Date of Submission

21-3-2018

Abstract

The activity profiles of team sports such as soccer incorporate high-intensity, intermittent running patterns combined with match specific actions. Performing these activities during competition results in acute and longer-term disruptions to homeostasis, which may be exacerbated during periods of fixture congestion. Better understanding of these responses may provide greater insight into the mechanisms and potential mitigating factors of team-sport fatigue. In turn, this could benefit athletes and practitioners by optimising player management and informing the training process. Therefore, the overall aim of this work was to describe the biological and perceptual responses to a single match, and to multiple team-sport matches within a given week. Assessing the within- and post-match responses to team-sport exercise is ideally completed following competitive matches. However, the proximity to laboratories and match contextual factors can limit experimental control. Match simulations aim to overcome these issues, but their ecological validity is questionable in current protocols. This issue stems from externally pacing participant effort, and from using motorised treadmills or tethered non-motorised treadmills (NMT) which can result in unrepresentative accelerations and decelerations, and limit maximal speed.

The aim of Study 1 was to create a reliable, self-paced running protocol that simulated the activity profile of team-sport while overcoming the limitations of current simulation protocols. A curved NMT is now available that allows untethered running, permitting more representative accelerations and decelerations when compared with previous tethered NMT models. Ten male team-sport athletes completed a 30-min match simulation protocol once a week for five weeks, including a familiarisation session. The 30-min protocol consisted of three identical ten-minute blocks, with participants self-selecting their locomotor speeds based on visual and audible commands, specifically: “stand still”, “walk”, “jog”, “run” and “sprint”. The inter-trial reliability of the protocol, as assessed via the coefficient of variation (CV), was < 6% for all locomotor speeds, which is comparable to other externally paced simulations. The self-paced design of this protocol provides a reliable approach to simulating team-sport activity profiles in a laboratory. Given the protocol is self-paced with respect to running speeds and accelerations and decelerations, it likely provides a more ecologically-valid match simulation than externally-paced alternatives. Therefore, this protocol provides the opportunity to directly measure fatigue during and following team-sport running using time-sensitive, laboratory-based techniques.

A principal method to directly determine central and peripheral fatigue following exercise is the interpolated twitch technique, which has been reported sparingly with respect to team-sport activity. Magnetic or electrical stimulation can be used for this assessment by calculating voluntary activation (i.e., central fatigue) using a superimposed stimulus during maximal voluntary contractions (MVC) and control twitches to potentiated muscle (i.e., peripheral fatigue). Given magnetic stimulation provides a less painful alternative to electrical stimulation, it may be more suitable for assessing central and peripheral fatigue with certain populations, or during periods where repeat trials are necessary (like post-exercise fatigue monitoring). For the latter, the test-retest reliability of the technique needs to be determined. Therefore, Study 2 assessed the reliability of magnetic stimulation when using the interpolated twitch technique to determine central and peripheral fatigue of the quadriceps femoris muscle group. Fifteen men completed two familiarisations and three reliability trials to assess muscle function. Within- and between-day reliability of torque and electromyographic (EMG) variables were estimated using typical error ± 90% confidence limits expressed as a percentage (CV) and the intraclass correlation coefficient. Within- and between-day torque variables for MVC were reliable (CV

With the reliability established for critical methods of the study design, Study 3 aimed to assess the biological, perceptual, and performance responses to a self-paced, simulated soccer match protocol using a curved NMT. Twelve male team-sport athletes performed the 90-min match simulation. Match activity, quadriceps twitch interpolation [voluntary activation (%VA) and potentiated twitch (POT)], biochemical markers, strength and power performance, rating of perceived exertion (RPE) and self-report wellness were collected pre-, half-time, post-, and 2, 24, 48, 72 and 96 h post-match. Change compared to pre-match was calculated using the effect size (ES) ±90% confidence limits, and relationships were assessed using regression analysis. Reductions in %VA and POT were present at half-time (-0.38 ± 0.46 and -0.79 ± 0.30, respectively), potentially contributing to reduced second-half running volume and intensity observed in the study. These reductions in %VA and POT persisted post-match, but the magnitude did not increase. Squat jump height decreased at half-time (-0.42 ± 0.31) and remained decreased until 96-h post-match. Perceived fatigue and soreness (-0.92 ± 0.88 and -1.49 ± 0.76, respectively) peaked at Post24, identified as reduced rating scores, and circulating creatine kinase (CK: 1.11 ± 0.43) peaked at Post24. Pre-test strength (N.kg-1) was inversely related to changes in CK (r = -0.58 to -0.81), while peak oxygen consumption (VO2peak) correlated with higher ratings of perceived wellness at Post24 (r = 0.44 to 0.58) and lower RPE post-match (r = -0.71 ± 0.28). The activity profiles and heart rate responses, as well as the magnitude and duration of the post-match responses, to the match simulation were similar to a competitive soccer match, providing support for the ecological validity of our NMT protocol. Therefore, the outcomes of this work likely have implications for competitive on-field performance. The associations observed between physical capacities (i.e., lower-body strength and aerobic capacity) and a reduction in the magnitude of post-match perturbations suggests a training focus should be placed on developing lower-body strength and lower-body strength for team-sport athletes.

To simulate fixture congestion that is common in professional soccer, Study 4 assessed the within- and post-match responses to two match simulations performed in a 72-hour period. In agreement with Study 3, reduced %VA (ES ± 90% CL: -1.52 ± 1.41 and -0.50 ± 0.58) and POT (-0.50 ± 0.37 and -0.31 ± 0.37) were observed at half time in the first and second matches, respectively, which may have influenced the reduced second-half running volume and intensity evident in both matches. However, differences in the activity profiles between matches were unclear. Both match simulations resulted in acute neuromuscular, biochemical, perceptual and performance decrements, with the magnitude and duration of these responses similar to competitive soccer matches. Also, consistent with Study 3, greater lower-body strength was associated with less perceived general muscle soreness and fatigue (range: r = 0.27 to 0.69), as well as less peripheral fatigue (i.e., change in POT). Additionally, greater aerobic fitness resulted in less of an increase in CK concentrations (r range = -0.28 to -0.70). This further supports the notion that lower-body strength and aerobic capacity are important for both improving match running performance and for reducing disruptions to homeostasis caused by match play.

In summary, this thesis outlines the biological and perceptual responses within and following a reliable, self-paced match simulation. The findings support the ecological validity of the match simulation, given the activity profiles performed during the protocol and the associated post-match responses are similar to competitive soccer. An important observation in both Studies 3 and 4 was the previously unreported finding that central and peripheral fatigue exist as early as half-time. This half-time fatigue may be responsible for reduced running volume and intensity in the second half of matches. Therefore, strategies to mitigate this half-time fatigue might assist in maintaining second-half activity. The physical qualities of lower-body strength and aerobic capacity were associated with greater running volume and intensity, and a smaller magnitude of post-match perturbations. Due to the performance benefit and protective effect, development of these physical qualities should be prioritised in training for team-sport athletes.

School/Institute

School of Exercise Science

Document Type

Thesis

Access Rights

Open Access

Extent

204 pages

Degree Name

Doctor of Philosophy (PhD)

Faculty

Faculty of Health Sciences

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