( ( ( ( Sarcopenia , ) ( ( the ( age-related loss ) ) ( of muscle ) ) ) , ) ( ( is ( ( a ( key factor ) ) ( of ( the ( central problem ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NNP Sarcopenia)) (, ,) (NP (NP (DT the) (JJ age-related) (NN loss)) (PP (IN of) (NP (NN muscle)))) (, ,)) (VP (VBZ is) (NP (NP (DT a) (JJ key) (NN factor)) (PP (IN of) (NP (DT the) (JJ central) (NN problem))))) (. .)))
Sarcopenia, the age-related loss of muscle, is a key factor of the central problem.
(ROOT (S (NP (NP (NNP Muscle)) (ADJP (RB atrophy) (JJ due) (PP (TO to) (NP (NN age))))) (VP (VBZ is) (VP (VBN called) (NP (NN sarcopenia)))) (. .)))