254 Journal of Sport Rehabilitation, 2013, 22, 254-256 © 2013 Human Kinetics, Inc. www.JSR-Journal.com ORIGINAL RESEARCH REPORT The author is with the Faculty of Sport, Exercise and Physio- therapy, University of Salford, Manchester, UK. The Effect of Pelvic Position on Popliteal Angle Achieved During 90:90 Hamstring-Length Test Lee Herrington Context: Hamstring muscle length is commonly measured because of its perceived relationship to injury of both the hamstrings themselves and the pelvis and lumbar spine. The popliteal (knee-extension) angle mea- sured from the starting position hip and knee at 90° is a commonly used indirect measure of hamstring muscle length. When this measure has been undertaken in the literature previously, little attention was paid to the position of the pelvis, which may signifcantly infuence measurements taken. Design: Repeated-measures. Setting: University human performance laboratory. Participants: 60 healthy physically active males (mean age 20.1 ± 1.8 y, range 18–24 y). Intervention: The 2 extremes of pelvic position (anterior and posterior). Main Outcome Measure: Popliteal angle (with maximal knee extension) was measured in 2 positions, 1 of full anterior and 1 of full posterior pelvic tilt. Results: The mean difference in popliteal angle between ante- rior to posterior pelvic positions was 13.4° ± 9° (range 0–26°); this was statistically signifcant (P = .0001). Conclusion: The fndings of the study indicate that pelvic position has a signifcant effect on popliteal angle and therefore should be taken into account when measuring hamstring muscle length. Keywords: measurement, pelvis position, validity Hamstring muscle length (HML) is routinely measured because of its perceived relationship to performance, 1 injury prevention, 2 postural alignment and lumbopelvic motion, 3 low back pain, 4 and hamstring muscle injury. 5 Clinically, HML is commonly measured indirectly by angular mea- surements of unilateral active or passive knee extension with the hip fexed to 90° (popliteal angle [PA]). 6 Those undertaking this measurement have rarely taken the posi- tion of the pelvis into consideration in the literature. The position of the pelvis has been shown to have a signifcant effect on HML 7 ; therefore, if this is not taken into account during the measurement of HML it is likely to affect the construct validity of the resulting knee angle measured, along with the repeatability of the measurement. In their systematic review of hamstring muscle-stretching methods Decoster et al 8 commented on the generally poor standard of the research undertaken and the lack of consistent fnd- ings for any given technique. Of the 28 studies included in their review, 8 none standardized the pelvic position during testing, which may have had an effect on the reliability and repeatability of their outcome measures and, so, the results. Apart from the potential effect on measurement error in not taking pelvic position into account, which could infuence the fndings of, for example, stretching studies and athlete screening, failure to control pelvic position may have a signifcant impact on rehabilitation outcome. As mentioned, hamstring length would appear to signifcantly infuence pelvic position. 7 Congdon et al 7 found that extending the knee in a position of hip fexion signifcantly increased pelvic posterior rotation, and this relationship occurred to a greater degree and at greater ranges of knee fexion in subjects with short hamstrings on straight-leg-raise testing. This would appear to indicate that individuals with short hamstrings compensate for the lack of extensibility by posteriorly pelvic tilting to allow extremes of knee extension to occur. The use of posterior pelvic tilt to compensate for short hamstrings could then increase load on the sacroiliac joints and the lumbar spine, possibly leading to pathology. It may prove useful in these individuals to assess fexibility in the uncompensated ante- rior pelvic-tilt position to assess how much uncontrolled pelvic tilting is being used to mask hamstring infexibility. Davis-Hammonds et al 9 found that males dem- onstrated signifcantly greater anterior pelvic tilt than females at maximum knee extension during running. Taking into account the work of Congdon et al, 7 this would then mean that males would require greater rela- tive fexibility of the hamstring muscles to achieve this. As it is believed that the majority of high-speed-sprinting hamstring injuries occur during terminal swing phase, 10 it might be that these individuals lack the necessary fex- ibility (range) in an anterior tilted position and so place greater internal stress on their hamstring muscles. The aim of this study was to assess the effect of the 2 extremes of pelvic position (maximally anterior and posterior tilt) on popliteal angle during the standard clinical test of HML passive knee extension from the 90° hip-fexed position.