TRUNK EXTENSOR AND FLEXOR STRENGTH MEASURED BY THE CYBEX-6000 DYNAMOMETER - ASSESSMENT OF SHORT-TERM AND LONG-TERM REPRODUCIBILITY OF SEVERAL STRENGTH VARIABLES

Study Design. Isokinetic trunk extensor and flexor strength (peak torq ue, total work, power, acceleration time, and torque acceleration ener gy) at 30 degrees/sec, 120 degrees/ sec, and 180 degrees/sec and isome tric extensor and flexor peak torque were measured in 24 healthy women . Measurements were performed in three separate sessions at the same t ime of day and by the same experienced examiner. The number of days be tween Session 1 and Session 2 and between Session 1 and Session 3 rang ed from 1 to 7 (median, 2 days) and from 23 to 48 (median, 32 days), r espectively. The test results were not revealed before all sessions we re completed. Objectives. To determine the intrasession, shortterm, an d long-term reproducibility of several trunk strength variables measur ed by the Cybex 6000 isokinetic dynamometer (Lumex, Inc., Ronkonkoma, NY). Summary of Background Data, Only few and insufficient data regard ing the reproducibility of trunk strength measurements exist. Previous studies have focused on coefficients of correlation to express reprod ucibility, Correlations, however, are misleading and inappropriate for this purpose. The critical difference is the difference between two r esults that would be statistically significant when applied to a refer ence group in steady state. The critical difference in percentage is c alculated as 2.77 x coefficient of variation (%). Methods. Isokinetic dynamometry (Cybex 6000). Reproducibility was expressed as pooled coef ficients of variation, individual coefficients of variation, and criti cal differences. Results. Substantial between-subject variation of coe fficients of variation was found for all strength variables; for examp le, the 80% central range for individual coefficients of variation for long-term reproducibility of extensor strength measurements at 30 deg rees/sec ranged from 2.5% to 19.5%. Critical differences calculated us ing the pooled variances for long-term reproducibility were higher tha n 20% for all measures, mounting to 80% for acceleration time. Conclus ions. Strength testing is of limited value in the individual subject b ecause of considerable day-today variability. This finding has importa nt clinical implications.