The influence of velocity overshoot movement artifact on isokinetic knee extension tests

EXERCISE ON AN ISOKINETIC DEVICE INVOLVES THREE DISTINCT MOVEMENT PHASES: acceleration, constant velocity, and deceleration. Inherent in these phases are unique occurrences that may confound test data and, thereby, test interpretation. Standard methods of data reduction like windowing and other techniques consist of removing the acceleration and deceleration phases in order to assure analysis under constant velocity conditions. However, none of these techniques adequately quantify the velocity overshoot (VO) movement artifact which is a result of the devices resistance imposed to the limb. This study tested the influence of VO on isokinetic data interpretation. A computational algorithm was developed to accurately identify each movement phase and to delineate the VO segment. Therefore, the VO was then treated as a fourth and independent phase. A total of sixteen healthy men (26.8 ± 4.7 yrs, 1.76 ± 0.05 m, and 79.2 ± 9.4 kg) performed two sets of ten maximal concentric extension repetitions of their dominant knee (at 60°·s(-1) and 180°·s(-1)), on separate days and in a counterbalanced order, on a Biodex System 3 Pro dynamometer. All the phases of the isokinetic exercise were measured in terms of their biomechanical descriptors and according to the developed algorithm, the windowing method, and a data reduction technique that eliminates the first and last 10° of the total range of motion. Results showed significant differences (p < 0.05) between the constant velocity phases found by each method: the largest segment was obtained with the windowing method; the second one, with the algorithm; and the smallest, with data reduction technique. The point of peak torque was not affected by none of the techniques, but significant differences (p < 0.05) were found between the data including and not including the VO phase, concerning total work, time interval, and average length of load range: VO represents more than 10% of the amount calculated in constant velocity phase. As a consequence, the correct removal of VO was suggested as a required procedure to adequately interpret isokinetic tests. Therefore, the use of the proposed algorithm is advisable in order to perform analysis according to the isokinetic definition. Key pointsIsokinetic test interpretation must be focused on the constant velocity range; traditional analysis usually removes the acceleration and deceleration phases but does not give particular attention to velocity overshoot range.The study of effects of velocity overshoot artifact requires a specific method for accurately delineate its interval and investigate its impact over biomechanical descriptors; this paper proposed a computational algorithm for identifying the velocity overshoot interval.Velocity overshoot has significant impact over biomechanical descriptors analyzed during isokinetic knee extension tests at 60°·s(-1) and 180°·s(-1); the algorithm proposed is an advisable method for performing isokinetic tests analysis according to the isokinetic definition.