( ( Whether ( ( calcium channel ) ( ( ( blockers ( ( decrease force ) ( of ( contraction ( of muscle ) ) ) ) ) or ) decreases ) ) ) ( ( underlying stimulus ) ( ( is unknown ) . ) ) )
(ROOT (S (SBAR (IN Whether) (S (NP (NN calcium) (NN channel)) (VP (VP (VBZ blockers) (NP (NP (NN decrease) (NN force)) (PP (IN of) (NP (NP (NN contraction)) (PP (IN of) (NP (NN muscle))))))) (CC or) (VP (VBZ decreases))))) (NP (JJ underlying) (NN stimulus)) (VP (VBZ is) (ADJP (JJ unknown))) (. .)))
Whether calcium channel blockers decrease force of contraction of muscle or decreases underlying stimulus is unknown.
(ROOT (S (NP (NNS Muscles)) (VP (VBP need) (NP (NN stimulus)) (PP (TO to) (NP (NN contract)))) (. .)))