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A LOW CARBOHYDRATE–PROTEIN SUPPLEMENT IMPROVES ENDURANCE PERFORMANCE IN FEMALE ATHLETES
ERIN L. MCCLEAVE, LISA FERGUSON-STEGALL, ZHENPING DING, PHILLIP G. DOERNER III, BEI WANG, LYNNE M. KAMMER, AND JOHN L. IVY
Exercise Physiology and Metabolism Laboratory, Department of Kinesiology and Health Education, The University of Texas at Austin, Austin, Texas ABSTRACT
McCleave, EL, Ferguson-Stegall,L, Ding, Z, Doerner, PG III, Wang, B, Kammer, LM, and Ivy, JL. A low carbohydrate–protein supplement improves endurance performance in female athletes. J Strength Cond Res 25(4): 879–888, 2011—The purpose of this study was to investigate if a low mixed carbohydrate (CHO) plus moderate protein (PRO) supplement, provided during endurance exercise, would improve time to exhaustion (TTE) in comparisonto a traditional 6% CHO supplement. Fourteen (n = 14) trained female cyclists and triathletes cycled on 2 separate occasions for 3 hours at _ intensities varying between 45 and 70% VO2max, followed by a ride to exhaustion at an intensity approximating the individual’s ventilatory _ threshold average 75.06% VO2max. Supplements (275 mL) were provided every 20 minutes during exercise and werecomposed of a CHO mixture (1% each of dextrose, fructose, and maltodextrin) + 1.2% PRO (CHO + PRO) or 6% dextrose only (CHO). The TTE was significantly greater with CHO + PRO in comparison to with CHO (49.94 6 7.01 vs. 42.36 6 6.21 minutes, respectively, p , 0.05). Blood glucose was significantly lower during the CHO + PRO trial (4.07 6 0.12 mmolÁL21) compared to during the CHO trial (4.47 6 0.12mmolÁL21), with treatment 3 time interactions occurring from 118 minutes of exercise until exhaustion (p , 0.05). Results from the present study suggest that the addition of a moderate amount of PRO to a low mixed CHO supplement improves endurance performance in women above that of a traditional 6% CHO supplement. Improvement in performance occurred despite CHO + PRO containing a lower CHO and caloriccontent. It is likely that the greater performance seen with CHO + PRO was a result of the CHO–PRO combination and the use of a mixture of CHO sources.

INTRODUCTION

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KEY WORDS aerobic capacity, exercise, glucose, time to exhaustion, ventilatory threshold
Address correspondence to Dr. John L. Ivy, johnivy@mail.utexas.edu. 25(4)/879–888 Journal of Strength and Conditioning Research Ó 2011National Strength and Conditioning Association

revious research has demonstrated that consuming a carbohydrate (CHO) supplement during prolonged endurance exercise improves performance compared to water or placebo (4,5,10,18,21,37,38). The addition of protein (PRO) to a CHO supplement, however, has demonstrated enhanced performance beyond that of CHO alone (19,29,30), but these findings are notuniversal (23,33). Investigations from our laboratory recently found PRO added to either a low CHO (3% CHO + 0.75% PRO) or moderate CHO supplement (4.5% CHO + 1.2% PRO) maintained endurance performance efficacy relative to a traditional 6% CHO supplement (25). In an effort to improve the effectiveness of our CHO plus PRO supplement, we altered the CHO source from a single source of dextrose to amixture of glucose, fructose, and maltodextrin. Multiple sources of CHO appear to increase CHO oxidation rates above that achieved by a single CHO source. The maximal rate of exogenous CHO use during prolonged exercise while providing a single CHO source is about 1.0–1.1 gÁmin21 (22,35). The oxidation rate, however, can increase to 1.7 gÁmin21 when a combination of CHO is ingested during exercise (20).Furthermore, the combination of multiple CHO sources has been shown to further enhance endurance performance above that of glucose alone (6,32). We previously reported that a 3% mixed CHO plus 1.2% PRO supplement did not improve time to exhaustion (TTE) in comparison to a traditional 6% CHO treatment. However, on closer inspection, it was noted that improvement in performance did occur in...
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