performance indicators, with ES being highest for the number of high acc-% (ES = 0.91) and high acc-abs (>3m·s−2: ES = 0.86; >4m·s−2: ES = 0.87), as well as for covered distance in jogging (ES = 0.94). Conclusions: Estimated physical load, discriminative ability of physical indicators, and positional requirements largely depend on the applied method. A combination of speed-based and acc-% methods is recommended to get a comprehensive view.
PURPOSE: There are several approaches to quantifying physical load in team sports using positional data. Distances in different speed zones are most commonly used. Recent studies have used acceleration data in addition in order to take short intense actions into account. However, the fact that acceleration decreases with increasing initial running speed is ignored and therefore introduces a bias. The aim of our study was to develop a new methodological approach that removes this bias. For this purpose, percentage acceleration was calculated as the ratio of the maximal acceleration of the action (amax,action) and the maximal voluntary acceleration (amax) that can be achieved for a particular initial running speed (percentage acceleration [%] = amax,action / amax * 100). METHODS: To define amax, seventy-two highly trained junior male soccer players (17.1 +/- 0.6 years) completed maximal sprints from standing and three different constant initial running speeds (vinit; trotting: ~6.0 km.h-1; jogging: ~10.8 km.h-1; running: ~15.0 km.h-1). RESULTS: The amax was 6.01 +/- 0.55 from a standing start, 4.33 +/- 0.40 from trotting, 3.20 +/- 0.49 from jogging and 2.29 +/- 0.34 m.s-2 from running. The amax correlated significantly with vinit (r = -0.98) and the linear regression equation of highly-trained junior soccer players was: amax = -0.23 * vinit + 5.99. CONCLUSION: Using linear regression analysis, we propose to classify high-intensity actions as accelerations >75% of the amax, corresponding to acceleration values for our population of >4.51 initiated from standing, >3.25 from trotting, >2.40 from jogging, and >1.72 m.s-2 from running. The use of percentage acceleration avoids the bias of underestimating actions with high and overestimating actions with low initial running speed. Furthermore, percentage acceleration allows determining individual intensity thresholds that are specific for one population or one single player.
Zusammenfassung Die Bedeutung der Explosivkraft als Leistungsvoraussetzung fur schnelle, azyklische und zyklische Bewegungen in vielen Sportarten nimmt zu. Die Leistungsdiagnostik als Teil der Leistungs- und Trainingssteuerung benotigt als Grundlage fur die Trainingsempfehlungen Kenngrossen oder Normwerte. Einzelne Diagnostik-Verfahren werden zunehmend bereits im Junioren- oder Nachwuchsbereich eingesetzt. Es bestand daher die Absicht, das Explosivkraftniveau der unteren Extremitaten von Schweizer Nachwuchsathleten aus verschiedenen Sportarten und verschiedenen Altersklassen zu ermitteln. 1518 Athleten (870 mannlich und 648 weiblich) aus 21 verschiedenen Sportarten (18 mannlich und 17 weiblich) in den Altersklassen bis 12, 14, 16, 18 und 20 Jahre absolvierten in einer Trainingslagerwoche beim ≪Talenttreff in Tenero (3T)≫ einen Sprungkrafttest (bestehend aus Countermovementjump [CMJ], Squatjump und einbeinigen Sprungen links und rechts) auf Kraftmessplatten. Dabei wurde die relative maximale mechanische Leistung (Pmax) und die Sprunghohe gemessen, sowie das bilaterale Defizit errechnet. Aufgeteilt nach Sportart, Geschlecht und Altersklasse wurden fur diese Parameter Mittelwerte und Standardabweichungen umfangreich dokumentiert. Die Grosse der Explosivkraftwerte im Nachwuchsbereich schwankte erwartungsgemass nach dem jeweiligen Anforderungsprofil der Sportart und nach der Altersklasse beim CMJ-Mittelwert Pmax zwischen 38.9 W/kg (Badminton U12) bis 66.6 W/kg (LA-Sprint U18) bei den Jungen und zwischen 35.3 W/kg (Squash U14) bis 55.2 W/kg (LA-Sprint U16) bei den Madchen. Bei den 12-jahrigen ist das Explosivkraftniveau der unteren Extremiaten zwischen Jungen und Madchen praktisch identisch. Danach entwickeln sich Jungen immer besser bis zu einer Differenz von ca. 17% ab dem 18. Lebensjahr. Als Referenz fur die Normierung der Explosivkraftmessungen der unteren Extremitaten ist diese Dokumentation aus 21 sportartspezifischen Kadermittelwerten im Altersbereich zwischen 12 und 20 Jahren sicher geeignet. Diese bilden dann eine Basis fur eine sportgerechte individuelle Beratung.
