( ( when ( ( the triceps ) contracts ) ) ( , ( ( the arm ) ( extends . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB when)) (S (NP (DT the) (NNS triceps)) (VP (VBZ contracts)))) (, ,) (NP (DT the) (NN arm)) (VP (VBZ extends)) (. .)))
when the triceps contracts, the arm extends.
(ROOT (S (NP (DT The) (NNS triceps)) (VP (VBP help) (S (NP (DT the) (NN body)) (VP (VB extend) (NP (DT the) (NN arm))))) (. .)))