Hit count using Vibration sensor data

Hi, I am stuck at one of the parts of my Project.I want to count the number of punches to a punching bag.I am using the vibration sensor and using its results to deduce the number of hits.when the punches are thrown with a significant time gap its easy to count them by simply setting a threshold to the vibration sensor values.But when the punches are thrown at rapid fire,the shock waves make it difficult to differentiate between the shock waves or new hits because of the interference between them.Attached are some of the results.Can anyone help me deducing the right algorithm for the hit detection.Since i have to display the hit count on screen live ,all of it has to be done in real-time.I plotted the results on Matlab which are attached as follows.