Carbohydrate-Restricted Exercise With Protein Increases Self-Selected Training Intensity in Female Cyclists but Not Male Runners and Cyclists

• Oosthuyse, Tanja ^[1] ; Florence, Gabriella E. ^[2] ; Correia, Arron ^[2] ; Smyth, Camilla ^[2] ; Bosch, Andrew N. ^[2]
  1. [1] University of the Witwatersrand

     University of the Witwatersrand

     City of Johannesburg, Sudáfrica

     
  2. [2] University of Cape Town

     University of Cape Town

     City of Cape Town, Sudáfrica

     
• Localización: Journal of strength and conditioning research: the research journal of the NSCA, ISSN 1064-8011, Vol. 35, Nº. 6, 2021, págs. 1547-1558
• Idioma: inglés
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• Resumen

  • Carbohydrate-restricted training challenges preservation of euglycemia and exercise intensity that precludes ergogenic gains, necessitating countering strategies. We investigated the efficacy of ingesting casein protein hydrolysate in overnight-fasted male runners, male cyclists, and female cyclists. Twenty-four overnight-fasted athletes ingested 15.8 g[middle dot]h-1 casein hydrolysate or placebo-water during exercise (60-80 minutes) comprising an incremental test to exhaustion, steady-state exercise (70% Vmax or 60% peak power output, 87 +/- 4% HRmax), and 20-minute time trial (TT) in a double-blind randomized crossover design, with p < 0.05 accepted as significant. Ingesting protein vs. placebo increased metabolic demand {oxygen consumption, +4.7% (95% confidence interval [CI] +/- 4%), p = 0.0297; +3.2% (95% CI +/- 3.4%), p = 0.061}, heart rate (p = 0.0083; p = 0.007) and rating of perceived exertion (RPE) (p = 0.0266; p = 0.0163) in male cyclists and runners, respectively, but not female cyclists. Protein vs. placebo increased carbohydrate oxidation (+0.26 [95% CI +/- 0.13] g[middle dot]min-1, p = 0.0007) in female cyclists alone. Cyclists reported +2 +/- 1 higher RPE than runners (p = 0.0062). Glycemia was maintained only in runners and increased with protein vs. placebo after 20 minutes of steady-state exercise (+0.63 [95% CI +/- 0.56] mmol[middle dot]L-1, p = 0.0285). TT performance with protein vs. placebo ingestion was modestly compromised in runners (-2.8% [95% CI +/- 2.2%], p = 0.0018), unchanged in male cyclists (+1.9% [95% CI +/- 5.6%], p = 0.5794), and modestly improved in female cyclists (+2.5% [95% CI +/- 1.8%], p = 0.0164). Casein hydrolysate ingestion during moderate to hard carbohydrate-restricted exercise increases glycemia in runners, but not cyclists. Casein hydrolysate increases metabolic demand in male athletes and carbohydrate oxidation in female cyclists and is suitable for improving carbohydrate-restricted training intensity in female but not male endurance athletes