( ( Contracting ( skeletal muscle ) ) ( ( ( ( is not ) ( the ( only contributor ) ) ) ( to ( ( the rise ) ( in ( ( arterial lactate ) ( during exercise ) ) ) ) ) ) . ) )
(ROOT (S (NP (VBG Contracting) (JJ skeletal) (NN muscle)) (VP (VBZ is) (RB not) (NP (DT the) (JJ only) (NN contributor)) (PP (TO to) (NP (NP (DT the) (NN rise)) (PP (IN in) (NP (NP (JJ arterial) (NN lactate)) (PP (IN during) (NP (NN exercise)))))))) (. .)))
Contracting skeletal muscle is not the only contributor to the rise in arterial lactate during exercise.
(ROOT (S (NP (JJ Skeletal) (NNS muscles)) (VP (MD must) (VP (VB work) (PP (IN in) (NP (NNS pairs))) (S (VP (TO to) (VP (VB move) (NP (NNS bones)) (ADVP (RB back) (CC and) (RB forth)) (PP (IN at) (NP (NP (DT a) (NN joint)) (SBAR (IN because) (S (NP (PRP they)) (VP (MD can) (ADVP (RB only)) (VP (VB contract)))))))))))) (. .)))