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Title: Non-invasive and invasive assessment of carbohydrate intakes and muscle glycogen utilisation in Rugby League and AFL
Author: Routledge, H.
ISNI:       0000 0004 7964 2611
Awarding Body: Liverpool John Moores University
Current Institution: Liverpool John Moores University
Date of Award: 2019
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The importance of muscle glycogen availability for both endurance and high-intensity intermittent exercise performance has been recognised for several decades. The measurement of muscle glycogen in human skeletal muscle has traditionally been performed through the invasive muscle biopsy technique. However, recent data from laboratory-based cycling studies suggests that ultrasound technology (using commercially based software known as MuscleSound) provides a valid and non-invasive assessment tool for which to measure exercise-induced glycogen utilization. Nonetheless, no data currently exist to evaluate the validity of the MuscleSound software in team sport athletes in response to field-based training or match play situations. Accordingly, the aim of the present thesis was to therefore examine the reliability and validity of ultrasound technology (via the MuscleSound system) to non-invasively assess muscle glycogen concentration in skeletal muscle of team sport athletes. The aim of Study 1 (Chapter 3) was to quantify the test re-test reproducibility of the MuscleSound scoring system between (vastus lateralis, VL; vastus medalis, VM; rectus femoris RF) and within (25, 50 and 75% of the muscle length) muscles. Using a test-retest (60 minutes apart) scanning protocol in 100 recreationally active subjects (78 males, 22 females), it was identified that 50% of the VL muscle provided the most reliable anatomical site for which to obtain reproducible MuscleSound scores, as evidenced from the coefficient of variation (CV) - 5.8, intraclass correlation (ICC) - 0.89 (0.85 - 0.93), and ratio limits of agreement 1.02 (1.17) reliability statistics. Having identified the optimal anatomical location for which to obtain reproducible MuscleSound scores, the aim of Study 2 (Chapter 4) was to evaluate the validity of the MuscleSound scoring system to non-invasively assess muscle glycogen utilisation in elite male Rugby League players (n=16) during competitive match play. Although match play depleted absolute muscle glycogen in the VL muscle by approximately 200-250 mmol·kg-1 dw, there were no significant differences in MuscleSound scores obtained before and after the game. As such, these data suggest that MuscleSound is not a valid tool to assess muscle glycogen utilisation during the high-intensity intermittent activity profiles that are inherent to team sports. Given that these data are in contrast to previous validation studies conducted with cycling-based protocols, it was suggested that differences in mechanical loads and fluids shifts between exercise protocols may explain the discrepancies between studies. To eliminate the potential confounding effects of acute changes in fluid shifts associated with differing exercise stimuli, the aim of Study 3 (Chapter 5) was to assess the validity of the MuscleSound system to detect changes in muscle glycogen re-synthesis across a time-scale in which acute changes in fluid shifts have been restored to pre-exercise values. Using a combination of glycogen depleting cycling-based exercise followed by 36 h of an isonenergetic high CHO or low CHO diet, resting muscle glycogen of the VL muscle (from 16 recreationally active males) was approximately 500 versus 250 mmol·kg-1 dw in the high and low CHO trials, respectively. However, no differences were observed in the MuscleSound scores obtained between the high and low trials. When considered with the results of Chapter 4, these data collectively suggest that the MuscleSound system is unable to detect differences in muscle glycogen concentration within the physiological range that typically occurs as a result of exercise-induced glycogen utilisation and/or post-exercise muscle glycogen re-synthesis. Given that MuscleSound was not deemed a valid measurement tool, it was recommended that evaluations of the daily CHO and muscle glycogen requirements of team sport athletes should therefore be undertaken using traditional assessments of energy intake and muscle biopsies, respectively. Accordingly, the habitual CHO intakes of 44 elite professional male Australian Rules Football (AFL) players were quantified across the weekly micro-cycle in Study 4 (Chapter 6). These data demonstrate that elite AFL players practice elements of daily CHO periodisation in accordance with fluctuations in daily training load and proximity to the match day itself. Nonetheless, such data also highlighted that players do not consume CHO at the recommended dose to achieve glycogen storage that is likely required to facilitate optimal match day physical performance. In Study 5 (Chapter 7), muscle glycogen utilisation in the VL muscle was subsequently quantified using the muscle biopsy technique in two elite professional males during competitive match play. Importantly, players commenced the match after adhering to a 24 h CHO loading protocol of 8 g·kg-1 and after consuming a pre-match meal of 2 g·kg-1. Data demonstrate that such a dietary protocol achieves pre-match muscle glycogen concentration >500 mmol·kg-1 dw and that match play can induce an absolute glycogen utilisation >400 mmol·kg-1 dw. However, with the different demands observed between positions, total glycogen utlisation may vary. As such, it appears that the metabolic demands of AFL maybe more CHO dependent than other invasive team sports such as soccer and rugby. In summary, the work undertaken in this thesis has demonstrated that the MuscleSound software is not valid to detect differences in muscle glycogen concentration within the physiological range (i.e. 200-300 mmol·kg-1 dw) that typically occurs as a result of exercise-induced glycogen utilisation and/or post-exercise muscle glycogen re-synthesis. For this reason, assessment of the CHO requirements of team sport athletes is likely dependent on the traditional approaches of dietary assessment and muscle biopsy. Using the latter methods, the present data also demonstrate that the CHO requirements of AFL match play is potentially different (though larger sample sizes are required) than other team sports such as soccer and rugby. Further studies are also required to quantify the glycogen requirement of the typical training sessions undertaken by professional players of specific team sports.
Supervisor: Morton, J. ; Close, G. ; Erskine, R. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: TX341 Nutrition. Foods and food supply ; RC1200 Sports Medicine