## 2 Materials and Methods
### Outcome Measures  
An initial screening using questionnaires was conducted to evaluate the participants' cognitive state (using the Mini-Mental State Examination, MMSE) [30], disability in daily activities (using the Barthel [31] and Lawton [32] indexes), fear of falling (using the Fall Efficacy Scale--International, FES-I) [33] and sarcopenia (using the SARC-F scale [34]). Thereafter, the IKE, SPPB, IHS, and TUG evaluations were conducted. Two trials of each physical test were recorded 2 minutes apart, and the highest value was used to analyze the pre-post changes after the training or inactive period. The physical assessments are detailed below:  
For _the isometric knee extension (IKE) test (main outcome)_, the participants assumed a sitting position on a custom-built bench and conducted a 3-s trial of maximal voluntary contraction for both the dominant and non-dominant legs, which were measured separately at a comfortable knee angle of 110-120\({}^{\circ}\) knee (180\({}^{\circ}\) = full extension) [22]. A portable strain gauge sampling at 80 Hz (Chronojump, Barcelona, Spain) was secured to the bench and attached at the end to a chain connected to a padded resistance anklet. This padded ankleet was specifically designed for maximal isometric testing to guarantee mechanical rigidity and minimize movement [35]. The chain length was adapted depending on the anthropometric characteristics of the participants to obtain the above-mentioned target angle [36]. Before the trial, the knee angle was measured using a human-held goniometer (Nexgen Ergonomics, Point Claire, Quebec, Canada). The strain gauge was calibrated before the session using a 5.0 kg Eleiko disc (Eleiko, Halmstad, Sweden) according to the manufacturer's instructions. The initial pre-tension was standardized and confirmed using real-time visual feedback to avoid countermovement [35; 36]. The maximal voluntary contraction force (instantaneous highest value of force) was obtained from the manufacturer software in relative terms (highest force value/subject's body mass). _The Short Physical Performance Battery (SPPB) test (secondary outcome)_[37] was assessed to evaluate the participants' functional capacity using the following tests: static balance, 4-m gait speed, and 5 sit-to-stand (STS) repetitions. The static balance test included tandem, semi-tandem, and side-by-side positions. For each balance stand, the timing was evaluated based on when the participants moved their feet, or when 10 s (highest possible score) was achieved. The 4-m gait speed test was conducted from a static position at the usual walking pace. The participants performed the 5-repetitions STS test with their arms across their chest and were timed from the initial sitting position to the final standing position at the end of the fifth repetition. Moreover, the relative mean power (watts/subject's body mass) resulting from the 5-repetitions STS test was estimated using a mathematical formula [36]. Based on the results achieved in each test, this battery was scored from 0 (worst) to 12 (best). The resulting scores are part of the Vivifrail program to determine each individual's physical exercise program (described later in detail) [28]. The participants' _isometric handgrip strength (HIS, secondary outcome)_ was evaluated separately for each hand (i.e., dominant and non-dominant hand) in a seated position, with their shoulders neutrally rotated and adducted, elbows flexed at 90\({}^{\circ}\), forearms in neutral, and wrists between 0 and 30\({}^{\circ}\) of dorsiflexion [38]. A calibrated digital dynamometer adjustable (Takei 5401-C, Shinagawa-Ku, Tokyo, Japan) was used. The results derived from this test (in kg) were expressed in relative terms (kg achieved in the test/subject's body mass). _The Timed Up and Go (TUG) test (secondary outcome)_ measured the time it took the participants to (i) stand up without using their arms, (ii) walk 3 m, and (iii) turn around and sit back down [39].