An isokinetic study of combined activity of the hip and knee extensors

The purpose of this study was twofold: to derive isokinetic concentric and eccentric normal strength values obtained during combined activity of the knee and hip extensors and to compare these values with those based on testing of knee extensors only. Fifteen men took part in the study. Combined extension was tested in the supine position with the knee and hip at an initial position of 95 degrees. Knee extension was tested in the seated position with the knee at the same initial position. The range of motion and angular velocities were equal in both configurations: 15 degrees and 8 degrees s(-1) and 15 degrees s(-1) respectively. The average peak force in the CKH mode was close to 10 Nm/kg bw and over 15 Nm/kg bw in the concentric and eccentric contractions respectively, whereas for the knee extensor mode the respective figures were approximately 8 Nm/kg bw and 10 Nm/kg bw. With respect to the same performance parameters, there were low and insignificant correlations between the two modes. RELEVANCE:--Isokinetic testing of knee extensors performance in what is commonly known as single-joint configuration is somewhat limited in its functional scope and, if applied wrongly, is potentially harmful in various dysfunctional states of the knee. On the other hand, multi-joint testing configuration, involving muscles of the hip as well as the knee, is possibly more functional and safe. To assess the muscle performance status of knee patients using the latter mode, data regarding what should be expected from normal individuals is essential. This paper supplements existing material concerning knee and hip extensors and looks into the relationship between the two dynamic contraction modes as well as the association between combined activity and knee extensors only. This association which was found to be very limited indicates that the two configurations reflect different muscle action paradigm and therefore may not be used interchangeably.