No abstract

The aim of this study was to analyze fatigue occurrence during the repetition of rugby union specific tasks. Eight high-level rugby players (age 23 ± 1.1 y; body mass 90.9 ± 9.8 kg; height 1.83 ± 7.3m) performed three sessions, in a random order, to investigate specific rugby union tasks (Scrum, Maul and Running sprints). Each session consisted in 5 repetitions of 5-s maximal exertion interspersed with 20-s passive recoveries. The scrums were performed into a fixed yoke, while the mauls were realized into a moving yoke. Forces were recorded during the scrums and speeds were monitored during both mauls and sprints. Performance decrease was calculated and complemented by EMG recordings of the vastus lateralis, blood lactate accumulation and rating of perceived exertion (RPE) were also obtained. The repetition of Scrums, Mauls and Sprints induced a decrease in the performance of respectively 23.3 ± 5.3%, 12.6 ± 2.5 % and 7.3 ± 0.9 %. The EMG level decreased only after Scrums and Mauls (respectively 20.8 ± 3.2 % and 12.6 ± 2.5 %; p < 0.0001) while blood lactate accumulation was significantly higher for Sprints (9.2 ± 1.1 mmol. L−1; p = 0.0061) and Maul (8.8 ± 0.8 mmol. L−1; p = 0.0028) compared to Scrum (2.9 ± 1.2 mmol. L−1). Average RPE was higher during the repetition of Scrums (7.8 ± 0.6) compared to Mauls (7.2 ± 0.6; p = 0.0086) and Sprints (7.1 ± 0.5; p = 0.001). The repetition of scrums led to a greater fatigue linked to activation perturbation while during sprints the fatigue was lower and associated with a great metabolic activity. The mauling task showed intermediate characteristics: the fatigue was moderate and both EMG losses and lactate accumulation were substantial. This confirms that conditioning, testing and substitutions should differ according to the players' position in modern rugby.

No abstract

Rapid force production is critical to improve performance and prevent injuries. However, changes in rate of force/torque development caused by the repetition of maximal contractions have received little attention. The aim of this study was to determine the relative influence of rate of torque development (RTD) and peak torque (Tpeak) on the overall performance (i.e. mean torque, Tmean) decrease during repeated maximal contractions and to investigate the contribution of contractile and neural mechanisms to the alteration of the various mechanical variables. Eleven well-trained men performed 20 sets of 6-s isokinetic maximal knee extensions at 240°·s-1, beginning every 30 seconds. RTD, Tpeak and Tmean as well as the Rate of EMG Rise (RER), peak EMG (EMGpeak) and mean EMG (EMGmean) of the vastus lateralis were monitored for each contraction. A wavelet transform was also performed on raw EMG signal for instant mean frequency (ifmean) calculation. A neuromuscular testing procedure was carried out before and immediately after the fatiguing protocol including evoked RTD (eRTD) and maximal evoked torque (eTpeak) induced by high frequency doublet (100 Hz). Tmean decrease was correlated to RTD and Tpeak decrease (R²=0.62; p<0.001; respectively β=0.62 and β=0.19). RER, eRTD and initial ifmean (0-225 ms) decreased after 20 sets (respectively -21.1±14.1, -25±13%, and ~20%). RTD decrease was correlated to RER decrease (R²=0.36; p<0.05). The eTpeak decreased significantly after 20 sets (24±5%; p<0.05) contrary to EMGpeak (-3.2±19.5 %; p=0.71). Our results show that reductions of RTD explained part of the alterations of the overall performance during repeated moderate velocity maximal exercise. The reductions of RTD were associated to an impairment of the ability of the central nervous system to maximally activate the muscle in the first milliseconds of the contraction.

The aim of this study was to evaluate the influence of the fatigue on the machine scrum pushing sagittal forces during repeated scrums and to determine the origin of the knee extensor fatigue. Twelve elite U23 rugby union front row players performed six 6-s scrums every 30 s against a dynamic scrum machine with passive or active recovery. The peak, average, and the standard deviation of the force were measured. A neuromuscular testing procedure of the knee extensors was carried out before and immediately after the repeated scrum protocol including maximal voluntary force, evoked force, and voluntary activation. The average and peak forces did not decrease after six scrums with passive recovery. The standard deviation of the force increased by 70.2 ± 42.7% (P < 0.001). Maximal voluntary/evoked force and voluntary activation decreased (respectively 25.1 ± 7.0%, 14.6 ± 5.5%, and 24 ± 9.9%; P < 0.001). The standard deviation of the force did not increase with active recovery and was associated with lower decrease of maximal voluntary/evoked force and voluntary activation (respectively 12.8 ± 7.9%, 4.9 ± 6.5%, and 7.6 ± 4.1%; all P < 0.01). As a conclusion repeated scrummaging induced an increased machine scrum pushing instability associated with central and peripheral fatigue of the knee extensors. Active recovery seems to limit all these manifestations of fatigue.