Isometric strength and dynamic back extensor endurance are unrelated in children ages 6-10 years: a pilot study.

Abstract

This study assessed the correlation between back extensor isometric force and dynamic endurance in 69 children 6-10 years of age. Subjects were positioned prone with legs and hips supported and restrained on two folded 6-in. mats. 42 subjects (20 girls; 22 boys) performed three 5-sec. isometric back extension efforts against a calibrated dynamometer and peak force values were averaged. An additional 27 subjects (9 girls; 18 boys) also performed a dynamic (0 degrees --> 45 degrees flexion-->0 degrees) back extension test at a frequency of 20 per minute, and the number of repetitions was recorded. Both tests were repeated at a 1-wk. interval. Pearson correlations for the endurance, the isometric force test, and test-retest, and between the functional concentric endurance vs isometric force were .55, .79 (both p<.01), and .03, respectively. These tests have moderate to high reliability but they examine different aspects of back muscle fitness. They should not be used interchangeably to assess back extensor muscle fitness. Further investigation must determine whether different dynamic test frequencies and mat heights yield different results.