The influence of isoinertial-pneumatic ratio on force-velocity-power relationships

Introduction:
Isoinertial contractions are effective to generate maximal force during the initiation of the movement whereas they do not provide an appropriate training stimulus to generate force once accelerative phase has been developed (1). Pneumatic resistance is one alternative that has been developed to overcome the aforementioned limitations associated with isoinertial contractions. This technique allow higher initial velocity and reduce the decrease of force towards the end of the concentric phase (1). There is some training interest by combining isoinertial and pneumatic loading. The aim of this study was to determine how different isoinertial-pneumatic ratio influence the force-velocity-power relationships during bench-press.
Methods: Fifteen participants performed bench press at 30%, 45%, 60%, 75%, and 90% of their 1RM, with five isoinertial(I)-pneumatic(P) resistance ratio : 100%I/0%P, 75%I/25%P, 50%I/50%P, 25%I/75%P, and 0%I/100%P. Velocity, force and power were assessed using a linear transducer and mechanical parameters measured by the pneumatic ergometer. Force-, velocity- and power-time patterns were averaged over the push-off phase to build the corresponding force-velocity and power-velocity relationships for each resistance ratio.
Results: The increase in pneumatic part in resistance ratio elicited higher movement velocity and lower force level from 0% to 80% of the concentric phase. The increase in isoinertial part in resistance balance resulted in higher velocity towards the end of the movement. As a consequence, the use of isoinertial resistance oriented the force-velocity relationship towards force, whereas pneumatic resistance elicited a more velocity-oriented profile.
Conclusion: Pneumatic-oriented resistance could be used to develop initial velocity and force towards the end of the push-off. Isoinertial-oriented resistance should be used to develop maximal force and maximal power. Resistance modality could be modulated according to training objectives.
Références : 1. Frost et al. A comparison of the kinematics, kinetics and muscle activity between pneumatic and free weight resistance. Eur J Appl Physiol. 2008;104:937-56.