Trading the floor or a weighted core training machine for a Swiss ball can add the element of balance to your core routine — something missing entirely from traditional crunches and sit-ups.
An August 2012 study in the International Journal of Sports Physical Therapy examined the basic crunch and found that, despite a machine’s supposed advantage of adding load to the exercise, performing crunches on a Swiss ball can “improve joint position, posture, balance, and neural feedback.”
Additionally, the study (“Swiss Ball Abdominal Crunch with Added Elastic Resistance is an Effective Alternative to Training Machines,” Sundstrup, Jakobsen, et al.) showed greater muscle activation in the rectus abdominis on the Swiss ball than on the machine, with lower activation of the hip flexors as well.
According to the authors, reducing hip flexor activation during abdominal training can reduce lower back pain, a benefit which applies regardless of age, gender, or pre-existing levels of pain.
The authors hypothesized that “the unstable surface provided by the ball alters proprioceptive demands, thereby stimulating the core muscles to a greater extent than stable surfaces.”
Furthermore, the authors noted, “As strong abdominal muscles provide support for the lumbar spine during everyday movements, strengthening the abdominal muscles may decrease the occurrence of low back pain.”
The take-home message, then, is two-fold: strengthening the abdominal muscles — although not to the point of creating an imbalance with the muscles of the lower back — can improve spinal stability, reducing the likelihood of lower back pain; doing so on a Swiss ball or other unstable surface can make the training even more effective.