Muscle Thickness, Echo-Intensity, Peak Force, Time Under Tension, Total Load Lifted, and Perception of Effort...

The primary purpose of this study was to evaluate acute dose response of different intensities with total volume equalized during the abdominal crunch exercise on muscle thickness, echo-intensity, peak force, time under tension, total load lifted, and perception of effort in recreationally-trained participants. Fifteen resistance-trained participants (23 ± 3 years) performed the abdominal crunch exercise in one of two different resistance training (RT) protocols in a randomized order: RT_4×10RM (4 sets of 10RM / 1-min rest) or RT_1×40RM (1 set of 40RM). Muscle thickness (MT), echo-intensity (EI), peak force (PF), time under tension (TUT), total load lifted (TLL), and session rating of perceived exertion (sRPE) were measured pre-test and post-test (0-min and 15-min). Two-way repeated-measures ANOVAs (2 × 3) were used to test differences between RT protocols (RT_4×10RM and RT_1×40RM) and time (pre-test, post-0, and post-15) for MT, EI, and PF. Paired t-test was used to compare RT protocols for sRPE, TLL, and TUT. For MT, there were significant differences for RT_4×10RM between pre-x post-0 (p = 0.011), pre-x post-15 (p < 0.001), and post-0 × post-15 (p = 0.02); and for RT_1×40RM between pre-x post-0 (p < 0.001) and pre-x post-15 (p = 0.003). For EI, there was a significant difference for RT_4×10RM between pre-x post-0 (p = 0.002). For sRPE, there was no significant difference between RT protocols. For TLL and TUT, there were significant differences between RT protocols (p < 0.05). In conclusion, both RT protocols (RT_4×10RM and RT_1×40RM) induced similar increases in MT but not for EI. TLL and TUT were higher for RT_4×10RM. PF and sRPE were similar between RT protocols.