Mechanical loading of the patellofemoral joint and its correlation with various body mass indices in older adults practicing Tai Chi exercises

Abstract

BACKGROUND: As the aging population grows in China, overweight and obesity are increasingly leading to lower limb joint injuries in older adults. OBJECTIVE: To compare the biomechanical data of the lower limb patellofemoral joint during Tai Chi movements and normal walking among older adults with different body mass indices, analyze the correlation between body mass index and biomechanical data of the lower limb patellofemoral joint, and investigate the impact of different body mass indices on the mechanical loading of the patellofemoral joint in older adults. METHODS: The older adults with obesity (n=17), overweight (n=17), and normal body mass index (n=19) who had been practicing Tai Chi for an extended period were recruited based on body mass index classification. The VCION 3D infrared motion capture system and Kistler force measurement system were used to collect kinematic and dynamic data during typical Tai Chi movements and normal walking. A biomechanical model of the patellofemoral joint was established to calculate biomechanical parameters of the patellofemoral joint. The effects of body mass index on the mechanical characteristics of the patellofemoral joint during walking and Tai Chi in the older adults were quantified using analysis of variance and correlation analysis. RESULTS AND CONCLUSION: (1) Compared with the normal group, patellofemoral joint force and contact area peak during normal walking were significantly lower in the overweight and obese groups (P < 0.05); during Tai Chi movements, knee flexion moment, patellofemoral joint force, and quadriceps muscle force were significantly lower (P < 0.05). (2) Body mass index was significantly negatively correlated with the maximum knee flexion angle, maximum and minimum patellofemoral joint contact area during the Tai Chi movement 'Reversing the Wind' (P < 0.05); and with the maximum knee extension moment, maximum and minimum patellofemoral joint reaction force, maximum quadriceps muscle force, maximum knee angle, and maximum and minimum patellofemoral joint contact area during the 'Brush Knee and Twist Step' movement (P < 0.05). These results indicate that as body mass index increases, the dynamic load on the patellofemoral joint during Tai Chi movements decreases; compared with normal-weight individuals, overweight and obese older adults show significantly lower maximum patellofemoral joint force during the 'Brush Knee and Twist Step' movement, indicating lower dynamic load. Therefore, Tai Chi is recommended as a fitness exercise for overweight and obese older adults to avoid sports injuries caused by high joint loads.

1. Introduction

The seventh national population census data show that people aged 60 and above account for 22% of China's population, with over 50% of them being overweight or obese (according to the Fifth National Physical Fitness Monitoring Bulletin). Data indicate that the risk of bone and joint diseases in overweight and obese older adults is 7 times higher than in those with normal body mass index [1]. Overweight and obesity may lead to overload of the patellofemoral joint during exercise, increasing the risk of joint pain and injury [2]. Studies have shown that knee joint load during walking and running increases significantly with body mass index in older adults [3]. Therefore, investigating the mechanical loading of lower limb joints during fitness exercises is of great significance for preventing sports injuries in overweight and obese populations.

Tai Chi, as a highly popular aerobic exercise among older adults, has been shown to improve lower limb muscle strength and endurance [4], joint flexibility [5], dynamic and static balance [6-9], and postural control [10-11]. Nevertheless, Tai Chi practitioners sometimes experience varying degrees of knee pain, especially among older adults [12]. During Tai Chi practice, the body maintains a semi-squatting posture with flexed knees, increasing the load on the knee joint [13] and friction between the patella and femoral articular surfaces, thereby raising the risk of joint pain [14]. Additionally, walking, jogging, and stair climbing are common forms of exercise that can induce knee pain, sharing similar movement characteristics, such as repeated knee flexion and extension during single-leg support, as seen in Tai Chi movements like 'Brush Knee and Twist Step' and 'Reversing the Wind'. However, existing research has mostly focused on qualitative analysis of lower limb joint loading during Tai Chi movements, with insufficient precise quantitative results.

Studies have found that patellofemoral joint stress (PFJS) can better explain the internal loading of the knee joint than knee joint moments, and increased PFJS is an important factor in patellofemoral pain [15-16], as confirmed in activities such as walking [17], cycling [18], and stair climbing [19]. However, the patellofemoral joint loading in overweight and obese older adults during Tai Chi exercise remains unknown. Research shows that with increased body mass, older adults experience greater pressure and stress on lower limb joints during exercise, leading to increased joint wear and a higher risk of patellofemoral pain and osteoarthritis [20]. This study aims to compare the differences in patellofemoral joint mechanical indicators between obese, overweight, and normal-weight older adults during Tai Chi movements and normal walking, quantify the correlation between body mass index and patellofemoral joint mechanical indicators, and explore the impact of body mass index on lower limb patellofemoral joint loading, providing data reference for the selection of scientific fitness exercises for overweight and obese older adults. The research hypothesis is that compared with normal-weight older adults, overweight and obese older adults will show significantly increased patellofemoral joint mechanical indicators during Tai Chi movements and normal walking, and body mass index will be positively correlated with patellofemoral joint loading.