Validity of oxigen uptake efficiency slope to monitor changes induced by health-enhancing phisical activity

BACKGROUND: regular exercise and physical activity have favourable effects on cardiorespiratory fitness attenuating the impairment of oxygen metabolism associated to low aerobic capacity and reducing the risk of all-cause of mortality. Traditionally maximal oxygen uptake (VO2max) is considered the best indicator of exercise capacity and aerobic power. A plateau in VO2 despite increasing workload is the most important criterion for the attainment of VO2 max. However, this plateau is not always observed in both healthy subjects and individuals with various health diseases. In addition, the VO2 max determination requires demanding maximal efforts limiting its use in daily practice (e.g. fitness club). To overcome these shortcomings Baba et al. have developed a new index of cardiorespiratory functional reserve that can be obtained even when the true maximal effort is not achieved: the oxygen uptake efficiency slope (OUES). The OUES is derived from the slope of the relationship between VO2 and ventilation during incremental tests. The OUES is considered an integrated measure of cardiovascular, muscular and respiratory function. In the literature studies have reported contrasting results about its validity to monitor training –induced changes. The aim of this study was to examine the relationship between OUES and VO2 max in previously inactive subjects, and the association between changes in VO2max and OUES induced by training. METHODS: eighteen subjects (mean±SD: age 35±7, height 173±6, body mass 74±11 kg) recruited in a fitness club participated to the study. Before and after 6 months of training (aerobic and strength exercises), VO2 max, OUES and blood lipid profile were measured. OUES was calculated using the following equation: VO2 = a • log Ventilation + b; where the constant a is the OUES and b is the intercept. RESULTS: VO2max improved from 34.9±6.6 to 37.2±7.7 mL/kg/min (P<0.05), while the increase in OUES did not reach the significance (18.2±3.0 vs 19.0±3.8; P=0.14). However, significant correlations were found between VO2 max and OUES before and after the training period (r=0.74 and r=0.77; P<0.01), and between training-induced changes in VO2 max and OUES (r=0.66; P<0.01). Total cholesterol (TC) decreased from 216±31 to 189±44 mg/dL (P=0.03), low-density lipoprotein (LDL) from 135±27 to 110±41 mg/dL. No changes were found in high-density lipoprotein (58±16 to 58±16 mg/dL; P=0.89) and triglycerides (116±119 to 96±72 mg/dL; P=0.59). DISCUSSION: These results confirm the efficacy of regular participation to health-enhancing physical activities. Indeed, VO2 max increased and TC and LDL levels decreased after training. The improvement in OUES showed only a trend, but a significant correlation between changes in VO2 max and OUES was found. This suggests that OUES may be useful to monitor training-induced changes but is less sensitive than VO2 max.