 All depletion drinks will be mixed with 300ml of juice, to cover the taste of the amino acid mixture prepared. Male participants receiving a tyrosine-free formula, will drink a mixture of amino acids as administered in work by Sheenan et al 1996: L-isoleucine 7.5g; L-leucine 11.25g, L-lysine monohydrochloride 8.75g, L-methionine 2.5g, L-valine 8.75g, L-threonine 5g; L-tryptophan 1.25g. Female subjects will receive drinks of the same composition, but 20 less by weight of each amino acid. Similarly, the tryptophan-free formula for males will be as prepared by Hughes et al 2000, Hughes, Dunne Young 2000, and formula that is 20 less, by weight, of amino acids will be used for females: L-alanine 5.5g; L-arginine 4.9g; L-cysteine 2.7g; L-glycine 3.2g; L-histidine 3.2g; L-isoleucine 8g; L-leucine 13.5; L-lysine monohydrochloride 11g; L-methionine 3g; L-phenylalanine 5.7g; L-proline 12.2g; L-serine 6.9g; L-threonine 6.5g; L-tyrosine 6.9g; L-valine 8.9g. 