If not high intensity then what?

The short version: the evidence does not tell you whether lower-intensity rehabilitation beats high-intensity for long COVID. The studies that exist tested different populations.

The 2022 narrative review found that a mixed program of low-intensity continuous sessions and higher-intensity interval sessions improved 6-minute walk distance by 80-170 meters in 12 post-COVID patients aged 26-84 [1]. Nine of the 12 achieved progressive intensity increases [1]. But these were people recovering from acute COVID, not people with long COVID and post-exertional malaise.

The same review found that low-intensity (40-60% HRmax) and high-intensity (60-80% HRmax) aerobic training combined with resistance training produced comparable improvements in lower limb muscle size in COVID-19 patients with sarcopenia at 8 weeks and 6 months [1]. That is the closest comparison of low versus high intensity in the evidence. It was tested in older patients with muscle wasting, not in people with post-exertional malaise.

A 2022 case report described a 27-year-old runner who developed POTS after mild COVID and improved over a year with a graduated exercise program starting from recumbent to seated to standing [3]. That is the only record that matches the long COVID population. It is a single case, not a trial.

My call: the evidence does not answer whether lower-intensity rehabilitation improves outcomes more than high-intensity for long COVID. The only direct comparison of low versus high intensity was in patients with sarcopenia, not post-exertional malaise. For people with POTS or post-exertional malaise, starting low and graduated is the conservative approach, but no trial has tested it against high-intensity in this population. Confidence: low.