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Intrasubject controls with randomized intervention order.To quantify the immediate change in posteroanterior (PA) spinal stiffness produced by different combinations of trunk muscle contraction.The abdominal hollow and the abdominal brace are 2 different combinations of trunk muscle contractions that are commonly prescribed to increase spinal stability. Unfortunately, the immediate effect of these different contractions on spinal stiffness (one indicator of spinal stability) has not yet been quantified directly.Twenty-eight asymptomatic subjects were taught abdominal hollow and brace contractions then performed them in a randomized order framed by periods of rest. Surface electromyography and B-mode ultrasound confirmed that all contractions were performed appropriately. During each test condition (hollow, brace, and rest), a noninvasive indentation technique was used to quantify PA spinal stiffness. A repeated measures analysis of variance was used to assess the significance of changes in the PA spinal stiffness between test conditions.Both the abdominal hollow and abdominal brace contractions increased PA spinal stiffness significantly when compared with the rest condition (P < 0.001). When the abdominal hollow and brace contractions were compared with each other, the abdominal brace contraction produced significantly greater PA spinal stiffness (P < 0.05).In asymptomatic subjects, the abdominal brace contraction provided an immediate PA stiffening effect that was significantly greater in magnitude when compared with conditions of rest and abdominal hollowing. These findings may allow clinicians to better match commonly prescribed contraction-based interventions with specific patient needs. Future work is required to assess the long-term effect of repeated abdominal brace and hollow contractions on PA spinal stiffness and low back pain.