Statistical Parametric Mapping Analysis of Muscle-Oxygenation Kinetics in Response to Repeated-Sprint Training in Hypoxia

PURPOSE: To examine the effect of repeated-sprint training in hypoxia (RSH) on oxygenation kinetics in the vastus lateralis muscle using statistical parametric mapping during repeated treadmill sprints in world-class female Rugby Sevens players. METHODS: All players performed 4 repeated-sprint cycle-training sessions in either normobaric hypoxia (RSH, exercise, and interset rest at inspired oxygen fraction of 10.6% and 20.9%, respectively; n = 12) or normoxia (n = 11) during a 9-day training camp before international competition. Repeated-sprint ability (8 × 5-s treadmill sprints with 25-s recovery) was assessed preintervention and postintervention in normoxia only. Continuous assessment of tissue saturation index (TSI) in the vastus lateralis muscle was conducted using near-infrared spectroscopy. RESULTS: There was a difference in TSI signal amplitude between conditions during the last second of the 5-second sprint phase and the first 3.7 seconds of the 25-second recovery phase. In the RSH group, TSI magnitude during the sprints and recovery phases was lower after compared with before the intervention (from 4.3 to 8.7 s; P < .001). The cumulated distance covered in sprints 1 to 8 significantly increased from preintervention to postintervention (pooled values: +1.9% [3.0]%; P = .019), regardless of the condition (P = .149). CONCLUSION: Statistical parametric mapping analysis revealed a noticeable change in TSI in the RSH group toward the end of both the active and the early recovery phase of a normoxic repeated-treadmill-sprints test, whereas no differences were detected in the normoxic group postintervention. Despite improvements in repeated-sprint ability in both groups, addition of severe hypoxia during repeated-sprint training did not yield further performance enhancement.