Unstable or Stable?
Unstable or Stable? A summary of the Canadian Society for Exercise Physiology Position stand on instability to train the core
George Cho, MFSc, CEP, EIM-2, ND
The use of stability balls and other devices and exercises to train the core muscles is a popular practice but is this method superior than traditional stable, ground-based exercises fordeveloping the core? Dr David Behm and colleagues wrote a position paper for the Canadian Society for Exercise Physiology (CSEP) addressing this subject. A summary is provided below in question and answer format.
What is defined as the core?
Some of the global axial skeleton stabilizers include: rectus abdominis (what most typical think of as "abs"), external oblique abdominis (the muscles on the side of the "abs"), and erector spinae. But the authors refer to all soft tissues that have a proximal attachment originating on the axial skeleton (heads, ribs, spine) as part of the core. This is regardless of whether the termination point of the soft tissue is on the axial skeleton itself or the arms/legs Thus the core includes more than just the "abs."
What is the most important spinal stabilizer?
It is difficult to pinpoint a single muscle since spinal stability is achieved when passive (ligaments, discs, and articulations), active muscles and neural systems work in concert. It is also task dependent.
How might exercises on an unstable surface be superior?
Resistance training of the core on an unstable surface (eg. stability ball) may increaseactivation of the core muscles greater than the same exercises on a stable surface (eg. the ground). There may be increased limb muscle activation too.
However, studies show that lifts such as squats and deadlifts (stable surface exercises) provide greatercore activation than callisthenic-style exercises performed on unstable surfaces. Also, unstable exercises may decrease the force output, power, velocity and range of motion.
What is recommended for athletes?
If the aim is maximal strength, power, and velocity of movement, then ground-based exercises like squats, deadlifts and olympic lifts should be emphasized over the use of devices like stability balls. However, destabilizing activities are still important, but even then, this can be achieved by both stable ground-based and unstable surface exercises. Athletes can add a destabilizing component to ground-based activities by including a transverse stress or destabilizing torque.
So should athletes never use unstable surfaces?
Resistance training programs should follow the periodization principle (periods where loads and volumes increase and decrease). So, during low load phases, it is reasonable to incorporate unstable surface core exercises.
What is recommended for the general population?
Similar to athletic populations, it is recommended that ground-based free weight lifts like back squats, deadlifts, olympic lifts and other lifts involving trunk rotation, should form the foundation of core training. Open chain isolation exercises such as trunk flexion while supported on an unstable surface may be most useful for localized muscular endurance development or for aesthetic goals.
Are unstable surfaces useful for rehabilitation?
The use of unstable surfaces and devices may lower incidence of low back pain and sensory efficiency of soft tissues that stabilize the knee and ankles. Unstable surfaces can be included as part of an overall prehabilitation or rehabilitative exercise program.
Conclusion from the Review paper
"Ground-based free-weight lifts are highly recommended for athletic conditioning of the core musculature because they can provide the moderately unstable environments to augment core and limb muscle activation while still providing maximal or near maximal force and power outputs. However, the concept of periodization illustrates the need to modulate volumes and intensities of training over time; thus, during phases involving lower loads, instability training devices and and exercises can stimulate high muscle activation. Based on the relatively high proportion of type 1 fibers, the core musculature might respond particularly well to multiple sets that involve many repetitions (e.g., <15 per set). However, the characteristics of a given sport may necessitate repetition ranges that emphasize strength and power development (e.g., < 6 per set)." (p. 111).
Devices like stability balls and other unstable surfaces / devices can be a part of a core muscle development program, but having other more stable, ground-based type of exercises such as squats and deadlifts should be the foundation if strength, power and velocity are the main goals.
Behm D et al. Canadian Society for Exercise Physiology Position Stand: The use of instability to train the core in athletic and nonathletic conditioning. Applied Physiology, Nutrition, and Metabolism, 2010, 35(1): 109-112