L hand too stretched and tense in octaves section in Chopin's Polonaise Op. 53

[kujiraya]

I can play everything else in Chopin's Polonaise Op. 53 but it seems like I just can't stretch and relax my left hand sufficiently to play the repeated octaves section without creating extreme tightness and tension. My hands have a small stretch in any case. Is there some technique or exercise I can use to increase my left hand's stretch while avoiding tension, so that I can play those L hand octaves lightly, rather than what sounds like sumo wrestlers' heavy stomping at the moment?

[faulty_damper]

Try squeezing the 1 and 5 together to depress the keys.  This, as opposed to only locking the hand and hammering away.

[kujiraya]

Thanks! That advice is helping. I am now concentrating on keeping the L hand relaxed, not locked. A lot more wrist movement and a smooth circular shoulder movement also helps. I am keeping the tempo extremely slow to avoid any build-up of tension, and hopefully building up more stamina in the L arm, L forearm and L hand's stretch muscles. I have found that practising repeated legato broken octaves up and down the E major scale for a couple of octaves with my L hand helps (1-5-(stretch)-1-5-(stretch)-1-5...going up, and 5-1-(stretch)-5-1-(stretch)-5-1...going down), especially between E-F# and B-C#. But, at least I am making some small progress.