EFFECTS OF SELECTED UNWElGHTlNG CONDITIONS ON KNEE TORQUES DURING PARTIAL SQUATS WHILE TETHERED
AbstractINTRODUCTION - This study examined the effects of different tethering conditions on knee torques during partial squats. Six college males were unweighted 0%, 25%, and 50% of their BWT while supported in a Kinney upper body vest by an active traction prototype (Conva-lift) They performed partial squats in a 2 second cadence at a depth of about 5 cm. Reflective markers were placed on the toe, ankle, knee, hip, shoulder, elbow, wrist, and the harness strap and 4 squats were videotaped from a sagittal view at 60 fps. The best trial was digitized, smoothed with a low-pass digital filter at a frequency of 10 Hz., and analyzed with an Ariel APAS system. The squat movement was delineated into a down-phase to deep knee flexion, and an up-phase to full extension, and joint torques were calculated for the knee joint. RESULTS - An ANOVA with repeated measures on the load factor was used to analyze the knee torques at deep knee. flexion, squat time, knee ROM, and depth of squat. The analysis found significant differences between the knee torques at deep knee flexion (p=.03) for the 3 unweighting conditions. The mean knee torques were 163.3+50.6 Nm, 106.7+35.7 Nm, and 124.3+26.7 Nm, for the 0%, 25%, and 50% unweighting conditions, respectively. These torque values were similar to the values reported by Smidt (1973), and higher than those reported by Lunnen (1981 ). The unweighting conditions significantly reduced the knee torques utilized at deep crouch. The mean depth of crouch was 10.8+3.9 cm, 5.3+1.2 cm, and 4.6+1.4 cm for the 0%, 25%, and 50% unweighting conditions. The fully weighted partial squat resulted in a deeper squat (p=.003) than the tethered squats. The knee angle at the bottom of the squat was 114 0+7.2, 135.0+6.5, and 136.9+6.0 deg for the 0%, 25%, and 50% tethering conditions. These knee angles were significantly different (p= 000) and also, significant differences in the ROM for the knee were found at the ,001 level. CONCLUSION - In summary, as the degree of unweighting provided by the Conva-Lift active traction prototype was increased, a corresponding decrease in the knee torques was observed. Besides the tethering device reducing the knee torques, it also controlled the depth of squat and these factors would be beneficial in the rehabilitation of knee injuries without adversely loading the anterior cruciate ligament (Haynes et al., 1 990). REFERENCES - Haynes, D.W., Pepe, C.L., Feinstein, J.A & Hungerford, D S., (1990). The changing excursions of the hamstring muscles during flexion, rotation, varus and valgus movements of the tibia. Proceedings of the 36th Annual Meeting of the Orthopaedic Research Society, New Orleans, Louisiana, 15:496 Lunnen, J., Yack, J., & LeVean, B. (1981). Relationship between muscle length, muscle activity and torque of the hamstring muscles Phys. Therapy, 61 :I 90-195. Smidt, G.L., (1 973). Biomechanical analysis of knee flexion and extension. J. Biomech., 6179-92.
Injuries / Rehabilitation
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