Changes in energy metabolism and intermittent sprint performance in healthy active individuals following a 6-week low carbohydrate eating plan

Pretorius, Johanna Mercia (2020-12)

Thesis (M Sport Sc)--Stellenbosch University, 2020.

Thesis

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.

AFRIKAANSE OPSOMMING: Die meeste veld-en baansportsoorte word gekenmerk deur onderbroke naelloop bewegingspatrone. Dit is goed gevestig in onderbroke naelloop energie-metabolisme fisiologie dat die anaërobiese glikolitiese energiesisteem afgereguleer word gedurende latere naellope, om sodoende metaboliese byproduk-geïnduseerde spieruitputting te verminder. Hierdie studie is egter, na my beste wete, die eerste om die meriete van ‘n lae-koolhidraat (LC) dieet as ‘n voedingsbenadering vir onderbroke naellope te ondersoek. Dit was gehipotetiseer dat koolhidraat (CHO)-beperking opregulering sal stimuleer in die ander twee hoof energiesisteme: ATP-PCr en aërobiese metabolisme. Metings van die metaboliese energiesisteme en krag-uitset gedurende onderbroke naellope (6 x 10 s fietsergometer naellope; 2 min hersteltyd) is deur 15 aktiewe deelnemers (7 mans, 8 vrouens ) uitgevoer, tydens hulle gewone basislyn-dieet (HD: 35% CHO, 45% vet, 20% proteïen) en 2-weekliks deur die loop van ‘n 6-weke LC intervensie (7% CHO, 66% vet, 28% proteïen). Pre-en post-intervensie maksimale aërobiese kapasiteitstoetse was uitgevoer en weeklikse bloed [ketone] en welstand metings was verkry. ‘n Liniêre toename in absolute ATP-PCr energie bydrae het elke 2 weke plaasgevind om ‘n statisties-beduidende verandering teen LC week 6 teweeg te bring (+22.0 ±43.15 Joules; p=0.019; ES = 0.47). Uitgedruk as persentasie van totale energie-uitset, was ‘n groot(2.1±2.61%) toename in ATP-PCr-bydrae van basislyn tot LC week 2 duidelik (p = 0.072: ES = 0.81), met baie groot beduidende verandering by LC week 4 (2.5 ±2.29%; p = 0.011; ES = 1.10) en 6 (3.5 ±2.36%; p = 0.002; ES = 1.50). ‘n Beduidende matige afname in absolute anaërobies glikolitiese bydrae het plaasgevind by LC week-2 (-14.4 ±28.16 Joule; p = 0.031; ES = -0.10), en het laag gebly regdeur die hele LC intervensie. Hierdie anaërobies glikolitiese sisteemverandering het ‘n baie groot (-3.0 ±2.91%) beduidende afname in persentasie-bydrae in LC week 6 (p = 0.028: ES = -1.04) getoon. Geen beduidende verandering was egter duidelik in absolute aërobiese energie-bydrae nie (p=0.85). Hierdie energiesisteem-aanpassings het gelei tot matige laer uitputtingsvlakke in LC week-6 na afloop van ‘n superkompensasie-kurwe aanpassing (7.4 ±3.92% vs. 5.7 ±2.64; p = 0.332; ES = -0.50). Maksimale aërobiese kapasiteit piek krag-uitset is gehandhaaf oor die LC intervensie (271.6 ± 60.19 W vs. 272.7 ± 54.48 W; p = 0.772; ES = 0.02), vergesel deur ‘n beduidende (5.3 ± 5.66%) toename in relatiewe VO2maks(p = 0.005; ES = 0.32), ‘n baie groot (-19.1 ± 18.34%) beduidende afname in pieklaktaat (p = 0.005; ES = -1.00) en ‘n beduidende (12.1 ± 12.77%) verbetering in aërobiese draaipuntkrag (p = 0.002; ES = 0.43). Gemiddelde bloed [ketoon] van 0.8 ±0.47 mmol.L-1vir die LC 6-weke was beduidend hoër as by basislyn (0.3 ±0.09 mmol.L-1; p=0.002), terwyl ‘n matige verbetering in welstand tellings gevind was vir die LC-fase (p=0.062; ES= 0.54). Hierdie uitkomste maak dit duidelik dat die LC intervensie beduidend en gunstige aanpassings in anaërobiese energie metabolisme gestimuleer het, wat gelei het tot superkompensasie-kurwe verandering in uitputting tydens onderbroke naellope.

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