Knee Joint Loads and Surrounding Muscle Forces of Selected Movement Elements in 42-form Tai Ji

Abstract

Knee joint loads for Tai Ji are unknown and such information is needed for designing Tai Ji intervention for people with knee pathologies. PURPOSE:To estimate joint loads to knee medial and lateral compartments and related muscle forces of selected Tai Ji movement elements compared to slow walking. METHODS:Five healthy subjects (age: 24.2 ± 3.6 years, height: 1.74 ± 0.06 m, mass: 70.5 ± 14.9 kg) with two weeks of Tai Ji experience performed level walking at 0.8 m/s and seven Tai Ji movement elements: high- (35 ± 5°) and low-pose (80 ± 5°) lunges and pushdowns, high-pose (hip height) and low-pose (knee height) kicks, and pseudo step. The motion capture data of experimental trials were exported from Visual3D into the OpenSim. A musculoskeletal model with 18 segments, 23 degrees of freedom and 92 muscle-actuated was scaled to the height and weight of each subject to generate subject-specific models. Muscle forces were estimated using static optimization minimizing the sum of squared of muscle activations. The compressive forces (CF) of the medial and lateral knee compartments were computed using the joint reaction analysis tool. Paired-sample t-tests were used to compare differences among the high-pose lunge, pushdown and kick and the low-pose lunge, pushdown and kick with pseudo-step and walking, respectively. RESULTS:Peak medial CF was greater for high- (4.16 BW) and low-pose (5.09 BW) lunges than walking (2.63BW, all p<0.05). Peak lateral CF was greater for low-pose lunge (2.98BW) and pushdown (3.79BW) than walking (0.64 BW, all p<0.01). Peak overall CFs were greater for the low-pose lunge (7.85 BW) and pushdown (8.23BW) than low-pose kick (3.63BW) and walking (3.09BW), respectively (all p<0.03). The peak muscle forces of vastus medialis, vastus lateralis and vastus intermedius, and quadriceps femoris were greater for low-pose lunge (1.54BW, 1.51BW, 2.92BW, and 6.3BW) and pushdown (1.67BW, 1.60BW, 3.19BW, and 6.97BW) compared to walking (0.1BW, 0.12BW, 0.21BW and 0.73BW, all p<0.05). CONCLUSIONS:Knee loads in pseudo-step, high-pose pushdown and high- and low-pose kick were similar to that in slow walking. Thus, these movements may be suitable for Tai Ji participants with knee pathologies. The lunge and low-pose pushdown should be modified to minimize overall and medial knee joint loads if to be used for these participants.