Impact of caffeine intake on squat performance and biomechanics: A randomized crossover trial

Abstract Study aim To analyze the effect of 6 mg/kg of caffeine (CAFF) on performance and technique. Material and methods In a randomized, crossover, double-blind study, 14 trained naïve-low consumers of CAFF executed 6 back squats, both unfatigued and fatigued, in a control, a placebo (PLA), and a CAFF session at the same setting, with a 7-day wash-out. Computer-generated random numbers allocated participants to intervention sequences. The primary outcomes were performance and biomechanical parameters. Results The analyses considered the seven participants randomized per sequence. Hip flexion at the bottom position in PLA ( d = 0.72), and its eccentric ( d = 0.94–1.32) and concentric ( d = 0.68–1.01) range of motion (ROM) in PLA and CAFF, increased, while fatigue augmented it at the final position ( d = 0.47), and decreased its eccentric ( d = 0.60) and concentric ( d = 0.84) ROM. Fatigue decreased knee flexion at the bottom position ( d = 0.21) and concentric ROM ( d = 0.94) but augmented it at the final position ( d = 0.53), and PLA increased its eccentric ROM ( d = 0.79). CAFF and PLA reduced ankle dorsiflexion at the bottom ( d = 0.85–0.89) and final ( d = 0.78–0.86) positions. PLA worsened concentric time ( d = 1.07), peak vertical force (PVF) ( d = 0.74), and rate of force development (RFD) ( d = 0.88). Fatigue reduced eccentric ( d = 0.57) and concentric ( d = 0.70) PVF, concentric RFD ( d = 0.47), and mean propulsive bar velocity ( d = 0.66). Most of CAFF common side effects were reported. Conclusion CAFF was not ergogenic for squats, while PLA hindered performance. CAFF, PLA, and fatigue modified the squat technique, potentially affecting its benefits. This trial was supported by “AGAUR-FI ajuts Joan Oró” and prospectively registered on ClinicalTrials.gov (NCT06039358).