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Martin Buchheit, Yannick Cholley and Philippe Lambert

Purpose:

To examine in elite soccer players after traveling across 6 time zones some psychometric and physiological responses to a competitive camp in the heat.

Methods:

Data from 12 elite professional players (24.6 ± 5.3 y) were analyzed. They participated in an 8-d preseason summer training camp in Asia (heat index 34.9°C ± 2.4°C). Players’ activity was collected during all training sessions and the friendly game using 15-Hz GPS. Perceived training/playing load was estimated using session rating of perceived exertion (RPE) and training/match duration. Psychometric measures of wellness were collected on awakening before, during, and after the camp using simple questionnaires. Heart-rate (HR) response to a submaximal 4-min run (12 km/h) and the ratio between velocity and force-load (accelerometer-derived measure, a marker of neuromuscular efficiency) response to four ~60-m runs (22–24 km/h) were collected before, at the end of, and after the camp.

Results:

After a large increase, the RPE:m/min ratio decreased substantially throughout the camp. There were possible small increases in perceived fatigue and small decreases in subjective sleep quality on the 6th day. There were also likely moderate (~3%) decreases in HR response to the submaximal run, both at the end of and after the camp, which were contemporary to possible small (~8%) and most likely moderate (~19%) improvements in neuromuscular efficiency, respectively.

Conclusions:

Despite transient increases in fatigue and reduced subjective sleep quality by the end of the camp, these elite players showed clear signs of heat acclimatization that were associated with improved cardiovascular fitness and neuromuscular running efficiency.

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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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Martin Buchheit, Yannick Cholley, Mark Nagel and Nicholas Poulos

Purpose:

To examine the effect of body mass (BM) on eccentric knee-flexor strength using the Nordbord and offer simple guidelines to control for the effect of BM on knee-flexor strength.

Methods:

Data from 81 soccer players (U17, U19, U21, senior 4th French division, and professionals) and 41 Australian Football League (AFL) players were used for analysis. They all performed 1 set of 3 maximal repetitions of the bilateral Nordic hamstring exercise, with the greatest strength measure used for analysis. The main regression equation obtained from the overall sample was used to predict eccentric knee-flexor strength from a given BM (moderate TEE, 22%). Individual deviations from the BM-predicted score were used as a BM-free index of eccentric knee- flexor strength.

Results:

There was a large (r = .55, 90% confidence limits .42;.64) correlation between eccentric knee-flexor strength and BM. Heavier and older players (professionals, 4th French division, and AFL) outperformed their lighter and younger (U17–U21) counterparts, with the soccer professionals presenting the highest absolute strength. Professional soccer players were the only ones to show strength values likely slightly greater than those expected for their BM.

Conclusions:

Eccentric knee-flexor strength, as assessed with the Nordbord, is largely BM-dependent. To control for this effect, practitioners may compare actual test performances with the expected strength for a given BM, using the following predictive equation: Eccentric strength (N) = 4 × BM (kg) + 26.1. Professional soccer players with specific knee-flexor-training history and enhanced neuromuscular performance may show higher than expected values.

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Mathieu Lacome, Ben M. Simpson, Yannick Cholley and Martin Buchheit

Purpose: To (1) compare the locomotor and heart rate responses between floaters and regular players during both small and large small-sided games (SSGs) and (2) examine whether the type of game (ie, game simulation [GS] vs possession game [PO]) affects the magnitude of the difference between floaters and regular players. Methods: Data were collected in 41 players belonging to an elite French football team during 3 consecutive seasons (2014–2017). A 5-Hz global positionning system was used to collect all training data, with the Athletic Data Innovation analyzer (v5.4.1.514) used to derive total distance (m), high-speed distance (>14.4 km·h−1, m), and external mechanical load (MechL, a.u.). All SSGs included exclusively 1 floater and were divided into 2 main categories, according to the participation of goalkeepers (GS) or not (PO) and then further divided into small and large (>100 m2per player) SSGs based on the area per player ratio. Results: Locomotor activity and MechL performed were likely-to-most likely lower (moderate to large magnitude) in floaters compared with regular players, whereas differences in heart rate responses were unclear to possibly higher (small) in floaters. The magnitude of the difference in locomotor activity and MechL between floaters and regular players was substantially greater during GS compared with PO. Conclusions: Compared with regular players, floaters present decreased external load (both locomotor and MechL) despite unclear to possibly slightly higher heart rate responses during SSGs. Moreover, the responses of floaters compared with regular players are not consistent across different sizes of SSGs, with greater differences during GS than PO.

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Mathieu Lacome, Ben M. Simpson, Yannick Cholley, Philippe Lambert and Martin Buchheit

Purpose: To compare the peak intensity of typical small-sided games (SSGs) with those of official matches in terms of running demands and mechanical work (MechW) over different rolling average durations and playing positions. Methods: Data were collected in 21 players (25 [5] y, 181 [7] cm, and 77 [7] kg) belonging to an elite French football team. SSG data were collected over 2 seasons during typical training sessions (249 files, 12 [4] per player) and official matches (n = 12). Players’ locomotor activity was recorded using 5-Hz Global Positioning System. Total distance (m), high-speed distance (HS, distance above 14.4 km·h−1, m), and MechW (a.u.) were analyzed during different rolling average periods (1–15 min). The SSGs examined were 4v4+goalkeepers (GKs), 6v6+GKs, 8v8+GKs, and 10v10+GKs. Results: Peak total distance and HS during 4v4, 6v6, and 8v8 were likely-to-most likely lower than during matches (effect size: −0.59 [±0.38] to −7.36 [±1.20]). MechW during 4v4 was likely-to-most likely higher than during matches (1–4 min; 0.61 [±0.77] to 2.30 [±0.64]). Relative to their match demands, central defenders performed more HS than other positions (0.63 [±0.81] to 1.61 [±0.52]) during 6v6. Similarly, central midfielders performed less MechW than the other positions during 6v6 (0.68 [±0.72] to 1.34 [±0.99]) and 8v8 (0.73 [±0.50] to 1.39 [±0.32]). Conclusion: Peak locomotor intensity can be modulated during SSGs of various formats and durations to either overload or underload match demands, with 4v4 placing the greatest and the least emphasis on MechW and HS, respectively. Additionally, in relation to match demands central defenders and central midfielders tend to be the most and least overloaded during SSGs, respectively.

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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.