( ( ( ( Make ( two fists ) ) , ) ( ( tighten ( the muscles ) ) ( in ( your fingers ) ) ) ) . )
(ROOT (S (VP (VP (VB Make) (NP (CD two) (NNS fists))) (, ,) (VP (VB tighten) (NP (DT the) (NNS muscles)) (PP (IN in) (NP (PRP$ your) (NNS fingers))))) (. .)))
Make two fists, tighten the muscles in your fingers.
(ROOT (S (NP (JJ Intrinsic) (NNS muscles)) (VP (VBP allow) (NP (PRP$ your) (NNS fingers)) (S (VP (TO to) (VP (ADVP (RB also)) (VB make) (NP (NP (JJ precise) (NNS movements)) (PP (IN for) (NP (NNS actions)))))))) (. .)))