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Martin Buchheit and Ben Michael Simpson

With the ongoing development of microtechnology, player tracking has become one of the most important components of load monitoring in team sports. The 3 main objectives of player tracking are better understanding of practice (provide an objective, a posteriori evaluation of external load and locomotor demands of any given session or match), optimization of training-load patterns at the team level, and decision making on individual players’ training programs to improve performance and prevent injuries (eg, top-up training vs unloading sequences, return to play progression). This paper discusses the basics of a simple tracking approach and the need to integrate multiple systems. The limitations of some of the most used variables in the field (including metabolic-power measures) are debated, and innovative and potentially new powerful variables are presented. The foundations of a successful player-monitoring system are probably laid on the pitch first, in the way practitioners collect their own tracking data, given the limitations of each variable, and how they report and use all this information, rather than in the technology and the variables per se. Overall, the decision to use any tracking technology or new variable should always be considered with a cost/benefit approach (ie, cost, ease of use, portability, manpower/ability to affect the training program).

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Martin Buchheit, Mathieu Lacome, Yannick Cholley and Ben Michael Simpson

Purpose: To examine the reliability of field-based running-specific measures of neuromuscular function assessed using global positioning system (GPS)–embedded accelerometers and their responses to 3 typical conditioned sessions (ie, strength, endurance, and speed) in elite soccer players. Methods: Before and immediately after each session, vertical jump (countermovement jump [CMJ]) and adductor squeeze strength (groin) performances were recorded. Players also performed a 4-min run at 12 km/h followed by four ∼60-m runs (run = 12 s, r = 33 s). GPS (5 Hz) and accelerometer (100 Hz) data collected during the 4 runs and the recovery periods, excluding the last recovery period, were used to derive vertical stiffness (K), peak loading force (peak force over all the foot strikes [F peak]), and propulsion efficiency (ie, the ratio between velocity and force loads [Vl/Fl]). Results: Typical errors were small (CMJ, groin, K, and Vl/Fl) and moderate (F peak), with moderate (F peak), high (K and Vl/Fl), and very high ICCs (CMJ and groin). After all sessions, there were small decreases in groin and increases in K, but changes in F were all unclear. By contrast, the CMJ and Vl/Fl ratio responses were session dependent. There was a small increase in CMJ after speed and endurance, but unclear changes after strength; the Vl/Fl ratio increased substantially after strength, but there were a small and a moderate decrease after endurance and speed, respectively. Conclusions: Running-specific measures of neuromuscular function assessed in the field via GPS-embedded accelerometers show acceptable levels of reliability. Although the 3 sessions examined may be associated with limited neuromuscular fatigue, changes in neuromuscular performance and propulsion efficiency are likely session-objective dependent.

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Mathieu Lacome, Simon Avrillon, Yannick Cholley, Ben Michael Simpson, Gael Guilhem and Martin Buchheit

Aim:

To compare the effect of low- vs. high-volume of eccentric-biased hamstring training programs on knee-flexor strength and fascicle length changes in elite soccer players.

Methods:

Nineteen elite youth soccer players took part in this study and were randomly assigned into two subgroups. For 6 weeks in-season, groups performed either a low (1 set per exercise; 10 reps in total) or a high (4 sets; 40 reps) volume eccentric training of their knee flexors. After 6 weeks (MID), players cross-overed and performed the alternate training regimen. Each training set consisted in 4 repetitions of the Nordic hamstring exercise and 6 repetitions of the bilateral stiff-leg deadlift. Eccentric knee-flexor strength (Nordbord) as well as biceps femoris long head (BFlh) and semimembranosus (SM) fascicle length (scanned with ultrasound scanner) were assessed during PRE, MID- and POST-training tests.

Results:

Knee-flexor eccentric strength very likely increased from PRE to MID (+11.3±7.8% [low-volume] and 11.4±5.3% [high-volume]), with a possibly-to-likely increase in BFlh (+4.5±5.0% and 4.8±2.5%) and SM (+4.3±4.7% and 6.3±6.3%) fascicle length in both groups. There was no substantial changes between MID and POST. Overall, there was no clear between-group difference in the changes from PRE to MID and MID to POST for neither knee-flexor eccentric strength, BFlH nor SM fascicle length.

Conclusion:

Low-volume knee-flexor eccentric training is as effective as a greater training dose to substantially improve knee-flexor strength and fascicle length in-season in young elite soccer players. Low-volume is however likely more appropriate to be used in an elite team facing congested schedules.