Instant soreness vs onset soreness

Hardly happening with upper body, more so with lower body.

When I have some serious leg training I can barely walk for the rest of the day and the -muscular ache- starts during the workout.

Which is different from what I get sometimes, more often with my upper body but happens to legs too…but rarely. No -muscular ache- during the working day but incredible soreness the day after and the day after that.