Fatigue Index Isn’t Related To Exercising Microvascular Oxygenation During Repeated Sprinting In Collegiate American Football

Repeated sprint ability (RSA) may be an important physical characteristic for American football players as some positions require near maximal running with shorter recovery durations between plays within a series. Microvascular oxygenation (StO2) responses measured via near-infrared spectroscopy (NIRS) displays the balance of oxygen delivery and oxygen utilization at the level of the microvasculature during exercise. PURPOSE: This study investigated the possible relationship between the fatigue index (FI) and exercising StO2 responses observed throughout an RSA test in collegiate American football student-athletes. METHODS: 15 male, collegiate (NCAA Division II) offensive American football student-athletes (age = 20 ± 1 years, height = 1.79 ± 0.06 m, weight = 83.3 ± 8.4 kg), completed an RSA test while StO2 responses were recorded from the medial gastrocnemius of their dominant leg via wireless NIRS. Participants sprinted 20 meters for 8 repetitions with 35 seconds of inter-repetition active recovery and sprint speed was measured via a laser timing gate system. FI was calculated as [1 - ((sum of speeds) / (best speed x 8))] x 100%. The exercising StO2 response was averaged during the sprint, normalized to a 2-minute resting baseline, and presented as a delta value (ΔBSL). Pearson correlation was used to assess the possible relationship between FI and the exercising StO2 response. Statistical significance was established at p < 0.05. RESULTS: No significant relationship (r = 0.15, p = 0.59) was observed between FI (-2.6 ± 1.1 %) and exercising StO2 (-24.1 ± 7.5 ΔBSL). CONCLUSION: The present results suggest that the microvascular deoxygenation (lower StO2 values) observed during sprinting did not seem to influence how much fatigue was induced during the RSA test (FI) in collegiate American football student-athletes. This could be due to a lower exercise time (cumulative sprint time = 24.8 ± 0.8 sec) and higher recovery time (recovery time = 245 sec) that was used during the RSA test to mimic the in-game demands of American football.