Reliability and Validity of Critical Force Estimated From a 3-Minute All-Out Squat Test

ABSTRACT: Yang, Y-R, Wang, H-J, Lin, C-Y, Lin, Y-D, and Cheng, C-F. Reliability and validity of critical force estimated from a 3-minute all-out squat test. J Strength Cond Res XX(X): 000-000, 2026-This study aimed to develop a 3-minute all-out squat test (3MST) to determine critical force (CF) in the squat exercise and to evaluate its reliability and validity. Fifteen trained men participated in the study and completed a maximal strength test, 3 repetitions-to-exhaustion tests to estimate CF and F', and 2 3MSTs to assess end-test force (EF) and work above EF (WEF). Heart rate (HR) and changes in deoxyhemoglobin concentration (Δ[HHb]) were recorded during the 3MSTs. Blood lactate concentration ([La]) was collected 5 minutes after the 3MSTs. Both EF (intraclass correlation coefficient [ICC] = 0.975-0.980, p < 0.05) and WEF (ICC = 0.767-0.882, p < 0.05) demonstrated good-to-excellent reliability. Critical forces, derived from the 3 mathematical models, exhibited strong relationships and high agreement with EF (r = 0.783-0.913, p < 0.05), and did not differ significantly from EF (p > 0.05). However, WEF was significantly greater than F' estimated from the 3 models (p < 0.05). In addition, both HR and Δ[HHb] reached a plateau during the 3MST, with no significant differences observed between the first and second trials (p > 0.05), as did [La]. These results indicated that the 3MST is a valid and reliable tool for estimating CF in squat exercise and may be used to identify anchor intensity before prescribing a resistance training program.