Assessment of abdominal muscle contractility, strength, and fatigue

We evaluated abdominal muscle contractility and fatigue by measuring twitch gastric pressure (Pga,) after percutaneous supramaximal electrical stimulation of the abdominal wall before and after sit-ups to task failure. Mouth pressures during maximal voluntary expulsive rp maneuvers (PEmax) at TLC and FRC with superimposed twitches, and maximum voluntary ventilation (MVV) were also assessed. Mean fresh Pga, was 36.1 +/- 3.0 cm H2O with a coefficient of variation that ranged between 3.0 to 4.8%. Pga(t) decreased by 25% (p < 0.001) and 37% (p < 0.001) at: 1 and 30 min after sit-ups. During maximal voluntary contraction twitch occlusion never occurred. PEmax at TLC and FRC decreased by 15% (p < 0.001) and 11% (p < 0.017) at 1 min, and 8% (p < 0.036) and 9% (p < 0.030) at 30 min after sit-ups, respectively. Despite the abdominal muscle fatigue, MVV values at 1 and 30 min after situps were not: significantly different: from the value obtained before the sit-ups. We conclude that (1) Pga, is a useful objective indicator of abdominal muscle contractility and fatigue; (2) during maximal voluntary expulsive maneuvers the abdominal muscles are never fully activated; (3) sit-ups lead to substantial law-frequency fatigue but little high-frequency fatigue of the abdominal muscles, which has little effect on maximal breathing capacity.