Can a fatigue test of the isolated lumbar extensor muscles of untrained young men predict strength progression in a resistance exercise program?

Aim. The aim of this exploratory study was to investigate the predictive value of a fatigue test of the lumbar extensor muscles for training progression in a group of 28 healthy but predominantly sedentary male students, in an 8-week resistance exercise program.Methods. A three-phased fatigue test of the lumbar extensor muscles was designed, consisting of two consecutive measurements of full-range isometric back strength on a lumbar measurement device, separated by a dynamic back extension set to volitional fatigue. Differences between the strength values of the 1(st) and 3(rd) step is thought to reflect individual back muscle fatigue characteristics. The training program was primarily aimed at improving lumbar extensor endurance, by using a relative high number of repetition and low training loads. Linear regression analysis was used to evaluate the relationship between lumbar strength progression and several fatigue test parameters.Results. The main fatigue indicator in our regression models (isometric strength decline between 1(st) and 3(rd) step) did not show predictive value in lumbar strength progression in training and testing, respectively. On the other hand, the work capacity that subjects delivered in the dynamic set (2(nd) step) had some predictive value.Conclusions. Based on the results, isometric strength decline measurement has no additional value to a standardized set of repetitions until failure in predicting future training performance. In practice, this means that a lower back training machine could be used at baseline to assist in tailoring individual lumbar training regimes, without the additional use of an isometric-strength testing module.