Fig. 1.

Number of participants studied for each protocol. The square with dashed lines indicates the 53 subjects, who were tested twice in order to evaluate the difference between the original and the ‘half-Bruce’ (Group I). The square with solid lines indicates the 53 subjects, who were included in the determination of reference values (Group II): those who were tested twice and started with the original protocol (n = 28) and those who were only tested once (n = 25)