2 Rehabilitation Research and Practice Figure 1: Single leg squat. Figure 2: Dip test. between vertebrae was provided by an interaction between active, passive, and neural systems. Likewise, within the pelvis, stability is maintained by passive structures [22, 23] and active muscular forces [24]. Other researchers have investigated the active muscular and neural stability systems of the lumbar spine making important contributions to understanding the stability of the lumbopelvic region. Desirable patterns of muscle activation of transverse abdominus and multiﬁdus have been described [8, 25–29]. Less desirable motor patterns have been described as substitution strategies [26, 28, 30, 31]. These may include excessive use of other muscles and pelvic tilt that may increase or decrease lumbar lordosis. By synthesising the literature in this area, LPS could be deﬁned as the ability of an individual to attain and then maintain optimal body segment alignment of the spine (lumbar and thoracic), the pelvis, and the thigh in both a static position and during dynamic activity. Stability is attained and maintained by passive structures and with optimal muscle recruitment patterns, that is, without substitution strategies. The clinical importance of LPS highlights the need for valid clinical tests of LPS. To examine LPS, it has been recommended that assessment should be performed in an upright position with evaluation of dynamic trunk control over the weightbearing leg, in all planes of motion: sagittal, frontal, and transverse planes [1]. This type of assessment is in keeping with the above deﬁnition of LPS where the alignment of segments of the body during dynamic activity is the key feature of interest. A number of dynamic tests of LPS have been reported in the literature. These include the single leg stand [32– 34], single leg squat [32, 35–38], dip test [33], lateral step down [3, 36], anterior step down [36], hop test [33], and runner pose test [33, 37]. Tests of individual planes of movement were also identiﬁed [1, 36]. Several of these tests lack aspects of validity; single leg stand test, anterior step down, and lateral step down predominantly assess pelvic, hip, and knee movement in the frontal plane, and hop test has a ballistic nature that may make assessment of optimal Figure 3: Runner pose test. muscle recruitment and substitution strategies diﬃcult to achieve and to assess clinically. Of the reported clinical tests of LPS, the single leg squat (SLS, Figure 1), dip test (DT, Figure 2), and runner pose test (RPT, Figure 3), appear to assess body segment alignment of the trunk, pelvis, and thigh in multiple planes making them suitable as tests of LPS. For DT and RPT, assessment of performance has been described but there are no agreed rating criteria for these tests. For SLS, rating criteria were used in three studies [3, 32, 39]. Two of these studies assessed the magnitude of deviation from neutral alignment and degree of movement oscillation on a four-point rating scale with movement described as having excessive, moderate, small, or no deviation [3, 39]. Limited agreement in rating was reported using the criteria, and it was suggested that lack of explicit criteria for rating performance hampered reliability [3]. The rating criteria used by DiMattia et al. (2005) [32] only examined hip and knee alignment, so the use of these criteria for the clinical rating of LPS is limited. Since the three clinical tests lack valid rating criteria, it is not currently possible to use them to reliably assess LPS.