Vascular and Blood Flow Responses to Acute Upper Limb Exercise: Impact of Sex and Menstrual Cycle Phase

Purpose This study sought to determine whether fluctuations in estrogen levels throughout the menstrual cycle (early (EF) vs late follicular (EF) phase) altered the vascular and blood flow responses to acute upper limb exercise and if these responses were different when compared to males. Methods Ten young females (YF: 21±3 yrs) were recruited and completed two identical visits (EF and LF) consisting of an acute upper limb exercise bout (progressive, rhythmic handgrip). Peripheral (brachial artery (BA) diameter, shear rate, and blood flow) and central (mean arterial pressure, heart rate) hemodynamic measurements were obtained during the last minute of each 3‐minute handgrip workload (3kg, 6kg, and 9kg) via Doppler ultrasonography and finger plethysmography, respectively. Male controls (YM: n = 21; 21±3 yrs) matched for age completed one visit to provide a biological sex comparison. Data is presented as mean ± standard deviation. Results In young females, brachial artery flow mediated dilation (controlled for shear rate) [EF (3kg: 0.006±0.01; 6kg: 0.015±0.01; 9kg: 0.022±0.01); LF (3kg: 0.008±0.01; 6kg: 0.017±0.01; 9kg: 0.024±0.01)], blood flow [EF (3kg: 162±61; 6kg: 236±74; 9kg: 332±104 ml.min −1 ); LF (3kg: 151±23; 6kg: 237±47; 9kg: 330±104 ml.min −1 )], and vascular conductance [EF (3kg: 1.8±0.7; 6kg: 2.5±0.7; 9kg: 3.1±0.7 ml.min −1 .mmHg −1 ); LF (3kg: 1.8±0.4; 6kg: 2.6±0.6; 9kg: 3.3±1.1 ml.min −1 .mmHg −1 )] were significantly increased with each progressive handgrip workload but were unaltered when comparing the EF and LF conditions. When compared to young males (YM), young females reported no differences in BA FMD [YF vs YM (3kg: 0.006±0.01 vs 0.007±0.01; 6kg: 0.015±0.01 vs 0.013±0.01; 9kg: 0.022±0.01 vs 0.018±0.01)], but did report significantly lower blood flow [YF vs YM (3kg: 162±61 vs 228±64; 6kg: 236±74 vs 347±94; 9kg: 332±104 vs 474±119 ml.min −1 )] and vascular conductance [YF vs YM (3kg: 1.8±0.7 vs 2.5±0.7; 6kg: 2.5±0.7 vs 3.8±0.9; 9kg: 4.9±1.1 vs ml.min −1 .mmHg −1 )]. Conclusion The findings of this study revealed that fluctuations in estrogen throughout the menstrual cycle do not alter vascular and blood flow regulation during exercise, but, when compared to young males, young female’s exhibited lower blood flow/vascular conductance. Additional research is necessary to determine if these sex differences in blood flow/conductance represent adequate or inadequate blood flow regulation during exercise.