Fig 4. Graphical display of variables contributing to principal component 1 (PC1) and principal component 2 (PC2) and amount of total variance explained per each PC showing strong association of sperm quality parameters including sperm concentration around PC1 and concentration of elements around PC2.

The variables concentrated around graphical centre do not contribute significantly to these two PCs, although they could be interpreted by subsequent PCs describing remaining data variance. The projection of K, Ca, Cu, Zn and Y variables on PC1 describing 31% of total variance shows weaker negative correlation to motility parameters and sperm concentration. Higher concentrations of these elements negatively impact forward progression parameters and sperm concentration, but contribute to hyperactivation motility expressed as low STR and LIN, accompanied with low “elongation” (a morphological parameter). This also implies that hyperactivation activates on expense of forward progression. PC2 describing 21% of remaining variance shows that all elements are correlated between themselves although Br and Sr express lower contribution. Their higher concentrations are associated to greater forward progression and sperm concentration. These results imply that, although of secondary importance, the higher baseline status of elements improves forward progression and sperm concentration.