Protecting the back from injury is a major focus of the Physical Therapists (PT). In this study PTs from Canada take data from five abdominal and two back extensor muscles. The measurements are recorded during a core strengthening exercise.
The "core" abdominal and back muscles are thought to hold the spine in a neutral position. A strong core may protect the spine during repetitive activities. Eighteen healthy adults (men and women) with no back problems were included in this study.
Electrical activity of the seven muscles was recorded during a core training exercise. The exercise had five total levels. Each level was harder to do than the last level. The researchers thought there would be different amounts of muscle activity based on the demands of the exercise levels.
Instead what they found was that the abdominal muscles stayed the same until the highest level. This suggests the load on the muscles was low until the last exercise. Level five had the highest muscle activity for all the abdominal muscles. At level five the load on the abdominal muscles increases. This occurs as they help counteract rotation of the pelvis and extension of the low back.
Results from the back muscles showed each muscle was active at different times. None of the muscles used more than 40 percent of their maximum capacity. There wasn't the expected increase in activity as the exercise got harder.
Results show how each muscle has a different job to do with each exercise. From this study it looks like core-training exercises don't increase muscle strength. The authors think that with increased repetitions, the exercises may improve muscle endurance.
Krista L. Clarke Davidson, MSc, and Cheryl L. Hubley-Kozey, PhD. Trunk Muscle Responses to Demands of an Exercise Progression to Improve Dynamic Spinal Stability. In Archives of Physical Medicine and Rehabilitation. February 2005. Vol. 86. No. 2. Pp. 216-223.