Human hand achieves complex and various actions with cooperative activities of muscles in the forearm. Muscles' activity measurements are available to evaluate the work efficiency of human hands operations and quantify the degree of disease related in the hands. Surface electromyography (EMG) is a generally used method for the measurement using some electrodes attached on the skin surface. Though, for the forearm muscles, the measurement of the activity of individual muscle is difficult because of the superimposition of the EMG signals from muscles, called "cross-talk problem". Previously we developed a muscle analytical system to estimate the individual muscle activity from the surface EMG distributions detected on the skin of forearm. In this study, we apply the system to analyze the synergetic activities of the forearm muscles during the palmar flexion load applying to the carpal joint. The result shows that both the synergetic muscles and antagonist muscles operated against the palmar flexion load. The individual muscle activity could be identified from the surface EMG measurements analyzed in this system.