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A weightlifter performing a curl with a 320 N barbell stops the lifting motion with his forearms
in a horizontal position. (a) If the line of action of the weight of the barbell is 27 cm from the
axis of rotation (elbow joint), what is the magnitude of the moment that the elbow flexors must
exert to maintain that position? (b) If the weight of the weightlifter’s forearms and hands were
taken into account, would the moment that the elbow flexors had to exert be more or less than
that calculated in part (a)? If the biceps were the only elbow flexor muscle active (a rather
unlikely event) and its moment arm about the elbow joint was 4.3 cm, calculate the biceps
muscle force needed to maintain this equilibrium position.

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