Fatigue Index and Fatigue Rate during an Anaerobic Performance under Hypohydrations

Background: Since hypohydration commonly occurs in sports, studies on anaerobic exercise performance under this condition have been extensively carried out. When describing anaerobic performance, authors usually refer to a drop in anaerobic performance as fatigue index (FI) which is conventionally calculated using peak and low power data points. Meanwhile, another possible method in explaining anaerobic fatigue is using the rate constant which is derived from the exponential decline of power output known as fatigue rate (FR). Few studies have demonstrated that there was no change in anaerobic performance under mild hypohydrations. Purpose: This study aimed to compare the kinetics of power output using FI and FR of an anaerobic performance (Wingate test) under 2, 3 and 4% state of hypohydrations. Method: Thirty two collegiate cyclists (age = 22 +/- 2 years; body weight = 71.45 +/- 3.43 kg; height = 173.23 +/- 0.04 cm) were matched using their baseline anaerobic peak power (APP) then randomly divided into 4 groups of EU (euhydrated), 2H, 3H and 4H respectively. Results: As expected the, FI, APP, anaerobic lower power (ALP) and rating of perceived exertion (RPE) did not show significant differences between and within the groups. However, the FR in 3H (0.018 +/- 0.005s(-1)) and 4H (0.019 +/- 0.010s(-1)) were significantly lower than EU (0.033 +/- 0.012s(-1)). Post-test FR also showed significant reduction in 3H and 4H compared to their pre-test values (p<0.05). Conclusion: Despite the lack of changes in APP and RPE, subjects in 3H and 4H showed evidence of lower reduction of power output over time. The findings support earlier reports which showed no change in anaerobic performance under mild hypohydrations. The relatively lower FR suggests higher drive in maintaining power output under hypohydrations of 3 and 4% body weight.