Official Journal of ICAPA www.JAPA-Journal.com ORIGINAL RESEARCH 18 Journal of Aging and Physical Activity, 2015, 23, 18-23 http://dx.doi.org/10.1123/JAPA.2012-0328 © 2015 Human Kinetics, Inc. Monda, Goldberg, and Smitham are with the UCL Institute of Orthopaedics and Musculoskeletal Science, Royal National Orthopaedic Hospital, Middlesex, UK. Thornton is with the Royal National Orthopaedic Hospital, Middlesex, UK. McCar- thy is with the Pedestrian Accessibility and Movement Environment Laboratory, University College London, London, UK. Address author correspondence to Ian McCarthy at i.mccarthy@ucl.ac.uk. Use of Inertial Measurement Units to Assess Age-related Changes in Gait Kinematics in an Active Population M. Monda, A. Goldberg, P. Smitham, M. Thornton, and I. McCarthy To study mobility in older populations it can be advantageous to use portable gait analysis systems, such as inertial measurement units (IMUs), which can be used in the community. To deine a normal range, 136 active subjects were recruited with an age range of 18 to 97. Four IMUs were attached to the subjects, one on each thigh and shank. Subjects were asked to walk 10 m at their own self-selected speed. The ranges of motion of thigh, shank, and knee in both swing and stance phase were calculated, in addition to stride duration. Thigh, shank, and knee range of movement in swing and stance were signiicantly different only in the > 80 age group. Regressions of angle against age showed a cubic relationship. Stride duration showed a weak linear relationship with age, increasing by approximately 0.1% per year. Keywords: healthy aging, gait, inertial measurement units The ability to walk comfortably is an important aspect of con- tinuation of independent living during aging. With life expectancy increasing signiicantly in both the developed world and many parts of the developing world, maintaining quality of life and mobility of the older members of the population is becoming increasingly important. Understanding changes in the locomotor system will contribute to intervention strategies and appropriate design of the built environment to facilitate independent living. The effects of aging on gait have been investigated in a number of publications. One approach has been to use optoelectronic gait systems combined with force-plate measurement. This has provided very useful information on the kinematics and kinetics of gait in three dimensions on speciic groups of subjects (Boyer, Andriacchi, & Beaupre, 2012; Kerrigan, Todd, Della, Lipsitz, & Collins, 1998; Kerrigan, Lee, Col- lins, Riley, & Lipsitz, 2001; Ko, Ling, Winters, & Ferrucci, 2009; McKibbon and Krebs, 2004; Silder, Heiderscheit, & Thelen, 2008; Winter, Patla, Frank, & Walt, 1990). Analysis of joint function has shown that a redistribution of joint torques occurs as people age, with reduced ankle plantar lexion and ankle power generation in the older population, and compensatory increases in work at the hip. Findings on the spatiotemporal characteristics of gait (step length, cadence, and resultant velocity) are slightly inconsistent, though most papers suggest that step length decreases and cadence increases with age. Alternatively, a population-based approach has been used, in which walking speed is typically measured by stopwatch (Tolea et al., 2010), a portable walkway (Beauchet et al., 2009), or an acceler- ometer (Puthoff, Janz, & Neilsen, 2008). Such studies also indicate that walking speed decreases with age. It has also been shown that walking speed is related to peak muscle power in the lower limbs of adults with functional limitations (Puthoff et al., 2008). However, data on walking speed alone is relatively nonspeciic with regard to understanding changes in limb kinematics with age, particularly with regard to pathologies such as hip and knee osteoar- thritis which increase in prevalence with age. Recent developments of inertial measurement units (IMUs), based on accelerometers and gyroscopes, can allow determination of some aspects of gait kinematics in a portable package that can be used either out in the community or in a busy outpatient clinic (Cooper et al., 2009). Such systems also have the potential to measure function while subjects are walking on more complex terrain in the built environment such as slopes, cross-slopes, curbs, and uneven surfaces. To date, no study of lower limb kinematics in the aging population has been reported using portable IMUs. The aim of this study was to investigate whether a system of four IMUs attached to the segments of the lower limbs could provide useful informa- tion about the kinematics of limb segment movement in gait in an active population. An initial pilot study was performed comparing data from the IMUs with those of an optical system. Subsequently, a more extensive study of participants with a wide age range was performed using IMUs. Methods Pilot Study Initially, a direct comparison was made between an IMU system containing three orthogonal gyroscopes and three orthogonal accel- erometers (GaitSmart, ETB, UK) and an optoelectronic gait system (Coda Motion, Charnwood Dynamics, UK). Four participants took part in this (2 male, 2 female; age range 23 to 58 years; BMI 19.5 to 26.9 kg/m 2 ). Participants wore shorts and the standard external marker set was applied for the measurement of gait kinematics. Four elastic straps with Velcro attachments were applied to each thigh and shank. Thigh straps were attached to a belt itted around the waist with a further Velcro strap. They were attached so as to lie approximately 10 cm above the knee joint/lateral condyle of the femur. The shanks straps were applied around the widest part of the calf rather than a set distance from the knee joint. as this varied with people of different heights with regard to calf musculature. Four IMUs (Pegasus, ETB, UK) were inserted into pockets in the elastic straps. The thigh IMUs were then orientated along an imaginary line from the greater trochanter to the lateral condyle of the femur; tibia IMUs were orientated along an imaginary line drawn between the head of the ibula and the lateral malleolus. Participants then walked along a walkway between two cameras that recorded the