Abstract
Athletes are a unique population whose energy expenditure (EE) fluctuates daily as a result of the varying exercise demands in different macro and micro-cycles within their periodised training program. Whilst studies in non-athletic populations have found that there is a modest correlation between adjustments in an individual’s energy intake to match changes in their EE, the high total energy expenditure and congested training schedule for professional athletes provides distinct challenges to consistently meet current sports nutrition recommendations for health and performance. Thus, the primary aim of the series of studies in this thesis was to determine the energy intake and energy expenditure of elite team sport athletes and the implications of training and performance on dietary intake.The first study in the present thesis aimed to synthesise current knowledge on the effect of exercise duration, intensity and mode on energy intake. Accordingly, a systematic review was undertaken(Chapter Two)of randomised, non-randomised, and observational studies including active, healthy males, aged 18-50 years that reported on the effect of exercise on energy intake. MEDLINE, Sport Discuss, Embase, Cochrane and Science Direct were systematically searched from database inception through to May 2019.A total of 36 publications were included in the review (of participants aged 20-44 years). Meta-analysis on the effect of exercise events lasting 2 hours or less (acute duration)on energy intake showed a significant increase in subsequent energy intake after exercise (mean difference[MD]= 0.65 megajoules 95% CI = 0.18 to 1.12, p= 0.007). However, neither moderate or chronic durations of exercise that included multiple bouts of exercise/training(exercise occurring for 2-48 hours or >48 hour time frame), nor variation in exercise intensity, had any meaningful impact on ad libitum energy intake. These results indicate increased energy intake was only evident after an acute exercise bout in the laboratory-based environment in healthy active males but this effect was not exercise intensity dependent. The exercise-induced modulation of energy intake was not apparent during moderate or chronic exercise programs indicating that purposeful, well-planned strategies may be needed if comparable energy intake and energy expenditure are desired in close temporal proximity to individual training sessions for active individuals such as athletes.
The ability to investigate energy balance requires the quantification of both energy intake and energy expenditure. Technology for quantification of energy expenditure has become increasingly available in recent years, however many devices have limited validity in applied settings, especially for the high exercise intensities undertaken by athletic populations. Thus, the aim of the study described in Chapter Three was to assess the validity of the GeneActiv accelerometer for use within an athlete population and compare energy expenditure with energy and macronutrient intake of elite Australian Football athletes during a competition week. First, indirect calorimetry was utilised to assess the utility of the GeneActiv to quantify energy expenditure during high intensity exercise in semi-professional Australian Football athletes. Thereafter, fourteen professional Australian Football athletes (age 24±4[SD] y, height 187±0.8 cm, body mass 86±10 kg) wore the accelerometer and had dietary intake assessed via dietitian led 24 h recalls throughout a continuous 7 d competition period (including match day). There was a significant relationship between metabolic equivalents (MET) and GeneActiv raw acceleration values (g.min-1; SEE 1.77 METs, r2= 0.64, p<0.0001)during a graded running test to volitional fatigue. Thus, the GeneActiv provided effective estimation of energy expenditure during weekly preparation for a professional Australian Football competition. The energy intake and energy expenditure showed a significant difference only occurred on the high load training days 3 and 4 during the competition week (day 3: EI 137 ±31 kJ/kg/d, 11763±2646 kJ/d and EE 186 ±14 kJ/kg/d, 16018±1973 kJ/d p<0.05, d= -1.4; day 4: EI 179±44 kJ/kg/d, 15413±3960 kJ/d and EE 225 ±42 kJ/kg/d, 19313±3072 kJ/d; d= -0.7). Carbohydrate intake was substantially below current sports nutrition recommendations on six of seven days with deficits ranging from -1 to -7.2 g/kg/d (p<0.05), while daily protein and fat intake was adequate. The data indicate Australian Footballers may attempt to periodise dietary energy intake to varying daily training loads but remain in a negative energy balance on higher energy expenditure days. In part this is due to the inadequacies seen in carbohydrate intake. Thus, specific dietary strategies to increase carbohydrate intake may be beneficial to achieve appropriate energy balance, particularly on days where athletes undertake multiple training sessions.
The final study (Chapter Four)aimed to determine the effect of increased carbohydrate availability on daily energy and macronutrient intake and distribution in professional Australian Football athletes during six high-load training days. A cross sectional study was performed measuring six 24-h energy and macronutrient intakes of Australian Football athletes (n= 20 males; age 25 ±4 y, stature 187±8 cm, mass 88 ±9 kg). Dietary intakes were quantified using dietary software (Foodworks) analysis of photographic food diaries on the high-load training days. Energy expenditure was estimated for the same period using the GeneActiv accelerometers. During the initial three control (CONT)days, athletes had ad libitum access to food, while the three days of intervention included control foods, plus increased carbohydrate availability (ICA), achieved through greater prompting and access to carbohydrate foods at the training facility. The results showed daily energy intake and carbohydrate intake (185 ±40 kJ/kg/d, 5.0 ±0.2 g/kg/d) was higher during the intervention compared with control days (172 ±31 kJ/kg/d; p<0.05, 4.0 ±0.2 g/kg/d; p<0.05) but remained below estimated energy expenditure. Energy expenditure was highest during the morning (0600-1159 time period) which coincided with lowest energy intake on all days(CONT 29 ±12 kJ/kg; ICA 39 ±12 kJ/kg).While the intervention was associated with greater carbohydrate intake in the morning(0.6 g/kg, p< 0.05) there was a small decrease in protein intake in the afternoon(1200-1759time period)but intake remained adequate (-0.2 g/kg, p< 0.05). Thus, increasing availability of carbohydrate during days with the highest training loads generated a modest increase in carbohydrate and energy intake, and the intervention was most effective in improving carbohydrate intake during the morning period. Athletes failed to match estimated energy requirements on high-load training days but having improved access to carbohydrate reduced the energy deficit.
In summary, the studies conducted for this thesis provide new information on the impact of exercise on energy intake in active individuals, and the energy intake and energy expenditure of elite Australian Football athletes both within and across training/competition days. Importantly, the findings of study one indicates high levels of physical activity have the potential to acutely increase energy intake but as high daily physical activity levels are prolonged with chronic exercise training an energy balance is less likely to be achieved. Similar results were found, when the energy and nutrient intakes of Australian Football athletes were quantified into daily proportions in study two. It was apparent that the highest daily energy demands of these athletes necessitates greater energy intake, because their daily intake did not match their energy requirements on the days with the highest training loads. Moreover, the inadequate energy intake when training several times a day appears to stem from low carbohydrate intakes. Notably, specific strategies to promote carbohydrate intake across days with high training loads, and in particular the morning, can generate a meaningful increase in total energy intake but while effective, the greater carbohydrate availability outlined in study three did not enable the athletes to increase their energy intake substantially enough to achieve an energy balance. These results highlight the need for ensuring greater availability and prompting for carbohydrate intake in team sport athletes especially during morning periods to increase energy intake and reduce energy deficit for days when energy expenditure is high.
| Date of Award | 9 Feb 2022 |
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| Original language | English |
| Supervisor | Kristen MacKenzie-Shalders (Supervisor), Gary R. Slater (Supervisor), Christopher McLellan (Supervisor) & Vernon Coffey (Supervisor) |