Motion Analysis of an Eccentric Step Test Performed by 100 Healthy Subjects

Purpose This work forms part of a larger study investigating outcome measures suitable for patients with patellofemoral problems. The current study investigated the normal inter-subject variation of two kinematic variables during an eccentric step test. These were the knee joint angle at which subjects lost control of the movement (critical angle) and the angular velocity of the knee. Methods One hundred healthy subjects were recruited. The sample consisted of 69 females and 31 males. The length of each volunteer's right tibia was measured, to determine the height of the step, which was adjusted to 50% of the length of the tibia. This was to standardise the height of the step against the anthropometric differences between members of the study group. Subjects were videoed while performing two eccentric step tests, one with the dominant and one with the non-dominant leg. Video data were analysed using a two-dimensional motion analysis system. Results The mean critical angle (CA) for 200 healthy knees was 61.3¼and the mean angular velocity for knee flexion at the instant of contralateral heel strike was 54.9¼ per second. There were statistically significant sex and limb dominance differences for CA but not for velocity measurements. There was a significant positive correlation between weight and velocity. Conclusion The inter-subject range of CA and velocity has been established for 100 healthy subjects (200 knees) performing an eccentric step test. These data will be added to those for intra-subject variation, which will enable the interpretation of data from an ongoing clinical trial investigating outcome measures suitable for patients with patellofemoral problems