Thirty-six 45-55-year-old men with healthy low backs were studied with respect to body composition, isokinetic and isometric trunk strength, trunk muscle endurance, and cross-sectional area and radiological density of mm erector spinae. Results were compared to those of men in the same age group with intermittent low back pain (LBP) (n = 91) and with chronic LBP (n = 21). The back healthy group was significantly stronger and had longer trunk muscle endurance times than men with chronic LBP. Men with intermittent LBP had strength and endurance values in between the back healthy and chronic groups. There were no significant differences between any of the groups with respect to body composition and cross-sectional area of mm erector spinae. Radiological density for mm erector spinae was significantly decreased in the chronic LBP group compared to the back healthy and intermittent LBP groups. The deconditioning syndrome and its relationship to intermittent and chronic LBP is discussed.