Comparative analysis of a bench press using strength methods with and without intra-repetition variable resistance

Background: In line with the recommendations for sustainable development, SDG 3 highlights the importance of working on health and well-being. In this respect, strength training has proven to be highly effective. Improved physical performance in most sports is associated with increased maximum dynamic strength. The existing literature on strength training methods is extensive, varied and has a certain tradition in the scientific field. Therefore, the regulation and optimal treatment of the load/stimulus with which one works in the development of strength is a key point. The analysis and study of the variability in loads or training stimuli is essential since it is modified according to the objective of the training and adapted to the circumstances. The aim of this study was to compare the differences measured in average and maximum strength, rate of force development (RFD) and the perception of effort (RPE) between two training methods (constant resistance (CR) vs. intra-repetition variable resistance (IRVR) in a bench press. Methods: Due to the methodological difficulties involved in generating an IRVR, fifteen men executed different percentages of one maximum repetition (40%, 60%, 80% and 100%) with CR and IRVR. The percentage to graduate the selected load was 20% of variable resistance. An intra-subject design was used to compare the acute differences between intra-repetition variable resistance and constant resistance. Results: The results showed significant differences in IRVR for maximum force at 1RM (p = 0.001). A significant decrease in RPE with IRVR was documented for all percentages evaluated (p = 0.011). Less accumulated load during execution with IRVR in the first phases of the range of motion (ROM), provides a greater acceleration of the external load, consequently, in the last phase of the concentric extension a faster speed is produced compared to the traditional method with CR (p = 0.036). Conclusion: IRVR method requires a lower load accumulated in the first phase of the ROM allows more acceleration of the external load and therefore overcome the sticking point with a higher velocity. The constant adaptations in the pattern of strength production during the ROM cause the muscles to stay closer to their best "length-tension" ratio in the concentric phase; therefore, they can generate higher levels of strength. In addition, the results obtained show that the IRVR method requires less perceived effort. For all these reasons, it should be considered an effective method for developing maximum dynamic force, mainly for sub-maximum and maximum loads.