Optimal spinal strength normalization factors among male railroad workers.

In spite of increasing interest in techniques and devices for quantifying trunk strength and lifting capacity, relatively little research has been done to determine optimal normalizing factors for strength. The isolation of the ideal factors is a critical prerequisite for comparison of patient data to expected physical capacities in the uninjured population. In the present study, 160 incumbent railroad workers from four heavy laboring jobs were tested for isokinetic trunk strength and lumbar/cervical isokinetic lifting capacity as part of a study to establish normative data (Union Pacific RR, Omaha, NE). Three variables relating height and weight were studied to determine optimal normalization: actual body weight (BW), ideal weight (IW) and adjusted weight (AW). "IW" is actually a height/weight variable based on a weight control chart specifying ideal weights for given heights and genders. "AW" represents the lesser of BW or IW. Subjects were tested for isokinetic trunk extension/flexion for lumbar (floor-to-knuckle) and cervical (knuckle-to-shoulder) lifts. Results demonstrated that the isolated trunk strength tests showed the best correlation coefficients with BW for flexion-extension work at 60 and 150 per sec. Moreover, the correlation coefficients between the lumbar isokinetic lifting peak force measures and BW were high (ranging 0.49-0.67, P < 0.001), with much lower correlations for AW or IW. By contrast, cervical correlations between Liftask peak force and the height/weight variables were all lower, and were also better for AW than for BW or IW (ranging 0.37-0.50). It appears that body weight is the best normalizing factor for isokinetic trunk flexor/extensor strength and lumbar (floor-to-knuckle) lifting.(ABSTRACT TRUNCATED AT 250 WORDS)