Effect of Lower Extremity Muscle Strength on Aerobic Capacity in Adults with Cerebral Palsy
Authors: You Jungwan , Choi Seungwook 
Published: April 2022

The purpose of this study is to analyze the effect of lower extremity muscle strength of HIP joint and KNEE joint on the aerobic capacity to provide the basic data for developing an exercise program that can effectively improve the aerobic capacity of adults with cerebral palsy (CP) by identifying the part of the lower extremity muscle. A total of 18 ambulant adults with CP were recruited for this study. Seven ambulant adults with CP were excluded because they did not achieve the criteria of maximal exercise. The data from 11 subjects (11 men) with CP were used for the analysis. The mean (±SD) age, height, weight, and BMI of the subjects were 37.00 ± 12.72 years, 170.45 ± 6.37 cm, 67.02 ± 8.62 kg, and 23.09 ± 2.78 kg/m2, respectively. To measure the muscle strength of HIP joint and KNEE joint in lower extremities, the variables of the isokinetic muscle strength and the muscular endurance were performed using the isokinetic equipment (Biodex Co., Shirley, NY, USA). For the isokinetic muscle strength measurement of HIP joint, the 45°/sprotocol indicating the muscle power and the 300°/s protocol indicating the muscle endurance were used. Additionally, the measurement of KNEE joint was performed once on the left and right side, using the protocol of 60°/s indicating the muscle power and 300°/s indicating the muscular endurance. Progressive exercise tests were conducted on the treadmill (Quinton model—4500) using previously developed protocols targeting CP. The initial protocol speeds were 5 km/h−1 and 2 km/h−1 for the subjects who have been classified as Gross Motor Function Classification System (GMFCS) level I and II, respectively. Using a portable cardiopulmonary indirect breath-by-breath calorimetry system (MetaMax 3B; Cortex Biophysik, Leipzig, Germany), pulmonary ventilation (VE), respiratory exchange ratio (RER), and oxygen uptake (VO2) have been persistently measured. HR monitor (Polar Electro, Kempele, Finland polar Co. RS-800) was used to measure heart rate (HR). A correlation analysis was conducted to find out how the lower extremity muscle strength and aerobic capacity with cerebral palsy are related. Therefore, as a result, VO2peak among aerobic capacity displayed a significant positive correlation in 45° and 300°/s peak torque/BW of HIP joint, and with 60° and 300°/s peak torque/BW of KNEE joint. It was the same with 60°/s Agon/Antag ratio of KNEE Joint (p < 0.05). VEpeak showed a significant positive correlation with 45° and 300°/s peak torque/BW of HIP joint, as well as correlation with 60° and 300°/s peak torque/BW and 60°/s Agon/Antag ratio of KNEE joint (p < 0.05). However, HRpeak showed a significant positive correlation only in 45°/s peak torque/BW of HIP joint (p < 0.05). The result of step-wise analysis was to find out which muscle strength significantly affects VO2peak and HRpeak among aerobic abilities in the lower extremity muscles of those disabled with cerebral palsy. Among the muscle functions of lower extremity muscle strength, 300°/s peak torque/BW of KNEE Joint was found to have the greatest effect on VO2peak (p < 0.001). As a result, 300°/s peak torque/BW of KNEE Joint was found to be the predictable factor that could explain the VO2peak in the disabled people with cerebral palsy at 67% (R2 = 0.661). In particular, among the muscle functions of lower extremity muscle strength at 45°/s peak, torque/BW of HIP Joint was found to have the greatest effect on HRpeak (p < 0.001). As a result, this factor was found to be the predictable factor that could explain the HRpeak in disabled people with cerebral palsy at 39% (R2 = 0.392). In this study, the muscle strength of the lower extremity of CP was closely related to the aerobic capacity, and the muscle endurance of KNEE Joint and the muscle power of HIP Joint were found to be important factors to predict the aerobic capacity of CP.