Joint coordination variability during overground and treadmill running

Using a treadmill to monitor locomotion is extremely convenient for sport and exercise research (Nigg et al., 1995). A problem exists if kinematic, kinetic, and metabolic or other variables, for example, are not uniform between treadmill and overground locomotion. As Nigg et al. (1995) suggested discussion about the degree of similarity between overground and treadmill running is inconsistent throughout the literature. For example, Schache et al. (2001), in their study of the three-dimensional kinematics of the lumbopelvic- hip complex, found subtle but significant differences in the sagittal plane movement of the hip joint. However, Williams (1985) concluded that the only significant differences in kinematics present between overground and treadmill running were at speeds greater than 5 m.s-1. Variability is inherent within and between all biological systems (Newell and Corcos, 1993). Given the huge number of degrees of freedom in the body, with its 102 joints, 103 muscles, 103 cell types and 104 neurones and neural connections (Kelso, 1995), it would seem that some degree of variability should be expected in all movements. Furthermore, as opposed to the traditional view that variability is error, variability is now seen as functional in many disciplines (Newell and Corcos, 1993; Hamill et al., 1999). Hamill et al. (1999) reported two separate experiments: one compared the effect of the quadriceps angle on coordination variability, whilst the other examined the relationship between coordination variability and patellofemoral pain. Variability in the coordination between body segments was seen in all groups, in both experiments. The former experiment was conducted overground and the later was conducted on a treadmill. Through visual inspection of the data (comparing the 'healthy' individuals in each study) there is evidence of decreased coordination variability during treadmill running. There is also evidence in the literature of differences in the amount of variability in angular kinematics between the two forms of locomotion. For example, Dingwell et al. (2001) compared sagittal plane ankle, knee and hip angles collected during overgound and treadmill walking. The results demonstrated significantly lower variability in the treadmill condition. Additionally, Nelson et al. (1972) reported reduced variability in the horizontal and vertical velocities of the centre of mass during treadmill as opposed to overground running. The aim of this study was to assess any differences in the variability of lower extremity coordination between overground and treadmill running. It was hypothesised that there would be significantly lower variability in lower extremity coordination in the treadmill condition than the overground condition.