Can't get taxonomy to work properly (frontend/admin issues)

Given the following taxonomy and the code required to echo the results:

<?php 

	add_action( 'init', 'create_muscle_taxonomies', 0 );
	function create_muscle_taxonomies()
	{
	  $labels = array(
		'name' => __( 'Muscoli o gruppi muscolari', 'taxonomy general name' ),
		'singular_name' => __( 'Muscolo o gruppo muscolare', 'taxonomy singular name' )
	  ); 

	  register_taxonomy('muscoli', 'post', array(
		'hierarchical' => false,
		'labels' => $labels,
		'show_ui' => true,
		'query_var' => true,
		'rewrite' => array( 'slug' => 'muscoli' ),
	  ));
	}

?>

<?php

	echo '<ul>';

	$terms_of_post = get_the_term_list( $post->ID, 'muscoli', '<li>','<li>', '</li>', '' );
	echo $terms_of_post;

	echo '</ul>';

?>

I can’t make it work properly: either it works on the admin side and doesn’t on the frontend, or viceversa.
If I use this code:

register_taxonomy('muscoli', 'post', array

a new label appears inside the “Posts” menu, but I get no results on the frontend of the site if I try to echo em with the code I’ve pasted above.
On the other hand, if I don’t specify ‘post’ as $object_type, as it follows:

register_taxonomy('muscoli', '', array

I can see the results echoed on the frontend of the site, but obviously the tag disappears from the admin side.

I don’t understand what am I missing, anyone can help me?

Thanks in advance