Problem Statement: an important goal of of our study is to make the fitness instructor aware of the importance of correct posturing and movements during the workout aiming to prevent muscular and joint injuries. Purpose of Study: Our study on 80 fitness instructors performend in 2017 aimed to identify the fitness movement mistakes. Methods: The instructor had to indentify the errors in each figure and to write the number of errors. The research applied a worksheets containing 50 fitness initial positions and movements which include the most frequent errors in execution: basic aerobic, step aerobic, TRX, fitball.Before applying the test, we explained and showed the instructors the way to solve it. They were supposed to mark with arrows the errors zones of movements and they had to calculate the number of errors in each figure.After that we compared their results with our evaluation and we ranked them into one of the 5 cathegories: unsatisfactory (>125 errors), poor (126-150 errors), medium (151-175 errors), good (176-200 errors), very good (over 201 errors). Results of study: mean±SD 57.8±30.93; minumum 78, maximum 212, Shapiro-Wilk normality test 0.9730 for p ≤ 0.05; coefficient of variation 19.60%;t=45.63 (df=79), pvalue< 0.0001.Conclusions: The study highlights a medium level knowleadge of correct posture and of the intructors’ capacity to identify and correct the movement errors. The instructors have identified the folowing causes for this insufficent correcting of the posture and movements: the dimension of group, sometime more then 30; the unhomogenouse of group in regard of fitness level, age, and motor skills.