The Critical Power - W’ model has many advantages compared to the traditional VO2max test, including tracking fitness changes over time in well trained athletes, predicting performances due to its discrete aerobic and high intensity tolerance variables, and prescribing exercise intensities with increased accuracy. However, a major disadvantage of this model is the length of time in which testing can take, spanning over two weeks in the traditionally used protocol. Efforts have been made to shorten the testing duration by conducting multiple time to exhaustion runs within a single testing day, over the course of two testing days. There is concern, however, that this shorter protocol may introduce fatigue in consecutive testing trials when performing multiple trials within a single day. This study aimed to perform a secondary analysis on the two-day testing protocol, investigating the possible effect of multiple trials on residual error from a line of best fit when calculating CS and W'. A mixed effects model was used to calculate the estimated marginal means for trial/day combinations to determine if any single trial was different from the line of best fit. Results of this analysis revealed no significant differences between any day or trial (p > 0.05). These results demonstrate that the two-day critical power testing protocol did not introduce systematic fatigue into the testing protocol. Future research should further establish the validity of the two-day protocol by a direct comparison of this testing methodology with the traditional protocol.