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Key point

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    Optimal vascular function is critical for health, and endurance training (ET) has previously been shown to be an effective method of improving this.
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    Sprint interval training (SIT) has been proposed as a time efficient alternative to ET but its effect on skeletal muscle microvasculature has not been studied and no direct comparison with ET has been made.
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    ET and SIT in this study were equally effective at decreasing arterial stiffness and increasing skeletal muscle capillarisation and eNOS content.
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    The main results suggest that both training modes improve skeletal muscle microvascular and macrovascular function, with SIT being a time efficient alternative.

Abstract  Sprint interval training (SIT) has been proposed as a time efficient alternative to endurance training (ET) for increasing skeletal muscle oxidative capacity and improving certain cardiovascular functions. In this study we sought to make the first comparisons of the structural and endothelial enzymatic changes in skeletal muscle microvessels in response to ET and SIT. Sixteen young sedentary males (age 21 ± SEM 0.7 years, BMI 23.8 ± SEM 0.7 kg m−2) were randomly assigned to 6 weeks of ET (40–60 min cycling at ∼65%inline image, 5 times per week) or SIT (4–6 Wingate tests, 3 times per week). Muscle biopsies were taken from the m. vastus lateralis before and following 60 min cycling at 65%inline image to measure muscle microvascular endothelial eNOS content, eNOS serine1177 phosphorylation, NOX2 content and capillarisation using quantitative immunofluorescence microscopy. Whole body insulin sensitivity, arterial stiffness and blood pressure were also assessed. ET and SIT increased skeletal muscle microvascular eNOS content (ET 14%; P < 0.05, SIT 36%; P < 0.05), with a significantly greater increase observed following SIT (P < 0.05). Sixty minutes of moderate intensity exercise increased eNOS ser1177 phosphorylation in all instances (P < 0.05), but basal and post-exercise eNOS ser1177 phosphorylation was lower following both training modes. All microscopy measures of skeletal muscle capillarisation (P < 0.05) were increased with SIT or ET, while neither endothelial nor sarcolemmal NOX2 was changed. Both training modes reduced aortic stiffness and increased whole body insulin sensitivity (P < 0.05). In conclusion, in sedentary males SIT and ET are effective in improving muscle microvascular density and eNOS protein content.