Purpose <p>Beyond its clinical relevance, the 1-min sit-to-stand test (1STS) has gained attention in the general population as a measure of physical fitness. Relying solely on repetition counts may limit the interpretability of the 1STS following a training program aimed at improving muscle condition. We aimed to assess 1STS changes after a resistance program, incorporating strength and fatigability performance metrics for a more comprehensive evaluation.</p> Methods <p>23 healthy, active participants were randomly assigned to a training or control group. The training group followed a 4-week resistance program with short rest intervals (the 3/7 method) to improve muscle strength and local muscle endurance. Performance fatigability, sit-to-stand time, velocity, and power were assessed using a mobile app from a single sit-to-stand maneuver together with the number of repetitions performed (1STS_REP). Maximum theoretical load (<i>L</i>_<i>0</i>), velocity at zero load (<i>v</i>_<i>0</i>), the area under the load–velocity curve (A_<i>line</i>), and one-repetition maximum (1RM) were estimated using a linear encoder from a load–velocity test.</p> Results <p>The training group improved 1STS_REP (+ 16%), Sit to Stand app parameters (+ 8–25%), 1RM (+ 36%), and load–velocity metrics (<i>L</i>_<i>0</i>: + 45%, A_<i>line</i>: + 27%) (all <i>P</i> &lt; 0.05), with no change in <i>v</i>_<i>0</i>. No changes were observed in the control group. Improvements in 1STS_REP correlated with A_<i>line</i> (r = 0.379,&#xa0;P = 0.031) and Sit to Stand app parameters (r = 0.45–0.49,&#xa0;<i>P</i> &lt; 0.05). The training had no effect on performance fatigability.</p> Conclusion <p>These findings suggest that 1STS performance improvements result from strength-related gains rather than muscle endurance, informing better training strategies for lower-body functional capacity.</p>