“…Indeed, analysis of the 22 selected studies revealed that nine studies focused on HRV [ 36 , 38 , 44 , 45 , 46 , 47 , 48 , 50 , 51 ], six studies on stress [ 26 , 36 , 38 , 41 , 54 , 55 ], and nine on cortisol [ 40 , 42 , 43 , 51 , 52 , 54 , 55 , 56 , 57 ], while the remaining six focused on oxytocin [ 40 , 43 , 48 , 53 , 55 , 57 ]. The studies are summarized in Table 1 .…”