Divergent muscle functional and architectural responses to two successive high intensity resistance exercise sessions in competitive weightlifters and resistance trained adults

Peak force (PF), contractile rate of force development (RFD) and contractile impulse (CI) are of great importance to competitive weightlifters (WL). These athletes routinely perform successive bouts of high-intensity resistance exercise (HIRE) within the same day (double-day training) with the aim of improving muscular function and weightlifting performance. The purpose of this investigation was to determine and compare the PF, contractile RFD and CI responses to double-day training between WL and resistance trained (RT) adults (n = 16 per group). Furthermore, we sought to establish whether acute changes in muscle function were associated with acute changes in muscle architecture. Isometric front squat PF, contractile RFD, CI and the pennation angle (hp), anatomical and physiological thickness of the m. vastus lateralis (VL) were determined before and after two equivalent HIRE sessions separated by 4-6 h rest. Each session consisted of ten single repetitions of the dynamic barbell front squat interspersed with 2-min rest, using a load equivalent to 90% of the pre-session PF. Weightlifters demonstrated greater PF at all time points when compared to RT adults and exhibited no significant within or between session changes in PF, contractile RFD or CI. Conversely, RT adults demonstrated within- and between-session decreases in PF and between-session increases in contractile RFD and CI. As no correlations were found between the relative within-session changes in muscle function and the concomitant changes in muscle architecture, other factors must contribute to the divergent responses in PF, contractile RFD and CI between WL and RT adults.