Effects of High-Intensity Interval Training on Bone Health in Hong Kong Older Women

Bone mineral density

Bone mineral density at the non-dominant lumbar spine and femoral neck of hip will be measured by one registered technician using DXA (XR-46, Norland, Wisconsin, USA) at an assessment center in the Chinese University of Hong Kong.

Bone turnover markers

The two bone turnover markers, P1NP (ng/ml) and CTX (ng/L) will be used to assess the subjects' bone formation and bone resorption. Participants must arrive at the elderly center between 08:30 and 09:30 a.m. after a 12-hour overnight fast and avoid intense physical activity the night before. A qualified nurse will collect 5 mL of venous blood from the antecubital vein, which will coagulate at room temperature for 20-30 minutes before being transported to the lab within one hour. The blood will then be centrifuged at 4 °C and 3000 rpm for 50 minutes, with the resulting sample stored at -80 °C for serum biochemical marker assays. Serum P1NP and CTX levels will be measured using ELISA kits from Immunodiagnostic Systems Inc., and analysis will be conducted by the Hong Kong Polytechnic University test lab.

Physical fitness_Body mass index

BMI (kg/m²) was calculated by dividing weight in kilograms by the square of height in meters. Body weight was measured using a mobile scale that was accurate to 0.01 kg and calibrated before use. Participants were instructed to remain still until the digital display stabilized, at which point their weights were recorded. Height was measured using a mobile stadiometer accurate to 0.1 cm, and participants were asked to stand straight with their knees together during the measurement.

Physical fitness_Lower limb muscle strength

30-Second Chair Stand will used to assess lower limb muscle strength. The required tools will include a straight-backed chair (43 cm seat height) and a timer. Participants will sit in the middle of the chair with their feet shoulder-width apart, crossing their arms at the wrists close to their chest. They will then stand fully and sit back down, counting this as one movement, which will be repeated for 30 seconds after the initial instruction.

Physcal fitness_Upper limb muscle strength

30-second Arm Curl will be used to evaluate upper limb muscle strength. This test will measure upper body strength using a 5-pound dumbbell, a chair without armrests, and a timer. Conducted on the stronger arm, participants will curl their arm through a full range of motion, turning the palm upward. They will fully bend and straighten the arm at the elbow, repeating this as many times as possible within 30 seconds.

Physical fitness_Aerobic endurance

Aerobic endurance will be measured by a 2-Minute Step Test. A timer will be used for this procedure. Participants will stand straight next to a wall, where a mark will indicate the midpoint between the kneecap and hip bone. They will step for two minutes, lifting their knees to the mark's height.

Heart rate

Participants will be monitored by Polar verity sensor during exercise and their heart rate will be monitored to ensure their safety and intensity adherence of exercise protocol.

Self-reported Rate of Perceived Exertion (RPE)

Older women will be asked about the self-reported Rate of Perceived Exertion (RPE Borg CR-10 category scale) after they complete the main exercise training in each session. A higher score (closer to 10) means the individual feels they are working much harder, while a lower score (closer to 0) suggests a much easier level of activity.

Safety: adverse events

All adverse events will be recorded as safety endpoints.

Exercise acceptability

Exercise acceptability will be assessed post-intervention using ten questionnaire items responding to a 5-point Likert scale (strongly disagree, disagree, neither agree nor disagree, agree, and strongly agree). The score on this scale ranges from 9 to 40, the higher score shows better acceptability to the exercise intervention.