Determination of Lactate Turn Points by Gas Exchange, Salivary a-Amylase and Testosterone in Male Subjects

Abstract

PURPOSE: We measured changes in salivary α-amylase (AA) and salivary testosterone (ST) to determine lactate turn point one (LTP1) and two (LTP2) via respiratory gas exchange measures and blood lactate (LA) concentration. METHODS: Eight endurance trained athletes (mean age: 20.8 + 3.1; Wt: 67.2 + 2.8 kg; Ht: 177.8 + 5.1; % BF: 9.8 + 3.0) volunteered for this study. We conducted a single incremental electronically braked cycle ergometer test up to a workload of 240 Watts (W). The test began with 2 min seated rest; followed by 2 min of warm-up at 40 W followed by an increase of 20 W every 2 min thereafter until 240W. The respiratory gas exchange measures were collected and heart rate (HR) was monitored via telemetry system. Blood samples in the amount of 7 μ1 were collected at rest, at the end of warm up, at the end of every 2 min increment and analyzed for LA. Saliva samples were collected during rest, the last 30s of the warm-up, and during each increment, stored at - 20o C, and subsequently analyzed of AA and ST. RESULTS: Statistical analysis revealed significant differences for absolute and relative oxygen uptake (VO2 l.min-1 and ml.kg-1.min-1; P<0.001), min ventilation (VE l.min-1; P<0.001), carbon dioxide production (VCO2 l.min-1; P<0.001), respiratory exchange ratio (RER; P<0.001), ventilatory equivalents for oxygen (VE/VO2; P<0.001), ventilatory equivalents for carbon dioxide (VE/VCO2; P<0.001), and HR (P<0.001). There was statistically significant difference for salivary AA (U.ml-1;p0.25). The analysis of LA revealed that LTP1 (LA 2.44+0.73 mmol.1-1) occurred at a workload of 140 W or VO2 of 30.5 ml.kg-1.min-1 and LTP2 (LA 3.61 + 1.24 mmol.l-1) or VO2 36.6 + 1.6 ml.kg-1.min-1 at workload of 180 W. Correlation analysis yielded no statistically significant relationships between LA and any measured respiratory gas exchange variables at a workload of 180 W. However, there was a strong relationship between salivary AA and LA concentration at a workload of 200 W (r = 0.90; p<0.006) and for ST (r = 0.86; p<0.006) at a workload of 180 W. CONCLUSION: This study suggests that AA may be used for non-invasive determination of LTP1 but not LTP2. The ST does not appear to be sensitive to changes at lower to moderate intensities and thus it is not suitable for determination of LTP1 or LTP2.