Below are a few links to animations that explain the process of muscle contraction.
http://highered.mheducation.com/sites/0072495855/student_view0/chapter10/animation__breakdown_of_atp_and_cross-bridge_movement_during_muscle_contraction.html
http://wn.com/muscular_contraction
http://highered.mheducation.com/sites/0072495855/student_view0/chapter10/animation__myofilament_contraction.html
http://highered.mheducation.com/sites/0072495855/student_view0/chapter10/animation__breakdown_of_atp_and_cross-bridge_movement_during_muscle_contraction.html
http://wn.com/muscular_contraction
http://highered.mheducation.com/sites/0072495855/student_view0/chapter10/animation__myofilament_contraction.html