Background: Many patients with COVID-19 present the so-called post-acute sequelae of COVID-19 such as fatigue, post-stress discomfort, dyspnea, headache, pain mental impairment, incapacity to perform daily physical tasks ant exercise intolerance. This study aims to investigate the effects of different exercise programs on physical and mental fitness, physical condition and biomarkers of the immune system and oxidative stress in older COVID-19 survivors. Methods: The sample will be made up of 120 eligible participants, over the age of 60 years who have had COVID-19 disease and are survivors and present persistent COVID-19 symptomatology diagnosed by the corresponding physician. The participants will be randomly assigned to the experimental groups: supervised endurance group (SEG, n = 30), supervised strength group (SSG, n = 30), supervised concurrent group (SCG, n = 30), which will perform the corresponding exercise program 3 days a week compared to the control group (CG, n = 30), which will not carry out a supervised exercise program. The design of this project will include assessment of cardiorespiratory fitness, muscle fitness, pain and mental health, and biomarkers of inflammation and oxidative stress.

This project will carry out a randomized controlled trial to determine what type of supervised exercise program is the most effective compared with a control group (CG): supervised endurance group (SEG), supervised strength group (SSG), supervised concurrent group (strength and endurance) (SCG) and CG. The project will be divided into 3 subprojects and performed in coordination by three institutions as follows:

i) Subproject of the consolidated research group on pain, physical activity, nutrition and health (Acronym: DAFNiS) of the Campus Sant Joan de Deu. University of Barcelona. "Effects of a physical exercise program (aerobic, strength or combined/concurrent) on muscle fitness, pain and mental health in older COVID-19 survivors".

ii) Subproject of the Hospital of Matar: "Evaluation of cardiorespiratory and muscular fitness in older COVID-19 survivors".

iii) Subproject of the Department of Physiology and Immunology. University of Barcelona. "Evaluation of biomarkers of inflammation and oxidative stress in older COVID-19 survivors".

The sample will be made up of 120 eligible participants, over the age of 60 years who have had COVID-19 disease and are survivors and present persistent COVID-19 symptomatology with sequelae of fatigue, muscle weakness, pain, difficulty in performing daily life activities, etc. diagnosed by the corresponding physician. The participants will be recruited from Hospital of Matar. Candidates fulfilling the study inclusion criteria will provide signed informed consent prior to inclusion.

To calculate the sample size of this project a type 1 (α) error of 5% and a 95% confidence interval with a level of precision (d = 0.095) was established for the test of proportional hypotheses resulting in a sample size of n= 108 persons, increased by 10% (rounded up to n=120) to compensate for possible dropouts along the study period.

To know the sample size more precisely in the hypothesis test of means it will be necessary to carry out a pilot study which will provide the size of effect and statistical power (0.80), determine the analysis to perform, obtain delta values in the units corresponding to the principal study variable as well as know the standard deviation.

Program of supervised exercise The intervention will consist in a program of supervised physical exercise performed 3 times a week for 12 weeks. For the planning and control of the exercise program the progressive individualized planning model will be applied based on the subjective perception of effort and cardiorespiratory parameters (heart rate and ventilatory threshold determined in the evaluation tests) of the participants. This program has been used by our research group in previous studies for improving cardiorespiratory and muscle fitness. The basis of this periodization model establishes an initial period of individualization to obtain the personal parameters used for the training load

The COVID-19 survivors will be randomly assigned to 3 programs of supervised exercise :

1. Program of endurance exercise. The program of supervised endurance exercise will consist in walking for 1 hour 3 times a week. The intensity (step speed) will gradually be increased each week (approx. 5%) according to the perception of the participant. A pulsometer will be used to determine the safe range of heart rate at which the participant should perform.
2. Program of strength exercise This will consist in performing a program of traditional strength 1 hour 3 times a week. Circuit training methodology will be used (10 exercises) alternating muscle groups of the upper and lower extremities and trunk. The initial series be of 1 exercise, evolving to up to 3-4 along the program based on the individual adaptation of the individual. The intensity (load applied) will be gradually increased each week while the recovery times between each exercise activity will be reduced (approx. 5%) according to the perception of the participant. A pulsometer will be used to determine the safe range of heart rate at which the participant should perform.
3. Program of concurrent exercise (endurance and strength) The participants will perform 1 hour of concurrent exercise, combining walking (20 minutes) and the strength program for 40 minutes, maintaining the same instructions explained previously in each exercise program.
4. Control group The control group will not carry out any supervised exercise program but will maintain their same habits of daily life activities.

Process of evaluation To determine the effects of the exercise program, an initial evaluation will be made before beginning the exercise program to assess the initial status of the participants (Pre). This evaluation will be compared with the evaluation made at the end of the intervention program (Post) at 12 weeks

Inclusion Criteria:

• Persons of both sexes (and different expression of gender) older than 60 years of age.
• No history of physical diseases and no disease or disability that limits participation in the exercise program or precludes the corresponding measurement/evaluations.
• Be able to communicate without difficulty.
• Be able to understand the objectives of the project and provide informed consent. In this case, the consent form will be signed.
• Not taking any medication that can affect normal performance of the exercise program and the evaluations

Exclusion Criteria:

• Having acute or terminal disease or any other disease that may affect the normal practice of a supervised exercise program and the corresponding evaluations.
• Consumption of alcohol or drugs.
• Be performing any type of activity that may interfere in carrying out the supervised exercise program or the evaluations.
• Not completing the study once initiated or wishing to participate in the control group.