Engaging in muscle strength and balance (S&B) exercises and has numerous health benefits for older adults, promoting greater mobility, reducing risk of falling, and overall improved health and wellbeing. Given the rising age of global populations, reducing the burden associated with lost physical function is essential to minimise health and social care costs. Unfortunately, very few older adults engage in sufficient S&B exercise to reap these benefits, with a lack of time, self-efficacy and access to leisure facilities cited as the key barriers. Finding innovative ways promote an acceptable and engaging format of S&B exercise is consequently a public health priority.

One novel way that aims to address typical barriers to participation in older adults is through the promotion of exercise 'snacks', as opposed to a more traditional, lengthy structured exercise session at a leisure centre. Exercise snacking describes short bursts of exercise that are designed to be undertaken over a short period in the home environment and without the need for any specialised exercise clothing or equipment. In the initial laboratory and cross-sectional and pilot intervention research, the investigators have been testing two formats of 5-minute, twice-daily, strength exercise- and tai-chi-snacking, which has been shown to be acceptable and feasible to implement in older adults. This protocol presents initial efficacy for evoking improved physical function in people aged 65 years or more. The investigators' remote study demonstrated that remote assessment and delivery of 4-week exercise and tai-chi snacking interventions were acceptable and feasible. However, qualitative feedback indicated that exercise programmes may be more acceptable and interesting with simpler tai-chi movements and exercise snacking programme with upper body movements. Nevertheless, the investigators only recruited healthy older adults, doing short-term interventions in previous studies. This study aims to test the effectiveness of progressive S&B interventions over a sustained period in pre-frail older adults.

This study will take place over approximately 3 months and involve 5 assessments remotely. A subset of 60 participants will be assessed in person to validate the remote assessment and undergo more in-depth assessments.

Assessment 1: Familiarisation Participants will be directed to a web page with the participant information sheet and a consent tick box. Participants will then complete an online screening questionnaire that will assess eligibility. After this, participants will undertake a familiarisation session either online (all participants) or in person (lab participants only) to become accustomed to the physical function tests and undergo an exercise safety assessment.

Assessment 2: Baseline assessment. After familiarisation, eligible participants will then complete an online baseline questionnaire assessing demographic details, physical activity levels and psychological outcomes. A functional assessment will be arranged over video calling software, and in the laboratory for the lab participants. Functional outcomes will be completed at this visit. Following the baseline assessment participants will be randomised to either the intervention group, or the waitlist control group.

Assessment 3 and 4: Mid intervention. Participants in the intervention group will be given an exercise teaching video and written instructions on how to safely perform the exercise at home by email. The intervention will take place over 12 weeks and consists of three progressive phases that will be self-selected by participants. The participants will be asked to do the exercises and progress to the next level if they pass the progress criteria which will be clearly explained in the exercise guides and instructional videos. The participants will also be asked to record self-reported exercise logs and RPE for each session they complete. Participants will undergo follow-up assessments at weeks 4 and 8 through video calls and in person (if in the lab study).

Assessment 5: Follow-up assessment. After 12 weeks, participants will complete another online survey containing all psychosocial variables and an evaluation of the usefulness and acceptability of their assigned exercise activities. Participants will also undergo follow-up physical performance tests through video calls and in person (if in the lab study) and a subset will undergo a qualitative evaluation to provide further feedback on the intervention.

Inclusion Criteria:

• People aged 65 or greater and are able to perform daily physical activity independently.
• Not regularly engaging in recreational sports or structured exercise (once a week or more).
• Citizen of UK or Taiwan.
• Individuals who are able to do the 5 reps sit-to-stand in less than 60s and the feet side-by-side stand for at least 10s, following the initial safety screening.

Exclusion Criteria:

• Individuals with current ongoing medication or treatment for injuries or illness that would impact on any of the study outcomes.
• Individuals with a current musculoskeletal injury that would preclude participation in exercise ascertained through preliminary screening.
• Individuals with contraindications to exercise including chest pain, dizziness, or loss of consciousness, or who have been instructed by their doctor to only do physical activity recommended by them.
• Individuals who have been diagnosed with dementia.
• Individuals who are unable to consent for themselves or complete the familiarisation / baseline screening by themselves.
• Individuals who score more than 8 on the Short Physical Performance Battery, score more than 6 between strength and balance sections, or score zero on any component of the test.