NO FULL TEXT AVAILABLE. This thesis contains 3rd party copyright material. ----- Introduction: Professional Australian Football (AF) is a physically demanding field sport that requires prolonged, high-intensity, intermittent exercise, and is punctuated by many intense accelerations and decelerations (Gray & Jenkins, 2010; Harcourt, Marclay, & Clothier, 2014). In addition to these running demands, AF players are also required to jostle and tackle an opponent and complete very intense skill actions which contribute to the high physical demands of the game. With such high demands, there is a need for a better understanding of the factors that are related to training and match performance.
To meet these demands, developing optimal body composition, fat-free soft tissue mass (FFSTM) and fat mass (FM) are considered essential for success for professional AF players. Indeed, physical performance is reliant on muscular activity and therefore it is likely that FFSTM is an important physical characteristic for success in AF. Recent research has suggested FFSTM underpins physical performance in AF (Hrysomallis & Buttifant, 2012). Excess FM however, can be considered detrimental to performance as it is metabolically inactive. Therefore it is important that optimal levels of FFSTM and FM are developed in professional AF players.
Despite the perceived importance of FFSTM for AF players, very few studies have investigated the factors related to developing and maintaining optimal body composition in this group. Therefore, the overall goals of this thesis were to: 1) determine the most accurate and precise method to assess anthropometry in AF players, 2) compare the anthropometry, upper body strength and lower body power characteristics in elite junior, sub-elite senior and elite senior AF players, 3) examine the seasonal changes in body composition, dietary intakes, and upper body strength in professional AF players, 4 compare the variations in body composition of early, mid and late career professional AF players over three successive preseasons. The results of five separate studies were reported in five manuscripts.
Study 1: Different methods such as skinfolds, bioelectrical impedance (BIA), and dual-energy X-ray absorptiometry (DXA) are used to estimate FFSTM and FM in AF players. However, DXA is commonly reported to be the gold standard measurement device for this purpose. Therefore, a comprehensive evaluation of the precision and accuracy of two different DXA devices for measuring FFSTM, FM and BMC was completed. Additionally, a comparison of the construct validity and reliability of skinfold and BIA measures was also undertaken. DXA showed exceptional precision and accuracy for fat-free soft tissue mass (FFSTM), bone mineral content and fat mass. Body fat percentage derived from a football-specific skinfold equation and the Σ7 skinfolds both showed poor relationships with the criterion measures estimated from DXA. Bioelectrical impedance analysis also showed both poor accuracy and precision for AF players. These results showed that DXA provides an accurate and precise measure for body composition and that the other indirect methods may not be sensitive enough in elite AF players.
Study 2: Described the anthropometry, upper body strength and lower body power characteristics in elite junior (n =21), sub-elite senior (n = 22) and elite senior (n = 27) AF players. Relationships between the whole body and appendicular body composition and neuromuscular strength and power characteristics were determined. Elite senior and sub-elite senior players were significantly older and heavier than the elite junior players. Both elite playing groups had greater total FFSTM than both the sub-elite and junior elite players, however, there were only appendicular FFSTM differences between the junior elite and elite senior players. The elite senior playing groups were stronger and had greater counter movement jump performance than the lower level players. Both whole body and appendicular FFSTM were correlated with upper body strength measures. The FFSTM are different between AF players competing at different levels, which are likely due to training and partly explain the observed differences in strength and power performance. These findings highlight the importance of optimizing FFSTM in developing AF players and maintaining these levels during a professional career.
Study 3: A prospective longitudinal study examined the seasonal changes in body composition, dietary intakes, and upper body strength in 23 elite experienced (>4 years contracted) and 22 elite inexperienced (contracted <4 years) AF players. FM decreased during the preseason but was maintained through the competition season for both groups. Body mass was unchanged during the season, %FFSTM was increased during the preseason and remained constant thereafter. Upper body strength increased during the preseason and was maintained during the competition season. Total energy and carbohydrate intakes were similar between the experienced and inexperienced players during the season, but there were greater fat intakes at the start of the season, increased alcohol and reduced protein intake at the end (post) of the season. The inexperienced players consumed more fat at the start of season and less total protein during the season compared to the experienced players. Changes in FFSTM were related to changes in upper strength performance.
Study 4: This prospective longitudinal study examined the changes in anthropometry during the inseason and establish how they impact on performance and training variables in 34 elite Australian football players. Training characteristics, wellness scores, fatigue scores, nutrient intakes along with physical performance characteristics (bench press, bench pull,) were also taken at each of these time points. Players were categorised into groups that Gained, Maintained or Lost FFSTM during the inseason. There were no clear differences between groups in height, age or %FFSTM, number of training sessions or time (minutes) of training completed. Players that maintained FFSTM had a higher body mass (BM) and reported a higher session-RPE loads. The group that gained FFSTM had greater bench press strength and body mass loss whilst those who maintained FFSTM completed greater training loads and missed fewer games through injury. Players who maintained FFSTM played more first grade games whilst those who lost FFSTM played more second grade games.
Study 5: Compared the variations in body composition, via DXA, and dietary intakes of early, mid and late career professional Australian football players over 3 successive preseasons. 22 elite Australian football players were assessed for bone mineral content, fat mass and fat-free soft tissue mass four times per season over a 3-year period. Players were classified according to their age at the beginning of the observational period as either early (<21 y; N = 8), mid (21-25 y; N = 9) or late (>25 y; N = 5) career athletes. Regional and total body composition was assessed four times, at the same time of each season: 1) start preseason (SP); 2) end preseason (EP); midseason (MS); and end-season (ES) from 22 professional AF players using pencil beam dual energy x-ray absorptiometry. Nutritional intake for each player was evaluated concomitantly using 3-day food diaries. Players were classified according to their age at the beginning of the observational period as either early (<21 y; N = 8), mid (21-25 y; N = 9) or late (>25 y; N = 5) career athletes. Early career players had lower FFSTM, BMC and BM compared to mid and late career players FFSTM, %FFSTM, BMC and BM showed small variations throughout. FM and %FM had greatest variability, particularly in the early career players. FM reduced and FFSTM increased from SP to EP, whilst FM and FFSTM decreased from EP to MS. FM increased and FFSTM decreased from MS to ES, whilst FM and FFSTM increased during the offseason.