I am now 8 weeks on L4. It seems that I gain some muscles (L4D3 times are decreasing), but on L4D1 it seems that I improve only very slowly. Over the weeks I did 20, 23, 22, 24, 25, 27, 24, 28 rounds on L4D1. So I think my endurance does not increase, or only increases very slowly. Any ideas what I could do to improve this? Or am I just impatient?