Ask them what their sources are showing that parkour is dangerous. A doctor should understand the neccesity of evidence to make an argument ask him if he has searched pubmed for injury rates in parkour or similar sports. Has he surveyed traceurs on their injury rates, failing that what has he studied that indicates parkour is especially dangerous. Can he break down the physics of impact on concrete for an average mass traceur taking an average impact does have any idea what the average traceurs weighs, how strong he is, what the length, and height of an average traceurs techniques is?
You can not make a statistically valid argument for how dangerous parkour is right now because nobody has actually studied it enough to know.
I can offer you three logical arguments as to why parkour is less dangerous then most sports.
If you comb the data how injuries occur in sport you will see three broad patterns.
1. Player interaction, people get hurt when the get hit by other people. This does not happen in parkour, no slide tackles, no stiff arms, no face masks, no punches, kicks, throws etc.
2. Accelerators, a human body is not structural strong enough or neurological quickness to deal with falls in excess of 25 miles per hour very effectively, so falls while snowboarding, mt. biking, skateboarding, skiing, motorbiking, trampolines etc have far far higher injury rates and worse complications then falls while running or jumping as in track and field. Parkour has only one major potential accelerator gravity if you do stuff at height and mess up you will face major consequences, often the argument as to how dangerous parkour is comes down to the assumption most people make that we practice primarily at height.
3. Plant and twist sports, sports that regularly require you to plant on one foot and twist quickly to change direction are very hard on the knee and ankle so that a sport like soccer which seems relatively benign ends up having high incidence of injuries to to injuries to the ligaments of the knee and ankle from badly performed plant and twists. Again in parkour this is not a major issue as planting and twisting to change direction at speed unexpectedly is not a regular aspect of our practice.
Here is a non rigorous stastical argument as well, at Parkour Visions we have taught over a thousand athletes, in our classes have only had one major injury, Primal Fitness, Apex Movement, and the Monkey vault all have similar records.
Parkour when practiced intelligent is probably less dangerous then most sports.
