Women generally live longer than men but often experience a faster muscle mass loss due to inactivity, which can lead to weakness and disability. Despite these risks, women, particularly older women, are less active than men. In England, less than one-third of women engage in sufficient aerobic activity, and less than 5% do enough muscle strength training. Common reasons for not exercising include lack of time and enjoyment.

High-intensity interval training (HIIT) is an efficient and effective way to exercise that many women find more enjoyable than longer workouts. HIIT has been shown to be effective in older women, helping them improve their fitness with less time commitment. Because HIIT is time-efficient, it can be combined with muscle strength training without significantly increasing the duration of the exercise session, which may lead to even better fitness results.

This study will assess how practical it is for older women to do HIIT and strength exercise combined training. It will also investigate whether this combined approach can improve overall fitness, muscle strength, aerobic fitness, and quality of life more than HIIT alone.

Inclusion Criteria:

• Females (biologically at birth)
• At least 60 years of age at the time of signing the informed consent
• Non-smoker, including electronic cigarettes
• Not participating in routine high-intensity aerobic or muscle strength exercise training (≥ 75 min/week of structured vigorous aerobic exercise, or 2 times /week of structured muscle strength training)
• Able to perform a cardiopulmonary exercise testing (CPET) to exhaustion
• willing to complete baseline and follow-up measures, and attend prescribed exercise sessions at the University of Nottingham
• willing and able to give informed consent for participation in the study

Exclusion Criteria:

• Diagnosed with cardiovascular disease, kidney disease, diabetes, obstructive pulmonary disease, or uncontrolled hypertension
• History or current neurological or psychiatric illness, or motor or cognitive restrictions
• Contraindications to symptom-limited cardiopulmonary exercise testing (CPET), including resting hypertension with systolic blood pressure >200 mmHg or diastolic blood pressure > 110 mmHg, uncorrected medical conditions, such as significant anemia, important electrolyte imbalance, and hyperthyroidism, mental impairment with limited ability to cooperate, physical disability that precludes safe and adequate testing.
• Having taken part in a research study in the last 3 months involving invasive procedures or an inconvenience allowance.