Lactic build up?

[Quake]

This might be the wrong forum, but, the last couple of days when I've been working out I've been getting an intense burning in one of the muscles involved in the exercise e.g, doing bent over rows I got burning in my forearms. The muscle becomes solid, almost swollen in appearance, and whilst performing reps starts to burn like hell this leads to an inability to perform anymore reps. I am currently in the 3rd week of my cycle and remember experiencing this in other cycles, only not as pronounced as this time. I don't experience this when not on a cycle, only normal failure i.e. muscle fatigue. Anyone know what's going on?

[nsa]

It's called a pump. Its your muscles becoming engorged with blood, like an erection but for the muscles your working out.

[Quake]

It's a different kind of pump to the ones I am used to. It happened fairly quickly and with only light weights, it spoiled my session as I was unable to train hard and heavy due to the refusal of the muscle to move. It wasn't fatigued as I had only done a few sets. What is causing the burning though? Is it lactic acid?

[nsa]

It's the steroid pump...

[Quake]

Hapenned again today whilst training biceps, only this time it's onset was immediately from the first rep of the first set. It seems to be concentrated in my forearms and lower biceps around the "nook" of the elbow. I don't think it's a pump, but a quick build up of some biological fluid. I read somewhere that receptors for lactic acid are inhibited during cycles, which is why my first post asks about lactic acid. Does anyone know a little more. I am experienced enough to know this is not a biological pump as described by nsa, but am not experienced enough in taking gear to have come across these effects so pronounced before. Anyone experience this too or can give me the biological breakdown of what is hapenning?