The effect of varied hip angles on the generation of internal tibial rotary torque.

Previous researchers have determined that 90 degrees of knee flexion is an appropriate angle to condition the internal tibial rotators. Because the majority of internal tibial rotators are two-joint muscles crossing both the knee and the hip, the influence of the hip angle on the generation of rotary torque was examined. The purpose of this study was to investigate the effect of four hip angles on the generation of internal tibial rotational torque with the knee positioned at 90 degrees of flexion. Forty subjects, 20 males and 20 females, were tested at four positions of hip flexion (120 degrees, 90 degrees, 45 degrees, 10 degrees) using a modified Cybex II isokinetic dynamometer, and their maximal mean internal rotary torque values were recorded. The subjects were placed in a custom-made orthotic-type boot to minimize the motions of the talo-calcaneal joint. Sixty percent of the males and 65% of the females generated their greatest absolute torque value at 120 degrees of hip flexion. A procedure investigating the rankings of the maximal mean torque values at each of the tested hip positions revealed a significant difference between the hip positions of 120 and 10 degrees for both populations (P less than 0.001), and the male population also demonstrated significance between the angles of 120 and 45 degrees and 90 and 10 degrees (P less than 0.05). The practical significance of this study offers some additional information regarding the appropriate positioning for rehabilitation of the internal tibial rotators. The data suggests that if maximal torque generation is desired, the internal tibial rotators should be tested and exercised with the hip flexed to 120 degrees to take advantage of the length-tension relationship and the biomechanical principles of the rotary muscles.