An interventional study of Exercise snacks programme and Conversational agent in Obesity, Physical Inactivity and Sedentary Behavior, sponsored by Charles University, Czech Republic. Not yet recruiting at 3 sites in Czechia. Open to participants aged 18 Years to 65 Years. Per ClinicalTrials.gov, last updated 2026-10-09.
Sponsored by Charles University, Czech Republic · Not applicable, Interventional, and Prevention
Adults with obesity gain as much from regular physical activity as anyone else, but structured exercise programmes are hard to sustain once the programme ends. This trial tests a different approach, built around exercise snacks, that is short bouts of activity of a few minutes at a time, spread through an ordinary day.
Physically inactive adults aged 18 to 65 with obesity are invited by their own general practitioner. Everyone who takes part receives a wrist-worn activity tracker and keeps it at the end of the study.
Participants are allocated at random in two steps. At the start, two out of every three take part in a six-month programme of supervised group exercise sessions and individual counselling based on motivational interviewing. The remaining third receives the tracker together with brief standardised advice on physical activity. After six months, everyone who took part in the programme is allocated at random a second time, half and half: one half receives an automated conversational agent that supports them by message for the following twelve months, and the other half receives no further support.
The trial asks two questions. First, whether the six-month programme increases physical activity compared with the tracker and brief advice alone. Second, whether the automated conversational agent helps participants sustain their activity over the following year. Physical activity is measured with a research-grade accelerometer worn on the wrist for one week at the start, at six months and at eighteen months. Aerobic fitness, cardiometabolic blood markers, physical function and wellbeing are measured at the same three visits.
Background and rationale.
Physical activity is a cornerstone of obesity management, yet most interventions fail to embed activity into everyday life and their effects fade once supervised contact ends. A major obstacle is low initial fitness, which makes conventional exercise unpleasant and reinforces inactivity. Exercise snacks, that is brief structured bouts of activity distributed across the day, lower that barrier and lend themselves to being embedded in an ordinary routine. Sustaining the change beyond the supervised phase, however, requires continued support, which is expensive to deliver by human counsellors at scale. This trial evaluates a lifestyle physical activity programme centred on exercise snacks, initiated in general practice, and separately evaluates whether an automated conversational agent can take over the supporting role once the supervised phase ends.
Objectives and endpoints.
The trial has two objectives. Each is supported by its own randomisation, in its own population, over its own time window, and each therefore has its own primary endpoint.
The first objective is to determine the effect of the six-month programme compared with an active control condition. The first primary endpoint is the change in device-measured physical activity from baseline to six months.
The second objective is to determine the effect of automated maintenance support delivered by a conversational agent, compared with no further support, among participants who received the programme. The second primary endpoint is the change in device-measured physical activity from six to eighteen months. This comparison is not conditional on the result of the first.
Testing structure.
The two primary endpoints are treated as two separate confirmatory families. Each is tested at a two-sided alpha of 0.05, and no adjustment for multiplicity is applied between them. The justification is that the two comparisons rest on two physically separate randomisations, address different scientific questions, are estimated in different populations and cover different time windows. They are not co-primary endpoints, and success is not defined as statistical significance on both.
Within each family, the change in peak oxygen uptake over the same window is a secondary endpoint included in a fixed-sequence testing procedure, and is therefore tested only if the primary endpoint of that family reaches significance. All remaining outcomes are exploratory and are reported with effect estimates and confidence intervals rather than formally tested.
Design and randomisation.
Participants are randomised twice. At baseline, participants are randomised in a 2 to 1 ratio to the six-month programme or to the active control condition. At six months, once the six-month assessment has been completed for that participant and after the last programme contact contributing to it, all participants who were allocated to the programme are randomised 1 to 1 to the conversational agent or to no further support. Participants allocated to the active control condition are not randomised a second time and continue unchanged to eighteen months. Both randomisations are stratified and use blocked allocation sequences; the stratification factors and block sizes are specified in the statistical analysis plan. Randomisation is performed centrally in REDCap.
The second randomisation is unconditional. It does not depend on response, adherence, or any variable measured during the first six months, and the trial therefore does not embed adaptive interventions to be compared. What the design embeds is three fixed sequences, represented by the three arms.
Immediately after the second randomisation, every participant in the programme receives a single transition contact from their own counsellor, communicating the allocation and what happens next. In the arm allocated to the conversational agent, this contact continues into counsellor-led onboarding of the tool; in the arm allocated to no further support, it ends as a non-therapeutic check-in. This contact is not counted as counselling dose.
Setting, participants and recruitment.
The trial is conducted in 15 to 25 general practices within commuting distance of the two study sites, in Prague and in Ostrava. The general practice network is coordinated by the Institute of General Practice, First Faculty of Medicine, Charles University, which contracts and supports the participating practices. General practitioners invite potentially eligible patients from their own practice records. Interested patients register their interest online and are prescreened by telephone. Preliminarily eligible patients are then sampled at random and invited to an entry visit with their own general practitioner, who confirms eligibility, obtains written informed consent and takes blood samples. All remaining assessments take place at the study sites. Recruitment proceeds in four waves of three months.
Intervention.
The six-month programme comprises two supervised group sessions and six individual counselling sessions delivered remotely by video call, based on motivational interviewing and delivered by trained counsellors. The first group session introduces the concept of exercise snacks, sets up the activity tracker and practises technique; the second, two weeks later, works on exercise intensity and execution. Individual counselling is spread across the six months and focuses on embedding activity into the participant's own daily routine. All participants in the programme receive a wrist-worn activity tracker showing daily intensity minutes, calibrated to their individual heart-rate thresholds derived from their own cardiopulmonary exercise test. The target given to participants is at least 150 intensity minutes per week.
From six to eighteen months, participants allocated to maintenance support receive an automated conversational agent based on a large language model, grounded in motivational interviewing and the Health Action Process Approach, delivered through a widely used messaging application and drawing on the participant's own activity data. Participants allocated to no further support receive no programme contact during this period and keep their tracker.
Active control condition.
Participants allocated to the active control condition receive the same wrist-worn activity tracker, which they also keep, together with a short standardised leaflet on physical activity recommendations and on using the tracker. They receive no supervised sessions and no counselling, and attend the same three assessment visits.
Assessments.
Assessments take place at baseline, at six months and at eighteen months. At each assessment, participants wear a research-grade accelerometer on one wrist and a second wrist-worn device on the other for seven consecutive days. No programme contact takes place during the fourteen days preceding an assessment, so that measurement is not reactive.
Sample size.
A total of 306 participants are randomised at baseline. Assuming 10 per cent attrition to six months and 20 per cent to eighteen months, a two-sided alpha of 0.05 and 80 per cent power, the trial can detect a standardised effect size of 0.36 for the first primary endpoint and 0.44 for the second.
Statistical analysis.
Both primary endpoints are analysed on an intention-to-treat basis, using linear mixed models adjusted for the baseline value and prespecified covariates. Both primary endpoints use a treatment-policy strategy for all intercurrent events, including non-adherence, withdrawal from the programme, and initiation of a glucagon-like peptide-1 receptor agonist or bariatric surgery during follow-up. Group assignment is not changed by these events and assessments are sought regardless. The statistical analysis plan for each primary endpoint is finalised before the last data contributing to that endpoint are collected. There is no interim analysis for efficacy and no stopping rule; follow-up to eighteen months proceeds irrespective of the six-month result.
6,570 studies on the registry are indexed under Obesity; 1,718 are open to participants now.
This study's planned enrollment of 306 is above the median of 77 across 5,084 interventional studies indexed under Obesity.
Browse Obesity studies →Charles University, Czech Republic is the lead sponsor of 227 studies on the registry; 76 are open to participants now.
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Exclusion Criteria:
Months 0 to 6: two supervised group sessions, six individual motivational interviewing counselling sessions delivered remotely, and a wrist-worn activity tracker. Months 6 to 18: an automated conversational agent based on a large language model, delivering maintenance support by message.
Behavioral: Exercise snacks programme · Behavioral: Conversational agent · Device: Wrist-worn activity tracker
Months 0 to 6: identical to Arm 1. Months 6 to 18: no further programme contact; participants keep the tracker.
Behavioral: Exercise snacks programme · Device: Wrist-worn activity tracker
A wrist-worn activity tracker and a short standardised leaflet on physical activity recommendations and tracker use, from baseline to 18 months.
Device: Wrist-worn activity tracker · Behavioral: Standardised physical activity advice
Six-month lifestyle physical activity programme centred on exercise snacks, that is brief structured bouts of activity distributed across the day. Two supervised group sessions and six individual counselling sessions delivered remotely by video call, based on motivational interviewing and delivered by trained counsellors. The target given to participants is at least 150 intensity minutes per week, based on individual heart-rate thresholds derived from their own cardiopulmonary exercise test.
Automated conversational agent based on a large language model, grounded in motivational interviewing and the Health Action Process Approach, delivered from six to eighteen months through a widely used messaging application and drawing on the participant's own activity data.
Wrist-worn activity tracker showing daily intensity minutes, calibrated to the participant's individual heart-rate thresholds derived from their own cardiopulmonary exercise test. Participants keep the tracker at the end of the study.
A short standardised leaflet on physical activity recommendations and on using the activity tracker, given at baseline. No supervised sessions and no counselling are provided.
Change in device-measured physical activity, programme versus active control
Minutes per day of moderate to vigorous physical activity, measured by a wrist-worn accelerometer worn for seven consecutive days.
Time frame: Baseline to 6 months
Change in device-measured physical activity, conversational agent versus no further support
Minutes per day of moderate to vigorous physical activity, measured by a wrist-worn accelerometer worn for seven consecutive days.
Time frame: 6 months to 18 months
Change in peak oxygen uptake (L/min), programme versus active control
Peak oxygen uptake in litres per minute during a maximal walking cardiopulmonary exercise test on a treadmill. Tested only if Primary Outcome 1 is significant.
Time frame: Baseline to 6 months
Change in peak oxygen uptake (L/min), conversational agent versus no further support
Peak oxygen uptake in litres per minute during a maximal walking cardiopulmonary exercise test on a treadmill. Tested only if Primary Outcome 2 is significant.
Time frame: 6 months to 18 months
Fasting plasma glucose
Fasting plasma glucose concentration in millimoles per litre, measured in a venous blood sample taken at the general practice after an overnight fast.
Time frame: Baseline, 6 months, 18 months
Glycated haemoglobin (HbA1c)
Glycated haemoglobin (HbA1c) concentration in millimoles per mole, measured in a venous blood sample taken at the general practice.
Time frame: Baseline, 6 months, 18 months
Total cholesterol
Total cholesterol concentration in millimoles per litre, measured in a venous blood sample taken at the general practice after an overnight fast.
Time frame: Baseline, 6 months, 18 months
Low-density lipoprotein cholesterol
Low-density lipoprotein (LDL) cholesterol concentration in millimoles per litre, measured in a venous blood sample taken at the general practice after an overnight fast.
Time frame: Baseline, 6 months, 18 months
High-density lipoprotein cholesterol
High-density lipoprotein (HDL) cholesterol concentration in millimoles per litre, measured in a venous blood sample taken at the general practice after an overnight fast.
Time frame: Baseline, 6 months, 18 months
Triglycerides
Triglyceride concentration in millimoles per litre, measured in a venous blood sample taken at the general practice after an overnight fast.
Time frame: Baseline, 6 months, 18 months
Resting heart rate
Resting heart rate in beats per minute, measured in the seated position over approximately five minutes at the laboratory visit.
Time frame: Baseline, 6 months, 18 months
Handgrip strength
Maximal isometric handgrip strength in kilograms, measured with a hand dynamometer.
Time frame: Baseline, 6 months, 18 months
Lower-limb muscle function, 30-second chair stand test
Number of chair stands completed in 30 seconds. The participant rises fully from a chair and sits back down as many times as possible within 30 seconds, without using the arms. A single value is recorded at each assessment: the number of completed repetitions.
Time frame: Baseline, 6 months, 18 months
Mobility, Timed Up and Go test
Time in seconds to rise from a chair, walk three metres, turn, walk back and sit down.
Time frame: Baseline, 6 months, 18 months
Enjoyment of physical activity
Physical Activity Enjoyment Scale (PACES), a self-reported questionnaire; higher scores indicate greater enjoyment of physical activity.
Time frame: Baseline, 6 months, 18 months
Aspartate aminotransferase
Aspartate aminotransferase (AST) activity in units per litre, measured in a venous blood sample taken at the general practice.
Time frame: Baseline, 6 months, 18 months
Health-related quality of life
12-Item Short Form Health Survey (SF-12), a self-reported questionnaire; higher scores indicate better health-related quality of life.
Time frame: Baseline, 6 months, 18 months
Psychological well-being
World Health Organization Five Well-Being Index (WHO-5), a self-reported questionnaire; higher scores indicate greater well-being.
Time frame: Baseline, 6 months, 18 months
Maintenance self-efficacy
Maintenance self-efficacy scale of the Health Action Process Approach (HAPA), a self-reported questionnaire; higher scores indicate greater confidence in maintaining physical activity.
Time frame: Baseline, 6 months, 18 months
Depressive symptoms
Ten-item Center for Epidemiologic Studies Depression Scale (CES-D-10), a self-reported questionnaire; higher scores indicate more depressive symptoms.
Time frame: Baseline, 6 months, 18 months
Fat mass
Whole-body fat mass in kilograms, measured by dual-energy X-ray absorptiometry (DXA).
Time frame: Baseline, 6 months, 18 months
Sedentary time
Sedentary time in minutes per day, derived from a wrist-worn accelerometer worn for seven consecutive days.
Time frame: Baseline, 6 months, 18 months
Alanine aminotransferase
Alanine aminotransferase (ALT) activity in units per litre, measured in a venous blood sample taken at the general practice.
Time frame: Baseline, 6 months, 18 months
Platelet count
Platelet count in billions per litre, obtained from a full blood count in a venous blood sample taken at the general practice.
Time frame: Baseline, 6 months, 18 months
Fibrosis-4 index
Fibrosis-4 (FIB-4) index of liver fibrosis, calculated as age in years multiplied by aspartate aminotransferase activity, divided by the platelet count multiplied by the square root of alanine aminotransferase activity.
Time frame: Baseline, 6 months, 18 months
Systolic blood pressure
Systolic blood pressure in millimetres of mercury, measured in the seated position after a period of seated rest.
Time frame: Baseline, 6 months, 18 months
Diastolic blood pressure
Diastolic blood pressure in millimetres of mercury, measured in the seated position after a period of seated rest.
Time frame: Baseline, 6 months, 18 months
Body weight
Body weight in kilograms, measured on a calibrated scale in light clothing and without shoes.
Time frame: Baseline, 6 months, 18 months
Body mass index
Body mass index in kilograms per square metre, calculated from measured body weight and measured body height.
Time frame: Baseline, 6 months, 18 months
Waist circumference
Waist circumference in centimetres, measured with a tape at the midpoint between the lowest rib and the iliac crest.
Time frame: Baseline, 6 months, 18 months
Recovery self-efficacy
Recovery self-efficacy scale of the Health Action Process Approach (HAPA), a self-reported questionnaire; higher scores indicate greater confidence in resuming physical activity after an interruption.
Time frame: Baseline, 6 months, 18 months
Lean mass
Whole-body lean mass in kilograms, measured by dual-energy X-ray absorptiometry (DXA).
Time frame: Baseline, 6 months, 18 months
Appendicular lean mass
Appendicular lean mass in kilograms, the sum of the lean mass of the arms and the legs, measured by dual-energy X-ray absorptiometry (DXA).
Time frame: Baseline, 6 months, 18 months
Body fat percentage
Whole-body fat mass expressed as a percentage of total body mass, measured by dual-energy X-ray absorptiometry (DXA).
Time frame: Baseline, 6 months, 18 months
Sleep duration
Sleep duration in minutes per night, derived from a wrist-worn accelerometer worn for seven consecutive days.
Time frame: Baseline, 6 months, 18 months
Average acceleration
Average acceleration of the wrist in milligravitational units, derived from a wrist-worn accelerometer worn for seven consecutive days, as a measure of the overall volume of physical activity.
Time frame: Baseline, 6 months, 18 months
Intensity gradient
Intensity gradient, the gradient of the log-log relationship between acceleration intensity and the time accumulated at or above each intensity, derived from a wrist-worn accelerometer worn for seven consecutive days, as a measure of the intensity distribution of physical activity.
Time frame: Baseline, 6 months, 18 months
Step count
Number of steps per day, derived from a wrist-worn accelerometer worn for seven consecutive days.
Time frame: Baseline, 6 months, 18 months
Intensity minutes
Weekly intensity minutes recorded by a wrist-worn consumer activity monitor (Garmin CIRQA) worn for seven consecutive days alongside the research-grade accelerometer.
Time frame: Baseline, 6 months, 18 months
Plan to share: Yes — De-identified individual participant data underlying the results reported in each publication, together with a data dictionary. The exact set of variables will be agreed for each request. Data that could identify a participant will not be shared.
Supporting information: Study protocol, Statistical analysis plan, Informed consent form
Time frame: Beginning 12 months after publication of the primary results, with no end date.
Access criteria: Requests should be directed to the principal investigator. Data will be shared with researchers who provide a methodologically sound proposal, after approval of that proposal and signature of a data sharing agreement.
No publications or documents are linked to this record.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
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