Identifying yoga-based knee strengthening exercises using the knee adduction moment.

BACKGROUND: This study aimed to compare muscle activations, co-contraction indices, and the knee adduction moment between static standing yoga postures to identify appropriate exercises for knee osteoarthritis. METHODS: Healthy young women (24.4 (5.4) years, 23.1 (3.7) kg/m(2)) participated. Primary outcome variables were electromyographic activations of the vastus lateralis, rectus femoris, vastus medialis, biceps femoris, and semitendinosus; co-contraction between the biceps femoris and rectus femoris, and vastus lateralis and vastus medialis; and knee adduction moments of both legs during six static, standing yoga postures (two squatting postures, two lunging postures, a hamstring stretch, and a single-leg balance posture). A two-factor repeated measures analysis of variance was used to identify differences in muscle amplitudes, co-contractions, and knee adduction moment between postures and legs. FINDINGS: Quadriceps activations were highest during squat and lunge postures (p≤0.001). Hamstring activations were highest during the hamstring stretch (p≤0.003). Squat and lunge postures produced higher co-contraction indices than other postures (p≤0.011). The wide legged squat (Goddess) and lunge with trunk upright (Warrior) produced the lowest knee adduction moments (p≤0.006), while the single-leg balance posture elicited a higher knee adduction moment than all other postures (p<0.05). INTERPRETATION: Squatting and lunging postures could improve leg strength while potentially minimizing exposure to high knee adduction moments. Future work should evaluate whether these exercises are useful in people with knee osteoarthritis.

Muscle activation and knee biomechanics during squatting and lunging after lower extremity fatigue in healthy young women.

Muscle activations and knee joint loads were compared during squatting and lunging before and after lower extremity neuromuscular fatigue. Electromyographic activations of the rectus femoris, vastus lateralis and biceps femoris, and the external knee adduction and flexion moments were collected on 25 healthy women (mean age 23.5 years, BMI of 23.7 kg/m(2)) during squatting and lunging. Participants were fatigued through sets of 50 isotonic knee extensions and flexions, with resistance set at 50% of the peak torque achieved during a maximum voluntary isometric contraction. Fatigue was defined as a decrease in peak isometric knee extension or flexion torque ≥25% from baseline. Co-activation indices were calculated between rectus femoris and biceps femoris; and between vastus lateralis and biceps femoris. Fatigue decreased peak isometric extension and flexion torques (p<0.05), mean vastus lateralis activation during squatting and lunging (p<0.05), and knee adduction and flexion moments during lunging (p<0.05). Quadriceps activations were greater during lunging than squatting (p<0.05). Thus, fatigue altered the recruitment strategy of the quadriceps during squatting and lunging. Lunging challenges quadriceps activation more than squatting in healthy, young women.

Biomechanical changes at the knee after lower limb fatigue in healthy young women.

BACKGROUND: The purpose of this study was to identify changes in knee kinematics, kinetics and stiffness that occur during gait due to lower limb neuromuscular fatigue. METHODS: Kinematic, kinetic and electromyographic measures of gait were collected on healthy, young women (n=20) before and after two bouts of fatigue. After baseline gait analysis, two bouts of fatiguing contractions were completed. Fatigue was induced using sets of 50 isotonic knee extensions and flexions at 50% of the peak torque during a maximum voluntary isometric contraction. Fatigue was defined as a drop in knee extension or flexion maximum voluntary isometric torques of at least 25% from baseline. Gait analyses were completed after each bout of fatigue. Dynamic knee stiffness was calculated as the change in knee flexion moment divided by the change in knee flexion angle from 3 to 15% of the gait cycle. Co-activations of the biceps femoris and rectus femoris muscles were calculated from 3 to 15% and 40 to 52% of gait. Repeated measures analyses of variance assessed differences in discrete gait measures, knee torques, and electromyography amplitudes between baseline and after each bout of fatigue. FINDINGS: Fatigue decreased peak isometric torque. Fatigue did not alter knee adduction moments, knee flexion angles, dynamic knee stiffness, or muscle co-activation. Fatigue reduced the peak knee extension moment. INTERPRETATION: While neuromuscular fatigue of the knee musculature alters the sagittal plane knee moment in healthy, young women during walking, high intensity fatigue is not consistent with known mechanical environments implicated in knee pathologies or injuries.