Skeletal muscle accounts for approximately 45-55% of total body mass in healthy adults and plays a pivotal role in whole-body metabolic health, locomotion and physical independence. Undesirable loss of skeletal muscle mass (atrophy) is, however, a common feature of many diseases and scenarios including ageing, bed rest/immobilisation, cancer and physical inactivity. Despite the exact mechanisms causing muscle atrophy being not yet fully understood, "anabolic resistance" (reduced muscle building in response to protein feeding and exercise) is thought to be key, especially for age-related skeletal muscle losses (known as sarcopenia). As such, the search for optimal strategies (e.g., exercise and/ or nutritional interventions) to combat this anabolic blunting remains a hot-topic in scientific research.

Leucine, an essential and branched chain amino acid (EAA/BCAA), is thought to be the most potent AA for stimulating muscle protein synthesis (MPS; the muscle building process). Although, as a stand-alone supplement, leucine is unlikely to provoke a robust and prolonged state of MPS, low doses of leucine-enriched mixed-EAAs can elicit similar increases in MPS as compared to a large dose of whey protein. As reduced appetite and increased satiety (feeling fuller) are common with advancing age, supplementation of a low-dose protein (i.e., leucine-enriched) that can adequately stimulate MPS may contribute to muscle health maintenance in older adults and reduce satiation following a meal.

This study aims to examine which of three doses of a novel leucine-enriched whey protein ("super-whey") best stimulates muscle building in older adults

Inclusion Criteria:

• Participant is in the desired age-ranges (young adults: 18-35 years; older adults: 65+ years).
• Participant is willing and able to give informed consent for participation in the study.
• Participant is physically able to perform resistance exercise

Exclusion Criteria:

• A BMI <18 or >35 kg/m2
• Active cardiovascular, cerebrovascular or respiratory disease: e.g. uncontrolled hypertension (BP > 160/100), angina, heart failure (class III/IV), arrhythmia, right to left cardiac shunt, recent cardiac event, COPD, pulmonary hypertension or recent (6 mo) stroke
• Any metabolic disease
• Clotting dysfunction
• A history of, or current neurological or musculoskeletal conditions (e.g. epilepsy)
• Lactose intolerance
• Having taken part in a research study in the last 3 months involving invasive procedures or an inconvenience allowance