Background: Sarcopenia is an age-related geriatric syndrome characterized by progressive loss of muscle mass and function. Before the diagnosis of sarcopenia, a "possible sarcopenia" stage has been proposed recently, characterized by low muscle strength or poor physical performance, even with normal muscle mass. The definition of "possible sarcopenia" emphasizes the importance of early intervention. Due to the lack of effective pharmaceutical treatments, exercise is recommended as the most available intervention for sarcopenia. High-intensity interval training (HIIT), a time-efficient aerobic training, has gained increasing popularity for its benefits in physiologic outcomes such as muscle strength and physical functions in other populations. However, the benefits of HIIT have not been well-studied following older adults with possible sarcopenia. In the present study, we aim to investigate the effects of a 7-week HIIT and moderate-intensity continuous aerobic training (MICT) on physical performance in older individuals with possible sarcopenia. We hypothesize that HIIT will confer physical benefits over MICT (i.e., traditional endurance exercise) and will be generally well-tolerated in older adults.

Method: The participants will be randomly allocated into the HIIT or MICT group (1:1 ratio). The participants will receive the training 3 times per week over seven weeks. HIIT consists of 5 bouts of interval training intensity with 1-minute-high intensity (76-90% HRmax) and 1-minute recovery per session (total 15 minutes with warm-up and cool-down). MICT will adopt an intensity of 65-70% HRmax training that lasts less than 30 minutes per session (total 25 minutes with warm-up and cool-down). Evaluation will be performed at baseline, after 4 weeks, and 7 weeks of the intervention. The primary outcomes include 10-meter walking test and the five-time chair stand test. The secondary outcomes include grip strength, the functional stretch test; the Exercise Enjoyment Scale and the Physical Activity Enjoyment Scale for affective valence.

Discussion: This is the first study to investigate the effects of low-volume HIIT on physical performance and affective valence in older adults with possible sarcopenia. This study will provide critical evidence to guide early prevention and intervention of exercise regimens for possible sarcopenia.

Inclusion Criteria:

• individuals aged 60 years or older, living in the community
• Able to walk with or without assistive devices
• Recovery from COVID-19 over two months
• With a preliminary screening of SARC-F score ≥4 or calf circumference less than 34cm for man, 33cm for woman will be invited to strength and physical performance measurement
• Handgrip strength less than 28 kg for man, 18 kg for woman and/or gait speed<1m/s and/or 5-time chair stand test ≥12 s.

Exclusion Criteria:

• Inability to undertake exercise due to neuromuscular and/or musculoskeletal limitations
• Uncontrolled hypertension (systolic BP>170 or diastolic BP>100 mmHg)
• Reported chronic cardiopulmonary insufficiency in medical history
• Reported vital organ failure and malignancy in medical history
• Cognitive impairments (mini-mental test score<21) with low compliance
• History of lower limb surgeries, fractures, neurological problems, systemic problems, and any other contraindications for aerobic training will be excluded.