A single session of moderate‑intensity cardio (45 minutes cycling at about 70% of your max oxygen use) raises the blood level of the mitochondrial peptide humanin, which is linked to cell survival and metabolism. Lifting weights doesn’t have the same effect, and the peptide levels don’t seem tied to how fit you already are.

Mitochondrial-derived peptides (MDPs) humanin (HN) and mitochondrial open reading frame of the 12S rRNA-c (MOTS-c) are involved in cell survival, suppression of apoptosis, and metabolism. Circulating levels of MDPs are altered in chronic diseases such as diabetes type 2 and chronic kidney disease. Whether acute resistance (RE) or endurance (EE) exercise modulates circulating levels of HN and MOTS-c in humans is unknown. Following familiarization, subjects were randomized to EE (<i>n</i> = 10, 45&#x2009;min cycling at 70% of estimated V&#x307;O_2max), RE (<i>n</i> = 10, 4 sets &#xd7; 7RM, leg press and knee extension), or control (CON, <i>n</i> = 10). Skeletal muscle biopsies and blood samples were collected before and at 30&#x2009;min and 3&#x2009;h following exercise. Plasma concentration of HN and MOTS-c, skeletal muscle MOTS-c as well as gene expression of exercise-related genes were analyzed. Acute EE and RE promoted changes in skeletal muscle gene expression typically seen in response to each exercise modality (c-Myc, 45S pre-rRNA, PGC-1&#x3b1;-total, and PGC-1&#x3b1;-ex1b). At rest, circulating levels of HN were positively correlated to MOTS-c levels and age. Plasma levels of MDPs were not correlated to fitness outcomes [V&#x307;O_2max, leg strength, or muscle mitochondrial (mt) DNA copy number]. Circulating levels of HN were significantly elevated by acute EE but not RE. MOTS-C levels showed a trend to increase after EE. These results indicate that plasma MDP levels are not related to fitness status but that acute EE increases circulating levels of MDPs, in particular HN.<b>NEW &amp; NOTEWORTHY</b> In this manuscript, we report for the first time, to our knowledge, the response of circulating levels of mitochondrial-derived peptides humanin and MOTS-c to acute resistance and endurance exercise. Our data support that acute endurance exercise stimulates MDP levels in plasma, whereas acute resistance exercise does not.