To measure how much one is improving while running, one can consider wearing a specialized running watch like the Garmin Forerunner 965 which gives detailed data like VO2 Max, running dynamics, cadence, ground contact time, left-to-right balance among others. These can be utilized to gain insight about your running efficiency and measure progress as recovery and fitness rebuilding ensues. Such performance condition metrics also provide a good instant fitness assessment for a person while running at moderate speed for the initial minute or two. The use of these stats over the period of time will reflect the extent of progress one has made in terms of performance.