quasi-static squat: 5 knee flexion angles (0˚-70˚) for 5 s. Fast dynamic squats: as many cycles (0˚-70˚-0˚) as possible in 10 s. Standardization: positioning jig and foot wedges (Fig. 1.A). Comparison: the 5 positions where static and dynamic flexion angles were similar. Statistics: Wilcoxon signed-rank test (p=0.05). Acknowledgments We gratefully acknowledge the help of Felix Chenier and Samir Sidimamar for the EMG evaluation. This study was funded by the FQRNT, the FRSQ, the NSERC and the MENTOR program. Results Mean knee flexion angles achieved during quasi- static squats were 3.0˚, 37.1˚, 46.6˚, 55.2˚, and 71.8˚. Mean knee flexion speed achieved during fast dynamic squats was 61.5˚/s (4 full cycles). Data acquired on one healthy subject during quasi- static and fast dynamic squats are shown in Fig. 2. Mean internal tibial rotation was 1.33.6˚ during the quasi-static squat and 1.83.7˚ during the fast dynamic squats (Fig. 3). A significant difference (p=0.049) was found at 37.1˚ of knee flexion (Fig. 3). Mean anterior tibial translation was 7.84.4 mm during the quasi-static squat and 5.15.4 mm during the fast dynamic squats (Fig. 4). A significant difference (p=0.049) was found at 3.0˚ of knee flexion (Fig. 4). Julien Clément 1-3 , Nicola Hagemeister 1-3 , Rachid Aissaoui 1-3 , Jacques A. de Guise 1-3 1 École de technologie supérieure (ÉTS), Montréal, QC, Canada; 2 Laboratoire de recherche en imagerie et orthopédie (LIO), Montréal, QC, Canada; 3 Centre de recherche du Centre hospitalier de l’Université de Montréal (CRCHUM), Montréal, QC, Canada References Johal, P., Williams, A., Wragg, P., Hunt, D., Gedroyc, W., 2005. Tibio- femoral movement in the living knee. A study of weight bearing and non-weight bearing knee kinematics using 'interventional' MRI. Journal of Biomechanics 38, 269-276. Moro-oka, T.-a., Hamai, S., Miura, H., Shimoto, T., Higaki, H., Fregly, B.J., Iwamoto, Y., Banks, S.A., 2008. Dynamic activity dependence of in vivo normal knee kinematics. J. Orthop. Res. 26, 428-434. Mu, S., Moro-oka, T., Johal, P., Hamai, S., Freeman, M.A.R., Banks, S.A., 2011. Comparison of static and dynamic knee kinematics during squatting. Clinical Biomechanics 26, 106-108. Further information © Julien Clément, 2014 julien.clement.1@ens.etsmtl.ca Comparison of 3D kinematics, 3D kinetics and EMG of the lower limbs during quasi-static and dynamic squats Introduction 3D kinematics, 3D kinetics, and EMG of the lower limb have been extensively analyzed during squatting activities . Various squatting conditions were studied, from quasi-static squatting positions (Johal, 2005) to dynamic squatting movements (Moro-oka, 2008). But are quasi-static and dynamic squatting activities comparable? One study (Mu, 2011) has compared 3D kinematics of the knee during quasi-static and dynamic squatting activities. It concluded that they produce equivalent 3D knee kinematics. However, the study was conducted at low speed (19˚/s) on healthy subjects, and provided no information on kinetics and EMG of the lower limbs. The purpose of this study was to compare simultaneous recording of 3D kinematics, 3D kinetics and EMG of the lower limb during quasi-static and fast dynamic squats in healthy and osteoarthritis (OA) subjects. Figure 1. Experimental protocol Mean vertical ground reaction force was 818.54.9 N (100.10.6% of the subjects’ BW) during the quasi- static squat and 843.712.5 N (103.2%1.5% of the subjects’ BW) during the fast dynamic squats (Fig. 5). A significant difference (p=0.002) was found at 71.8˚ of knee flexion (Fig. 5). The EMG activities of the 8 muscles recorded during the quasi-static squat were less than those recorded during the fast dynamic squats, and several differences were significant (Fig. 6). Differences between EMG activities represented 10.05.7% of the dynamic data. Mean absolute differences between quasi-static and fast dynamic squats were 1.51.3˚ for rotations, 1.92.1 mm for translations, 2.13.0% of the subjects’ BW for forces, 6.68.9 Nm for torques, 11.210.5 mm for center of pressure, and 6.38.0% of maximum dynamic EMG activities. Figure 2. Black curves show evolution of knee flexion-extension (A), knee internal-external rotation (B), vertical ground reaction force (C), and vastus medialis EMG activity (D) during fast dynamic squat of one healthy subject (41 years, 183 cm, 72 kg). The squares, diamonds, triangles, crosses and circles represent the 5 knee flexion angles achieved during quasi-static squats. Dashed and dotted grey lines define the flexion and extension phases of the fast dynamic squats. C B A D Figure 3. Mean internal tibial rotation during quasi-static and fast dynamic squats (SD). Black squares represent static data and gray circles dynamic data. Black stars indicate significant differences (p<0.05). Figure 4. Mean anterior tibial translation during quasi-static and fast dynamic squats (SD). Black squares represent static data and gray circles dynamic data. Black stars indicate significant differences (p<0.05). Figure 5. Mean vertical ground reaction force during quasi-static and fast dynamic squats (SD). Black squares represent static data and gray circles dynamic data. Black stars indicate significant differences (p<0.05). Figure 6. Mean vastus medialis EMG activity during quasi-static and fast dynamic squats (SD). Black squares represent static data and gray circles dynamic data. Black stars indicate significant differences (p<0.05). Conclusions This study shows for the first time that quasi- static and fast dynamic squats are comparable in terms of 3D kinematics, 3D kinetics, and EMG of the lower limb. Few significant differences were found, and they remained small. Kinematic differences correspond to those found by Mu et al. (2011). Studies of quasi-static and dynamic squatting activities can be considered with equal confidence because they produce the same kind of results. Materials and methods Ten subjects were recruited: 5 women, 5 men, 5117 years, 17011 cm, 83.418.5 kg, 5 healthy subjects, and 5 OA subjects. 3D knee kinematics was recorded with the KneeKG™ (Emovi Inc., Laval, QC, Canada) (Fig. 1.C- D) and 12 optoelectronic cameras (VICON, Oxford, UK, 200 Hz) (Fig. 1.F). 3D kinetics, i.e. forces, torques and center of pressure, was recorded with a force plate (AMTI, Watertown, MA, USA, 2000 Hz) (Fig. 1.B). EMG activity of lower limb was recorded with surface electrodes placed on 8 muscles (Delsys Inc., Boston, MA, USA, 2000 Hz) (Fig. 1.E). Quasi-static LIO Website Gait & Posture article View publication stats View publication stats