In order to fully understand contact dynamics on a trampoline, a simulation approach using a musculoskeletal model coupled with a dynamic model of the trampoline is essential. The purpose of the study was to examine dynamics and selected lower extremity muscle forces in a landing and jumping movement on a trampoline, using a combination of finite element modeling and musculoskeletal modeling. The rigid frame of the trampoline was modeled in ADAMS and coupled with a finite element model of the elastic trampoline net surface in ANSYS. A musculoskeletal model of an elite trampoline athlete was further developed in LifeMod and combined with the finite element model of the trampoline. The results showed that the peak trampoline reaction forces (TRF) were 3400 N (6.6 BW) and 2900 N (5.6 BW) for the left and right limb, respectively. The right hip, knee and ankle joint reaction forces reached the maximum between 3000-4000 N (5.8 – 7.7 BW). The gluteus maximum and quadriceps reached the maximum muscle force of 380 N (0.7 BW) and 780 N (1.5 BW), respectively. Asymmetric loading patterns between left and right TRFs and lower extremities joint reaction forces were observed due to the need to generate the rotational movement during the takeoff. The observed rigid and erect body posture suggested that the hip and knee extensors played important roles in minimizing energy absorption and maximizing energy generation during the trampoline takeoff.
[Purpose] The purpose of the study was to design and implement a multichannel dynamic
functional electrical stimulation system and investigate acute effects of functional
electrical stimulation of the tibialis anterior and rectus femoris on ankle and knee
sagittal-plane kinematics and related muscle forces of hemiplegic gait. [Subjects and
Methods] A multichannel dynamic electrical stimulation system was developed with 8-channel
low frequency current generators. Eight male hemiplegic patients were trained for 4 weeks
with electric stimulation of the tibia anterior and rectus femoris muscles during walking,
which was coupled with active contraction. Kinematic data were collected, and muscle
forces of the tibialis anterior and rectus femoris of the affected limbs were analyzed
using a musculoskelatal modeling approach before and after training. A paired sample
t-test was used to detect the differences between before and after training. [Results] The
step length of the affected limb significantly increased after the stimulation was
applied. The maximum dorsiflexion angle and maximum knee flexion angle of the affected
limb were both increased significantly during stimulation. The maximum muscle forces of
both the tibia anterior and rectus femoris increased significantly during stimulation
compared with before functional electrical stimulation was applied. [Conclusion] This
study established a functional electrical stimulation strategy based on hemiplegic gait
analysis and musculoskeletal modeling. The multichannel functional electrical stimulation
system successfully corrected foot drop and altered circumduction hemiplegic gait
pattern.
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