So how can you tell when a runner is using correct running form or incorrect running form? A lot of this depends on how the runner is using his or her arm motion and also how the runner uses his or her legs in terms of foot placement, stride length. Those are key areas of what you look for in terms of whether a runner is using correct running form. Many runners that I have trained when we first start out training I do an observation of the running forms and what I would have them do is run around the track for a few laps and I take notes in terms of how they use their arms. Some runners I have noticed use their arms from side to side like this or they hunch their shoulders up in a very stiff way moving from side to side and also in terms of the foot placement. Some runners I have noticed run with their feet to the side like this which is incorrect running form. So what I do is make suggestions to them in terms of how to properly use their arms, how to properly use their foot placement and what this does is over time they learn to become more efficient runners. So with this demonstration you saw that my arms were going along side to side like this and at a pretty good stride length and straight foot placement. Unfortunately some runners are swinging their arms from side to side, their feet come out to the side but if you want to be an efficient runner it is important that you have a really really good arm swing, elbow adjacent to your waist and move forward. Now it takes time to adapt to this new form of running and so you may not get it the first time or the second time but with continued practicing and the help of an experienced trainer you will in time be able to make those corrections with your running form.