The investigators plan to measure changes in muscle protein metabolism in response to feeding, comparing between a single large essential amino acid (EAA) feed (the normal building blocks of protein) and the provision of the same dose in 4 smaller feeds at 45min intervals. The investigators will perform this study in healthy older (65-75y) and younger (18-28) men. The investigators will also explore how feeding affects muscle blood flow as this is important in the delivery of the nutrients we eat to the muscle where they are used.

The investigators plan to supplement the feed with arginine, a safe and widely found non-essential amino acid, to explore if this can improve muscle blood flow.

We will provide a 15g mixed essential amino acid feed or 4 x 3.75g.

There is sexual dimorphism thus initially we will just recruit males. Powering calculations dictate n=8 in each group.

We will use well established stable isotope tracer techniques (with 13C6 Phenylalanine) to measure muscle protein synthesis and breakdown by Gas Chromatography - combustion - isotope ratio mass spectroscopy.

We will measure leg blood flow by phase shift Doppler and muscle microvascular flow by contrast enhanced ultrasound.

Inclusion Criteria:

• age 65-75 or 18-28

Exclusion Criteria:

• BMI >30
• Diabetes
• Beta blocker or steroid use
• Established cerebrovascular, peripheral vascular or ischaemic heart disease.