Fig. 4

Heart rate (A) and blood lactate concentration (B) during graded exercise tests. Heart rate data from all three tests of two participants were excluded due to technical error. The peak blood lactate concentrations were 9 ± 2 mmol/L with no mask, 7.8 ± 1.4 mmol/L with surgical mask and 6.6 ± 2.0 mmol/L when wearing a taped filter mask (Main effect F(2,14) = 6.356, p = 0.011), respectively. Post-hoc analyses reveal that the maximal blood lactate concentration reached with a taped filter mask is significantly lower than that reached with no mask (p = 0.009)