An inefficient stride.
Here is an example of inefficient running mechanics. The person was running in an upright position for maintaining speed. The path of the foot is shown here. Since each movement of the foot and leg depends on the previous movement or position. Let’s pick a starting point and analyze what might be happening through the stride.
Starting at ground contact, the runner landed on his heel and the foot did not move backward before striking the ground. The heel landed in front of the body. This shows that the glutes were passive before ground contact and will probably never be able to be engaged at any point during the stride. The leg just reached forward and let the foot contact the ground in front of the body absorbing all of the force. This is braking and is a forward force that pushes the body backward. The runner is probably using the quadriceps to support his body and push on the ground rather than pulling on the ground with the glutes.
At the end of ground contact after the foot left the ground, the path of the foot stayed low. This shows that the hamstrings were probably passive and the leg didn’t shorten by bending. The long leg is slower and will not be able to move forward fast enough to be able to activate the glutes before ground contact.
What went wrong first and what should be corrected first: the passive trail leg or the passive lead leg? Making a correction after the above sequence is established can be difficult. It is easier to establish the proper sequence from the start which means having an aggressive start. A passive start that eases into the maintenance speed could establish the passive cycle. An aggressive start including pulling the foot with the glutes before ground contact does not use that much energy, accelerates the body to the desired speed quickly, and establishes an efficient sequence of movements. Including scissoring with this start will make the trail leg hip flexor active, the knees can come together, and the foot can contact the ground under the body.