Effect of Low Volume Sprint Interval Training on Cardiorespiratory Fitness

The Effect of Low Volume Sprint Interval Training on Cardiorespiratory Fitness--a Randomized Controlled Trial

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.

Study Overview

• Status: Active, not recruiting
• Conditions: Healthy Participants; Inactivity, Physical; Overweight (BMI > 25)
• Intervention / Treatment: Other: High intensity interval training

Detailed Description

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.

• Study Type: Interventional
• Enrollment (Estimated): 60
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United States
  • California
    • San Marcos, California, United States, 92096
      • California State University--San Marcos Human Performance Laboratory

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Healthy
• BMI < 35 kg/m2
• younger than 65 yr old
• no joint issues

Exclusion Criteria:

• Those adults who are currently active and not weight stable
• Adults with BMI > 35 kg/m2
• Use of medications which may alter study outcomes

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Prevention
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Intervention group; This group will perform long term REHIT.	Other: High intensity interval training; Participants will complete 24 sessions of REHIT and their responses will be compared to a non exercising control group.
Placebo Comparator: Non exercising control group; 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.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
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.	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.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
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.	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.	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.	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.	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.	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

Collaborators and Investigators

• Sponsor: California State University, San Marcos
• Investigators: Principal Investigator: Todd A Astorino, Ph.D, California State University, San Marcos

Study record dates

Study Major Dates

• Study Start (Actual): September 1, 2025
• Primary Completion (Estimated): August 30, 2028
• Study Completion (Estimated): August 30, 2028

Study Registration Dates

• First Submitted: October 31, 2025
• First Submitted That Met QC Criteria: January 7, 2026
• First Posted (Actual): January 9, 2026

Study Record Updates

• Last Update Posted (Actual): January 9, 2026
• Last Update Submitted That Met QC Criteria: January 7, 2026
• Last Verified: January 1, 2026

More Information

Terms related to this study

• Keywords: body composition; exercise adherence; high intensity interval training; maximal oxygen uptake; fat metabolism; affective valence
• Additional Relevant MeSH Terms: Nutrition Disorders; Overnutrition; Body Weight; Pathological Conditions, Signs and Symptoms; Behavior; Nutritional and Metabolic Diseases; Signs and Symptoms; Overweight; Sedentary Behavior; Motor Activity; Movement; Musculoskeletal Physiological Phenomena; Musculoskeletal and Neural Physiological Phenomena; Physical Conditioning, Human; Exercise; High-Intensity Interval Training
• Other Study ID Numbers: R15AG093525 (U.S. NIH Grant/Contract)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: All participant data will be reported in articles published related to this project.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No