Combined carbohydrate-protein supplementation improves competitive endurance exercise performance in the heat

Journal Title (Medline/Pubmed accepted abbreviation): Eur. J. Appl. Physiol.
Year: 2011
Volume: 111
First page: 2051-2061
doi (if applicable): 10.1007/s00421-011-1831-5

Summary of background and research design:

Background: Ingestion of carbohydrates during endurance events provides fuel and improves endurance in events of moderate temperature.  However, these benefits are not always seen when the endurance event is in the heat.  Some studies have shown a benefit of adding protein to carbohydrate/electrolyte sports beverages because of improved recovery, additional energy availability, improved temperature regulation, improved fluid retention, and/or other mechanisms.

Hypothesis: A protein + carbohydrate supplement will improve temperature regulation, reduce muscle damage, and ultimately improve performance compared to a carbohydrate supplement during a multi-day cycling race in a hot environment.

Subjects: Twenty-eight trained mountain bikers, age 30-32, competing in the 2007 TransAlp Challenge mountain bike race.

Experimental design: random, placebo-controlled, double-blind design

Treatments : CHO: 76 g carbohydrate, 460 mg sodium, 120 mg potassium per liter
CHO + PRO: 72 g CHO, 4 g whey protein, 648 mg sodium, 170 mg potassium per liter
All supplements were consumed ad libitum (as desired).

Protocol : On the day before the race, the subjects were evaluated for VO2maxand assigned to a treatment group, equally distributing gender and fitness levels between groups.  The race was 8 days long.  On all days of the race, the subjects were weighed before breakfast and provided a urine sample.  Temperature was taken and a fingertip blood sample was acquired at selected time points throughout the race.  Blood samples were assessed for glucose and creatine kinase.

Summary of research findings:
  • There was no significant difference in rate of ingestion between groups (0.53 ± 0.05 L/hr for CHO, 0.69 ± 0.08 L/hr for the CHO + PRO group).  The CHO + PRO group had a slightly higher rate of energy intake (p = 0.03).
  • Between race days 1 and 8, the CHO group lost weight (weight measured before exercise for that day), p = 0.03) whereas there was no weight change in for those in the CHO + PRO group.
  • There was no significant difference in circulating CK values or reported muscle soreness between groups at any stage during the race (p > 0.04).
  • No difference in blood glucose was observed between groups.
  • The CHO + PRO group exhibited higher urine osmolality on race days 4-8.  The significance of this finding is not clear, but it appeared to have no adverse effect on thermoregulation or performance (actually each of these variables tended toward improvement with CHO + Pro vs. CHO alone).
  • There was a significant rise in body temperature from pre- to post-exercise on days 5, 6, and 7 for CHO but not for CHO + PRO.
  • Those consuming CHO + PRO finished the race significantly quicker than those in the CHO group (2277 ± 127 min vs. 2592 ± 68 min, p = 0.02).

Key practice applications:

Addition of protein to carbohydrate sport beverages can improve performance in long, duration, hot weather endurance events. The mechanism of this benefit is not known, but the additional protein could help regulate body temperature, provide additional energy, and/or help with fluid retention.

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