Supramaximal Isometric Holds Enhance Squat Performance: An Integrated Analysis of Barbell Kinematics, Force Production, and Postural Stability

Optimizing acute performance during strength training and competition has become an important objective for coaches and athletes. This study aimed to analyze the acute effect of supramaximal isometric holds (SMHs) on squat performance integrating barbell kinematics, force production, and postural stability. Fourteen resistance-trained subjects completed six experimental sessions encompassing squats at 60% and 80% of one-repetition maximum (1RM) following a 10 s SMH at 110% of 1RM with either 1 min or 5 min recovery, or in a control condition (CON) with no SMH. Barbell kinematics were assessed using a linear position transducer, as were vertical ground reaction force, inter-limb asymmetries, and center-of-pressure metrics via dual-force platforms. An SMH with 1 min recovery produced significant increases in mean propulsive velocity at both intensities compared to CON (+0.05 m·s−1; d ≥ 0.94), a higher rate of force development at 80% of 1RM (p < 0.01), and non-significantly increased peak concentric force at 80% of 1RM (p = 0.056). An SMH with 5 min recovery had little to no effect. No significant differences were found in inter-limb force asymmetries or center-of-pressure metrics. A 10 s SMH coupled with a 1 min recovery period is a practical and costless strategy to enhance squat performance in strength-trained individuals through increased barbell velocity, force production, and unchanged postural stability.