Twenty patients (9 men, 11 women) between the ages of 30 and 60 years who had been
hospitalized for COVID-19 in an ICU volunteered for this study. Participants were
hospital-discharged at least 6 months before the start of the study and had not undergone
rehabilitation after hospital discharge.

This study utilized a two-treatment crossover design. Each treatment was eight weeks in
duration, with a two-week washout period. The order of treatments was randomized and
counterbalanced. Twenty participants were recruited and completed this study. This sample
was deemed sufficient as an a-priori power analysis (G*Power 3.1.9, Germany) estimated
that 18 patients were required to test the anticipated effect, considering a statistical
power of 0.8 and alpha <0.05. This effect was estimated based on the 18.7% increase in
the 6-minute walking test observed after 12 weeks of eccentric training [10]. Considering
a 10% dropout, we recruited 20 participants for this study.

Condition order was randomly arranged as either ECC then STD REHAB (n=10) or STD REHAB
then ECC (n=10) to account for a potential order effect of treatments. Both interventions
lasted eight weeks, and assessments were performed before and after the interventions. As
shown in Fig. 1A, during the ECC participant performed eccentric cycling using an
arm-and-leg motorized cycle ergometer (Model ABJ-107-2, Medical Technology Co LTD, China)
while during the STD REHAB condition participants performed functional rehabilitation
using strengthening exercises with elastic bands (Fig. 1B). During the 2-week wash-out
period, the participants refrained from training in preparation for their second
intervention.

2.3 Interventions The exercise intensity was matched between conditions throughout the
intervention period using the 6-20 point rating of perceived exertion (RPE; Borg´s Scale)
[10]. For both groups, RPE progressively increased during the first two weeks from 9
(very light) to 11 (fairly light), and then over the next five weeks from 13 (somewhat
hard) to 15 (hard). Additionally, heart rate (HR) and blood pressure (Omron Serie 5/7156,
USA), and oxygen saturation (Heal Force A3, CHOICEMMED, China) were measured immediately
after all training sessions to quantify the cardiovascular demands of training, which
were averaged between training sessions.

The training protocol for the ECC consisted of a 5-minute warm-up on a stationary
ergometer (RS1 Go, Life fitness, USA) before completion of the prescribed workout. In the
first two weeks, participants completed two sets of 10 minutes of eccentric cycling at an
RPE between 9-11 with 2 minutes of inter-set rest. Then, during weeks 3-8, participants
completed two sets of 15 min of eccentric cycling at an RPE between 13-15 with 2 min
inter-set rest.

The training protocol for STD REHAB consisted of the same 5 min warm-up protocol used in
ECC, followed by three sets of 8 repetitions of bicep curls, triceps extensions, shoulder
abduction, bodyweight squats, deadlifts, and leg abductions with an elastic band with 2
min inter-set rest. The resistance of the elastic band tension was progressively
increased according to the participant's tolerance based on RPE. ECC training was
programmed for ~20-30 min, while STD REHAB lasted ~60 min per session.