Introduction There are no protocol recommendations per-taining to nutrition before the performance assessment. The aim of this study was to determine the influence of three vari-ous 48-hour dietary protocols on parameters obtained during three trials of the maximal incremental treadmill test.

Methods Thirteen physically active subjects (age: 25.73±3.09) underwent all-out treadmill test using a breath-by-breath analyzer. During the 13-day experiment, the subjects were submitted to the three controlled 48-hour dietary protocols. The obtained data were divided in three subgroups with respect to dietary conditions that prevailed during each trial. Three 48-hour dietary protocols consisted of (1) a low carbohydrate (CHO) diet 1.06 gkg-1 body mass of CHO; (2) a mixed diet 2.6 gkg-1 body mass of CHO; and (3) a high carbohydrate diet 5 gkg-1 body mass of CHO.

Results The results confirmed the difference in the observed metabolic parameters after implementing the 48-hour high-carbohydrate diet. It is important to note that the metabolic indicators corresponding to the anaerobic threshold and maximal work load significantly change and reach higher values under the influence of a high-carbohydrate diet at maximal workload. Respiratory exchange ratio and blood lactate concentration contributed the most to the observed differences (p<0,03).

Conclusions Energy sources pertaining to different nutri-ents have to be accurately defined and balanced during both competition but also functional testing. Otherwise, errors can occur in the given physiological parameters which serve as the guidelines for planning and programming the training process, which is a precondition for maximizing the com-petition performance. An athlete, before the physiological assessment, should take approximately the same amount of carbohydrate (>75%) and other nutrients, just like before a competition depending on duration and intensity of the sports activity.