Assessing the Impact of Age, and a Short-term High-intensity Interval Training (HIIT) on Skeletal Muscle Mass and Mitochondrial Activity

The goal of this interventional study is to learn about the role of mitochondrial function in healthy aging, and then go on and assess the role of a home-based exercise program on the changes seen. The main question\[s\] it aims to answer are: * What alterations in skeletal muscle mitochondrial function are seen in healthy aging? * Can a short-term exercise program alter these alterations seen? The older participants will be invited to take part in a home-based 4 week exercise intervention involving either: * High intensity interval training * Resistance based training (resistance bands will be provided) Researchers will compare the two exercise groups to see if it alters mitochondrial function.

Inclusion Criteria: * ● Healthy male or female aged over 18 years old able to give informed, written consent. Exclusion Criteria: * ● Current participation in a formal exercise regime * Inability to use a static exercise bike * A BMI \35 kg/m2 * Active cardiovascular disease: * Uncontrolled hypertension (BP \> 160/100) * Angina * Heart failure (class III/IV) * Significant arrhythmia * Right to left cardiac shunt * Recent cardiac event * Taking beta-adrenergic blocking agents * Cerebrovascular disease: * Previous stroke * Aneurysm (large vessel or intracranial) * Epilepsy * Respiratory disease including: * Pulmonary hypertension * Significant COPD * Uncontrolled asthma * Malignancy * Clotting dysfunction * Significant musculoskeletal or neurological disorders * Any suspected or confirmed diagnosis of Covid-19