Author(s): RODRÍGUEZ-BARBERO EXPÓSITO, S., GONZÁLEZ-RAVÉ, J.M.1, MUÑOZ DE LA CRUZ, V.1, RODRIGO-CARRANZA, V.1, AGUDO-ORTEGA, A.1, SALINERO, J.J.1, GONZÁLEZ-MOHÍNO, F.1,2, Institution: SPORT ERFORMANCE RESEARCH GROUP, UNIVERSITY OF CASTILLA-LA MANCHA, Country: SPAIN, Abstract-ID: 451

INTRODUCTION:
Near-infrared spectroscopy (NIRS) is a non-invasive method to measure and evaluate muscle oxygenation in local tissue (1). It is important to note that possible sex-related differences affect the oxygen transport system depending on exercise intensity (2). However, there is a lack of information on possible sex-related differences in muscle oxygenation responses in other exercise modes such as running. Therefore, the present study aimed to analyze possible sex-related differences in muscle oxygen saturation in trained runners.
METHODS:
Twelve male and sixteen female trained runners participated in the study. A maximal graded exercise test (GXT) (HP Cosmos Pulsar, HP Cosmos Sports & Medical GMBH, Nussdorf-Traunstein, Germany) was performed. The test started at 8 km·h-1 and 10 km·h-1 for females and males, respectively, and the speed was then increased by 1 km·h-1 every minute until voluntary exhaustion. Two portable NIRS devices (Moxy Monitor) were placed to measure muscle oxygen saturation (SmO2) in the vastus lateralis (VL), at 2/3 of the distance between the line from the anterior spina iliac superior to the lateral side of the patella; and at the most prominent bulge of the medial gastrocnemius (GN). During GTX, respiratory variables were measured using a gas analyzer (CPX Ultima Series MedGraphics). First (VT1) and second (VT2) ventilatory thresholds and maximal oxygen uptake (VO2max) were identified for each participant. A repeated measures ANOVA was used to compare the differences in SmO2 produced at each threshold with sex as an inter-subject factor.
RESULTS:
There were no significant differences in the interaction threshold (VT1, VT2 and VO2max) × sex (men vs. woman) in SmO2. The mean values in SmO2 of VL and GN were significantly lower (p<0.001) at VT2 and VO2max in comparison with VT1. Woman presented higher values (p<0.001) in SmO2 of VL at VT1 (76.5 vs. 45.5%), VT2 (56.4 vs. 28.0%) and VO2max (41.1 vs. 12.5%) compared to men. The percentage of reduction in SmO2 between VT2 and VO2max were significantly higher (p<0.004) in men (56.0 vs. 27.4%) compared to women.
CONCLUSION:
The measurement of SmO2 in GN and VL allow to identify a breaking point between the oxygen supply and consumption through NIRS. However, SmO2 had a different behavior in both muscles. Thus, women had higher SmO2 in the three points analyzed in VL but not in GN. Both sexes showed similar patterns of decrease in SmO2 as metabolic demand increases. However, men displayed a strong decline in the VL at VT2 which indicates a better oxygen supply in the active tissues. This fact can be related to a higher muscle vasodilation capacity in females that leads to a redistribution of oxygen to the active tissues and to a higher estrogen concentration.

REFERENCES
1. Kitada T, Machida S, Naito H. BMJ Open Sport Exerc Med. 2015;1(1):e000062.
2. Sendra-Perez C, Priego-Quesada JI, Salvador-Palmer R, Murias JM, Encarnacion-Martinez A. J Appl Physiol (1985). 2023;135(5):1092-101.