Effects of Intensity and Fatigue on the Kinetics and Kinematics of the Barbell Squat, Bench Press, and Deadlift in Experienced Lifters: A Systematic Review.

Background: Powerlifting is a competitive strength sport focused on achieving the highest possible single-repetition load in three barbell lifts: the back squat, bench press, and deadlift, each testing maximal force output under standardized conditions. Increases in training intensity and the accumulation of fatigue can lead to measurable alterations in kinetic and kinematic variables, with potential implications for both performance and injury risk. Although trained lifters typically exhibit more stable movement patterns than novices, the biomechanical responses to intensity and fatigue remain complex and variable. This systematic review aimed to identify consistent, observable changes in kinetic and kinematic variables in experienced lifters during the back squat, bench press, and deadlift under conditions of increasing intensity and fatigue.

Methods: A keyword search was performed on MEDLINE Complete, SPORTDiscus, and CINAHL Plus up to June 2024. Studies that examined the effects of load and fatigue on the kinetics and kinematics of the back squat, bench press, and deadlift in experienced lifters were included. The quality of studies was rated according to the Quality Assessment of Observational Cohort and Cross-sectional Studies scale. Results were summarized in tables and with a narrative synthesis.

Results: Twenty-two studies, with a total of 293 participants, met the inclusion criteria. Increased intensity was consistently associated with decreases in mean and peak barbell velocity and power, increased force production, longer concentric durations, and greater joint variability, especially in the acceleration and sticking regions. Fatigue led to similar reductions in velocity and power, although findings on force production were inconsistent across studies. Only two studies examined the deadlift, and reporting practices varied between studies.

Conclusion: Increased intensity and fatigue produce predictable kinetic and kinematic changes in the back squat, bench press, and deadlift, particularly during the acceleration and sticking phases. Velocity consistently decreased with intensity and fatigue, while power and joint mechanics showed greater variability across individuals and studies. Coaches and clinicians should monitor these changes to inform programming and technical interventions. However, different lifters may adopt distinct mechanical strategies as intensity increases, especially near the sticking point. Future research should distinguish between- and within-individual variability in kinetic and kinematic expression and address underrepresented movements, particularly the deadlift.

Registration: This systematic review was registered with PROSPERO (CRD42024550339).