Intra-abdominal pressure increases during exhausting back extension in humans

Area of Science:

• Biomechanics
• Human Physiology
• Exercise Science

Background:

• Understanding the physiological responses to sustained spinal loading is crucial for preventing low back pain.
• Trunk muscle activation patterns and intra-abdominal pressure (IAP) changes during fatiguing tasks are not fully elucidated.

Purpose of the Study:

• To investigate the effects of maintained spinal load on intra-abdominal pressure (IAP), low back kinematics, and trunk muscle activity in humans.
• To examine trunk muscle fatigue and compensatory activation strategies during prolonged, fatiguing low back exercises.

Main Methods:

• Nine healthy subjects underwent two endurance tests: an upright-test and an incline-test (45 degrees inclination).
• Surface electromyography (EMG) recorded activity from erector spinae, iliocostalis lumborum, rectus abdominus, and oblique muscles.
• Intra-abdominal pressure (IAP) and rate of perceived exertion were continuously measured during the tests.

Main Results:

• No significant difference in endurance time was observed between the upright and incline tests.
• EMG amplitude increased significantly over time for most abdominal muscles, indicating increased activity.
• A decrease in median frequency for the erector spinae muscle suggested fatigue, with no corresponding increase in EMG amplitude, implying reduced force output.

Conclusions:

• Trunk extension exercises leading to low back muscle fatigue stimulate increased activity in abdominal muscles.
• Sustained spinal load results in a significant increase in intra-abdominal pressure (IAP) as a compensatory mechanism.
• Individual responses in IAP increase varied, but the pattern of increased IAP with fatigue was consistent across subjects.