The intensity of exercise above which oxygen uptake (Vo2) does not account for all of the required energy to perform work has been associated with lactate accumulation in the blood (lactate threshold, LT) and elevated carbon dioxide output (gas exchange threshold). An increase in hydrogen ion concentration ([H+]) is approximately concurrent with elevation of blood lactate and CO2 output during exercise. Near-infrared spectra (NIRS) and invasive interstitial fluid pH (pHm) were measured in the flexor digitorum profundus during handgrip exercise to produce a mathematical model relating the two measures with an estimated error of 0.035 pH units. This NIRS pHm model was subsequently applied to spectra collected from the vastus lateralis of 10 subjects performing an incremental-intensity cycle protocol. Muscle oxygen saturation (SmO2) was also calculated from spectra. We hypothesized that a H+ threshold could be identified for these subjects and that it would be different from but correlated with the LT. Lactate, gas exchange, SmO2, and H+ thresholds were determined as a function of Vo2 using bilinear regression. LT was significantly different from both the gas exchange threshold (Delta = 0.27 +/- 0.29 l/min) and H+ threshold (Delta = 0.29 +/- 0.23 l/min), but the gas exchange threshold was not significantly different from the H+ threshold (Delta = 0.00 +/- 0.38 l/min). The H+ threshold was strongly correlated with LT (R2 = 0.95) and the gas exchange threshold (R2 = 0.85). This initial study demonstrates the feasibility of noninvasive pHm estimations, the determination of H+ threshold, and the relationship between H+ and classical metabolic thresholds during incremental exercise

Treadmill exercise is commonly used for aerobic and anaerobic conditioning. During non-motorized treadmill exercise, the subject must provide the power necessary to drive the treadmill belt. The purpose of this study was to determine what factors affected the time to fatigue on a pair of non-motorized treadmills. Twenty subjects (10 males/10 females) attempted to complete five minutes of locomotion during separate trials at 3. 22, 4.83, 6.44, 8.05, 9.66, and 11.27 km·h -1 . Total exercise time (<5 min) was recorded.Exercise time was converted to the amount of 15 second intervals completed. Peak oxygen uptake (VO 2 ) was measured using a graded exercise test on a standard treadmill, and anthropometric measures were collected from each subject before entering into the study. A Cox proportional hazards regression model was used to determine significant predictive factors in a multivariate analysis. Non-motorized treadmill speed and absolute peak VO 2 were found to be significant predictors of exercise time, but there was no effect of anthropometric characteristics. Gender was found to be a predictor of treadmill time, but this was likely due to a higher peak VO 2 in males than in females. These results were not affected by the type of treadmill tested in this study. Coaches and therapists should consider the cardiovascular fitness of an athlete or client when prescribing target speed since these factors are related to the total exercise time than can be achieved on a nonmotorized treadmill.

No abstract

No abstract