Time for health: Investigating the real-world impact of time-restricted eating with exercise on health and well-being.

The interventions have a dietary component - with all participants undertaking time-restricted eating (TRE) with a 9 hour eating window, alongside an exercise component, with participants randomised to either high-intensity interval training, moderate intensity exercise, resistance training. Thus, the interventions groups are comprised of: TRE with High-Intensity Interval Training TRE with Moderate Intensity Exercise TRE with Resistance Training Exercise Dietary Intervention – Time-Restricted Eating All groups will be instructed to undertake TRE during the intervention phase. This involves limiting energy intake to a 9-hour window each day. Participants will be instructed to not consume any food after 8pm as this can disrupt circadian rhythm, thus the 9-hour eating windows can be any time before this (e.g., 9.30am-6.30pm, or 11am-8pm). No other dietary restrictions or recommendations will be made. Participants may consume non-caloric beverages outside of the eating window. Exercise Interventions To better represent how people undertake HIIT, MIE and resistance training exercise in the real-world, all participants will be offered a 12-week gym membership in which they can undertake their exercise interventions safely as group fitness classes and/or by utilising gym equipment. TRE with High-Intensity Interval Training (HIIT): Participants in the TRE with HIIT group will undertake TRE and be instructed to undertake HIIT three times per week. High intensity exercise is defined as “exercise that uses most of your body and is very hard to do within seconds.” HIIT typically involves short intervals (ranging from 20 seconds to 4 minutes) of hard exercise, interspersed with short periods of light activity. It is expected that each HIIT session will take between 30-45 minutes to complete. Participants should attain a rating of perceived exertion of at least 7-8 on a 10-point scale - perceived exertion is known to effectively guide exercise intensity and is routinely used in exercise guidelines. Participants can opt to do group HIIT classes, which is consistent with how many people achieve HIIT in the real-world. It is expected that most participants will utilise this option, during which the gym fitness instructor will provide the guidance on how to undertake HIIT. The recommended HIIT classes will include cycle classes with sprint intervals, mixed martial arts classes that include exercises such as kickboxing and burpees, and high-intensity functional movement classes that utilise bodyweight exercises, weights and steps. Participants will also receive written guidance on how to undertake independent HIIT if they prefer; this will be explained by the researcher at the first 60 minutes intervention visit. Participants can choose to do HIIT independently by hill or stair climbing, sprinting, using cardio exercise equipment such as rowing machines, or home-based exercises such as star jumps, burpees and high-knee running. A range of validated HIIT protocols (such as 5 x 60 second intervals aiming for RPE of 9) will be included in the resources. Participants will be given a FitBit in weeks 1, 6 and 12. They may use the FitBits to monitor their heart rate (a target heart rate of 80% of their estimated maximum will be calculated for them based on age) to help aid in attaining sufficient intensity. Fitbit recordings of HIIT sessions will be reviewed to assess if the correct level of intensity has been attained. Adherence to HIIT training will also be measured by the exercise diaries as described in the outcomes section. TRE with Moderate Intensity Exercise (MIE): Participants in the MIE group will undertake TRE and be advised to undertake at least 30 minutes of moderate physical activity on most days of the week, as per current New Zealand exercise guidelines. Moderate intensity exercise should be continuous and performed at an intensity of 5-6 on a 10-point scale – an effort that leads to breathing harder but still being able to maintain a conversation. Participants in the MIE group can utilise their gym membership to access exercise equipment such as elliptical trainers and rowing machines, and participants will be instructed as to which group fitness classes are suitable to support MIE, such as cycle classes. Participants may also undertake MIE outside of the gym with activities such as brisk walking, jogging, cycling or swimming. Adherence to the MIE exercise intervention will be recorded on weeks 1, 6 and 12 by the participants in the exercise diaries, and FitBit recordings will be reviewed to assess adherence and intensity. TRE with Resistance Training Exercise (RT): Participants in the resistance training exercise group will undertake TRE and be advised to undertake resistance training exercise. Participants in this group will perform resistance training at least three times a week for 30-60 minutes. Again, participants can opt to utilise group fitness classes that provide guided resistance training - these classes last 30-60 minutes and typically train all major muscle groups utilising barbells and weight plates, with standard exercises such as squats, lunges, chest press, barbell rows, clean and press. If participants prefer, they may utilise appropriate gym equipment for weight training using the same types of exercises. Adherence to the RT intervention will also be assessed by participant exercise diaries on weeks 1, 6 and 12.