Undesirable effects of the eccentric isokinetic contractions
Prof Jean-Louis CROISIERa, Dr Jean-François KAUXa, Prof Jean-Michel CRIELAARDa, Prof Bénédicte FORTHOMMEa
a Département des Sciences de la Motricité - Université de Liège
Introduction: Even though sub-maximal eccentric exercises do not entail specific risks, the eccentric contractions at maximal intensity could increase the risk of injury in comparison with the other contraction modes. Based on the length-tension relationship, the maximal eccentric contraction allows to develop the highest torque (for instance on the isokinetic dynamometer), particularly in the elongated position of the muscle groups. Therefore, the injury risk is increased for the muscle, tendon and joint structures. In spite of specific safety mechanics inherent to the isokinetic tool, the risk of injury must be taken into consideration by the clinician.
Methods: A quadriceps injury was reported in a professional soccer player subjected to eccentric testing of this muscle group at the occasion of a possible transfer. Do we consider such a testing as relevant?
Results: After surgical repair of the ACL, we refer to the possible risk for the graft in the case of maximal eccentric contraction of the quadriceps. Complaints frequently reported during eccentric contractions of the shoulder rotators are sometimes incompatible with testing, because of safety and measurement validity. Such an eccentric testing should concern mainly specialized healthy athletes involved in overhead gestures.
The isokinetic dynamometer is also used for eccentric training and not only for testing. Strengthening in eccentric allows frequently improving very efficiently the maximal performance for this contraction mode, yet the improvement extent for the other modes remains controversial. On the other hand, intense and unusual eccentric exercises are known to induce Delayed Onset Muscle Soreness (DOMS).
Discussion and conclusion: Although functional consequences of DOMS are transitory, they could disturb the rehabilitation and/or training process. Clinician and trainers must be aware of this side effect in order to amend their eccentric strengthening interventions.
Keywords : Isokinetics, eccentric, risk, testing, rehabilitation