Browsing Faculty of Medicine, Dentistry and Life Sciences by Subjects
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Changes in anthropometry and performance, and their inter-relationships, across three seasons in elite youth rugby league playersThis study investigated changes in anthropometry and performance, and their inter-relationships, across three consecutive seasons (under-15 to under-17 age group) in elite youth rugby league players. Each player took part in annual anthropometrical and performance assessments, comprising measurements of stature; body mass; limb lengths and circumference; skinfolds, predicted muscle cross-sectional area (CSA); 20 m speed, counter-movement jump height, vertical power and aerobic power. Lean body mass % changed (P < 0.05) between the under-15 (70.9 ± 5.9 %), under-16 (72.0 ± 5.8 %) and the under-17 age groups (74.1 ± 5.7 %). Likewise, predicted quadriceps muscle cross-sectional area (CSA) also changed (P < 0.05) between each age group (under-15 = 120.9 ± 37.8 cm2; under-16 = 133.2 ± 36.0 cm2; under-17 = 154.8 ± 28.3 cm2). Concomitant changes between the under-15 and under-16 group were found for 20 m speed (3.5 ± 0.1 cf. 3.4 ± 0.2 s; P = 0.008) and predicted jumping power (3611.3 ± 327.3 W cf. 4081.5 ± 453.9 W; P = 0.003). Both lean body mass and quadriceps muscle CSA consistently, related to both 20 m sprint time and jumping power, with r-values ranging between -0.39 to –0.63 (20 m sprint time) and 0.55 to 0.75 (jumping power). Our findings demonstrate the importance of gains in lean body mass across later-adolescence that support the ability to generate horizontal speed and predicted vertical power. This information should inform the expectations and subsequent training programs of elite rugby league practitioners.
An examination of a modified Yo-Yo test to measure intermittent running performance in rugby playersThis study examined how starting each shuttle in the prone position altered the internal, external and perceptual responses to the Yo-Yo Intermittent Recovery Test Level 1. Using a randomized crossover design, 17 male rugby players completed the Yo-Yo IR1 and prone Yo-Yo IR1 on two separate occasions. External loads (via microtechnology), V ̇O2, heart rate (HR), rating of perceived exertion (RPE) were measured at 160, 280 and 440 m (sub-maximal) and when the test was terminated (peak). The pre-to-post change in blood lactate concentration (∆[La]b) was determined for both tests. All data were analysed using effect sizes and magnitude-based inferences. Between-trial differences (ES 90%CL) indicated total distance was most likely lower (-1.87 0.19), whereas other measures of peak external load were likely to very likely higher during the prone Yo-Yo IR1 (0.62-1.80). Sub-maximal RPE was likely to most likely higher (0.40-0.96) and peak RPE very likely higher (0.63 0.41) in the prone Yo-Yo IR1. The change in [La]b was likely higher after the prone Yo-Yo IRl. Mean HR was possibly lower at 440 m (-0.25 0.29) as was peak HR (-0.26 0.25) in the prone Yo-Yo IR1. "V" ̇E, "V" ̇O2 and "V" ̇CO2 were likely to very likely higher at 280 and 440 m (ES = 0.36-1.22), while peak values were possibly to likely higher (ES = 0.23-0.37) in the prone Yo-Yo IR1. Adopting a prone position during the Yo-Yo IR1 increases the internal, perceptual and external responses, placing greater emphasis on metabolically demanding actions typical of rugby.
The internal and external demands of multi-directional running and the subsequent effect on side cut biomechanics in male and female team sport athletesThe aim of this thesis was to examine the physiological and biomechanical responses to multi-directional running in male and female team sport athletes. Chapter 4 compared measures of energy expenditure derived from indirect calorimetry and microtechnology, as well as high power and high-speed activity, during linear and multi-directional running. Measured energy expenditure was higher during the multidirectional trial (9.0 ± 2.0 cf. 5.9 ± 1.4 kcal.min-1), whereas estimated energy expenditure was higher during the linear trial (8.7 ± 2.1 cf. 6.5 ± 1.5 kcal.min-1). Whilst measures of energy expenditure were strongly related (r > 0.89, p < 0.001), metabolic power underestimated energy expenditure by 52% (95% LoA: 20-93%) and 34% (95% LoA: 12-59%) during the multi-directional and linear trial, respectively. Time at high power was 41% (95% LoA: 4-92%) greater than time at high speed during the multidirectional trial, whereas time at high power was 5% (95% LoA: -17-9%) lower than time at high speed during the linear trial. Chapter 5 explored the internal and external responses to linear and multi-directional running, specifically examining if measures of high speed and high power reflect changes in internal load. High speed distance (p < 0.001) was higher during the linear trial, whereas time at high power (p = 0.046) and accelerations performed (p < 0.001) were higher during the multi-directional trial. Summated HR (-0.8; ±0.5, p = 0.003), B[La] (-0.9; ±0.6, p = 0.002) and RPE (-0.7; ±0.6, p = 0.024) were higher during the multi-directional trial. There was a large difference in the ratio of high speed:summated HR (1.5; ±0.5, p = 0.001) and high speed:total V̇O2 (2.6; ±1.2, p < 0.001) between linear and multi-directional running, whilst high power:summated HR (0.3; ±0.5, p = 0.246) and high power:total V̇O2 (0.1;±0.8, p = 0.727) were similar. A small decrement in knee flexor torque was observed after the multi-directional (0.4; ±0.4, p = 0.017) and linear (0.2; ±0.3, p = 0.077) trials, respectively. Collectively, Chapters 4 and 5 reveal that more directional changes induce a greater internal response, despite reducing the high-speed distance someone is likely to cover. High power better reflects internal responses to multidirectional running than high speed, but microtechnology cannot be used to determine the absolute energy cost of multi-directional running. Chapters 6 and 7 explored alterations in side cut biomechanics in males and females immediately (Chapter 6) and 48 h (Chapter 7) after multi-directional running. In Chapter 6, 20 m sprint time was higher (ES: 0.65 – 1.17, p < 0.001) after multidirectional running, indicating the presence of fatigue. Males and females displayed trivial to moderate changes in trunk flexion (0.16 – 0.28, p = 0.082), peak hip internal rotation (0.46 – 0.54, p = 0.090), and knee flexion (0.17 – 0.41, p = 0.055) and higher knee abduction (0.40 – 0.51, p = 0.045) and internal rotation (0.59 – 0.81, p = 0.038) angular velocities, during the weight acceptance phase of side cuts after multidirectional running. Peak hip extensor (0.19 – 0.29, p = 0.055) and knee internal rotation moment (0.22 – 0.34, p = 0.052) displayed trivial to small increases after multidirectional running, whereas peak hip external rotation (0.44 – 0.57, p = 0.011), knee extensor (0.33 – 0.45, p = 0.003) moment and knee to hip extensor ratio (0.15 – 0.45, p = 0.005) were lower. In addition, IGRF displayed trivial to moderate changes (0.04 – 0.79, p = 0.066) and lateral GRF was lower (0.29 – 0.85, p = 0.002) after multidirectional running. In Chapter 7, CK concentration (2.4 – 4.94, p = 0.009), perceived muscle soreness (4.2 – 4.8, p < 0.001) and 20 m sprint time (0.6 – 0.9, p < 0.001) were higher 48 h after multi-directional running, indicating the presence of EIMD. Males and females displayed trivial to moderate changes in peak torso flexion (0.13 – 0.35, p = 0.055), hip internal rotation angular velocity (0.43 – 0.64, p = 0.073) and more knee internal rotation (0.31 – 0.5, p = 0.009) 48 h after multi-directional running. A tendency for an interaction between sex and time was noted for peak knee flexion (p = 0.068) and internal rotation angular velocity (p =0.057), with males only displaying a moderate increase. Males and females also displayed a lower peak knee extensor moment (0.43 – 0.56, p = 0.001) and a small increase in extensor moment (0.21 –0.46, p = 0.066) and knee external rotation moment (0.34 – 0.78, p = 0.062). An interaction between sex and time was noted for IGRF (p = 0.037); there was a large increase in IGRF at 48 h in females (1.4) but not males (0.08). For the first time, these data highlight multi-directional running which elicits fatigue and EIMD causes alterations in side cut biomechanics which can persist for at least 48 h. Specifically, both males and females performed side cuts in a more extended position, with higher peak angular velocities, and peak knee external rotation moments and less knee extensor moments both immediately and 48 h after multi-directional running.
A three-season comparison of match performances among selected and unselected elite youth rugby league playersThis study compared technical actions, movements, heart rates and perceptual responses of selected and unselected youth rugby league players during matches (under-15 to under-17). The players’ movements and heart rates were assessed using 5 Hz Global Positioning Systems (GPS), while their technical actions were analysed using video analysis. The maturity of each player was predicted before each season for statistical control. There were no differences (P > 0.05) between selected and unselected players in the under-15 or the under-17 age groups for any variables. However, in the under-16 group, the selected players (57.1 ± 11.9 min) played for longer than the unselected players (44.1 ± 12.3 min; P = 0.017; ES = 1.08 ± CI = 0.87), and covered more distance (5,181.0 ± 1063.5 m cf. 3942.6 ± 1,108.6m, respectively; P = 0.012; ES = 1.14 ± CI = 0.88) and high intensity distance (1,808.8 ± 369.3 m cf. 1,380.5 ± 367.7 m, respectively; P = 0.011; ES = 1.16 ± CI = 0.88). Although successful carries per minute was higher in the selected under-15 group, there were no other differences (P > 0.05) in match performance relative to playing minutes between groups. Controlling for maturity, the less mature, unselected players from the under-16 group performed more high-intensity running (P < 0.05). Our findings question the use of match- related measurements in differentiating between selected and unselected players, showing that later maturing players were unselected, even when performing greater high-intensity running during matches.