Veilstone.
you get hm strength and hm defog after defeating two gym leader.Fantina(defog) Byron(strength).
If you have beaten Mauville Gym and have gotten HM ROCK SMASH, go to RUSTURF TUNNEL and clear out the rocks. The digger will grant you HM STRENGTH.
u get to use certain HM's once u beat the gym leaders
In Pokémon FireRed, for defeating Brock, his Badge will allow you the use of the Flash HM, Misty's Badge will allow you to use the Cut HM, Lt. Surge's Badge will allow you the use of the Fly HM, Erika's Badge will allow you the use of the Strength HM and Koga's Badge will allow you the use of the Surf HM.
The Gym Leader that allows you to use the HM move Strength in Pokemon FireRed is Erika. Erika is the Gym Leader of Celadon City and is the 4th Gym Leader the player faces.
Veilstone.
you get hm strength and hm defog after defeating two gym leader.Fantina(defog) Byron(strength).
i am pretty sure it's strength.
beat the forth gym leader
In Pokemon Liquid Crystal, you can obtain HM Strength by defeating the Sootopolitan Gym Leader. After defeating the Gym Leader, he will give you the HM as a reward for your victory.
by wining a certain gym battle
6th gym on platinum
The HM strength
You can get the HM Strength after you beat the 7th Gym Leader, Byron. He will give you the HM immediately after defeating him.
To get Strength, you have to go to the Lost Tower nearby Solaceon Town. At the top floor, one of the ladies there wil give you the HM for Strength. However, you must have defeated Byron, the Gym Leader of Canavalve City, to use the HM for Strength.
If you have beaten Mauville Gym and have gotten HM ROCK SMASH, go to RUSTURF TUNNEL and clear out the rocks. The digger will grant you HM STRENGTH.