Effects of horizontally versus vertically loaded resistance exercises on performance and muscle architecture

Background: The aim of this study was to compare a training program based on horizontally (HT) versus vertically (VT) loaded exercises on performance and muscle architecture of the lower body muscles. Methods: Nineteen resistance trained individuals were randomly assigned to HT (N.=10; age: 25.9±4.2 y; body mass: 72.7±11.4 kg; height: 174.0±6.0 cm) or VT group (N.=9; age: 26.9±4.4 y; body mass: 76.2±10.8 kg; height: 174.2.0±5.8 cm). Both 6-week training programs included 4 training sessions per week and were equated for the total number of repetitions. One repetition maximum (1RM) was assessed for squat and hip thrust, together with vertical and horizontal jumps and sprint. Muscle thickness (MT) and echo intensity (EI) of vastus lateralis, vastus medialis and gluteus were also evaluated pre- and post-training period. Results: A significantly greater increase in 1RM hip thrust was detected in HT (+17.9%; P=0.004) while greater increases in 1RM squat were found in VT (+10.5%; P=0.007). A greater increase (P=0.009) in vastus medialis MT was detected in VT (4.1%) compared to HT (-7.9%). Similar increases in MT of gluteus were registered in both groups (P<0.05). A greater improvement in standing long jump (P=0.004) was detected in HT (+7.6%) compared to VT (+1.6%), while both groups significantly improved vertical jump performance. Combining both groups, strong correlations were detected between gluteus EI and 20-m sprint (r=0.79; P<0.001). Conclusions: Results indicate that HT was more effective than VT for horizontal jumps while both HT and VT were equally effective on vertical jumps. Both HT and VT promoted similar changes in muscle architecture of the gluteus, but not of the vastus medialis.