# Home-Based HIIT and Traditional MICT Prescriptions Improve Cardiorespiratory Fitness to a Similar Extent Within an Exercise Referral Scheme for At-Risk Individuals PMID: 34858205 Journal: Frontiers in physiology Published: 2021-11-10 Authors: Hesketh K, Jones H, Kinnafick F, Shepherd SO, Wagenmakers AJM, Strauss JA, Cocks M ## Question In an exercise referral scheme for at-risk individuals, does home-based HIIT improve cardiorespiratory fitness, adherence, compliance, and cardiometabolic outcomes more than traditional moderate-intensity continuous training? ## Summary This pragmatic exercise-referral-scheme trial let at-risk primary-care participants choose either 12 weeks of home-based bodyweight HIIT or traditional moderate-intensity continuous training. Home-HIIT was popular and improved cardiorespiratory fitness by a similar amount to MICT, with improvements maintained 3 months after the program. However, adherence was poor in both groups, early drop-off was higher in Home-HIIT, and MICT produced more favorable body-composition and blood-pressure findings. The study is highly relevant for real-world home HIIT but is not randomized. ## Population - At-risk adults enrolled in a United Kingdom exercise referral scheme who selected either a structured MICT or Home-HIIT prescription. - Sample size: 154 - Age: 48 +/- 10 years overall. - Sex: 88 male and 66 female overall. - Fitness level: Mean VO2peak 25.6 +/- 7.6 ml/kg/min; Home-HIIT had lower baseline CRF than MICT. - Health status: Mean BMI 30.5 +/- 6.1 kg/m2 with multiple cardiometabolic, respiratory, musculoskeletal, mental-health, and sedentary risk factors. ## Methodology - Pragmatic non-randomized patient-preference trial embedded in a United Kingdom exercise referral scheme. - 12-week intervention plus 3-month follow-up - Primary-care exercise referral scheme in Sefton/Liverpool, United Kingdom; Home-HIIT was home based and MICT used gym/leisure-center/local-environment options. - Controlled study design. ## Protocol - Home-HIIT. - Modality: Home-based bodyweight intervals. - Work intervals: 1 minute: two bodyweight exercises for 30 seconds each with no rest between. - Recovery: 1 minute rest. - Sets or repetitions: 4 intervals/session in weeks 1-4, increasing by 1 interval every fortnight to 9 intervals. - Intensity: >=80% predicted HRmax during intervals. - Session duration: 8-18 minutes of interval/rest sequence plus 2-minute warm-up. - Frequency: 3 sessions/week. - Program length: 12 weeks. - Progression: Add 1 interval every fortnight after week 4 until 9 intervals. - Traditional MICT exercise referral prescription. - Modality: Moderate-intensity continuous exercise using gym equipment, classes, walking groups, or local environment. - Work intervals: Continuous exercise. - Sets or repetitions: Continuous sessions. - Intensity: 50-70% predicted HRmax after a 5-minute warm-up. - Session duration: 15 minutes/session in weeks 1-2, progressing to 45 minutes/session by week 12; total time excludes warm-up and cool-down. - Frequency: At least 3 sessions/week. - Program length: 12 weeks. - Progression: Weekly time commitment progressed from 45 minutes/week to 135 minutes/week. ## Outcomes ### VO2peak Status: improved Both Home-HIIT and MICT significantly improved relative VO2peak after 12 weeks and maintained significant improvements at follow-up; between-group differences were not significant. Post: MICT +3.9 +/- 6.0 ml/kg/min, P<0.001; Home-HIIT +2.7 +/- 4.4, P<0.001; between P=0.130. Follow-up: MICT +2.9 +/- 5.1, P<0.001; Home-HIIT +2.0 +/- 5.7, P=0.015; between P=0.298. ### Adherence and compliance Status: mixed Adherence was poor in both groups and did not differ significantly; completed sessions were often compliant with the prescribed intensity. Weekly adherence ITT: MICT 48 +/- 35%, Home-HIIT 39 +/- 36%, P=0.772. Per-protocol compliance: MICT 88 +/- 23%, Home-HIIT 82 +/- 23%, P=0.104. ### Drop-off Status: worse/safety concern No exercise uptake and total drop-off were greater in Home-HIIT than MICT. No exercise uptake: Home-HIIT n=27 vs MICT n=8. Total drop-off: Home-HIIT n=66 vs MICT n=32. ### Body composition Status: mixed MICT produced more favorable body-mass, BMI, and fat-mass changes than Home-HIIT; Home-HIIT showed less durable or no body-composition benefit. Fat mass post: MICT -1.5 +/- 6.3 kg, P=0.010; Home-HIIT -0.2 +/- 2.0 kg, P=1.000; between P=0.030. BMI follow-up between-group P=0.001. ### Blood pressure Status: mixed MICT reduced systolic, diastolic, and mean arterial pressure at follow-up; Home-HIIT did not improve blood pressure. Follow-up systolic BP: MICT -6 +/- 9 mmHg, P<0.001; Home-HIIT +1 +/- 10, P=1.000; between P<0.001. Diastolic between P<0.001; MAP between P<0.001. ### Glucose and lipids Status: no clear change Fasting glucose, OGTT outcomes, and blood lipids were not improved in either group. No significant within-group improvements in fasting glucose, OGTT measures, triglycerides, cholesterol, HDL, or LDL. ## Practical Insights - Home bodyweight HIIT can be offered as a viable, popular option for at-risk adults who value time efficiency and convenience. - A simple 1-minute work / 1-minute rest progression from 4 to 9 intervals can produce CRF improvements, but adherence support is critical. - Home-HIIT should not be positioned as superior to MICT for cardiometabolic outcomes based on this study. - Workout apps should include lower-impact substitutions and adherence prompts because illness, injury, tiredness, motivation, and life demands affected participation. ## Limitations - Participants self-selected intervention groups rather than being randomized. - Home-HIIT had lower baseline CRF than MICT. - No no-treatment comparator group. - Observed CRF variability exceeded the a priori estimate, so type II error cannot be ruled out. - Predicted HRmax rather than measured HRmax was used for prescription. - HR lag limits interpretation of short HIIT intervals. - Heart-rate monitors were provided for research and may have influenced motivation. - Dietary records were not collected. - Detailed eligibility criteria were in supplementary material and not extracted as explicit full-text evidence here. ## Safety And Adherence - Formal adverse-event counts were not reported. - Survey responses included illness or injury as reasons for missed sessions and need to adapt exercises. - Home-HIIT used impact exercises such as squat jumps, tuck jumps, burpees, and jumping jacks, which may require modification for some users. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/34858205/) (pubmed) - [DOI](https://doi.org/10.3389/fphys.2021.750283) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8631444/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.