# Biomechanical Analysis of Gait Compensation Strategies as a Result of Muscle Restriction
## 4 Discussion
### Compensation Strategies
#### 4.1.2 CT-Restriction  
For the following discussion, it is important to consider that the CT-restriction restricts the RF, HAM, and VAS muscles in addition to muscles restricted by the C-restriction. **Effect on the ankle motion:**  
We observed an increased ankle dorsal flexion during the swing phase (see Figure 3b), which suggests an increased activity of the TA muscle, that is a compensation for the restricted HAM muscles in [PERSON]'s simulations. This action might serve to safely clear the ground, as the knee and hip may not be able to compensate with a higher flexion as they did in C-restriction. The higher ankle dorsal flexion observed in the terminal stance suggests a weak GAS muscle, as also seen in the C-restriction, but in this case, the flexion is higher. The weak GAS is one of the reported effects from restricting the RF muscle in [PERSON]'s simulations. **Effect on the knee motion:**  
We observed a higher knee extension in the terminal swing phase (see Figure 3d). This might be caused by the decreased activity in the HAM muscles and/or increased activity in the VAS muscles, as reported by [PERSON] during the swing phase when the VAS muscles are weakened. During the swing phase in the normal gait, the HAM muscles modulate the rate of knee extension, and the VAS muscles act to ensure a complete extension, so as to prepare for the abrupt weight transfer at HC. Weak HAM muscles would fail to regulate the knee extension, and a higher activated VAS would produce a higher knee extension, and compensate for the lower hip flexion that we observed in the majority of subjects at terminal swing (section below). This would otherwise significantly reduce the step length. **Effect on the hip motion:**  
We observed a lower hip flexion at pre-swing (see Figure 3f), suggesting weakness in the RF and gracilis (GRA) muscles. These contribute to flexing the hip, to prepare for the swing phase in the normal gait. This partially agrees with [PERSON]'s results, as in that study, a higher activity in the RF muscle during pre-swing and a lower activity in the GRA muscles along the gait cycle were reported as effects of the RF muscle restriction. The observed reduced hip flexion during the initial and middle swing phases also suggests lower activity in the GRA muscle, which normally supports the flexion at this time. This would mean that the hip cannot compensate to clear the ground, as it did in C-restriction. However, as mentioned in the compensations for the ankle, the TA muscle compensates to clear the ground. The observed higher extended hip in the terminal swing phase is the result of the previously mentioned lack of the flexion action of the GRA muscle. As a result of the weak hip flexion during the swing phase, the step length would be shorter than normal. By comparing the compensation actions manifested in the C- and CT-restrictions, we see a more dynamic compensation activity in C-restriction; this is because the ankle, knee, and hip joints (kinematic chain) are able to compensate for each other, and in some cases even themselves. One of the reasons for this is the severity of the restriction. As the knee and hip joints are minimally affected in C-restriction, they can supply what the overall kinematic chain needs. However, in CT-restriction, the muscle restriction affects the complete kinematic chain; therefore, the body has to prioritize what to compensate. We found that the prioritization includes the prevention of foot drop, knee hyperextension in the terminal stance phase, and knee hyperflexion in the loading response phase, as well as the preservation of the step length. This suggests that the priority is to adapt the gait patterns for safe walking, as also seen in the elderly [24]. Moreover, the evaluation of the significance of every joint motion characteristic in every subject showed that the significance increased at a faster walking speed of 4 km/h in both C- and CT-restriction.