To improve in your running and to get faster you have to repeatedly threaten the bodies survival instincts with training stimuli so that your body adapts and is able to physiologically overcompensate. So that when the same stress is encountered again you do not suffer the same degree of physiological stress again and your body is able to handle the threat
Obviously though, it is a question of balance. Not enough stress and there will be little improvement, too much and the body will breakdown.
Sitting here typing this post with an ice pack strapped to a swollen right knee would suggest that in my efforts to get back as quickly as possible, I have been heading for the latter. So it will be a case of backing off a little over the next couple of days.
Last night was a track session of 4 x 1000m with 2 min jog recovery at Chester -le- Street. The conditions were good despite the usual stiff breeze down the home straight. Unfortunately, my knees, particularly the right one, became increasingly painful. So decided to opt for the cautious approach and ended the session after the third rep.
For the record the times were 3.30; 3.31; 3.37
Every cloud has a silver lining though. When looking back at the session of 3 x 1000m I did on 4th May with 2min 30sec recovery the times were 3.37; 3.41; 3.42. So there is some improvement at least. I will just have to be patient and keep the progress slow but steady, I guess.