Abstract
Introduction
Athlete monitoring in soccer commonly relies on external load measures despite considerable inter-individual variation in the physiological responses elicited by similar external demands. Near-infrared spectroscopy (NIRS) provides a non-invasive method of continuously assessing local muscle oxygen saturation (SmO₂) and may provide additional insight into the physiological demands experienced during soccer. However, SmO₂ responses during full soccer match play remain poorly characterized. The purpose of this study was to characterize muscle oxygen saturation responses in NCAA Division I soccer players during a 90-min match and explore within-player changes in SmO₂ alongside external match demands.
Methods
Three male NCAA Division I soccer players (age: 20.3 ± 1.5 y) completed a full-length soccer match while wearing a portable MOXY Monitor over the rectus femoris of the dominant leg to continuously measure SmO₂. External workload during match play was quantified using GPS-derived distance, load, top speed, sprint activity, and accelerations. Match data were segmented by half and into approximately 15-min epochs to characterize temporal changes in SmO₂ and external workload. Due to the exploratory nature and small sample size, analyses emphasized descriptive and within-player responses.
Results
SmO₂ demonstrated substantial inter- and intra-individual variability throughout the 90-min game. Among players with complete match-level SmO₂ data (n=2), mean SmO₂ for time on the field was 38.9% and 40.8%. Across approximately 15-min epochs, mean SmO₂ ranged from 32.6 to 59.8% in one player and 39.6 to 42.9% in another. Importantly, changes in local muscle oxygenation did not consistently parallel changes in external workload. In one player, second-half mean SmO₂ for time on the field decreased from 40.6% to 36.5% while distance covered and GPS-derived load per time on the field increased by 17.5% and 26%, respectively, even though playing time decreased by 13 min or 28.9%. In another player, average SmO₂ remained relatively stable between halves (40.3% vs. 41.2%) despite changes in external demands, including a 35% reduction in sprint count.
Conclusion
Rectus femoris SmO₂ demonstrated substantial temporal and inter-individual variability during the 90-min match, and changes in SmO₂ did not consistently correspond with changes in external workload. These preliminary findings suggest that local muscular oxygenation may provide physiological information that is complementary to conventional GPS-based monitoring. Portable NIRS may therefore offer a feasible field-based approach for integrating internal physiological responses with external load monitoring in soccer to further understand training and game demands.