Intra-abdominal Pressure and Trunk Muscular Activities during Abdominal Bracing and Hollowing.

This study examined the difference in intra-abdominal pressure (IAP) between abdominal bracing and hollowing in relation to trunk muscular activities. IAP with a pressure transducer placed in the rectum and surface electromyograms for rectus abdominis, external oblique, internal oblique, and erector spinae during the 2 tasks were obtained in 7 young adult men. The difference between IAP at rest and its peak value (ΔIAPmax) showed high intra- and inter-day repeatability, and was significantly greater in abdominal bracing (116.4±15.0 mmHg) than in abdominal hollowing (9.9±4.5 mmHg). The trunk muscular activities at ΔIAPmax were significantly higher in abdominal bracing than in abdominal hollowing, and in the internal oblique than in the other 3 muscles. In both abdominal bracing and hollowing, the changes in IAP during the tasks were linearly correlated with those in trunk muscular activities, but the slope of the regression line for the relationship differed between the 2 tasks. The current results indicate that 1) abdominal bracing is an effective maneuver to elevate IAP compared with abdominal hollowing, and 2) in the 2 tasks, the changes in IAP are linked with those in trunk muscular activities, but the association is task-specific.

Low-load Slow Movement Squat Training Increases Muscle Size and Strength but Not Power.

We tested a hypothesis that low-load squat training with slow movement and tonic force generation (LST) would increase muscle size and strength but not necessarily power. Healthy young men were assigned to LST [50% one-repetition maximum (1-RM) load, 3 s for lowering/lifting without pause: n=9] or low-load normal speed (LN: 50% 1-RM load, 1 s for lowering/lifting with 1-s pause; n=7) groups. Both groups underwent an 8-week squat training program (10 repetitions/set, 3 sets/day, and 3 days/week) using the assigned methods. Before and after the intervention, quadriceps femoris muscle thickness, maximal torque during isometric hip extension and knee extension, 1-RM squat, lifting power from squatting position and rate of electromyography rise (RER) in knee extensors during the task, leg extension power and vertical jump height were measured. After the intervention, the LN group showed no changes in all the variables. The LST group significantly (P<0.05) increased muscle thickness (6-10%), isometric hip extension torque (18%) and 1-RM squat (10%), but not isometric knee extension torque, lifting power and RER, leg extension power and vertical jump height. These results suggest that LST can increase muscle size and task-related strength, but has little effect on power production during dynamic explosive movements.