[Discussion on the application of ventilatory threshold in classification of physical workload in plateau]

Objective: To explore the application of the first ventilatory threshold (VT1) and the second ventilatory threshold (VT2) in the classification of physical workload for plateau workers, to provide reference for formulating the classification in plateau. Methods: In August 2018, 88 male workers from substations at different altitudes (500 m, 2000 m, 3000 m and 4000 m) of a company were selected as study subjects by cluster sampling. They were divided into plain group and plateau groups.The intensities of workload were simulated by power bicycle, and physiologic parameters, including VO(2), heart rate (HR) and energy metabolic rate per body surface area (E/BSA) , were recorded in test system when reaching VT1, VT2 and peak oxygen uptake (VO(2)Peak) . The ratios of VT1, VT2 and VO(2)Peak to the quiet and work potential at different altitudes were compared. Results: In a quiet state, compared with the plain group, the HR and E/BSA of the workers in the 2000 m and 3000 m groups increased, and the differences were statistically significant (P<0.05) . At VT2, compared with the plain group, the HR of the workers in the 4000 m group decreased, the difference was statistically significant (P<0.05) . VO(2) and E/BSA of workers in each plateau group were lower than those in the plain group at VO(2)Peak, and the differences were statistically significant (P<0.05) . At VT2 and VO(2)Peak, the ratios of VO(2), HR, and E/BSA relative to the quiet state of the workers in each plateau group were lower than those of the plain group, and the differences were statistically significant (P<0.05) . In the quiet state and VT1, compared with the plain group, the remaining percentages of VO(2) and E/BSA of workers in each plateau group decreased, and the differences were statistically significant (P<0.05) . Taking VT1, VT2 and VO(2)Peak as cut-off points and VO(2), HR and E/BSA as indicators, the physical workload in plateau could be divided into four levels, namely medium, heavy, extremely heavy and extreme physical workload. Conclusion: It is practicable to use ventilatory threshold to classification of physical workload. VT1 and VT2 can be applied to the classification in plateau to supplement and optimize current national standard of physical workload.