Presentation 0409, Physical Therapy 1 – Orthopaedics. 11:00, Room 101CD
S388
EFFECTS OF STRENGTH TRAINING ON KNEE JOINT MECHANICS AND BALANCE DURING A SINGLE LEG SQUAT TASK IN PATIENTS WITH KNEE OSTEOARTHRITIS K McQuade1, J Coppersmith1, Z Ashwell1 1 University of Washington, Department of Rehabilitation medicine Email:
[email protected] Introduction Strengthening exercises are commonly prescribed for patients with knee arthritis with the idea that the stability of the knee will be improved. While patients report positive outcomes associated with such exercise training, little is know about the influence of strength training on knee joint mechanics. These results represent preliminary findings of a clinical trial testing the influence of knee strengthening on knee joint biomechanics. Methods Six patients with physician diagnosed mild Osteoarthritis of the knee completed a two month strength training program for knee extension/flexion. Subjects underwent a pre training assessment consisting of establishing base line strength and undergoing 3D motion analysis during several tasks including single leg squat task on a force platform. A seven-segment model of the lower extremities using passive infrared marker system was used to determine lower extremity kinematics. Surface muscle activity was recorded from six muscles about the knee and used in an EMG driven musculoskeletal model (SIMM, Musculographics, Chicago, IL) to estimate joint reaction forces at the knee using an inverse dynamics approach. Data were normalized by defining the squat task starting with the knee straight (0%), performing a single leg squat with no balance support and returning to the upright position (100%). The mean of three squat trials was used for analysis. Data presented here are for subjects involved knee.
Figure 2: Pre and post mean changes in net moments during single leg squat The lack of significant changes in joint moments (Fig 2) at the hip or knee indicates that the net muscular response to the squat task is not affected by strength. Figure 3 shows the mean change in the net displacement of the center of pressure suggesting that the magnitude of the COP displacement was less after training
Results and Discussion All subjects improved their maximum isometric strength by about 50% on average. There were no changes in the amount of knee flexion or Varus/valgus angles. Figure 1 & 2 show the Pre-Post mean changes for the knee net joint reaction forces (JRF) and joint moments. Since muscle forces are the dominant contributor to the JRF, this indicates that increased strength did not result in increased muscular force generated during a single leg squat.
Figure 3: Pre and post mean changes in Resultant Center of pressure (COP) displacement Conclusions Preliminary results suggest that strength training does not alter knee joint kinetics during a dynamic unsupported squatting task. However the decreased magnitude of the COP suggests that subject’s balance may be improved. The mechanism of the balance improvement requires further investigation and verification. Figure 1: Pre and post mean changes in net Tibiofemoral joint reaction force
Journal of Biomechanics 40(S2)
Acknowledgements: Robert Price and Marcia Ciol for Technical Assistance
XXI ISB Congress, Podium Sessions, Wednesday 4 July 2007
