I think of it this way. In a 'normal' bullish or bearish phase, a certain amount of volume should result in a certain price excursion. If not, then the market may be primed for reversal of trend.
Moderate buying volume with moderate upwards movement is 'normal' bullish. Often seen mid way through a mark up phase. Same for downwards movement.
Extreme buying volume with moderate or low upwards price movement is bearish. Reason: the bears are pushing back hard, preventing 'normal' price excursion, showing their commitment. Vice versa if the price is moving down. It may be about to reverse.
Low buying volume with extreme upwards price movement is potentially bullish. It indicates bears are running away, pulling their offers. Vice versa for downwards ease of movement.
