“…Ten studies investigated plasma samples [ 34 , 36 , 40 , 41 , 44 , 45 , 47 , 50 , 51 , 53 ], eight analyzed serum samples [ 35 , 37 – 39 , 48 , 49 , 52 , 54 ], two investigated urine samples [ 43 , 46 ], one analyzed skeletal muscle [ 42 ], and one investigated sweat [ 55 ]. Twelve studies applied a targeted approach [ 34 – 38 , 42 , 44 , 46 , 47 , 49 , 51 , 52 ], and eight studies applied an untargeted approach [ 39 , 40 , 43 , 48 , 50 , 53 – 55 ]. Depending on the nature of metabolites, one study used a targeted or untargeted approach [ 41 ], whereas another used a targeted or semi-targeted approach [ 45 ].…”