Objective: To determine changes in multifidi muscle endurance and functional status after a 4-week spinal stabilization exercise program for patients presenting with chronic low back dysfunction (LBD).

Design: Short-term longitudinal cohort study.

Setting: A rehabilitation facility.

Participants: Sixteen patients (10 men, 6 women) with chronic LBD.

Interventions: Patients were evaluated pre- and posttreatment for outcomes of functional status and muscle fatigue. Treatment consisted of patients participating in supervised spinal stabilization exercises 3 times a week over a 4-week period. Main outcome measures Oswestry Low Back Pain Disability Questionnaire and muscle fatigue based on electromyographically based median frequency assessed during the first 4 seconds and the last 4 seconds of a modified 1-minute Sorenson test.

Results: Oswestry scores improved significantly from pre- to posttreatment (22.9 vs 18.3, P<.027). A significant treatment by gender interaction (P<.031) indicated significant pre- to posttreatment loss of endurance for men (149.3 vs 143.2, P<.045) and a slight, but not statistically significant increase in endurance for women (110.7 vs. 115.5, P<.20).

Conclusions: A 4-week spinal stabilization exercise program significantly improved functional status in patients presenting with LBD. However, a significant pre- to posttreatment increase in multifidi muscle fatigue for men (P<.045) coupled with a nonsignificant improvement in multifidi muscle endurance for women (P<.20) was unexpected; this may reflect an insufficiency of a 4-week program to effect muscle fatigue or a lack of sensitivity of electromyographically based median frequency as the method for assessing muscle endurance. Additional randomized controlled trials to more fully investigate treatment effects and factors that may mediate these effects are needed.