1. Introduction
At present, wearable devices have been widely used in mass fitness and competitive sports [
1], and the devices can monitor the training load, competition quality and injury recovery of athletes. Additionally, these devices can scientifically and effectively detect the kinematical indexes of the exercisers, can correct the wrong actions in real-time, and can standardize the movement technology. Wearable equipment is a new product of modern science and technology, with the devices possessing good quality, low weight, a strong ability to function for long time periods without electricity and a reduction in the verification of performed actions. Moreover, the application of wearable devices with fine-tune sensors in strength training can allow for more suitable exercise load plans for athletes [
2]. Additionally, the evaluation of the teaching effects on students through the use of wearable devices has a certain guiding significance for allowing for timely feedback [
3]. In regard to strength training, scientific research in the aspect of biomechanics has been more developed in foreign countries [
4], and further in-depth research has also been conducted in China. Squat, bench press and hard pull have become a significant focus of biomechanical research [
5]. The purpose of this study was to test the strength factors of squat, bench press and hard pull, in order to provide a scientific basis and theoretical reference for strength training.
4. Discussion
The wearable device can record the data accuracy of the motion test information, can monitor the path target parameters, can adjust for the angles and calculation accuracy. Research involving resistance training is of great significance, which can stimulate muscle growth.
Table 1,
Table 2 and
Table 3 calculates the characteristics of the kinematic parameters, and
Table 4,
Table 5 and
Table 6 calculates the characteristics of the dynamic parameters.
Squatting is a movement in which the body speed is added to the vertical track. To ensure that the core area is tight, the human body relies on the ground reaction force to complete the knee and hip extension actions, in order to accelerate muscle growth and to improve the metabolic rate [
14]. Walilko et al. [
15] found that the deep squat can improve hamstring muscle flexibility, bilateral symmetry and balance ability, which is an important method for developing the maximum strength of the lower limbs. This study is consistent with these results. When squatting, the hip joint is flexed and extended in the sagittal plane. The bending of the hip joint and the knee joint changes the center of gravity of the trunk’s forward tilt. When lifting the bar, the tendon senses the stimulus feedback and receives feedback from the nervous system, thus allowing for the simultaneous control of the muscles. The muscle is then stimulated and quickly reacts to complete deep squat.
The bench press is an important method of upper limb strength training [
16]. Sakamoto et al. [
17] found that the muscle activation and fatigue degree are different when different speeds of the bench press. Yamanaka et al. [
18] found that, if the wrist posture is wrong, then small muscle will weaken the weight of the bench press. Therefore, the feet cannot be lifted of the ground to prevent the human body from losing the power of the feet. Ramos et al. [
19] studied the bench press tests of 20–70% 1RM of the subjects, and they found that there was no significant difference between adjacent loads and that the optimal output power was 1RM of 20–40%. Similar to the results of Thiesfield and Ramos, we found that the optimal power of the bench press was 40% 1RM, which indicates that resistance exercise has a consistent influence on human motion performance and functional mode.
The hard pull mainly focuses on back and hip leg training. Suchomel et al. [
20] studied the hard pullmaneuvers of college students to make their back arches straight. With the help of the flexibility and force detection of the thigh, the back muscle group maintained static contraction. It was found that the main muscle groups involved in the hard pull were the quadriceps femoris, the hamstring muscle, the erector spinalis and the trapezius muscle. It was also found that 70–80% of the training limit weight can produce the best training effect. The results showed that the maximum peak force appeared at the 70–80% 1RM load intensity. The results of this study showed that the hard pull force of 80% 1RM are the highest, which indicates that the best explosive force training with this weight can produce significant effects. Therefore, it is suggested that people with certain strength training bases should perform explosive force training with an 80% 1RM load in the future.
The knee joint provides support when people walk, sit, squat. In the process of knee joint modeling, the distribution of trabeculae and bone cortex is positively correlated with stress. The denser the trabeculae is, the more active osteoblasts are and the greater the stress is. The conventional material properties of knee joint are cancellous bone and dense bone, and Poisson ratio and elastic modulus are given in the same direction. Based on the different mechanical properties of bone region during deep squat and hard pull, the results are different. The stress distribution of the above model shows the relationship between the force and the load weight, which indicates that the external force is the main factor of bone change.
In addition, previous studies have focused on neuromuscular characteristics, which can be combined with kinematics, dynamics, and neuroelectromyography parameters to verify data consistency, It has been observed that different levels of research objects muscle strength levels were different, which may cause errors. Additionally, the lack of comparisons of different load cases at different speeds will have a certain impact on individual differences. Based on the improvement of anti-interference, it is necessary to perform joint research on neuromuscular characteristics.
5. Conclusions
The hip joint and knee joint exhibit increased angles, angular velocities and angular accelerations of the deep squat and the hard pull, whereas the elbow joint exhibited increased angles, angular velocities and angular accelerations of the bench press. The best force and power of the deep squat elbow joint, the hip joint and the knee joint is 40% 1RM, that of the bench press is 40% 1RM and that of the hard pull is 80% 1RM. The main force producing portions of the deep squat are the hip joint and the knee joint, the dominant force producing portions of the bench press are the shoulder joint and the elbow joint, and the main force generating portions of the hard pull are the hip joint, the knee joint and the trunk. The external force is the main factor of bone change. The mechanical characteristics of knee joint can be simulated after the Finite Element Analysis and the simulation of AnyBody are verified.