Assessing muscle fitness changes to resistance training in healthy young adults using the 1-min sit-to-stand test: insights from a mobile app analysis.

Abstract

Purpose: 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.

Methods: 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 (L₀), velocity at zero load (v₀), the area under the load-velocity curve (A_line), and one-repetition maximum (1RM) were estimated using a linear encoder from a load-velocity test.

Results: The training group improved 1STS_REP (+ 16%), Sit to Stand app parameters (+ 8-25%), 1RM (+ 36%), and load-velocity metrics (L₀: + 45%, A_line: + 27%) (all P < 0.05), with no change in v₀. No changes were observed in the control group. Improvements in 1STS_REP correlated with A_line (r = 0.379, P = 0.031) and Sit to Stand app parameters (r = 0.45-0.49, P < 0.05). The training had no effect on performance fatigability.

Conclusion: 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.