Mitochondria-derived peptides are newly discovered small bioactive peptides thought to communicate metabolic status to other cells. Two such peptides, MOTS-c and Humanin, have been shown to have particularly strong regulatory effects on metabolism and oxidative stress in tissues, but their response to exercise training remains unknown. Thigh muscle biopsies were obtained from nine healthy young subjects, before, and at 0 and 2h after one acute bout of cycling exercise (1 hour at 70% of peak VO2) and after 3, 5, 7, and 14 days of exercise training at same cycling intensity and duration. A total of 8 training sessions were conducted in the 14 days. The skeletal muscle samples were analysed in duplicates for mRNA content of MOTS-c and Humanin. A one-way repeated measure analysis of variance (ANOVA) was performed to evaluate the effect of acute exercise or 14 days of exercise training. Tukey’s honestly significant difference post-hoc test was used to locate differences and FDR-adjusted p-values are reported. Data are reported as mean ± SEM.
The results showed that MOTS-c and Humanin mRNA content was higher by 19% and 24%, respectively (fig. 1a, p<0.05), at 2h after acute exercise compared to at rest. Furthermore, MOTS-c and Humanin content were 43% and 35% higher, respectively, than pre-training (fig. 1b, p<0.05) after the 14-days of exercise training.  
In conclusion, we show that MOTS-c and humanin are elevated both by acute exercise and exercise training at moderate intensity. Further studies are required to elucidate the role of these mitochondrial peptides for metabolic and performance adaptations to exercise training.