## 4 Discussion  
So far, there have been more studies that investigated the motor abilities of children with cerebral palsy than those of adults with cerebral palsy [34; 35; 36; 37]. Additionally, most of the studies examining the relationship between muscle strength and aerobic capacity were conducted on the general public or the diseased patients, not on those disabled with cerebral palsy [47; 48; 49]. Therefore, this study investigated the relationship between the muscle strength and the aerobic capacity in adults with cerebral palsy based on the fact that there is a close relationship between the muscle strength and the aerobic capacity. As a result of correlation analysis, VO2 peak showed a significant positive correlation between 45\({}^{\circ}\) and 300\({}^{\circ}\)/s peak torque/BW of HIP joint, 60\({}^{\circ}\) and 300\({}^{\circ}\)/s peak torque/BW of KNEE, and 60\({}^{\circ}\)/s Agon/Antag ratio of KNEE (_p_! 0.05). Additionally, 45\({}^{\circ}\)/s peak torque/BW of HIP joint showed a significant positive correlation with HRpeak (_p_! 0.05). The characteristics of gait that generally appear in CPs are caused by the limited range of motion of HIP Joint and KNEE Joint, the excessive adduction and internal rotation of HIP, the tilt of front pelvis, the pelvic obliquity, and the persistent plantar flexion at the ankle [34; 50]. Due to these factors, CP gait has the general characteristics of reduced heel strike, reduced gait speed, and reduced stride length, and these gait parameters (stride, gait speed, gait posture, heel strike, etc.) are closely related to the muscle strength, in which gait speed has an especially high correlation with the muscle strength [18]. In general, the muscle weakness and the decrease in gait ability in CP lower the efficiency of gait and require a lot of energy from the body, which affects the decrease in stride length [51]. In addition, it was reported that the high oxygen cost (poor gait economy) of CP comes from muscle co-activation and total body mechanical power [52; 53]. Among all the factors that measured the lower extremity muscle strength in this study, the following factors showed a significant correlation with VO2 peak: 45\({}^{\circ}\)/s peak torque/BW representing the muscle power of HIP, 300\({}^{\circ}\)/s peak torque/BW representing the muscle endurance of HIP, 60\({}^{\circ}\)/s peak torque/BW indicating the muscle power, and 300\({}^{\circ}\)/s peak torque/BW indicating the muscle endurance of KNEE (_p_! 0.05). Additionally, 45\({}^{\circ}\)/s peak torque/BW of HIP showed a significant correlation with HRpeak (_p_! 0.05). This is consistent with the previous studies above which showed that the muscle strength of CP is closely related to gait ability and exercise ability, and it can be considered an important result that can explain the relationship between the lower limb muscle strength of CP and the gait ability and the exercise ability in CP. Eventually, the abnormal muscle development of CP degrades the lower limb muscle strength, which leads to the abnormal gait patterns. Therefore, it can be considered that it adversely affects the aerobic capacity as a result of inefficiently using a large amount of physical energy for gait, resulting in the decrease in aerobic capacity. Additionally, in this study, 60\({}^{\circ}\)/s Agon/Antag ratio of KNEE showed a significant positive correlation with VO2 peak (_p_! 0.05). In a previous study, the EMG pattern was used to observe the muscle movement during CP gait, and as a result, it was reported that the agonist and antagonist muscles around the joint contracted simultaneously [52]. In addition, it was reported to increase in the KNEE extensor and reduce the flexor by introducing CPs into the lower limb muscle strength enhancement program, which eventually resulted in the improved gait ability by increasing the stride, which was due to the improved abnormal balance of KNEE agonist and antagonist muscles [54].