This intervention will report results of a strength training programme in people with no fibromyalgia diagnosis

The dynamometer TKK 5105 (Takei Scientific Instruments Co., Ltd., Niigata, Japan) will be a typical analog handgrip dynamometer with an adjustable handle. This dynamometer will be used to assess the strength of the handgrip. The participant will be placed in a standing position, with the arms parallel but not touching the body, the shoulder adducted and neutrally rotated, and handgrip strength will be measured. The gadget handle will be modified to fit the size of the participants' hands so that each hand's index finger will be 90 degrees bent from the proximal to middle phalangeal joint. Every side will undergo two trials, alternately, with at least a minute of rest in between each session.

Participants will be seated on the isokinetic dynamometer chair (Biodex Medical System, NY) with both legs flexed at 90° and the testing leg's ankle will be strapped directly to a customized apparatus with a load cell (Model SML500, Interface Scottsdale, AZ, USA). To warm up, each subject will perform 3 progressive MVICs with 3 min of rest between attempts. To assess RFD in each leg, verbal encouragement will be given to the participants to apply "as much force as possible, as fast as possible" throughout the 2 consecutive maximal contractions. RFD will be analyzed using the time interval 0-200 (RFDlate). Subsequently, participants will perform 2 MVICs, each lasting for 5 s with 3 min of rest between contractions, with verbal encouragement. Maximal torque (MVIC) and time to peak voluntary torque (time-to-MVIC) will be evaluated. The right leg will always be evaluated first, and the trial with the highest value will be used for both RFD and MVIC.

The Karolinska Sleepiness Diary (KSD) will measure subjective sleep quality (Akerstedt et al., 1994). The KSD will be administered upon awakening in the morning following each of the training sessions (low and high intensity) assessing the following factors using a Likert scale: feeling of rest (1= no rest at all; 3= completely rested); sleep quality (1= very poor; 5= very good); sleep comfort (1= very restless; 5= very calm/relax); ease of falling asleep (1= very difficult; 5= very easy); waking up (1= woken up too early; 3= woken up late); ease of waking up (1= very difficult; 5= very easy); and did you get enough sleep (1= no, definitely very poor; 5= Yes, definitely enough). The higher the score, the higher the quality of sleep will be recorded.

Spanish version (Sanz et al., 2003) of the Beck Depression Inventory (BDI) aimed at determining possible signs of depression in the past week. Higher scores indicate higher levels of depression.

State-Trait Anxiety and Trait Anxiety Inventory (STAI), to analyse the levels of anxiety presented at a specific time and in general. Spanish version of Buela-Casal & Guillén-Riquelme (2017). Higher scores indicate higher levels of anxiety.

The Perceived Stress Scale (PSS), to assess the frequency with which participants experience stressful situations and thoughts in the last month. Higher scores indicate higher levels of stress. Remor (2006) was used in its Spanish version.

-Brief Pain Inventory (BPI). Used to determine the intensity and interference of pain in daily activities. The higher the pain perception, the higher the score obtained. The Spanish version of Badía et al. (2003) was used. -Brief Fatigue Inventory (BFI). This questionnaire measures the intensity of fatigue in the last 24 hours and its interference with daily activities and work. The higher the perception of fatigue, the higher the score obtained (Valenzuela et al., 2002).

Pittsburgh Sleep Quality Questionnaire (PSQI). This questionnaire analyses various parameters related to subjective sleep quality: latency, duration, efficiency and disturbances, as well as consumption of sleeping pills. The Spanish version of the PSQI was used, Hita-Contreras et al.

FIQ (Fibromyalgia Impact Questionnaire). The Spanish version of Rivera & González (2004) was used to assess the impact of fibromyalgia on physical and mental functions (pain, tiredness, fatigue, stiffness, anxiety and depression). Higher scores indicate a worse health condition.

The incremental protocol will include a 3-minute warm-up (4.5 km-h -1) followed by an increase to 6 km-h -1, with 1 km-h -1 increments every 45 seconds until exhaustion. Heart rate and the different spirometric variables, including respiratory exchange ratio (RER) and V̇O2 will be constantly monitored. The breath-by-breath method will be used to collect ventilation data during the incremental exercise test for individual assessment of maximal oxygen consumption capacity. The volume transducer and the Vyntus TM CPX gas analyser (Vyaire medical, INC, Hoechberg, Germany) shall be calibrated according to the manufacturer's instructions prior to each test.

HRV analysis. HRV analysis will be performed using a Polar H7 heart rate sensor (Kempele, Finland) to measure R-R intervals during the night at pre- and post-confinement. Analysis of HRV variables will be performed with Kubios HRV 3.0 software (Kuopio, Finland). Additionally, and if necessary, artefact correction will be performed with the same software by applying very low, low or medium threshold filters.

To carry out the blood extraction, a qualified person will perform a sterile puncture in the cubitus median vein. After 15 minutes of extraction (in the case of serum, essential to facilitate clot formation), both tubes are centrifuged for 10 minutes at 1,600 rpm and at 22ºC. By this process, serum or plasma is isolated in the corresponding tubes and then aliquoted into eppendorf tubes with a total volume of 400 μl in each tube. The serum and plasma samples must be gradually frozen as they are obtained, until they are finally stored at -80ºC.

Determination of monopodal and bipodal equilibrium levels.

The test volunteers will be seated upright in a chair that could be adjusted to suit their leg length, with their legs bent at a 90-degree angle and their arms folded across their chests. Participants were to get up from their seats, move three meters forward, turn around, walk back to the starting point, and then sit down again. Using video capturing, the fastest time between the two trials was found and utilized for analysis

The 5-times sit-to-stand test assesses the lower limb strength, transitional movements, balance and physical performance of older people. Test subjects were positioned upright in a chair that could be adjusted according to the length of their lower limbs, with their arms crossed over their chests and their legs bent to a 90-degree angle. Participants had to perform a total of five full squats in which the total execution time will be recorded.

Participants will be instructed to walk 10 m (marked by taped lines) as quickly as possible without running. The test will be repeated after 2 minutes of rest. Verbal encouragement will be given throughout the test. Two photocells (Witty, Microgate, Italy) will be placed at 6 and 10 m to record the walking time. The shortest running time will be used for analysis

Participants will walk for 2 minutes at the maximum speed they can sustain during that time. The test takes place on a rectangular track (40 x 20 m) with the corners defined by cones. Subjects will be allowed to rest if they need to, but time will not be stopped during their rest period. The total distance (m) covered after 6 min of walking will be measured. All participants will be accompanied by the investigator during the test, but will not be allowed to engage in conversation.

The dynamometer TKK 5105 (Takei Scientific Instruments Co., Ltd., Niigata, Japan) will be a typical analog handgrip dynamometer with an adjustable handle. This dynamometer will be used to assess the strength of the handgrip. The participant will be placed in a standing position, with the arms parallel but not touching the body, the shoulder adducted and neutrally rotated, and handgrip strength will be measured. The gadget handle will be modified to fit the size of the participants' hands so that each hand's index finger will be 90 degrees bent from the proximal to middle phalangeal joint. Every side will undergo two trials, alternately, with at least a minute of rest in between each session.

Participants will be seated on the isokinetic dynamometer chair (Biodex Medical System, NY) with both legs flexed at 90° and the testing leg's ankle will be strapped directly to a customized apparatus with a load cell (Model SML500, Interface Scottsdale, AZ, USA). To warm up, each subject will perform 3 progressive MVICs with 3 min of rest between attempts. To assess RFD in each leg, verbal encouragement will be given to the participants to apply "as much force as possible, as fast as possible" throughout the 2 consecutive maximal contractions. RFD will be analyzed using the time interval 0-200 (RFDlate). Subsequently, participants will perform 2 MVICs, each lasting for 5 s with 3 min of rest between contractions, with verbal encouragement. Maximal torque (MVIC) and time to peak voluntary torque (time-to-MVIC) will be evaluated. The right leg will always be evaluated first, and the trial with the highest value will be used for both RFD and MVIC.

The Karolinska Sleepiness Diary (KSD) will measure subjective sleep quality (Akerstedt et al., 1994). The KSD will be administered upon awakening in the morning following each of the training sessions (low and high intensity) assessing the following factors using a Likert scale: feeling of rest (1= no rest at all; 3= completely rested); sleep quality (1= very poor; 5= very good); sleep comfort (1= very restless; 5= very calm/relax); ease of falling asleep (1= very difficult; 5= very easy); waking up (1= woken up too early; 3= woken up late); ease of waking up (1= very difficult; 5= very easy); and did you get enough sleep (1= no, definitely very poor; 5= Yes, definitely enough). The higher the score, the higher the quality of sleep will be recorded.

Spanish version (Sanz et al., 2003) of the Beck Depression Inventory (BDI) aimed at determining possible signs of depression in the past week. Higher scores indicate higher levels of depression.

State-Trait Anxiety and Trait Anxiety Inventory (STAI), to analyse the levels of anxiety presented at a specific time and in general. Spanish version of Buela-Casal & Guillén-Riquelme (2017). Higher scores indicate higher levels of anxiety.

The Perceived Stress Scale (PSS), to assess the frequency with which participants experience stressful situations and thoughts in the last month. Higher scores indicate higher levels of stress. Remor (2006) was used in its Spanish version.

-Brief Pain Inventory (BPI). Used to determine the intensity and interference of pain in daily activities. The higher the pain perception, the higher the score obtained. The Spanish version of Badía et al. (2003) was used. -Brief Fatigue Inventory (BFI). This questionnaire measures the intensity of fatigue in the last 24 hours and its interference with daily activities and work. The higher the perception of fatigue, the higher the score obtained (Valenzuela et al., 2002).

Pittsburgh Sleep Quality Questionnaire (PSQI). This questionnaire analyses various parameters related to subjective sleep quality: latency, duration, efficiency and disturbances, as well as consumption of sleeping pills. The Spanish version of the PSQI was used, Hita-Contreras et al.

FIQ (Fibromyalgia Impact Questionnaire). The Spanish version of Rivera & González (2004) was used to assess the impact of fibromyalgia on physical and mental functions (pain, tiredness, fatigue, stiffness, anxiety and depression). Higher scores indicate a worse health condition.

The incremental protocol will include a 3-minute warm-up (4.5 km-h -1) followed by an increase to 6 km-h -1, with 1 km-h -1 increments every 45 seconds until exhaustion. Heart rate and the different spirometric variables, including respiratory exchange ratio (RER) and V̇O2 will be constantly monitored. The breath-by-breath method will be used to collect ventilation data during the incremental exercise test for individual assessment of maximal oxygen consumption capacity. The volume transducer and the Vyntus TM CPX gas analyser (Vyaire medical, INC, Hoechberg, Germany) shall be calibrated according to the manufacturer's instructions prior to each test.

HRV analysis. HRV analysis will be performed using a Polar H7 heart rate sensor (Kempele, Finland) to measure R-R intervals during the night at pre- and post-confinement. Analysis of HRV variables will be performed with Kubios HRV 3.0 software (Kuopio, Finland). Additionally, and if necessary, artefact correction will be performed with the same software by applying very low, low or medium threshold filters.

To carry out the blood extraction, a qualified person will perform a sterile puncture in the cubitus median vein. After 15 minutes of extraction (in the case of serum, essential to facilitate clot formation), both tubes are centrifuged for 10 minutes at 1,600 rpm and at 22ºC. By this process, serum or plasma is isolated in the corresponding tubes and then aliquoted into eppendorf tubes with a total volume of 400 μl in each tube. The serum and plasma samples must be gradually frozen as they are obtained, until they are finally stored at -80ºC.

Determination of monopodal and bipodal equilibrium levels.

The test volunteers will be seated upright in a chair that could be adjusted to suit their leg length, with their legs bent at a 90-degree angle and their arms folded across their chests. Participants were to get up from their seats, move three meters forward, turn around, walk back to the starting point, and then sit down again. Using video capturing, the fastest time between the two trials was found and utilized for analysis

The 5-times sit-to-stand test assesses the lower limb strength, transitional movements, balance and physical performance of older people. Test subjects were positioned upright in a chair that could be adjusted according to the length of their lower limbs, with their arms crossed over their chests and their legs bent to a 90-degree angle. Participants had to perform a total of five full squats in which the total execution time will be recorded.

The 5-times sit-to-stand test assesses the lower limb strength, transitional movements, balance and physical performance of older people. Test subjects were positioned upright in a chair that could be adjusted according to the length of their lower limbs, with their arms crossed over their chests and their legs bent to a 90-degree angle. Participants had to perform a total of five full squats in which the total execution time will be recorded.

Participants will be instructed to walk 10 m (marked by taped lines) as quickly as possible without running. The test will be repeated after 2 minutes of rest. Verbal encouragement will be given throughout the test. Two photocells (Witty, Microgate, Italy) will be placed at 6 and 10 m to record the walking time. The shortest running time will be used for analysis

Participants will be instructed to walk 10 m (marked by taped lines) as quickly as possible without running. The test will be repeated after 2 minutes of rest. Verbal encouragement will be given throughout the test. Two photocells (Witty, Microgate, Italy) will be placed at 6 and 10 m to record the walking time. The shortest running time will be used for analysis

The dynamometer TKK 5105 (Takei Scientific Instruments Co., Ltd., Niigata, Japan) will be a typical analog handgrip dynamometer with an adjustable handle. This dynamometer will be used to assess the strength of the handgrip. The participant will be placed in a standing position, with the arms parallel but not touching the body, the shoulder adducted and neutrally rotated, and handgrip strength will be measured. The gadget handle will be modified to fit the size of the participants' hands so that each hand's index finger will be 90 degrees bent from the proximal to middle phalangeal joint. Every side will undergo two trials, alternately, with at least a minute of rest in between each session.

The dynamometer TKK 5105 (Takei Scientific Instruments Co., Ltd., Niigata, Japan) will be a typical analog handgrip dynamometer with an adjustable handle. This dynamometer will be used to assess the strength of the handgrip. The participant will be placed in a standing position, with the arms parallel but not touching the body, the shoulder adducted and neutrally rotated, and handgrip strength will be measured. The gadget handle will be modified to fit the size of the participants' hands so that each hand's index finger will be 90 degrees bent from the proximal to middle phalangeal joint. Every side will undergo two trials, alternately, with at least a minute of rest in between each session.

Participants will be seated on the isokinetic dynamometer chair (Biodex Medical System, NY) with both legs flexed at 90° and the testing leg's ankle will be strapped directly to a customized apparatus with a load cell (Model SML500, Interface Scottsdale, AZ, USA). To warm up, each subject will perform 3 progressive MVICs with 3 min of rest between attempts. To assess RFD in each leg, verbal encouragement will be given to the participants to apply "as much force as possible, as fast as possible" throughout the 2 consecutive maximal contractions. RFD will be analyzed using the time interval 0-200 (RFDlate). Subsequently, participants will perform 2 MVICs, each lasting for 5 s with 3 min of rest between contractions, with verbal encouragement. Maximal torque (MVIC) and time to peak voluntary torque (time-to-MVIC) will be evaluated. The right leg will always be evaluated first, and the trial with the highest value will be used for both RFD and MVIC.

Participants will be seated on the isokinetic dynamometer chair (Biodex Medical System, NY) with both legs flexed at 90° and the testing leg's ankle will be strapped directly to a customized apparatus with a load cell (Model SML500, Interface Scottsdale, AZ, USA). To warm up, each subject will perform 3 progressive MVICs with 3 min of rest between attempts. To assess RFD in each leg, verbal encouragement will be given to the participants to apply "as much force as possible, as fast as possible" throughout the 2 consecutive maximal contractions. RFD will be analyzed using the time interval 0-200 (RFDlate). Subsequently, participants will perform 2 MVICs, each lasting for 5 s with 3 min of rest between contractions, with verbal encouragement. Maximal torque (MVIC) and time to peak voluntary torque (time-to-MVIC) will be evaluated. The right leg will always be evaluated first, and the trial with the highest value will be used for both RFD and MVIC.

The Karolinska Sleepiness Diary (KSD) will measure subjective sleep quality (Akerstedt et al., 1994). The KSD will be administered upon awakening in the morning following each of the training sessions (low and high intensity) assessing the following factors using a Likert scale: feeling of rest (1= no rest at all; 3= completely rested); sleep quality (1= very poor; 5= very good); sleep comfort (1= very restless; 5= very calm/relax); ease of falling asleep (1= very difficult; 5= very easy); waking up (1= woken up too early; 3= woken up late); ease of waking up (1= very difficult; 5= very easy); and did you get enough sleep (1= no, definitely very poor; 5= Yes, definitely enough). The higher the score, the higher the quality of sleep will be recorded.

The Karolinska Sleepiness Diary (KSD) will measure subjective sleep quality (Akerstedt et al., 1994). The KSD will be administered upon awakening in the morning following each of the training sessions (low and high intensity) assessing the following factors using a Likert scale: feeling of rest (1= no rest at all; 3= completely rested); sleep quality (1= very poor; 5= very good); sleep comfort (1= very restless; 5= very calm/relax); ease of falling asleep (1= very difficult; 5= very easy); waking up (1= woken up too early; 3= woken up late); ease of waking up (1= very difficult; 5= very easy); and did you get enough sleep (1= no, definitely very poor; 5= Yes, definitely enough). The higher the score, the higher the quality of sleep will be recorded.