Osteoporosis is a major contributor to loss of independence due to bone fractures and resulting hospital treatments lead to significant morbidity. While pharmacological treatments can reduce consequences of osteoporosis, there is a pressing need for non-pharmacological interventions to improve bone health across the life-course and to reduce likelihood of age-related bone disease.

This study will allow us to determine whether synergistic potentiating effects on bone metabolism are observed in humans in relation to the timing of food ingestion and what recommendations can be made to people with respect to food ingestion and exercise to obtain the maximal bone benefits from aerobic exercise. Furthermore, if we can identify interventions that potentiate bone's response to aerobic exercise in younger adults, then such interventions may have the ability to maximise bone mass in younger adults so that with ageing, the additional bone mineral density and improved bone microarchitecture would extend the time before osteoporotic "fracture thresholds" are reached. Therefore, understanding the bone metabolic response to exercise following fasting and feeding in younger adults is important.

Inclusion Criteria:

• Male (females excluded to remove the interplay between menstrual cycle and bone turnover)
• Caucasian ethnicity
• Aged 28 ± 4 years
• Are physically active (meet the UK guidelines for physical activity of at least 150 minutes moderate intensity activity and/or at least 75 minutes of vigorous intensity activity per week)
• Otherwise, healthy, able and willing to participate and provide written informed consent

Exclusion Criteria:

• Current smokers
• Excessive alcohol consumption (max 15 alcohol units/week)
• Any musculoskeletal injury/disabilities
• Any conditions known to affect bone metabolism (e.g. uncontrolled hyper-/hypothyroidism, hyperparathyroidism, hypo-/hypercalcaemia) or malabsorption syndromes (e.g. Crohn's disease, coeliac disease or inflammatory bowel disease).
• Taking any medication known to affect bone metabolism (such as glucocorticoids or bisphosphonates)
• Positive Covid-19 test within the last 8 weeks
• Suffered a fracture in the previous 12 months
• Sedentary status (see physical activity inclusion criteria above)
• Have been told by medical professionals that they should not take part in moderate to high intensity exercise
• Should not be a professional athlete or take part in significant competitive recreational activity (takes no more than 4 structured exercise sessions per week on average)
• History of diagnosed eating disorders