| Context. People with a history of low back pain (HxLBP) have a delayed activation of the transverse abdominus (TrA) muscle during hip flexion tasks. Proper activation timing of the TrA stabilizes the lumbar segments in the neutral zone and can compress the sacroiliac joints prior to initiation of the movement. Fatigue of the lumbar paraspinal musculature or manipulation of the sacroiliac joints can influence the motoneuron pool excitability of the quadriceps musculature at the spinal and supraspinal levels, but a training program to improve the activation timing of the local stabilizing muscles around the lumbar spine has never investigated quadriceps motoneuron pool excitability. Objective. To compare the Hmax:M max ratio of the vastus medialis oblique (VMO) on the stance leg during a single limb hip flexion task using subjects with a HxLBP before and after an abdominal muscle training or control intervention. Design. 2x3 factorial with repeated measures randomized controlled trial. Participants with a HxLBP were assigned to one of two treatments: abdominal training [AB] or control [CON] and Hmax:Mmax measurements were taken before training (PRE), after one session (PST1), and after two weeks (PST2wk). Setting. Data were collected in a sports medicine research facility or an athletic training clinic. Patients or other participants. 30 subjects with a significant history of low back pain (HxLBP). Intervention(s). All subjects had PRE Hmax:M max recorded from their stance leg during a hip flexion task. Subjects assigned to the AB group were treated for approximately 25-30 minutes in methods commonly used clinically to teach people to activate their deep abdominal muscles; the CON subjects were asked to sit for approximately 25 minutes. PST1 Hmax:Mmax ratio measurements were then taken. Subjects assigned to the treatment group were then treated every other day for two weeks and were given a home program. All participants returned after two weeks to have PST2wk Hmax:Mmax ratios measured. Main outcome measures. Hmax:M max ratios of the VMO in the stance leg. Results. The AB group had mean values of 0.411 (0.207), 0.419 (0.221), and 0.399 (0.149) at times PRE, PST1, and PST2, respectively. These values were compared with CON group values of 0.396 (0.223), 0.378 (0.198), and 0.401 (0.188). We saw no significant group by time interaction (F2,38=0.289, P=0.750, 1-beta=0.093) or main effects for time (F2,38=0.017, P=0.983, 1-beta=0.052) or group (F1,19=0.480, P=0.828, 1-beta=0.055). Conclusion. A two week TrA training program does not significantly affect the motoneuron pool of the VMO at the initiation of a contralateral limb standing straight leg raise.;Keywords. H-reflex, transverse abdominus, abdominal co-contraction, low back pain, vastus medialis, drawing-in maneuver. |
