Barre vs. haltère
While both words relate to weightlifting, there is a distinct difference in size and usage. In modern French, barre is the specific term for a long barbell used with two hands, whereas haltère primarily refers to a dumbbell (hand-held weight), though it is historically the generic term for lifted weights.
Barre
A2This is the direct translation of "barbell". It refers to the long metal bar (usually 1.2 to 2.2 meters) that you load with plates (disques) and lift with both hands. In a gym, if you want to use the squat rack or bench press, you are looking for a barre.
Tu dois charger la barre avant de commencer ton srie.
(You must load the barbell before starting your set.)
La barre olympique pèse exactement vingt kilogrammes.
(The Olympic barbell weighs exactly twenty kilograms.)
Il a lâché la barre car c'était trop lourd.
(He dropped the barbell because it was too heavy.)
Utilise les colliers pour sécuriser les poids sur la barre.
(Use clamps to secure the weights on the barbell.)
Le soulevé de terre se fait avec une barre standard.
(The deadlift is done with a standard barbell.)
Haltère
B1While this word technically means a weight consisting of two disks attached to a bar, in modern everyday French, haltère almost exclusively means "dumbbell" (the short bar held in one hand). While the sport of weightlifting is called haltérophilie, referring to a long barbell as an haltère (singular) is very uncommon and sounds unnatural; it is best used for hand-held weights.
Prends un haltère dans chaque main pour cet exercice.
(Take a dumbbell in each hand for this exercise.)
Les haltères de dix kilos sont déjà pris.
(The ten-kilo dumbbells are already taken.)
Je préfère utiliser des haltères plutôt qu'une machine.
(I prefer using dumbbells rather than a machine.)
Il a acheté un kit d'haltères réglables pour la maison.
(He bought a set of adjustable dumbbells for the house.)
Posez vos haltères doucement sur le sol.
(Place your dumbbells gently on the floor.)
Summary
To sound natural in French, use barre when referring to the long two-handed equipment (barbell) and haltère when referring to the short one-handed equipment (dumbbell).