Relationship Between Erector Spinae Isometric Endurance and Oxygenation Status in Healthy and Low-Back Pain Subjects

Abstract

0252 Isometric endurance of the low back muscles may be limited by oxygen availability. As well, reduced oxygen supply has been implicated in the incidence of low-back pain (LBP). Near Infrared Spectroscopy (NIRS) is a sensitive technique for differentiating the oxygenation status of the erector spinae (ES) between healthy and LBP subjects during isometric contractions (Miyake et al., 2003). PURPOSE: To: (1) compare the muscle oxygenation (Mox), blood volume (Mbv) and half recovery time (1/2 Rec) responses of the right and left ES to isometric contractions in healthy and LBP subjects using NIRS, and (2) determine the relationships between isometric endurance time and selected NIRS variables. METHODS: Thirty healthy and 30 non-spcific LBP subjects (age and gender matched) consented to the following protocol: two mins rest in the prone position, followed by the Biering-Sorensen test procedure to determine maximal isometric endurance time, followed by four mins of recovery. NIRS data were collected bilaterally at the 3rd lumbar vertebrae using a dual wave instrument. The difference in rd tissue absrobency between the 850 nm and 760 nm signals was used as an index of Mox, while the sum signal was used as an index of Mbv. The minimum, maximum, delta (minimum − resting), range (maximum − minimum) and 1/2 Rec for Mox and Mbv were calculated from on-line NIRS recordings averaged over 5 sec intervals. RESULTS: During the test, Mbv immediately increased for ∼30–60-sec, followed by a plateau and a striking decline towards baseline at test termination. In contrast, Mox demonstrated a systematic decrease with a levelling off towards the termination of the test. During recovery, the Mox and Mbv trends reversed rapidly during the first minute, followed by a leveling off during the latter stages. Two-way ANCOVA using skinfold thickness at the NIRS measurement site as the covariate indicated no significant interaction (P>.05), implying a similar trend in these variables on both sides in the two groups. Delta Mbv (an index of change in blood volume) was significantly higher (P<.05) in the healthy subjects and their 1/2 Rec for Mox was significantly faster (P<.05) when compared to the LBP subjects. No consistent correlations (P>.05) were observed between endurance time and any of the NIRS variables in either group. CONCLUSIONS: (1) the slower 1/2 Rec of the ES in LBP subjects could be due to their reduced oxidative capacity, and (2) factors other than regional changes in Mbv and Mox are associated with isometric back muscle endurance in healthy and LBP subjects. Support: Alberta Workers' Compensation Board