Association between the anaerobic threshold and the break-point in the double product/work rate relationship

Abstract

A break point in the double product versus work rate relationship (DPBP) during incremental exercise has previously been reported. The aim of the current study was to investigate the frequency and degree of inter-observer agreement with which a DPBP could be detected. We also wished to determine its relationship, if any, to the lactic acidosis threshold (LATla). Ten normal volunteers performed continuous incremental bicycle ergometer exercise under three different concentrations of inspired oxygen (FiO2 = 0.21, 0.15 and 0.12). In addition, a group of patients with diseases expected to result in impaired exercise tolerance performed exercise under room air conditions. Gas exchange was measured continuously and double product was measured at 15-s intervals throughout exercise using an automated sphygmomanometer. Four observers, unaware of subject identity and test condition, analysed a total of 39 tests. All four observers detected a DPBP in 29 cases (74%) and an LAT in 35 cases (90%). The intra-class correlation coefficient was 0.76 for the DPBP and 0.93 for the LATla, indicating a reasonable level of agreement among observers for both break points. The DPBP was closely related to the LATla (r = 0.865, P < 0.0001), although it occurred at a slightly higher oxygen consumption (VO2, bias 0.137 1.min-1, 95% confidence intervals 0.041-0.233). We conclude that the DPBP is a common occurrence during incremental exercise. The close relationship between the DPBP and the LATla suggests that both may reflect similar events at the level of the skeletal muscle cell.

The influence of aerobic exercise training on the double product break point in low-to-moderate risk adults

“…This difference may be a reflection of the two groups of subjects within this analysis, as significant CAD has been shown to decrease the VO 2 at which the AT can occur (Wasserman et al 1973). Riley et al further report that the DPBP and VT were correlated significantly (r = 0.86), which is also similar to the findings of the current study (Riley et al 1997). Omiya et al in 2004(Omiya et al 2004) also studied the relationship between the DPBP and VT in 65 cardiac patients and found the mean workload at both thresholds to be similar, with a significant correlation between the two thresholds (r = 0.76, p < 0.001).…”

“…While Tanaka and colleagues Tanaka and Shindo 1992) were the first to identify that the slope of the DP was greater above the LT as well as the presence of the DPBP, it was Brubaker et al (Brubaker et al 1997) and Riley et al (Riley et al 1997) who were the first to compare the occurrence of the DPBP to the VT. Brubaker successfully identified the DPBP in cardiac patients during treadmill exercise testing. Mean VO 2 values at the DPBP and VT differed by 5%, which was similar to the current study (5.5% difference at baseline in L .…”

“…Riley et al (Riley et al 1997) examined the relationship between the DPBP and VT in 10 healthy individuals and 10 patients with CAD undergoing cycle ergometer testing. They found the mean VO 2 value of the DPBP to be significantly higher than the VT (1.39 vs. 1.26 L .…”

“…The cause of the DPBP is not well understood, although it has been shown that catecholamine levels in the blood exhibit threshold phenomenon as well, with catecholamine levels significantly greater above the LT and/or VT (Mazzeo and Marshall 1989;Riley et al 1997;Tanabe et al 1994). This is suggesting that as exercise intensity and myocardial oxygen demand increases, a disproportionate increase in sympathetic activity occurs.…”

“…The DP has been a useful index in cardiac rehabilitation settings to identify specific workloads at which signs and symptoms of ischemia occur, and improvements in functional capacity relative to the onset of symptomatic ischemia (Arya et al 2005;Durstine and Tanaka and colleagues were the first to identify that the DP increases more rapidly above the LT than below it, and were the first to identify a breakpoint in the double product (DPBP) with incremental exercise in healthy subjects Tanaka and Shindo 1992). Several other studies have further examined the occurrence of the DPBP in healthy subjects as well as those with coronary artery disease (CAD), (Brubaker et al 1997;Kim et al 2003;Omiya et al 2004;Riley et al 1997), and have found that the DPBP occurs at similar exercise intensities to that of the lactate threshold (LT) and ventilatory threshold (VT). They conclude that the DPBP may be a useful non-invasive, and easier to obtain marker of the LT and VT in a wide range of individuals.…”