Effects of moderate dietary manipulations on swim performance and on bloodlactate-swimming velocity curves

Blood lactate responses are commonly employed for evaluation and prescripti on of training programmes. The purpose of the present studies was to examin e the effects of dietary manipulations on both swim performance and on the relationship between blood lactate and swimming velocity. The first study e ngaged 8 subjects in a regimen to reduce muscle glycogen by a combination o f diet and training. Subjects were monitored under a normal mixed diet comp rising 53.6 +/- 7.8% carbohydrate (CHO) and under a decreased CHO condition (39.4 +/- 10.7% CHO) over 3 days. Mean swim performance decreased signific antly (P < 0.05) over 400 yards as a result of the carbohydrate reduction r egimen. Mean blood lactates were reduced as a consequence of the glycogen d epletion regimen following swims at 85% and 100% of maximum velocities. The swimming velocity corresponding to 4 mM blood lactate (V-4 mM) was altered from 0.67 +/- 0.04 m . s(-1) on a mixed diet to 0.70 +/- 0.05 m . s(-1) on a CHO-reduced diet. The second study employed 7 subjects in a regimen to e nhance muscle glycogen stores. Subjects were monitored over 3 days under a normal diet (52.7 +/- 4.4% CHO) and on a separate occasion under an increas ed CHO intake (59.2 +/- 3.7% CHO). In contrast to the first study, mean swi m performance improved over 100 yards and 400 yards (P < 0.05). Mean blood lactates were evaluated after the carbohydrate-rich regimen at both 85% and 100% swim velocities (P < 0.05). The mean swim velocity associated with V- 4 mM was paradoxically reduced from 0.69 +/- 0.05 to 0.67 +/- 0.04 m . s(-1 ) as a result of the increased CHO condition. The results indicate that a m oderate reduction in CHO intake alters swimming performance adversely where as a moderate elevation in CHO intake above the normal diet improves perfor mance. The dietary manipulations affected the response of blood lactate to both submaximal and maximal swimming velocities. The observations highlight the limitations of applying lactate response curves to swim training.