The purpose of the present study was to examine the influence of high carbohydrate (CHO) diets on recovery of endurance capacity following a treadmill run to exhaustion. Two high CHO diets were used, one in which the normal diet was supplemented with complex carbohydrates and the other in which supplementation was achieved with simple carbohydrates. The thirty recreational runners who took part in this study (fifteen men and fifteen women) completed weighed food intake diaries two to three weeks before the start of the study. From an analysis of this information each subject's 'normal diet' was prescribed before Trial 1 and then a supplemented diet before Trial 2. The aim was to achieve an increase in carbohydrate content to 70% in the diets of the two high CHO groups and an equivalent increase in energy intake by the Control group. The subjects were required to run to exhaustion on a treadmill at a speed equivalent to 70% VO2max on two occasions separated by 3 days. After Trial 1 the subjects were divided into three equal groups. The Complex CHO group (301 +/- 86 mg vs 507 +/- 120 mg) and Simple CHO group (265 +/- 45 mg vs 462 +/- 81 mg) increased their CHO intake by approximately 70% (p less than 0.05) during the 3 days before Trial 2 whereas the Control group increased their energy intake with additional protein and fat so as to match the energy intakes of the two CHO groups.(ABSTRACT TRUNCATED AT 250 WORDS)