Browsing by Author "Pretorius, Johanna Mercia"

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    Changes in energy metabolism and intermittent sprint performance in healthy active individuals following a 6-week low carbohydrate eating plan
    (Stellenbosch : Stellenbosch University, 2020-12) Pretorius, Johanna Mercia; Terblanche, Elmarie; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Sport Science.
    ENGLISH ABSTRACT: Most field-and court sports are characterized by intermittent sprint movement patterns. With intermittent sprints, it is well-established that the anaerobic glycolytic pathway is downregulated during later sprints, to diminish metabolic by-product induced muscle fatigue. This study is, to my knowledge, the first to investigate the merits of a low-carbohydrate (LC) diet as a nutritional approach for intermittent sprints. It was hypothesised that carbohydrate (CHO) restriction will stimulate upregulation in the two main energy systems; ATP-PCr and aerobic metabolism. Measures of the metabolic energy systems and power output during intermittent sprints (6 x 10 s cycle sprints; 2 min recovery) was performed in 15 recreationally active participants (7 men, 8 women), on their baseline habitual diet (HD: 35% CHO, 45% fat, 20% protein) and 2-weekly throughout a 6-week LC intervention (7% CHO, 66% fat, 28% protein). Pre-and post-intervention, maximal aerobic capacity tests were performed and weekly blood [ketone] and wellness scores obtained. A linear increase in absolute ATP-PCr energy contribution occurred every 2 weeks to achieve a statistically significant change at LC week-6 (+22.0 ±43.15 Joule; p=0.019; ES = 0.47). Expressed as a percentage of total energy output, a large (2.1±2.61%) increase in ATP-PCr contribution from baseline to LC week 2 was evident (p = 0.072: ES = 0.81), with very large significant changes at LC week 4 (2.5 ±2.29%; p = 0.011; ES = 1.10) and 6 (3.5 ±2.36%; p = 0.002; ES = 1.50). A significant moderate decrease in absolute anaerobic glycolytic contribution occurred at LC week 2 (-14.4 ±28.16 Joules; p = 0.031; ES = -0.10) and remained low throughout the LC intervention. This change reflected a very large significant (-3.0 ±2.91%)decline in percentage contribution by LC week 6 (p = 0.028: ES = -1.04). No significant change was, however, evident in absolute aerobic energy contribution (p=0.85). These energy system adaptations resulted in moderately lower onset of fatigue by LC week-6 after a super compensation-curved adaptation (7.4 ±3.92% vs. 5.7 ±2.64; p = 0.332; ES = -0.50). Peak power output during a graded exercise test was unchanged over the LC intervention (271.6 ± 60.19 W vs. 272.7 ± 54.48 W; p = 0.772; ES = 0.02), accompanied by a significant (5.3 ± 5.66%) increase in relative VO2max (p = 0.005; ES = 0.32), a very large(-19.1 ± 18.34%) significant reduction in peak lactate (p = 0.005; ES = -1.00) and a significant (12.1 ± 12.77%) improvement in power at aerobic threshold (p = 0.002; ES = 0.43). Mean blood ketone levels of 0.8 ±0.47 mmol.L-1 for the LC 6-weeks, were significantly higher than at baseline (0.3 ±0.09 mmol.L-1; p=0.002), while a moderate improvement in wellness scores was evident during the LC phase (p=0.062; ES= 0.54). These outcomes suggest that the LC intervention stimulated significant and favourable adaptations in anaerobic energy metabolism, resulting in supercompensation-curved changes in intermittent sprint performance.