Muscle sections are stained with ATPase to differentiate between types of fibres and to display the ckecerboard pattern. But it is done at two different pH. The staining is reversed at acidic/basic pH.
To quote this site
Acid preincubations inhibit the myosin ATPase activity in fast (mammalian type 2A, 2X, and 2B) fiber types, but not slow (mammalian type 1, see Figure 1A). Conversely, basic preincubations inhibit myosin ATPase in slow fiber types only (Figure 1B).
Why is this so? Isn't the ATPase same in both the fibres?