Abstract
The purpose of the study was to investigate the effect of seven weeks inter-repetition rest vs. traditional strength training on lower body strength, rate of force development (RFD), and vastus lateralis (VL) muscle architecture. Sixteen male participants were assigned into two groups: the inter-repetition rest (IRRG) and the traditional (TG) group. Both groups performed the leg press exercise with four sets of six maximum repetitions (RM) for two training sessions per week. IRRG added a 20 s inter-repetition rest period between single repetitions. Before and after the training period, 1-RM in leg press, isometric leg press RFD, and peak force (PF), VL muscle architecture, vastus intermedius (VI) thickness, and quadriceps’ cross sectional area (CSA) with ultrasonography, were measured. Two way ANOVA for repeated measures was used for statistics. One-RM strength increased similarly for both groups (p < 0.05), while percentage increases in RFD were greater for IRRG compared to TG (p < 0.05). Isometric PF was increased similarly for both groups (p < 0.05). VL and VI thickness as well as CSA of the quadriceps increased similarly in both groups, while VL fascicle length increased more following IRRG compared to TG (IRRG: 4.8 ± 6.1% vs. TG: −3.9 ± 5.4%, p = 0.001). These results suggest that 20 s inter-repetition rest during strength training may effectively increase lower body explosive strength and muscle fascicle length without compromising muscle hypertrophy.
Highlights
Traditional resistance training is the most effective stimulus for increasing muscle mass and strength in individuals of all ages and training background [1,2]
Leg press 1 repetition maximum (1-RM) was significantly increased after inter-repetition rest group (IRRG) by 20.4 ± 5.9% (p < 0.001, η2 = 0.814) and after traditional group (TG) by 20.4 ± 10.8 (p < 0.001, η2 = 0.835), while there was no significant difference between groups (p = 0.417, η2 = 0.048)
vastus lateralis (VL) fascicle angle remained unchanged after IRRG (p = 0.983, η2 = 0.000) and TG (p = 0.366, η2 = 0.059); VL fascicle length increased only after IRRG from 8.3 ± 0.9 cm to 8.7 ± 1.1 cm (p = 0.044, η2 = 0.260) and the percentage increase was significant greater compared to TG (IRRG: 4.8 ± 6.1% vs. TG: −3.9 ± 5.4%, p = 0.009, η2 = 0.393)
Summary
Traditional resistance training is the most effective stimulus for increasing muscle mass and strength in individuals of all ages and training background [1,2]. Resistance exercise is performed by lifting an external resistance for a number of repetitions which are completed consecutively, with no rest between each repetition, while a rest period of a few seconds/minutes follows after this set of repetitions This training method results in a temporal decrease in muscle power output and movement velocity mainly due to phosphocreatine (PCr) depletion and lactate accumulation in exercised muscle cells [3,4], while other factors contribute to muscle fatigue, such as high ammonia concentration and reduced neural activation [5,6]. Whether inter-repetition rest training is superior in strength improvements or not to traditional resistance training remains largely unresolved
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