Validity of an Alternative Method for Estimating Anaerobic Contribution During Running in Normoxia and Hypoxia

Anaerobic metabolism is vital for sustaining work rates during severe-intensity exercise, particularly under environmental conditions such as hypoxia where aerobic metabolism is constrained. Accumulated oxygen deficit (AOD) is the gold-standard method for quantifying anaerobic contribution, yet its implementation is limited by extensive laboratory testing. An alternative approach (AOD_alt) estimates anaerobic contribution from a single exercise bout and provides insight into the distinct contributions of phosphocreatine and glycolysis. However, its validity during running under conditions of reduced oxygen availability remains unexplored. PURPOSE: To determine the validity of AOD_alt during severe-intensity treadmill running in normoxia and hypoxia. METHODS: Twenty-three adults (10W/13M; age 32 ± 7 y; VO2max 54 ± 6 mL∙kg-1∙min-1) completed incremental and constant-speed treadmill running tests in normoxia (FIO2 = 21%) and hypoxia (FIO2 = 15%). An incremental test was used to determine VO2max, oxygen demand, and a running speed for the subsequent tests. Two severe-intensity, constant-speed tests were performed at identical speeds across conditions of FIO2. AOD was calculated as the difference between estimated oxygen demand and accumulated oxygen uptake; AOD_alt was calculated as the sum of the phosphocreatine and glycolytic contributions derived from post-exercise VO2 recovery kinetics and blood lactate concentration, respectively. A two-way repeated-measures ANOVA (method x condition) and Pearson correlations were used for analyses. RESULTS: There was no method x condition interaction (p = 0.36) and no main effect of method (p = 0.74). Anaerobic contribution was greater in hypoxia than normoxia (main effect of condition, p < 0.001). In normoxia, AOD (49.4 ± 10.7 mL∙kg-1 O2) and AOD_alt (51.0 ± 11.2 mL∙kg-1 O2) were similar and strongly correlated (r = 0.68). In hypoxia, AOD (70.8 ± 12.2 mL·kg-1 O2) and AOD_alt (70.5 ± 17.6 mL∙kg-1 O2) were also similar and correlated (r = 0.67). CONCLUSION: Reduced oxygen availability increased anaerobic contribution without compromising AOD_alt estimates during severe-intensity running. These findings support AOD_alt as a valid measure of anaerobic contribution under hypoxic conditions and highlight its utility for coaches and athletes training at altitude who may have limited time for testing sessions.