# Reduced Exertion High-Intensity Interval Training is More Effective at Improving Cardiorespiratory Fitness and Cardiometabolic Health than Traditional Moderate-Intensity Continuous Training PMID: 30736402 Journal: International journal of environmental research and public health Published: 2019 Feb 7 Authors: Cuddy TF, Ramos JS, Dalleck LC ## Question The study sought to quantify acute cardiovascular and metabolic responses to REHIT and determine whether 8 weeks of chronic REHIT improves cardiorespiratory fitness and cardiometabolic health more effectively than MICT in a real-world workplace environment. ## Summary This randomized workplace study compared 8 weeks of reduced-exertion high-intensity interval training (REHIT) on a CAR.O.L cycle ergometer with traditional moderate-intensity continuous training (MICT) in physically inactive, low- to moderate-risk adult employees. REHIT required a 10-minute session with two 20-second all-out sprints, while MICT required 30 minutes of aerobic exercise 5 days per week. Among completers, REHIT produced larger improvements than MICT in cardiorespiratory fitness, systolic blood pressure, waist circumference, and metabolic syndrome severity, with high adherence but somewhat more dropout in the REHIT arm, largely attributed to illness. ## Population - Physically inactive, low- to moderate-risk adult faculty/employees from a university and hospital, without evidence of cardiovascular, pulmonary, or metabolic disease. - Sample size: 32 - Age: Completer group means: MICT 42.2 +/- 9.7 years; REHIT 40.8 +/- 10.8 years. - Sex: 16 men and 16 women recruited. - Fitness level: Physically inactive; low baseline CRF. - Health status: Low to moderate risk; no cardiovascular, pulmonary, or metabolic disease. ## Methodology - Randomized parallel-group workplace exercise training study with acute REHIT response testing during the intervention. - 8 weeks - Two local workplace environments, a university and hospital, with supervised exercise training. - Randomized and controlled study design. ## Protocol - REHIT CAR.O.L intense ride. - Modality: Cycle ergometer. - Work intervals: 20-second all-out sprint. - Recovery: 3 minutes slow pedaling between sprints. - Sets or repetitions: 2 sprints. - Intensity: All-out; measured sprint average 86.1 +/- 4.4% HRR and 74.4 +/- 11.5% VO2 reserve; peak 94% HRR and 92.9% VO2 reserve. - Session duration: 10 minutes. - Frequency: REHIT schedule shown in figure but not numerically captured in text; MICT 5 days/week. - Program length: 8 weeks. - Progression: CAR.O.L self-learning algorithm adapted resistance according to weight, power output, and fatigue index. - MICT. - Modality: Aerobic exercise. - Work intervals: Continuous 30-minute aerobic exercise. - Sets or repetitions: One continuous bout. - Intensity: 50%-65% heart rate reserve. - Session duration: 30 minutes. - Frequency: 5 days/week. - Program length: 8 weeks. ## Outcomes ### Cardiorespiratory fitness Status: improved CRF improved more with REHIT than MICT: 12% versus 7%; table values changed from 25.3 +/- 2.9 to 28.4 +/- 3.1 mL/kg/min in REHIT and 26.2 +/- 6.7 to 28.0 +/- 7.1 in MICT. F[1,24] = 9.9, p < 0.01; within-group p < 0.05 in both groups, change from baseline significantly different than MICT for REHIT. ### Systolic blood pressure Status: improved Systolic BP decreased more with REHIT than MICT: REHIT 130.4 +/- 8.8 to 123.8 +/- 6.6 mmHg; MICT 128.9 +/- 17.4 to 126.7 +/- 14.4 mmHg. REHIT -5% versus MICT -2%; F[1,24] = 8.1, p < 0.01. ### Waist circumference Status: improved Waist circumference decreased more with REHIT than MICT: REHIT 86.6 +/- 10.5 to 85.4 +/- 9.7 cm; MICT 87.6 +/- 10.1 to 87.3 +/- 9.1 cm. REHIT -1.4% versus MICT -0.3%; F[1,24] = 7.132, p = 0.01. ### Metabolic syndrome z-score Status: improved MetS z-score improved more with REHIT: REHIT -1.56 +/- 1.49 to -2.53 +/- 1.29; MICT -1.83 +/- 2.24 to -2.32 +/- 2.12. A favorable MetS z-score response occurred in 75% of REHIT versus 47% of MICT completers. Between-group change F[1,24] = 5.9, p = 0.02; responder incidence p < 0.05. ### Acute REHIT intensity and safety physiology Status: mixed REHIT elicited high acute cardiovascular strain: sprint mean 86.1 +/- 4.4% HRR and 74.4 +/- 11.5% VO2 reserve; peak HRR reached 94%, peak VO2 reserve 92.9%, and peak blood pressure 218/98 mmHg. ### Adherence and dropout Status: mixed Adherence was high in both groups, but dropout was higher in REHIT. REHIT adherence averaged 89.2% and MICT 87.8%; dropout was REHIT 4/16 and MICT 1/16. ## Practical Insights - A 10-minute cycling session with only 40 seconds of all-out work can improve CRF and several cardiometabolic markers in screened inactive adults when supervised. - Programming claims should pair ultra-low-volume REHIT with clear screening and intensity cautions. - The direct protocol depends on specialized cycling equipment, but the timing structure can inform app interval templates with modified intensity for safety. ## Limitations - Small sample with only 27 completers. - Diet was not strictly controlled. - Outside physical activity and sedentary behavior were not monitored. - Prescribed medications were not monitored. - REHIT dropout was higher than MICT. - No long-term follow-up. - Protocol used specialized CAR.O.L cycle ergometers in supervised workplace settings. ## Safety And Adherence - Authors report absence of untoward events. - Peak acute REHIT blood pressure reached 218/98 mmHg. - Authors recommend careful pre-participation screening for previously inactive and/or risk-factor-burdened individuals before REHIT. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/30736402/) (pubmed) - [DOI](https://doi.org/10.3390/ijerph16030483) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6388288/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.