Study design and setting

This study was a four-arm, pre-post, 4-week pilot feasibility randomised controlled trial that was designed to determine, in community-dwelling older adults, the feasibility and acceptability of undertaking a home-based resistance ‘exercise snacking’ intervention (performed either once, twice, or thrice daily). The study was conducted during November to December 2020 in Melbourne, Australia. The study period occurred shortly after an extended period of lockdown restrictions (including stay at home orders) as a result of the COVID-19 pandemic, which were in place in Melbourne, Australia between July 8th and October 28th, 2020. All study procedures, including the recruitment and screening of participants, completion of physical function assessments, and the delivery and monitoring of the exercise intervention, were performed remotely without any in-person contact between participants and the research team. Ethics approval was obtained from the Deakin University Human Research Ethics Committee (HREC 2020–011) and all participants provided written informed consent. The trial was retrospectively registered on 10/11/2021 with the Australian New Zealand Clinical Trials Registry (ANZCTR) (ACTRN12621001538831).

Participants and recruitment

A total of 38 community-dwelling older adults (convenience sample) aged 65–80 years were recruited (during November 2020) via email addresses listed in a database of participants from previous exercise intervention trials conducted within the Institute for Physical Activity and Nutrition (IPAN) who provided consent to be re-contacted for future trials. Participants were deemed eligible to participate if they were: 1) English-speaking, 2) non-smoking, 3) able to walk unaided or with minimal assistance for ≥50 m, 4) cognitively intact as indicated by a score of ≤2 on the Short Portable Mental Status Questionnaire (SPMSQ), and 5) had access to a computer, smart phone or tablet device with a stable network or internet/WiFi connection. Participants were excluded based on the following criteria: 1) participating in structured resistance training more than once per week in the previous 3 months, 2) acute or terminal illness likely to impact study involvement, 3) unstable or ongoing cardiovascular, metabolic, or respiratory disorders, 4) current use of insulin or corticosteroids that could influence skeletal muscle metabolism, 5) self-reported body mass index (BMI) ≥40 kg·m− 2, 6) musculoskeletal or neurological disorders impacting voluntary movement, or 7) inability to commit to the study and its requirements. The risk of participants experiencing an adverse event during exercise was determined using the Exercise and Sports Science Australia (ESSA) Adult Pre-exercise Screening System (APSS) [18]. Participants with signs or symptoms of unstable or unmanaged disease (i.e., if participants answered ‘yes’ to any of the Stage 1 questions of the ESSA APSS) were excluded. All participant screening procedures were completed over the telephone, which included gathering responses to the SPMSQ and APSS questionnaires.

A total of 54 older adults were screened for the study, of which 38 were included. Reasons for exclusion (n = 16) are shown in Fig. 1. After screening for eligibility and baseline testing, participants were randomised, stratified by gender, to one of three exercise groups (once-daily group, n = 9; twice-daily group, n = 10; thrice-daily group, n = 9), or a usual-activity control (n = 10). Group randomisation was computer-generated (using Microsoft Excel) by an independent person not directly involved in the study.

Fig. 1
figure 1

Exercise intervention

The exercise intervention involved home-based resistance ‘exercise snacking’ sessions performed either once, twice, or thrice daily for 4 weeks. The exercise program was designed to be pragmatic and time-efficient by: a) focusing on multi-joint exercises involving larger muscle groups; b) targeting improvements in strength (and elements of balance) in lower body muscles most susceptible to age-related declines in muscle mass and strength [19] c) including exercises requiring minimal equipment (i.e., no more than a chair or a step) and no external loading (i.e., bodyweight only), and d) using a time-based prescription that did not require participants to monitor repetitions or sets and allowed the level of effort during each set to be self-regulated.

Each resistance ‘exercise snacking’ session consisted of five exercises that were each performed continuously for 1 min, with 1 min of passive recovery between exercises (total time commitment of 9 min per session). For weeks 1–2, the prescribed exercises were: 1) chair sit-to-stand (no arms), 2) single-leg quarter squat (with chair support), 3) side lunges, 4) calf raise (with chair support), and 5) clock stepping (with chair support). For the clock stepping exercise, participants were instructed to imagine they are standing in the middle of a clock face, and while standing on one leg, to step the other leg forward to the 12 o’clock position and then back to the centre, before repeating this to either the 3 o’clock or 9 o’clock position (for stepping with the right or left leg, respectively) followed by the 6 o’clock position. To provide variety and progressive overload, the five exercises prescribed for weeks 3–4 were changed to: 1) squat into high knee march (knee to elbow), 2) single-leg quarter squat, 3) rapid step ups (involving a rapid concentric phase and performed using a staircase step, or another available step of a similar height), 4) single-leg calf raise, and 5) rapid clock stepping. For unilateral exercises (apart from the squat into high knee march and rapid step ups, both of which were performed in an alternating pattern), one leg was exercised for the first 30 seconds of the one-minute period, before switching to the alternate leg for the final 30 seconds. Participants were instructed to perform as many repetitions as possible in 1 min with appropriate technique for each exercise, and were encouraged to gradually increase both the number and speed of repetitions performed (with appropriate technique) during the intervention. Participants were not asked to record the number of repetitions performed for each exercise during each session, or to perform each ‘exercise snack’ at specific times during the day – rather they were asked to perform each session when convenient and to distribute multiple sessions (where relevant) throughout the day as much as possible.

The exercise intervention was remotely delivered via a commercially available, web-based exercise programming application (PhysiTrack™) and accompanying end-user application (PhysiApp™) accessible via a computer, smart phone, or tablet. The PhysiTrack™ application was used only to deliver instructions regarding the exercise intervention (including written instructions and video-based demonstrations for each exercise) to participants, and not for monitoring purposes. Rather, immediately after completing each resistance ‘exercise snacking’ session, participants recorded in an exercise diary (designed in Microsoft Word) whether they successfully completed the session (yes or no), their RPE (Rating of Perceived Exertion) using the CR-10 scale [20], and whether any adverse events or incidents were experienced. After the first week of the intervention, participants were asked to return the completed exercise diary to the research team via email at the beginning of each subsequent week.

Participants attended two (one each at baseline and follow-up) live videoconference meetings (conducted via Zoom) with the same member of the research team. At the first meeting, participants completed all baseline assessments, were shown how to access the exercise program and video demonstrations using PhysiApp™, and how to complete the exercise diary (including explanation of the RPE CR-10 scale). The researcher also demonstrated each exercise and ensured participants could perform each exercise with appropriate technique. Participants also received a weekly email from the research team reminding them to return their completed exercise diary for the previous week. In the week following completion of the intervention, a second live videoconference meeting was held during which follow-up assessments were performed.

Feasibility of the exercise intervention

Feasibility of the exercise intervention was considered based on participant retention within the study and adherence to the intervention. Participant retention was recorded as the number (proportion) of participants who were randomised and completed both the four-week exercise intervention (or control period) and follow-up assessments. Adherence to the exercise intervention was considered as the number of sessions completed as a proportion of the number of planned (prescribed) sessions. In addition, exercise adherence was also reported as the prescribed versus actual (completed): i) number of days exercised per week, ii) total number (frequency) of ‘exercise snacks’ per week, and iii) total number of ‘exercise snacks’ during the four-week intervention. The exercise intervention was considered feasible if participant retention was at least 90%, and if participants completed a mean of 80% of prescribed sessions.

Feasibility of remote physical function assessments

We also explored whether it was feasible for participants to perform home-based physical function assessments remotely using videoconferencing. This was assessed as the proportion of participants who could successfully complete all physical function assessments during both the baseline and follow-up videoconferencing meetings. In addition, the feasibility of the remote home-based physical function assessments was considered based on the occurrence of barriers regarding equipment availability [e.g., lack of a suitable chair for sit-to-stand (STS) assessments], technical issues (e.g., unstable internet connection), and the availability of sufficient space within the home environment to complete each test and achieve the camera angles necessary for test scoring (e.g., view of the participant’s feet and/or eyes for balance testing).

Adverse events and incidents

An adverse event was defined as an intervention-related event resulting in absence from, or modification to, the exercise intervention. An adverse incident was defined as a minor intervention-related event (such as muscle or joint soreness/stiffness) not requiring absence from, or modification to, the exercise intervention. Any reported adverse events or incidents were followed up by research staff who contacted participants via phone to obtain further information and to advise whether participants should continue (with any modifications as required) or cease the exercise program and seek medical advice.

Anthropometry and physical function assessments

Participants self-reported their height and body mass to the nearest 1 cm and 1 kg, respectively. Physical function was assessed using a standing balance testing battery, the five-times STS (5-STS) test, and the 30-second STS (30-STS) test. For all physical function tests, participants wore comfortable shoes or were barefoot, which was noted during baseline assessments and repeated at follow-up. The time-of-day at which physical function testing was performed was not controlled, but testing was conducted at a similar time-of-day at baseline and follow-up for each participant where possible.

Participants ability to maintain balance in three different stance positions (side-by-side, semi-tandem, and tandem) was assessed in accordance with the Short Physical Performance Battery (SPPB) protocol [21]. The ability to maintain balance in the tandem stance position with the eyes closed was also assessed. Participants were asked to stand with their feet in full view of the camera (either on a smartphone, tablet, or webcam) and position themselves close to a wall or bench to provide support if needed. After assuming the correct stance position, participants were instructed they may use their arms, bend their knees, or move their body to maintain their balance, but to not move their feet. Participants scored 1 point for each test in which balance was maintained for 10 seconds, and zero if balance was not maintained (for a maximum total score of 4 points). Where balance could not be maintained for a given test, participants did not perform any further balance tests.

For the 5-STS and 30-STS tests, participants were asked to use a chair that: a) had a firm seat and backrest, b) had no arm rests or wheels, and c) was at a height such that participants could place their feet flat on the floor while their upper body was in contact with the backrest. The same chair was used by each participant for both baseline and follow-up assessments. Before commencement of STS testing, participants were asked to position their chair side-on to the camera, and to adjust their camera so that their entire body was visible to the researcher when seated on the chair. If space limitations did not permit their entire body being visible on camera, the position of the chair and/or camera were adjusted so that at a minimum, the seat and backrest were within camera view.

For the 5-STS test, participants began from a seated position in the chair, with their arms folded across the chest, and were instructed to stand fully upright and then return to the seated position five times as quickly as possible. The final score was recorded as the time taken to perform five STS repetitions from initially leaving the chair to being seated after the fifth repetition. The 30-STS test was then performed after a 5-minute recovery following completion of the 5-STS. For the 30-STS test, participants performed repeated chair stands in a manner identical to the 5-STS test; however, they were instructed to instead complete as many repetitions as possible in 30 seconds. The final score was recorded as the number of complete sit-to-stands (defined as standing in a fully upright position) achieved in 30 seconds. Participants were unable to view the 30-second timer during the test and were not provided with any feedback other than when to start and stop the test.

Acceptability of the exercise intervention

Upon trial completion, process measures were collected (via Qualtrics software) using an author-derived questionnaire completed by participants to evaluate their experiences with, and perceptions about, the exercise intervention. Participants were asked to rate their level of enjoyment of the resistance ‘exercise snacking’ program on a 5-point Likert scale (1 = ‘not at all’, 2 = ‘a little’, 3 = ‘a moderate amount’, 4 = ‘a lot’, and 5 = ‘a great deal’), and if they planned to continue undertaking some form of resistance ‘exercise snacking’ exercise at home. Participants were also asked open-ended questions about what they liked and disliked about the resistance ‘exercise snacking’ program. In addition, if participants indicated they did not plan to continue performing similar exercises after completion of the intervention, they were asked to explain why this was the case, and to describe anything that could be modified about the exercise program to improve the likelihood they would continue performing a similar program at home. All open-ended questions were analysed (within the intervention groups) by researcher(s) (JF) in Microsoft Excel using a general inductive thematic approach [22].

Statistical analysis

As this was a pilot feasibility study [23], a convenience sample of 38 older adults was recruited and no sample size calculations were performed [24]. All baseline and follow-up data are presented as means ± SDs and all change data are reported as means with 95% confidence intervals (CIs) unless otherwise stated. Data relating to the feasibility of the intervention (i.e., participant retention and intervention adherence) was considered as descriptive in nature. Exploratory analysis was undertaken to evaluate within-group changes in 5-STS and 30-STS test performance using paired samples t-tests. Effect sizes (Cohen’s d) for within-group changes between baseline and week 4 were calculated according to the following formula: mean follow-up score minus mean baseline score divided by baseline standard deviation, and interpreted as < 0.2 = trivial, 0.2 to < 0.5 = small, 0.5 to < 0.8 = moderate, and ≥ 0.8 = large [25]. Mean changes, ES values, and associated 95% CIs were calculated using JASP software (Version 0.14.1, JASP Team, The Netherlands).

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