PARASPINAL PRECONTRACTION DOES NOT ENHANCE ISOKINETIC TRUNK EXTENSION PERFORMANCE

Study Design. This study investigated the influence of isometric contraction of the trunk extensor muscles, immediately preceding maximum effort isokinetic trunk extension (precontraction), on isokinetic performance variables and activation levels of the paraspinal muscles. Objectives. To determine whether agonist precontraction significantly improved the concentric and eccentric isokinetic trunk extension contraction. Summary of Background Data. Agonist precontraction has been reported to enhance agonist neural drive and force output of the knee and ankle joints. Methods. Subjects performed concentric and eccentric isokinetic trunk extension at 60, 90, and 120 deg/sec, each of which were preceded by isometric trunk extension precontraction force equal to 0%, 25%, and 50% body weight. Results. Concentric and eccentric contractions showed general, but no statistically significant performance enhancement 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 meaningful rehabilitation-related implications of the qualitative tendencies observed in the data that merit further consideration.