Muscle specific miRNAs, myomiRs, have been shown to control muscle development 
in vitro and are differentially expressed at rest in diabetic skeletal muscle. 
Therefore, we investigated the expression of these myomiRs, including miR-1, 
miR-133a, miR-133b and miR-206 in muscle biopsies from vastus lateralis of 
healthy young males (n = 10) in relation to a hyperinsulinaemic–euglycaemic 
clamp as well as acute endurance exercise before and after 12 weeks of endurance 
training. The subjects increased their endurance capacity, VO2max (l min−1) by 
17.4% (P < 0.001), and improved insulin sensitivity by 19% (P < 0.01). While 
myomiR expression remained stable during a hyperinsulinaemic–euglycaemic clamp, 
an acute bout of exercise increased mir-1 (P < 0.05) and mir-133a (P < 0.05) 
expression before, but not after, training. In resting biopsies, endurance 
training for 12 weeks decreased basal expression of all four myomiRs (P < 0.05). 
Interestingly, all myomiRs reverted to their pre-training expression levels 14 
days after ceasing the training programme. Components of major pathways involved 
in endurance adaptation such as MAPK and TGF-β were predicted to be targeted by 
the myomiRs examined. Tested predicted target proteins included Cdc42 and ERK 
1/2. Although these proteins were downregulated between post-training period and 
2 weeks of cessation, an inverse correlation between myomiR and target proteins 
was not found. In conclusion, our data suggest myomiRs respond to physiological 
stimuli, but their role in regulating human skeletal muscle adaptation remains 
unknown.