## 1 Introduction  
Sarcopeniaia is characterized by a progressive decline in functional capacity, muscle mass, and strength [1] and is the most common aging-related syndrome. In particular, lower-limb strength constitutes a relevant clinical outcome among older adults, specifically for those with sarcopenia, who have a higher risk of disability, frailty, institutionalization, and death [2, 3]. A recent estimation from the Eurostat online database (28 European countries) suggests an increase of 60-70% of individuals with sarcopenia by 2045, affecting 12.9 to 22.3% of older people [4]. Age-related deconditioning of lower-limb strength occurs mainly due to the loss of muscle mass, together with the deterioration of neural patterns and tendon proprieties [5, 6]. Declines of 24-30% in lower-limb strength were reported in older adults after 12 years of follow-up [7]. Moreover, inactivity periods due to illness, injuries, or hospitalizations--frequent in older adults [8]--accentuate loss in muscular function, reaching decrements of 11-16% after 7-10 days [9, 10]. Therefore, assessing lower-limb strength is crucial to develop effective approaches for preventing and even reversing the aforementioned aging-related alterations [11].  
Although several tests are available, they present limitations for older adults. For example, the one-repetition maximum and the number of repetitions to failure tests have been used to evaluate the dynamic lower-limb strength in older adults [12; 13; 14; 15]. The one-repetition maximum test refers to an incremental loading evaluation up to the heaviest load that the participant can properly lift without any external help, completing the full range of motion [16]. The number of repetitions to failure test requires the participant to perform as many repetitions as possible with a given load, and then the 1 RM is calculated using estimation formulas [17]. Nevertheless, both tests usually produce excessive fatigue and muscle soreness in the older population [18]. Advances in technology-based approaches have made it possible to accurately estimate lower-extremity strength without fatigue using the velocity-based method (i.e., monitoring the barbell velocity) [19; 20]. However, this approach requires specific equipment, such as a leg extension or Smith machine, which are not normally present in a geriatric context.  
Another practical and widely used tool to screen strength and neuromuscular capacity [21] is the isometric knee extension (IKE) test. This evaluation consists of a 3-s trial of maximal isometric contractions involving the extensor muscles of the knee [22]. The IKE test presents some advantages compared to dynamic methods, namely the technical simplicity, low injury risk, high reliability, and ease of use within clinical settings, as it can be implemented using portable devices, such as strain gauges [23]. In addition to being a specific tool for screening lower-limb strength, the resulting value of the IKE test is highly associated with two relevant health-related outcomes in aging--physical function (e.g., agility, gait speed, and standing ability) and muscle mass [22].  
However, to date, there is no information on the sensitivity of this practical test to detect clinical changes in lower-limb strength after training or an exercise cessation period. This interpretation of sensitivity is essential to be confident that changes detected by the IKE test when implemented as an evaluation method are produced by actual improvements or decrements in lower-limb strength and not by the protocol instability (i.e., biological and measurement device variations) [24; 25; 26].  
Against this background, this study aimed to examine the sensitivity of the IKE test within clinical settings to detect changes in the lower-limb strength of institutionalized older adults after exercise training and an inactivity period.