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

  • 2021-04-22
  • Journal of strength and conditioning research 35(6)
    • Tanja Oosthuyse
    • Gabriella E Florence
    • Arron Correia
    • Camilla Smyth
    • Andrew N Bosch

Study Design

Type
Randomized Controlled Trial (RCT)
Population
24 overnight-fasted male runners, male cyclists, and female cyclists
Methods
double-blind randomized crossover design, ingested 15.8 g·h-1 casein hydrolysate or placebo-water during exercise (60–80 minutes) comprising an incremental test to exhaustion, steady-state exercise, and 20-minute time trial
Blinding
Double-blind
Duration
60–80 minutes

Abstract

Oosthuyse, T, Florence, GE, Correia, A, Smyth, C, and Bosch, AN. Carbohydrate-restricted exercise with protein increases self-selected training intensity in female cyclists but not male runners and cyclists. J Strength Cond Res 35(6): 1547-1558, 2021-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·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·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·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.

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