Content area
Full Text
The majority of publications on the performance effects of acute ingestion of carbohydrate and carbohydrate-protein supplements show an ergogenic effect (for reviews see Bosch[1] or Jeukendrup[2]). The underlying mechanism is believed to be a fatigue delay that arises from the maintenance of high rates of carbohydrate oxidation necessary to sustain exercise intensity. In view of the long history of this research, the lack of a published meta-analysis is surprising. Meta-analysts may have been overawed by the diversity in performance tests and the poor reporting of inferential statistics. We have devised ways for converting performance outcomes in time-to-exhaustion tests and time trials to a common metric and for dealing with the lack of inferential information. We have derived meta-analysed effects of acute carbohydrate supplementation on performance with moderating effects for differences in subject characteristics (gender and level of athletes), supplement characteristics (type, timing and amount of carbohydrate ingestion, and the inclusion of protein and/or electrolytes), exercise protocols (any preload, and the type and duration of exercise), ambient temperature and fasting time.
1. Methods
1.1 Study Selection
We used Google Scholar to search for crossover investigations of acute effects of carbohydrate and/or carbohydrate-protein supplements on performance published between 1979 and 2009. Reference lists in reviews and research articles were also examined. Table I shows the study-estimate characteristics for studies that were included in the analysis. We considered all studies in which carbohydrate supplements were consumed with or without protein on the day of a physical performance test, including consumption before and/or during the test. Studies were excluded for the following reasons: published only as conference abstracts; substantial rest intervals in the preload (e.g. rest : work>1 : 4); >5 minutes rest between preload and performance test; performance tests with other than continuous exercise; an inappropriate control (e.g. no fluid consumed in the control); unrealistically high error and performance effect (probably arising from use of a poor ergometer); investigations of supplements with carbohydrates other than glucose, sucrose, fructose or glucose polymers (including maltodextrins); investigations of supplements containing any substances other than carbohydrate, protein and electrolytes, although we included supplementation of high-carbohydrate foods with known approximate content of carbohydrates and protein; a substantial preload preceding a time-to-exhaustion test; glycogen-depleting protocols other than an overnight fast before the start of...