( ( ( Do n't ) ( lock ( ( your ( knees ( , ( ( elbows or ) joints ) ) ) ) ( into position ) ) ) ) . )
(ROOT (S (VP (VB Do) (RB n't) (VP (VB lock) (NP (NP (PRP$ your) (NNS knees) (, ,) (NNS elbows) (CC or) (NNS joints)) (PP (IN into) (NP (NN position)))))) (. .)))
Don't lock your knees, elbows or joints into position.
(ROOT (S (NP (NNS Knees) (CC and) (NNS elbows)) (VP (VBP are) (NP (NP (NNS examples)) (PP (IN of) (NP (NP (DT the) (NNS joints)) (PP (IN of) (NP (DT the) (JJ skeletal) (NN system))))))) (. .)))