A proposal to identify the maximal metabolic steady state by muscle oxygenation and VO2max levels in trained cyclists

Purpose Near-infrared spectroscopy (NIRS) sensors measure muscle oxygen saturation (SmO 2 ) as a performance factor in endurance athletes. The objective of this study is to delimit metabolic thresholds relative to maximal metabolic steady state (MMSS) using SmO 2 in cyclists. Methods Forty-eight cyclists performed a graded incremental test (GTX) (100 W-warm-up followed by 30 W min) until exhaustion. SmO 2 was measured with a portable NIRS placed on the vastus lateralis. Subjects were classified by VO 2 max levels with a scale from 2 to 5: L2 = 45–54.9, L3 = 55–64.9, L4 = 65–71, L5 = > 71, which represent recreationally trained, trained, well-trained, and professional, respectively. Then, metabolic thresholds were determined: Fatmax zone, functional threshold power (FTP), respiratory compensation point (RCP), and maximal aerobic power (MAP). In addition, power output%, heart rate%, VO 2 %, carbohydrate and fat consumption to cutoff SmO 2 point relative to MMSS were obtained. Results A greater SmO 2 decrease was found in cyclists with > 55 VO 2 max (L3, L4 and L5) vs. cyclists (L2) in the MMSS. Likewise, after passing FTP and RCP, performance is dependent on better muscle oxygen extraction. Furthermore, the MMSS was defined at 27% SmO 2 , where a non-steady state begins during exercise in trained cyclists. Conclusion A new indicator has been provided for trained cyclists, < 27% SmO 2 as a cut-off to define the MMSS Zone. This is the intensity for which the athlete can sustain 1 h of exercise under quasi-steady state conditions without fatiguing.