Fig. 1

The association between mtDNAcn and semen parameters in multiple linear model while adjusting for age (continuous), BMI (continuous), smoking (categorical) and drinking status (categorical). Sperm concentration, total sperm count, and normal morphological rate and mtDNAcn were ln-transformed. *P < 0.05 and **P < 0.01. TZI teratozoospermia index, SDI sperm deformity index, VCL curve line velocity, VSL straight line velocity, VAP velocity of average path, ALH lateral head movement, MAD average motion degree, LIN linearity, STR straightness, WOB wobble, BCF beat cross frequency.