Exercise factors are circulating signalling molecules that are responsive to acute exercise and exercise training. This thesis investigated (i) whether circulating metabolites, a source of exercise factors, change in response to short term exercise training, (ii) whether circulating metabolites and small extracellular vesicles (EVs; ‘carriers’ of exercise factors) are altered in an association with divergent histories of exercise training, and (iii) whether plasma extracted from men divergent exercise training histories influenced BT-549 cells. Nine sessions of sprint interval training reduced the abundance of 11 fatty acids in circulation in blood samples taken at rest. A history of exercise training was associated with alterations in the abundance of 44 of metabolites. Under standardized measurement conditions the reliability of plasma metabolite concentrations varied largely at the level of individual metabolites with ~48% of metabolites displaying good-to-excellent reliability. A history of exercise training was not associated with an altered abundance of small EVs across multiple methods of small EV identification. BT-549 cells cultured with media supplemented with plasma derived from men with divergent exercise training histories had increased cell proliferation, greater anoikis, and lower extracellular matrix invasion compared to standard cell-culture media conditions. This thesis provides insight into whether circulating metabolites are altered at rest in response to, or associated with, exercise training. This thesis does not support a paradigm wherein the ‘exercise factor environment’ at rest is largely different between healthy individuals with divergent training histories as assessed in terms of metabolite profile, small EV presence, or bioactive effects on BT-549 cells.