The main aim of the present study was to analyze the effects of high intensity circuit training on isokinetic strength and body composition in untrained subjects. A quasi experimental design with pre and post test using an isokinetic dynamometer and a densitometer to perform the measurement was carried out. A total of 39 participants were divided according to the level of physical activity, body composition and sex into three training groups (TG) and one control group (CG), training with a frequency of 1, 2 or 3 days a week for 8 weeks. Regarding the isokinetic strength, although the TG1, TG2 and TG3 subjects achieved significant improvements (p ≤ 0,05) in all the variables analyzed in extension and knee flexion, no significant differences were found when comparing among training groups. Regarding body composition, results were only found tending to the significance in TG1 in muscle mass variable with a value of p= 0,06. In relation to CG, no statistically significant differences were observed in any of the variables undergone measurement. The proposed high intensity circuit training achieves an improvement in isokinetic strength in the knee joint by training one day, two days and three days a week and certain increases in muscle mass in untrained subjects.The main aim of the present study was to analyze the effects of high intensity circuit training on isokinetic strength and body composition in untrained subjects. A quasi experimental design with pre and post test using an isokinetic dynamometer and a densitometer to perform the measurement was carried out. A total of 39 participants were divided according to the level of physical activity, body composition and sex into three training groups (TG) and one control group (CG), training with a frequency of 1, 2 or 3 days a week for 8 weeks. Regarding the isokinetic strength, although the TG1, TG2 and TG3 subjects achieved significant improvements (p ≤ 0,05) in all the variables analyzed in extension and knee flexion, no significant differences were found when comparing among training groups. Regarding body composition, results were only found tending to the significance in TG1 in muscle mass variable with a value of p= 0,06. In relation to CG, no statistically significant differences were observed in any of the variables undergone measurement. The proposed high intensity circuit training achieves an improvement in isokinetic strength in the knee joint by training one day, two days and three days a week and certain increases in muscle mass in untrained subjects.