To determine whether erector spinae muscle oxygenation (OXY) and blood volume during a progressive isoinertial lifting evaluation (PILE) are modified by an exercise therapy program. Pre- (t1) and post- (t2) exercise therapy experimental design. Hospital. Subjects with chronic low back pain (LBP group) (n=24) and healthy subjects (control group) (n=24) were evaluated. Exercise program. The control group was evaluated once, and the LBP group was evaluated before (t1) the exercise therapy program and 28 days thereafter (t2). The maximal load lifted, total work, and total power were determined using the PILE test. Continuous-wave near-infrared spectroscopy was used to measure OXY and blood volume during the PILE test. The maximal load lifted, total power, and total work were significantly lower in the LBP group (-42%±5%, -46%±6%, and -67%±6% at t1, respectively; P<.05) than the control group. In the LBP subjects, these parameters improved significantly after the exercise therapy program (+20%±3%, +56%±4%, and +61%±5%; P<.05). At each submaximal power (ie, 25, 50, 75, and 100% of maximal load lifted at t1), OXY and blood volume were significantly higher at t2 than t1. One-half recovery time for OXY was significantly higher in the LBP group (at t1 and t2) than in control subjects. The findings in this study suggest that LBP subjects present an impairment in their capacity to deliver oxygen at the level of the erector spinae muscle, which can be partly restored by an exercise therapy program.