MicroRNAs (miRNAs) are intracellular mediators of essential biological 
functions. Recently, plasma-based 'circulating' miRNAs (c-miRNAs) have been 
shown to control cellular processes, but the c-miRNA response to human exercise 
remains unknown. We sought to determine whether c-miRNAs are dynamically 
regulated in response to acute exhaustive cycling exercise and sustained rowing 
exercise training using a longitudinal, repeated measures study design. 
Specifically, c-miRNAs involved in angiogenesis (miR-20a, miR-210, miR-221, 
miR-222, miR-328), inflammation (miR-21, miR-146a), skeletal and cardiac muscle 
contractility (miR-21, miR-133a), and hypoxia/ischaemia adaptation (miR-21, 
miR-146a, and miR-210) were measured at rest and immediately following acute 
exhaustive cycling exercise in competitive male rowers (n = 10, age = 19.1 ± 0.6 
years) before and after a 90 day period of rowing training. Distinct patterns of 
c-miRNA response to exercise were observed and adhered to four major profiles: 
(1) c-miRNA up-regulated by acute exercise before and after sustained training 
(miR-146a and miR-222), (2) c-miRNA responsive to acute exercise before but not 
after sustained training (miR-21 and miR-221), (3) c-miRNA responsive only to 
sustained training (miR-20a), and (4) non-responsive c-miRNA (miR-133a, miR-210, 
miR-328). Linear correlations were observed between peak exercise levels of 
miR-146a and VO2max (r = 0.63, P = 0.003) and between changes in resting miR-20a 
and changes in VO2max (pre-training vs. post-training, r = 0.73; P = 0.02). 
Although future work is required, these results suggest the potential value of 
c-miRNAs as exercise biomarkers and their possible roles as physiological 
mediators of exercise-induced cardiovascular adaptation.