Quadriceps inhibition after repetitive lumbar extension exercise in persons with a history of low back pain

Abstract

Context: A neuromuscular relationship exists between the lumbar extensor and quadriceps muscles during fatiguing exercise. However, this relationship may be different for persons with low back pain (LBP).

Objective: To compare quadriceps inhibition after isometric, fatiguing lumbar extension exercise between persons with a history of LBP and control subjects.

Design: A 2 x 3 factorial, repeated-measures, time-series design with independent variables of group (persons with a history of LBP, controls) and time (baseline, postexercise set 1, postexercise set 2).

Setting: University research laboratory.

Patients or other participants: Twenty-five subjects with a history of LBP were matched by sex, height, and mass to 25 healthy control subjects.

Intervention(s): Electromyography median frequency indexed lumbar paraspinal muscular fatigue while subjects performed 2 sets of isometric lumbar extension exercise. Subjects exercised until a 15% downward shift in median frequency for the first set and a 25% shift for the second set were demonstrated.

Main outcome measure(s): Knee extension force was measured while subjects performed an isometric maximal quadriceps contraction. During this maximal effort, a percutaneous electric stimulus was applied to the quadriceps, causing a transient, supramaximal increase in force output. We used the ratio between the 2 forces to estimate quadriceps inhibition. Quadriceps electromyographic activity was recorded during the maximal contractions to compare median frequencies over time.

Results: Both groups exhibited significantly increased quadriceps inhibition after the first (12.6% +/- 10.0%, P < .001) and second (15.2% +/- 9.7%, P < .001) exercise sets compared with baseline (9.6% +/- 9.3%). However, quadriceps inhibition was not different between groups.

Conclusions: Persons with a history of LBP do not appear to be any more or less vulnerable to quadriceps inhibition after fatiguing lumbar extension exercise.

Figures

Figure 1. Subject setup for measuring knee extension force. (Reprinted with permission from Hart JM, Kerrigan DC, Fritz JM, Saliba EN, Gansneder BM, Ingersoll CD. Contribution of hamstring fatigue to quadriceps inhibition following lumbar extension exercise. J Sport Sci Med. 2006;5:70–79)

Figure 2. Sample tracing of force and electromyographic activity measured during the superimposed burst (SB) technique, with labels showing maximal voluntary isometric contraction (MVIC) and SB force components of the curve

Figure 3. A subject performing fatiguing lumbar extension exercise