Investigating the relationship between aerobic fitness and lower-limb resistance vessel function before and after a bout of uninterrupted sitting

Prolonged sitting reduces lower-limb resistance vessel function (RVF), whereas increasing aerobic fitness levels enhance lower-limb RVF. However, it is unknown whether having higher aerobic fitness offers protection against prolonged sitting-induced declines in RVF. This study investigated the relationships between aerobic fitness versus reductions in lower-limb RVF following a 3 h bout of uninterrupted sitting. In 30 healthy young adults (19♀, 24 ± 6 years), aerobic fitness was assessed during a graded, maximal cycling test. Relative peak oxygen consumption (V̇O₂peak) was determined via indirect calorimetry (37.5 ± 8.6 (24.7-60.7 mLO₂/kg/min). Popliteal blood flow (PBF) was recorded via duplex ultrasonography. Lower-limb RVF was assessed in the seated posture and quantified as the peak PBF and area under the curve (PBF_AUC, first minute of hyperemia) responses to 5 min of distal cuff-induced ischemia. The lower-limb RVF assessment was performed before and after a sitting. Peak PBF decreased following sitting (473 ± 254 to 387 ± 199 mL/min, <i>P</i> = 0.024), while PBF_AUC remained unchanged (6145 ± 3063 versus 6446 ± 3826 mL, <i>P</i> = 0.758). Relative V̇O₂peak was not associated with Pre-sitting peak PBF (<i>R</i> = 0.236, <i>P</i> = 0.210) or PBF_AUC (<i>R</i> = -0.026, <i>P</i> = 0.889). Furthermore, relative V̇O₂peak was also not associated with sitting-induced reductions in peak PBF (<i>R</i> = -0.145, <i>P</i> = 0.444). The reductions in peak PBF following sitting support previous work demonstrating that prolonged uninterrupted sitting negatively impacts lower-limb RVF. In contrast, prolonged sitting did not alter the PBF_AUC response, suggesting that peak PBF responses may provide a more sensitive index of sitting-induced declines in RVF. In young, healthy individuals, aerobic fitness did not impact baseline or sitting-induced reductions in lower-limb RVF.