Fidelity, tolerability and safety of acute high-intensity interval training after hospitalisation for COVID-19: a randomised cross-over trial
Question
Whether three widely used supervised HIIT protocols can be performed with acceptable fidelity, tolerability, and safety by individuals recently discharged after hospitalization for severe COVID-19.
Summary
Ten adults recently discharged after hospitalization for severe COVID-19 completed three supervised cycle-ergometer HIIT protocols in randomized cross-over order: 4 x 4 minutes, 6 x 1 minute, and 10-20-30. Every participant completed all three 38-minute sessions with no adverse events, no angina, and no post-exercise ECG changes. All protocols were rated tolerable, though time spent above 85% maximum heart rate differed between protocols. The findings support feasibility and acute supervised safety in a small, selected post-COVID group, not long-term rehabilitation efficacy.
Methodology
- Adults recently discharged after hospitalization for severe COVID-19 requiring oxygen supplementation.
- 10 participants.
- Bicycle ergometer.
- Work intervals: 4 x 4: four 4-minute intervals; 6 x 1: six 1-minute intervals; 10-20-30: repeated 10-second all-out bouts within 30-20-10 cycles.
- Recovery: 4 x 4: 3-minute active pauses at 50-70% HRmax; 6 x 1: 3-minute active pauses at 30% Wattmax; 10-20-30: 3 minutes at 50-70% HRmax between 5-minute sets plus easy/medium segments within cycles.
- Intensity: 4 x 4 at intensity inducing >=85% HRmax; 6 x 1 at 100% Wattmax; 10-20-30 with 30 seconds easy, 20 seconds medium, 10 seconds all-out.
- 38 minutes each.
- Three acute sessions separated by 1-week washout.
- Acute cross-over trial.
- Randomized cross-over trial comparing three acute supervised HIIT protocols with 1-week washout between protocols.
- Fidelity/adherence, Tolerability, Adverse events, and Exercise intensity were tracked.
Outcomes
Protocol completion
All 10 participants completed all three HIIT protocols with 100% attendance.
Attendance 100%; all randomized participants included in analysis.
Safety
No adverse events were reported, and no angina or ECG changes were seen after HIIT training.
Time at HR >=85% HRmax
High intensities were achieved in all protocols, but time above 85% HRmax differed by protocol, with less time for 6 x 1.
4 x 4: 13.7 (6.4) min; 10-20-30: 12.1 (3.8) min; 6 x 1: 6.1 (5.6) min; p=0.03.
Tolerability
All three protocols were well tolerated with similar Likert scores.
4 x 4: 8 (2); 10-20-30: 8 (2); 6 x 1: 9 (2); p=0.72.
RPE
RPE did not differ between protocols.
4 x 4: 5 (2); 6 x 1: 5 (2); 10-20-30: 6 (2); p=0.28.
Insights
- Acute supervised cycle HIIT may be feasible in selected adults recently hospitalized for COVID-19 after screening and with medical-style safety monitoring.
- Protocol labels do not guarantee equivalent intensity exposure: 6 x 1 produced less time above 85% HRmax than 4 x 4 and 10-20-30 in this sample.
- Post-COVID HIIT safety claims should be limited to supervised, selected, acute settings until larger and longer trials are available.
Limitations
- Very small sample size of 10 participants.
- Likely selection bias because the main reason for declining participation was feeling too weak to exercise.
- Participants were heterogeneous.
- Only acute HIIT bouts were tested.
- No conclusions can be drawn about extended HIIT rehabilitation programs.
- Clinical supervised cycling setting limits generalization to unsupervised or bodyweight HIIT.
Safety
- No adverse events were reported during the study.
- No angina was reported during HIIT training.
- No ECG changes were seen after HIIT training.
- Safety termination criteria included angina, signs of poor perfusion, request to terminate due to intolerable dyspnea, and severe fatigue manifestations.