Here's a setup to play with including some tests to check whether a sproc will be fired or not.
USE tempdb
GO
if object_id('temp','U') is not null drop table temp
CREATE TABLE temp( idCourse INT, Libelle VARCHAR(300))
GO
CREATE TRIGGER compare
ON temp
INSTEAD OF UPDATE
AS
BEGIN
-- check if there is one single row where the value of column Libelle has changed
IF EXISTS
(
SELECT 1
FROM DELETED d
INNER JOIN INSERTED i ON i.idCourse = d.idCourse
WHERE i.Libelle <> d.Libelle
)
BEGIN
PRINT 'FIRE STORE PROCEDURE'
END
ELSE
BEGIN
PRINT 'NOT FIRE STORED PROCEDURE'
END
END
GO
INSERT INTO temp
SELECT 1,'1' UNION ALL
SELECT 2,'2'
UPDATE temp
SET Libelle = Libelle+1
UPDATE temp
SET Libelle = Libelle+1
WHERE idCourse = 2
UPDATE temp
SET Libelle = Libelle
WHERE idCourse = 2
UPDATE temp
SET Libelle = Libelle+1
WHERE idCourse = 3