joint effort wont work !!!!!!

edit

i'm working with nao in gazebo i was wondering that has effort been defined for nao model? because when run this service in terminal or c++ both answer me that it was successful and yet nothing happens. i expect to something happen because i set the shoulder joint's effort to zero and they wont drop. here is some of my code :

 ros::ServiceClient stiffclient = nexus.serviceClient<gazebo_msgs::ApplyJointEffort>("/gazebo/apply_joint_effort");
bool ppp ;
gazebo_msgs::ApplyJointEffort lcartman ;
lcartman.request.joint_name="LShoulderPitch";
lcartman.request.effort=0;
lcartman.request.start_time.fromSec(1);
lcartman.request.duration.fromSec(1000);
ppp=stiffclient.call(lcartman);