Analysis of Surface EMG Signals in Isometric Contraction at Different Angles Using Rainflow Counting Algorithms

Endurance and muscle strengthening are required in a number of applications including fitness training, sports and prosthetics. Optimal performance can be achieved by understanding the relationship between muscle activity and angular variation of the elbow joint. Biceps brachii is an important muscle of the upper arm that helps in providing stability during flexion and extension. In this work, an attempt is made to analyze isometric contraction at various elbow angles using surface electromyography and rainflow counting algorithm. The signals are recorded from biceps brachii muscles of twenty healthy subjects while performing well defined protocol using a 6kg dumbbell at three different angles: 30°, 60° and 90°. The recorded signals are preprocessed and subjected to rainflow counting algorithm to obtain rainflow cycles. A new feature, cycle crossing intensity (CCI) is calculated from the rainflow cycles. The intensity peak parameter is computed from each CCI. The results show that the CCIs are distinct for all the three angles of elbow flexion and shifts towards higher magnitude values with increase in the angle of flexion. The average peak intensity is 425, 1073 and 2336 for 30°, 60° and 90° respectively. This feature is found to have high statistical significance for 30°-90° flexion and 60°-90° elbow flexion. The results shows that this method is useful in understanding muscle contractions at various angles of elbow joint. This technique can be extended to analyze muscles in neuromuscular conditions such as fatigue.