This study was conducted to determine the activity of the rectus femoris muscle during various daily physical activities and sport games. The subjects were four healthy men and one healthy female. Integrated electromyographs were obtained from an analysis of the results of rectified filtered electromyography performed on the rectus femoris. Integrated electromyographs were recorded for each subject during maximal isometric voluntary contraction in the position of maximal leg extension. The relative muscle activity level during various activities was then calculated. The relative muscle activity during daily physical activities was found to be 5 to 50%. The highest relative muscle activity was reached when standing from a sitting position on the floor. Among resistance training activities using only body weight, the highest relative muscle activity was reached when squatting with one leg. The relative muscle activity level at this time was 70% of the maximal muscle activity. While playing softball, the highest relative muscle activity level was 50% of maximal muscle activity. These results indicate that resistance training may be important in order to set the training intensity, based on the level during the daily physical activity or while playing sports
