PARASPINAL PRECONTRACTION DOES NOT ENHANCE ISOKINETIC TRUNK EXTENSIONPERFORMANCE

Study Design. This study investigated the influence of isometric contr action of the trunk extensor muscles, immediately preceding maximum ef fort isokinetic trunk extension (precontraction), on isokinetic perfor mance variables and activation levels of the paraspinal muscles. Objec tives. To determine whether agonist precontraction significantly impro ved the concentric and eccentric isokinetic trunk extension contractio n. Summary of Background Data. Agonist precontraction has been reporte d to enhance agonist neural drive and force output of the knee and ank le joints. Methods. Subjects performed concentric and eccentric isokin etic trunk extension at 60, 90, and 120 deg/sec, each of which were pr eceded by isometric trunk extension precontraction force equal to 0%, 25%, and 50% body weight. Results. Concentric and eccentric contractio ns showed general, but no statistically significant performance enhanc ement with paraspinal precontraction. Eccentric contractions tended to improve to a greater extent than concentric contractions. Conclusions . It is possible that the addition of agonist precontraction increased the complexity of the trunk extension task, thus requiring a learning period, as is the case with most novel motor skills. There may be mea ningful rehabilitation-related implications of the qualitative tendenc ies observed in the data that merit further consideration.