Fatigue Induced by Repeated Maximal Efforts is Specific to the Rugby Task Performed

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.

The neuromuscular fatigue induced by repeated scrums generates instability that can be limited by appropriate recovery

“…To our knowledge no previous study focused on the influence of fatigue on the engagement phase. However, considering the average force, the present results are not in accordance with those of Morel et al (2015) which showed a decrease after five scrums. This discrepancy could be attributed to the different scrum conditions used.…”

“…These two parameters indicate a strong neural drive reduction (i.e., central fatigue) which confirmed the scrummaging‐induce‐central‐fatigue hypothesis previously made by Morel et al. (). Furthermore, the 12.6 ± 5.5% erector spinae electromyographic signal decrease suggested that the central motor drive may be impaired in other critical muscle groups when scrummaging.…”

“…However, although the scrum biomechanics has been well studied these last years under machine (Preatoni et al., ; Sharp et al., ) and live scrummaging condition (Du Toit et al., ; Cazzola et al., ), the influence of fatigue on scrums has received little attention (Hamilton et al., ). One recent study showed that the repetition of scrums induces a great force production loss (>20%) associated with a great decrease of the EMG signal of the knee extensors (Morel et al., ). This study also evidenced that the fatigue experimented during repeated scrums differs from the far more studied fatigue experimented during repeated sprints in terms of amplitude (i.e., greater) and origin (i.e., EMG decrease vs metabolic perturbations).…”

“…This highlights the importance to study the specific scrummaging task. The reported EMG signal decrease during scrummaging may be related to the maximal isometric contractions performed in this condition as this contraction mode is known to induce early and great central fatigue (Babault et al, 2006;Morel et al, 2015). Considering that central fatigue may alter intermuscular coordination (Cortes et al, 2013) and increase the injury risk (McLean & Samorezov, 2009), the origin of fatigue during scrums needs to be explored with the gold standard superimposed twitch technique.…”

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“…A reduction in muscle contractility and a decline in voluntary activation of the vastus lateralis has been purported and that both peripheral and central mechanisms may be responsible for scrummaging fatigue [14]. However, previous studies have only examined one or two muscles [13,14] and the activation levels of other muscles during scrummaging in front row forwards warrant further investigation [4,13,14,20]. Furthermore, the assessment of lower limb and 'core' muscles, (gluteus maximus, gastrocnemius, and the abdominal complex) have been inadequately examined and little is known…”