An interventional study of High intensity interval training in Inactivity, Physical, Overweight (BMI > 25) and Healthy Participants, sponsored by California State University, San Marcos. Recruiting at 1 site in United States. Open to participants aged 18 Years to 55 Years. Per ClinicalTrials.gov, last updated 2026-08-24.
Sponsored by California State University, San Marcos · Not applicable, Interventional, and Prevention
Low levels of physical activity (PA) are related to poor health and greater risk of premature death in adults. Lack of time is cited as a primary barrier to partaking in PA. In the last 20 years, a lot of attention has been directed towards the efficacy of high intensity interval training (HIIT), which consists of brief, intense bursts of PA separated by recovery. One primary benefit of HIIT is a sizable increase in cardiorespiratory fitness (CRF), which enables adults to exercise better and reduce health risks due to the strong link between health status and CRF.
Completion of cardiovascular exercise is typically recommended for all adults to increase CRF, yet it takes a lot of time and may be perceived as boring. Alternatively, HIIT requires less time and tends to cause greater feelings of enjoyment in many adults. Hundreds of studies report an increase in CRF in response to HIIT in various groups of adults ranging from athletes and those with obesity, diabetes, cancer, stroke, and even spinal cord injury, which emphasizes the potency of this vigorous form of PA. Yet, many studies are weakened by a small sample size which questions the feasibility of these findings.
This randomized controlled trial will test the efficacy and feasibility of a very small amount of HIIT, referred to as reduced exertion high intensity interval training (REHIT), in inactive adults. In the proposed study, REHIT will consist of 2 days per week of 1 to two 10 - 20 second sprints on a stationary bike. The proposed sample will include 60 adults who complete 18 sessions of REHIT over a 9 week period, and their responses will be compared to a non exercising control group. During the study, changes in CRF, fuel metabolism, and psychological responses will be monitored, with the latter outcome shedding light on the overall feasibility of HIIT in inactive adults.
Overall, this novel study has profound public health applications as it will assess fitness and health related changes to a small dose of PA in the largest sample to date. If substantial changes in CRF are shown, these data have the potential to modify public health guidelines for implementing PA in inactive adults.
Low levels of physical activity (PA) and cardiorespiratory fitness (CRF) are significant issues for societal health. Public health guidelines for adults recommend > 150 min of moderate-intensity continuous training (MICT) or 75 min of vigorous exercise per week, and strength training on > 2 days per week. However, in 2020, 75% of adult Americans did not meet these PA recommendations. Physical inactivity is the fourth leading cause of death worldwide, as it increases the risk of 40 chronic conditions. Low maximal oxygen uptake (V̇O2max; the gold standard index of CRF) is strongly associated with increased risk of future morbidity and all-cause mortality. In fact, many large-scale studies have reported V̇O2max to be a more powerful predictor of risk for future morbidity and all-cause mortality than more traditional risk factors such as smoking, hypertension, obesity, high cholesterol, and insulin resistance. For population-level health, the largest benefits from improved PA and CRF are gained by the least fit individuals, with even small increases in fitness shown to improve health. Despite exercise being the only viable means to improve V̇O2max, it remains underutilized for primary disease prevention. Nevertheless, adults do not engage in PA due to a perceived lack of time. High intensity interval training (HIIT) is a time-efficient form of PA requiring brief intense bursts of activity separated by rest periods. Empirical data show that HIIT elicits similar and in some cases superior benefits versus MICT, often with less time. A special type of HIIT is reduced exertion high intensity interval training (REHIT) requiring only two 20 second sprints within a 10 minute session. A few studies show that REHIT increases CRF and other health-related outcomes, yet these studies have been criticized due to their small sample size, which serves to question the broad application of REHIT in adults. The proposed randomized controlled trial will recruit 60 inactive adults to complete 24 sessions of REHIT and compare resultant changes in CRF, substrate metabolism, and psychological responses to a non-exercising control group. This sample size is threefold higher than used in prior work and provides adequate statistical power to detect meaningful increases in V̇O2max. The proposed study will advance further research in the area of HIIT and if successful, may promote inclusion of REHIT in PA recommendations as a feasible alternative or adjunct to moderate or vigorous-intensity exercise as promoted in current PA recommendations.
1,273 studies on the registry are indexed under Sedentary Behavior; 300 are open to participants now.
This study's planned enrollment of 60 is close to the median of 60 across 1,076 interventional studies indexed under Sedentary Behavior.
Browse Sedentary Behavior studies →California State University, San Marcos is the lead sponsor of 9 studies on the registry; 1 is open to participants now.
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Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
BMI (body mass index)
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
This group will perform long term REHIT.
Other: High intensity interval training
This group will not complete REHIT, and will be given the option to complete the training once post testing is performed.
Other: High intensity interval training
Participants will complete 24 sessions of REHIT and their responses will be compared to a non exercising control group.
Cardiorespiratory fitness
Cardiorespiratory fitness (CRF) is determined by oxygen transport from cardiovascular system to mitochondria and is strongly related to health status and premature mortality. It will be assessed using VO2max testing on a cycle ergometer and expressed in mL/kg/min.
Time frame: CRF will be assessed at baseline 48 - 72 hours before the start of training, and at 6 and 12 weeks of training, which represent halfway and end of training. The assessments will be performed at least 24 hours after sessions of exercise training.
Fat and Carbohydrate Oxidation
Substrate metabolism represents the breakdown of fat and carbohydrate for energy expenditure and is related to metabolic health. It is measured during submaximal exercise during which time, participants' expired air is collected continuously. In this study, participants will complete 10 min of low intensity exercise before the VO2max test, and gas exchange data will be acquired to estimate the respiratory exchange ratio (RER) which is used to assess the percent contribution of fat and carbohydrate use. Moreover, fat and CHO oxidation will be calculated from standard equations and expressed in g/min.
Time frame: Fat and carbohydrate oxidation will be measured at baseline before the start of training and at 6 and 12 weeks of training, representing halfway and end of training, and at baseline and at 12 weeks in the non exercising control group.
Cardiac output
Cardiac output (CO in L/min) refers to the amount of blood delivered by the heart each minute and is the product of stroke volume and HR. Its assessment can shed light on the factors explaining the increase in VO2max with exercise training. In this study, it will be measured noninvasively using thoracic impedance cardiography.
Time frame: CO will be measured at baseline and at 6 and 12 weeks of training, representing halfway and the end of training, and at baseline and at 12 weeks in the non exercising control group.
Enjoyment of REHIT
The real-world feasibility and efficacy of REHIT has been challenged, as it is thought that this type of vigorous exercise is not enjoyable for adults. One measure related to this is enjoyment, which can be assessed with the 18-item Physical Activity Enjoyment scale. This validated survey is frequently used in similar studies to gauge psychological responses to exercise training. The Physical Activity Enjoyment scale will be completed 5 minutes after sessions of exercise training.
Time frame: This outcome will be assessed during session #2 of each week of training in the exercise training group. So, this outcome will be assessed weekly during all 12 weeks of training.
Perceived exertion responses to REHIT
The real-world feasibility and efficacy of REHIT has been challenged, as it is thought that this type of vigorous exercise is not enjoyable for adults. One measure related to this is perceived exertion, which can be assessed with the 6 - 20 Borg scale of Rating of Perceived Exertion. This validated survey is frequently used in similar studies to gauge psychological responses to exercise training. This RPE scale will be administered throughout sessions of exercise training, including at baseline, during the warm-up, after sprint 1, midway during recovery, after sprint 2, and then at the end of the exercise session.
Time frame: This outcome will be assessed during session #2 of each week of training in the exercise training group. So, this outcome will be assessed weekly during all 12 weeks of training
Pleasure responses to REHIT
The real-world feasibility and efficacy of REHIT has been challenged, as it is thought that this type of vigorous exercise is not pleasing for adults which may cause poor adherence to training. One measure related to this is pleasure:displeasure, which can be assessed with the +5 to -5 Feeling Scale, where +5 = very good, 0 = neutral, and -5 is very bad. This validated survey is frequently used in similar studies to gauge psychological responses to exercise training. This Feeling Scale will be administered throughout sessions of exercise training, including at baseline, during the warm-up, after sprint 1, midway during recovery, after sprint 2, and then at the end of the exercise session.
Time frame: This outcome will be assessed during session #2 of each week of training in the exercise training group. So, this outcome will be assessed weekly during all 12 weeks of training
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Plan to share: No — All participant data will be reported in articles published related to this project.
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California State University, San Marcos