Lower Limb Endothelial Function is Augmented in Habitually Endurance Trained versus Untrained Postmenopausal Women
Authors: Craig Jennifer , Bailey Stephen J. , Ferguson Richard A. , O’Donnell Emma 
Published: April 2020

Background

Exercise‐mediated increases in blood flow, a known nitric oxide (NO) stimulus, is a key signal in vascular adaptations to exercise training, including augmented endothelial function. However, endurance trained postmenopausal women (PMW) demonstrate similar brachial artery endothelial function as untrained PMW, suggesting the vascular benefit of exercise is mitigated. To investigate whether endothelial function is also impaired in the lower limb skeletal muscle vascular bed, we compared calf blood flow (CBF), an index of endothelial function, in healthy habitually endurance trained and untrained PMW. To examine vascular responsiveness to exercise‐mediated increases in blood flow, we also assessed CBF after an acute bout of dynamic exercise. We hypothesised that, pre‐exercise endothelial function would not differ between groups, but that post‐exercise endothelial function would be augmented in both groups, with greater increases observed in trained versus untrained PMW.

Methods

Two groups of healthy, age‐matched (56±1 years; overall mean±SEM), habitually endurance trained (n=10; VO2peak 40±1 ml/kg/min; PMWtr) and untrained (n=13; VO2peak 29±1 ml/kg/min; PMWun) PMW were studied. Resting (CBFr) and peak (CBFpk) CBF were assessed using strain‐gauge plethysmography. Resting (VRr) and peak (VRpk) vascular resistance were calculated (mean arterial pressure/CBF). Heart rate and blood pressure were recorded using an automated cuff device. Venous blood samples were collected for the determination of plasma nitrite, a stable metabolite of NO bioavailability. All measures were assessed at baseline and 60 minutes after an acute bout of moderate intensity exercise (45‐min of brisk walking at 60% VO2peak).

Results

Baseline

Between‐groups, pre‐exercise CBFr and VRr did not differ (p>0.05). In contrast, CBFpk was higher (p<0.05) and VRpk lower (<0.05) in PMWtr. Plasma nitrite concentration did not differ between groups (p>0.05).

Post‐exercise

Within‐groups, resting and peak CBF were increased (p<0.05) and VR decreased (p<0.05). Plasma nitrite concentrations did not differ from baseline (p>0.05). Between‐groups, post‐exercise CBFr and VRr did not differ (p>0.05). However, CBFpk was higher (p<0.05) and VRpk lower (p<0.05) in PMWtr. Plasma nitrite concentration did not differ between groups (p>0.05).

Conclusions

In habitually endurance trained PMW, peak CBF is higher and VR lower compared to their untrained counterparts. Acute dynamic exercise increases CBF in trained and untrained PMW, yet peak responses are augmented in trained PMW in association with lower VR. Our findings suggest that, in contrast to previous findings in the brachial artery, the age‐associated decline in endothelial function is attenuated in the lower limb skeletal muscle vascular bed in endurance trained PMW. Greater vascular responsiveness to exercise‐mediated increases in blood flow also suggests that the favourable vascular adaptations to exercise training are not mitigated in the lower limb in PMW.

Support or Funding Information

The research was funded by Loughborough University and supported by NIHR Leicester Research Centre

Group characteristics

PMWun (n=13)

PMWtr (n=10)

Age (years)

56±1

57±1

Height (cm)

164±1

166±2

Weight (kg)

62±2

59±2

BMI (kg/m2)

23±1

21±1
†

VO2peak (ml/kg/min)

29±1

40±1
†

Heart rate (beats/min)

59±2

55±2

SBP (mmHg)

117±3

113±2

DBP (mmHg)

76±1

73±2

All values are mean±SEM

BMI, body mass index; VO2peak, peak oxygen uptake; SBP, systolic blood pressure; DBP, diastolic blood pressure

†Significant between group differences, p<0.05

Vascular measures pre‐ and post‐exercise

PMWun (n=13)

PMWtr (n=10)

Pre‐Ex

Post‐Ex

Pre‐Ex

Post‐Ex

Resting

CBF (ml/100ml/min)

1.4±0.2

2.3±0.3
*

1.7±0.3

2.5±0.3
*

VR (U)

74.3±7.3

43.6±3.8
*

57.7±6.1

39.2±6.0
*

Peak

CBF (ml/100ml/min)

26.4±2.0

29.4±1.9
*

31.6±2.0
†

37.0±1.8
†
*

VR (U)

3.6±0.2

2.9±0.2
*

2.8±0.2
†

2.4±0.2
†
*

Plasma nitrite (nM)

83.4±14.6

95.5±10.4

64.9±7.2

78.7±12.6

All values are mean±SEM.

CBF, calf blood flow; VR, vascular resistance

†Between groups, within condition p<0.05

*Within groups, pre‐ versus post‐exercise p<0.05