PURPOSE: Prolonged sitting impairs leg endothelial function, which seems to be mediated by a sustained reduction in blood flow-induced shear stress. However, whether regular endurance training is effective in preventing sitting-induced leg endothelial dysfunction remains largely unknown. Herein, we tested the hypothesis that sitting-induced leg endothelial dysfunction is prevented in high endurance-trained individuals.
METHODS: The endurance-trained group comprised 11 male collegiate cyclists (age, 19.7 ± 0.6 years; height, 168.4 ± 6.2 cm; weight, 62.7 ± 7.0 kg; body mass index, 22.1 ± 2.4 kg/m²), and the untrained group comprised 9 male with no regular endurance training (age, 21.1 ± 1.8 years; height, 170.1 ± 6.6 cm; weight, 72.2 ± 8.1 kg; body mass index, 24.8 ± 1.5 kg/m²). Peak oxygen uptake (VO₂peak) was initially determined in all participants using incremental exercise test (37.9 ± 4.7 mL/min/kg in the untrained group vs. 60.5 ± 3.6 mL/min/kg in the endurance-trained group). At second visit, the popliteal artery flow-mediated dilation (%FMD) was assessed before and after a 3-h sitting period. During the sitting period, the popliteal artery diameter and blood velocity were measured every hour.
RESULTS: The popliteal artery shear rate was significantly and similarly reduced during the sitting period in both groups (the untrained group and the endurance-trained group: 51.9 ± 19.2 sec^-1 vs. 58.3 ± 23.5 sec^-1 at pre-sit, 25.5 ± 10.9 sec^-1 vs. 25.5 ± 15.2 sec^-1 at 1h during sitting period, 19.4 ± 7.4 sec^-1 vs. 27.5 ± 12.3 sec^-1 at 2h during sitting period, 21.4 ± 8.1 sec^-1 vs. 20.8 ± 8.3 sec^-1 at 3h during sitting period, 29.4 ± 13.9 sec^-1 vs. 29.7 ± 15.8 sec^-1 at post-sit, P < 0.001). In a 3-h sitting, a significant impairment in popliteal artery %FMD was observed in the untrained group (4.5 ± 0.6 % vs. 1.6 ± 0.2 % P = 0.003), but it was prevented in the endurance-trained group (6.9 ± 0.7 % vs. 6.2 ± 1.3 %, P < 0.431).
CONCLUSIONS: In conclusion, the present study revealed that sitting-induced leg endothelial dysfunction is preventable in endurance-trained individuals.