Use of the iso-inertial force mass relationship in the prediction of dynamic human performance.

The purpose of this investigation was to develop a new test of muscle function, termed the iso-inertial force-mass relationship, and to determine its relationship to dynamic physical performance in comparison to an isometric test. A group of 13 trained subjects performed an isometric, and a series of iso-inertial maximal upper body tests, in a bench press movement at loads of 30%, 60%, 100% (concentric) and 100%, 130% and 150% (eccentric) of maximum. Vertical forces exerted throughout the movement were recorded by a force plate. In addition, the subjects performed the following three performance tests: a maximal bench press, a seated shotput, and two drop bench-press throws from a height of 0.25 m, with loads of 10 kg and 30% of maximum. Correlation analysis demonstrated that in each instance the iso-inertial force mass tests were the best predictors of performance (r = 0.78-0.88) with both contraction type and mass specific effects apparent. Maximal isometric force and rate of force development were significantly related to some performance variables (r = 0.22-0.78). However, for all the performance movements assessed, the iso-inertial test modality recorded the highest relationship to performance. The difference in the relationship between performance and iso-inertial and isometric test modalities was particularly evident in the light load dynamic performance of the seated shotput (r = 0.86 vs r = 0.38, respectively). These results are explained in part by the neural and mechanical differences between iso-inertial and isometric muscle actions and their respective specificity to dynamic physical performance.