iv. Results

Results will be displayed in both table and graphical presentation.

vi. Discussioni

The result follows the theory regarding the angle and the idea of biomechanical lever system in human motion. Movement of our arm is based on the third class lever where the effort (or the force generated) is located between the fulcrum and the load. Think of a forceps to exemplify such lever.

Figure 1 Measurement of Forearm Length

The figure above shows the approximate length of the lever in this experiment. Medial epicondyle is approximated to be the location of the fulcrum; elbow joint or articulation cubiti while the middle of the palm is approximated to be the point where the weight of the load will act on. The point of effort is the radial tuberosity located at the radius bone.

Figure 2 Diagram of the lever

i ? Barrett KE, Barman SM, Boitano S, Brooks HL. Ganong’s review of medical physiology. 23rd ed. New York: Mc Graw Hill Companies, Inc.; 2009

Note the actual direction of force. Contraction of biceps brachii muscle will produce a force in that direction hence the actual force needed is always larger than is needed. In this experiment, we estimate the distance of effort from the fulcrum to be 2.54 cm in fully extended arm. Using below figures, we can see as the angle of flexion increases, the distance of the load and the effort to the fulcrum will decrease. As the load becomes perpendicular to the joint; at 90° angle, there will be no more moment produced and hence there is no rotational force produced at this angle. It is the position where the arm is at mechanical advantage but it is the position where the arm has the lowest length-tension advantage since the muscles at this angle is already at its limit of shortening. Similarly, at angle 0°, muscle is at the length-tension advantage since it is in this position that muscle is already at its maximum length. However, at this angle, if we were to follow the trend, should have the lowest resistance to load as it has the least mechanical advantage because of the maximum distance of load to fulcrum and will produce the greatest moment of the force. It is concluded that the mechanical advantage overrides any length-tension advantage in the contraction of biceps brachii muscleii.

The possible explanation of the decrease in resistance after 90° flexion is because of the occurrence of moment of the force while at 90°, the force present is only compressive force which acts on the bone (radius and ulna).

ii Marieb EN, Hoehn K. Human anatomy & physiology. 7th ed. New Jersey: Benjamin Cummings; 2007. p. 230-260