Aim: The positive association between body size and blood pressure (BP) is well recognised. However, not all overweight individuals are hypertensive. This study aimed to examine the influence of body size and gender on the haemodynamic mechanisms driving systolic BP (SBP) at rest and during exercise, in young adults.

Method: Detailed anthropometric, biochemical and haemodynamic measurements including BP, cardiac index (CI) and peripheral vascular resistance (PVR) were obtained in 2497 untreated individuals (23±6 years) at rest. Subjects were classified as normal-weight (NW; BMI <25) or overweight (OW; BMI>25). A sub-set of 86 individuals (29±6 years) undertook steady-state, sub-maximal cycling exercise, with detailed haemodynamic measurements re-assessed.

Results: At rest, a positive association was found between SBP and cardiac index (CI) in NW but not OW males and females (p<0.001 for both). In contrast, a positive association was found between SBP and PVR in OW but not NW males (P<0.001 for both). Although BMI did not correlate with BP during exercise, body fat (BF) % was inversely associated with exercise-induced changes in PP, even after adjustment for gender. A higher BF% was also associated with a poorer maximum dilatory response to ischaemia.

Conclusion: The primary haemodynamic mechanisms driving SBP differ depending on body size in young adults. BF% may be a more useful tool than BMI to further examine the impact of body size on BP in young adults. Structural differences in resistance vessels may underlie the association between body size and BP responses to exercise.