Exercise and Artery Function in Twins: Sex Differences in a Cross-Over Trial

Background: Physical activity reduces cardiovascular risk, partly via direct effects on the arterial wall. We hypothesized that vascular function responses would be modality-specific, sex-dependent, and express a high degree of heritability. Methods: We recruited 90 same-sex twins (31 monozygotic, 14 dizygotic dizygotic pairs; 25.8±6.0 years) and randomized 70 (25 monozygotic, 10 dizygotic) to complete, as pairs, 3 months each of resistance and endurance training, separated by a 3-month washout. Results: Brachial artery flow-mediated (FMD%) and glyceryl-trinitrate induced dilation (GTN%) both increased following endurance (FMD%: ∆1.46%, P <0.001; GTN%: ∆1.76%, P =0.004) and resistance (FMD%: ∆1.73%, P <0.001; GTN%: ∆1.68%, P =0.045). About one-third of participants failed to respond to one or other mode; 10% failed to respond to both for FMD% (17% for GTN%). FMD% and GTN% increased significantly in response to both resistance and endurance in females ( P <0.05), but not males. Twin analysis revealed that responses to both FMD% and GTN% with exercise training for both modalities were dependent on factors shared by monozygotic pairs and that a large contribution from genetic effects is unlikely. Conclusions: Our findings indicate that both endurance and resistance can enhance vascular function and that responses in females were more marked. Most individuals respond to one or other form of training, with few unresponsive to both; a finding that has implications for optimizing exercise-based approaches for individualized benefit. Focusing on characteristics of exercise prescription may be more important than the impact of distinct candidate genes when considering exercise as a form of vascular medicine. REGISTRATION: URL: https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=37122 ; Unique identifier: ACTRN 12616001095459.