Trunk position modulates anterior cruciate ligament forces and strains during a single-leg squat

• Published in: Clinical biomechanics (Bristol) 2012-01, Vol.27 (1), p.16-21
• Main Authors: Kulas, Anthony S, Hortobágyi, Tibor, DeVita, Paul
• Format: Article
• Language: English
• Subjects: Anterior cruciate ligament; Anterior Cruciate Ligament - physiology; Elastic Modulus; Exercise - physiology; Humans; Joint; Knee biomechanics; Knee Joint - physiology; Male; Muscle Contraction - physiology; Muscle, Skeletal - physiology; Physical Medicine and Rehabilitation; Posture - physiology; Squat; Stress, Mechanical; Torso - physiology; Trunk position; Young Adult
• ISSN: 0268-0033; 1879-1271
• DOI: 10.1016/j.clinbiomech.2011.07.009

Abstract Background Although the squat exercise and its variations are commonly prescribed for anterior cruciate ligament rehabilitation, whether trunk position affects these ligament forces and strains during the squat is unclear. Our purpose was to evaluate the effects of trunk position on anterior cruciate ligament forces and strains during a single-leg squat. Methods While instrumented for biomechanical analysis, twelve recreationally active subjects performed single-leg squats with minimal and moderate amounts of forward trunk lean. A combination of inverse dynamics, Hill-type muscle modeling, and mathematical computations estimated anterior cruciate ligament forces, strains and quadriceps, hamstrings, and gastrocnemius forces. Findings The moderate forward trunk lean condition vs. minimal forward trunk lean condition had lower peak anterior cruciate ligament forces (↓24%), strains (↓16%), and average anterior cruciate ligament forces and strains during knee flexion ranges of motion of 25–55°(descent) and 35–55°(ascent). A moderate vs. minimal forward trunk lean also produced 35% higher hamstring forces throughout the majority of the squat, but lower quadriceps forces only at knee flexion angles greater than 65°. Interpretation Single-leg squats performed with a moderate forward trunk lean (~ 40°) can minimize anterior cruciate ligament loads. Mechanistically, trunk lean reduced anterior cruciate ligament forces and strains through concomitant modulations in hip flexion angle and biarticular thigh muscle forces. These findings are clinically relevant for anterior cruciate ligament rehabilitation as a common goal is to minimize anterior cruciate ligament forces and strains through enhancing hamstring and quadriceps co-contractions.