Intramuscular hemodynamics in bilateral erector spinae muscles in symmetrical and asymmetrical postures with and without loading

BACKGROUND: Although attention has been paid to the relationship between the changes in blood circulation in erector spinae muscles and back pain, little is known about their hemodynamics in several various comparable postures with and without loading. Studies on hemodynamics of erector spinae muscles using near-infrared spectroscopy have been performed on subjects and patients mainly in forward flexion positions. METHODS: Two near-infrared spectroscopes were used to measure oxygenated hemoglobin, deoxygenated hemoglobin, and total hemoglobin in bilateral erector spinae muscles at L2-3 in subjects in 9 postures, and holding no load, 10 kg or 20 kg in maximum flexed and lateral bending. Those three values in each posture and loading condition were expressed as a percentage of their corresponding values obtained in the standing upright position, and designated and statistically analyzed as %Oxy-Hb, %Deoxy-Hb and %Total-Hb, respectively. FINDINGS: %Total-Hb and %Oxy-Hb in maximum flexion were the most decreased. In maximum lateral bending, %Oxy-Hb only in the contralateral erector spinae muscles was decreased. When the load was 20 kg, the decreases in %Oxy-Hb were the largest in maximum flexion and lateral bendings. INTERPRETATION: Using two near-infrared spectroscopes allowed us to measure simultaneously the hemodynamics of bilateral muscles. They demonstrated different responses in each side. Asymmetrical posture and loading were accompanied by asymmetrical changes of the bilateral erector spinae muscles. Stretched muscle had less blood volume and oxygenation, both of which decreased with increasing load. These results showed that these postures and conditions might lead to fatigue of the ES muscles.