Competitive tennis can be considered to be an intermittent moderate to high intensity endurance sport where fatigue is compounded by heat and hydration issues. Thus, tennis athletes must maintain an adequate fuel-fluid balance throughout their competition. In college matches, it is common for players to compete in both doubles and single matches on the same day, often with only 45 minutes rest between matches. When difficult matches go three sets and thus last at least two hours, it is not unusual to see performance deteriorate rapidly by the 3rd set. Past research has shown that supplementing with a 6-8% carbohydrate (CHO) sports drink with electrolytes substantially reduces fatigue and assists to reduce dehydration. It has been suggested that adding a small amount of protein (PRO) to a sport drink would assist to delay fatigue by boosting insulin levels thereby sparing muscle glycogen stores. Therefore, the purpose of this study was to investigate whether ingestion of a new sport drink containing a small amount of protein at regular intervals would reduce fatigue in college tennis players. Eighteen male tennis athletes from two college teams (Means: age = 20 + 1.4; weight = 76.5 + 2.4 kg; height = 183.8 + 7.1 cm) volunteered to participate in a double-blind, randomized, counterbalanced study comparing the effect of a new sport drink (26 g CHO, 6.5 g PRO, 190 mg Na, 64 mg K per 354 ml) to a placebo drink similar in taste, texture and electrolytes but void of PRO and CHO during two 2-hour practice sessions spaced 1 week apart. Food intake was controlled prior to practice. Rest breaks were given every 15 minutes resulting in 8 fluid dosings of 230 ml at each break. Environmental conditions were similar between college sites (31° C, 44% RH). Practice consisted of a warm-up, drills and match play. All practices were considered "hard" (RPE=15) and were immediately followed by 10 trials of a repeated efforts agility test (spider test) with 25 seconds rest between trials. Nine athletes completed both conditions. Fluid intake (sport drink = 1641+200 ml; placebo = 1831+ 187 ml), pre-practice weight (76.5 + 2.4 kg ), and pre/post blood glucose (90+1 mg/dL) were not significantly different between test days. Weight increased pre to post for the placebo condition (+0.3 kg) but decreased (-0.4 kg) for the sport drink condition (Paired t tests, p <.02). For both drinks, urine specific gravity increased pre to post (1.013 to 1.024, p < .003). Time to complete each spider test trial (TIME), heart rate (HR), and rating of perceived exertion (RPE) were taken immediately after each trial. Analyses used a 2 x 10 totally within subjects ANOVA with post hoc pairwise comparisons with Bonferonni adjustments (p < .05). HR (155-187 bpm) and RPE (13-18) increased linearly across trials. TIME varied from 22.43-23.75 s/trial. No significant differences were found by Group (S vs. P) for any variable, but the main effect of Trial was significant (p < 0.0005) where Trial 2 was always greater than Trial 1. There were no significant Group x Trial interactions. It was concluded that the new sport drink did not delay fatigue in these tennis athletes. The high rate of non-completion was attributed to dislike for the taste and texture of the sport drink as well as gastric intolerance. Future studies with this sport drink utilizing tennis athletes should consider diluting the product mixture and/or decreasing the volume load.
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