The onset of anaerobic (lactate) metabolism during incremental exercise, which may be a result of an imbalance between tissue oxygen supply and demand, has been associated with the gas exchange ventilatory threshold (VT). This study was designed to examine whether near infrared spectroscopy (NIRS) could be used to detect the VT in healthy subjects. Twenty-one men and 19 women completed incremental cycle ergometry during which NIRS measurements were obtained from the right vastus lateralis and gas exchange measurements were monitored simultaneously using a metabolic cart. The VT was identified from the metabolic data by the V-slope method and from NIRS data as the intensity at which tissue absorbency crossed the resting baseline value observed immediately prior to the initiation of exercise. Pearson correlations for the relative oxygen uptake and power output observed for the two methods of detecting VT were 0.90 and 0.88, respectively, in men and 0.89 and 0.86, respectively, in women (P < 0.01). No significant differences were observed between the two methods of detecting VT for any of the physiological responses (P > 0.05). No significant (P > 0.05) gender differences were observed in muscle oxygenation values at the VT, 32% in men and 38% in women. These results validate the use of NIRS as an alternate noninvasive method for detecting VT during cycle exercise in healthy subjects.

%Mox was not an accurate predictor of mixed (a - v)O2diff during exercise because of the low common variance between these two variables, and it is unclear whether the gender difference in %Mox is a true physiological phenomenon or whether it is an artifact of the NIRS technique.

Abstract. We examined the effects of fluid and food intake on cardiopulmonary status during cardiopulmonary exercise testing (CPX). Twelve young men fasted for 12 hours, followed by CPX under three experimental conditions: 1) continuation of fasting; 2) ingestion of 420 ml of water; and 3) ingestion of 420 g of jelly. For the second and third experimental conditions a 30-min time lapse was imposed after intake of water or food before CPX. Each participant then underwent symptom-limited maximal CPX and also acted as his own control for each experimental condition. The respiratory gas exchange ratio was significantly smaller in the water condition (0.76 ± 0.06) than in the fasting (0.83 ± 0.01) and jelly (0.83 ± 0.05) conditions at rest, but no other differences in cardiopulmonary responses were evident. These findings suggest that blood distribution to skeletal muscles is prioritized at maximal exercise level even during the digestion and absorption of food. In conclusion, careful consideration should be given to the load on the cardiopulmonary system and quantity and types of fluid or food ingested, when engaging in physical exercise.