Playing the piano requires activation of muscles of the upper limbs, neck and back. to play the keys, the fingers must generate rapid, small movements that vary in force generation to play the keys sometimes very hard (larger amounts of force) and sometimes very soft (very little amounts of force), and everything in between. the elbow flexors hold the elbow joint at the same comfortable angle throughout the duration of play, which can last several hours. additionally, the player must also sit upright at the piano bench for these long durations without the back or neck muscles fatiguing. a. lactic acid is produced because no oxygen is available to the muscle cell. b. lactic acid is made when atp demands exceed oxygen availability in the cell. c. lactic acid is a byproduct of creatine phosphate production. d. lactic acid is made when there is insufficient glucose in an active cell