Objective: To investigate the feasibility of applying isokinetic dynamometry for identifying submaximal grip strength.
Design: Measurement of maximal and feigned concentric and eccentric strength at high and low contraction velocities.
Background: Identification of feigned grip strength is a highly problematic issue which has been challenged using various techniques, invariably related to isometric efforts. This study is based on recent research which has indicated that isokinetic dynamometry was highly efficient in identifying feigned efforts in other major muscle groups.
Methods: Seventeen healthy women aged 20-25 took part in the study. Prior to executing the feigned effort, subjects were told to exert lower than the maximal grip strength in an attempt to obtain financial compensation for a simulated injury to hand musculature which in fact did not result in weakness of grip.
Results: Findings indicated that based on a parameter termed DEC which was defined as the difference between the ratios of the eccentric to concentric strength at the high and low velocities, feigned efforts could very effectively be identified (P<0.0001). Furthermore, a multivariate model enabled this identification to be described in terms of the level of confidence by which a claim concerning weakness of grip may be proclaimed as genuine or insincere.
Conclusions: Though the neuromotor mechanisms responsible for grip strength may differ from those acting with respect to other muscle groups, the inability to adjust the eccentric and concentric force components during submaximal efforts is probably a general feature.
Relevance: Isokinetic dynamometry is a powerful method for quantifying various aspects of muscle performance. However, its application in the medicolegal area of muscle weakness has only recently been explored. Combined with previous research, this study strongly indicates that if certain trauma or pathology-related weakness does not result in variations in the force-velocity characteristics of the affected muscles, than this technique has the potential to validly differentiate between patients who have a genuine reason for compensation and those ('symptom magnifiers') who do not.