That stabbing pain in your back may not be a dagger after all. If you are a new runner who does not have a history of cross training, you may be predisposed to certain types of injuries because of a lack of strength in your dead ass. Running will help strengthen this area over time, but until that time comes, you may be needlessly suffering. There is a better way. Work your glutes.
The gluteus medius and gluteus minimus are are a couple of major players in running stability. They are the muscles that help abduct the thigh when the limb is extended and are principally called into action in supporting the body on one limb, like when you’re running. When these muscle are weak, it stresses the pelvic hip complex, and the pelvis and hips move around in directions that are not optimal to good running form. That poor running form in turn travels all the way down the kinetic chain and can lead to injuries like sciatica, inflamed hip, IT band syndrome, problems with the knee, Achilles tendinitis and plantar fasciitis. If you are suffering one of these lower leg injuries, and trying self diagnoses, you will want to start at the source and work your way down the chain. That source is the pelvic hip complex and the functionality of the glutes.
Do you have a weakness in these muscles? A simple test is to stand straight, hands on the kitchen counter, lift your right leg, from the knee to the rear. Did your right hip just drop, or did your hips stay square? Hip drop says you’ve got weakness. Next abduct your left leg, (raise it to the side) 10 times. Does your right hip, the stability side start to become sore or tired? You probably have a little weakness.
The exercise in the photo above is a good starting point to strengthen the minimus and medius. In my opinion the ultimate exercise to strengthen this group is a one leg squat. You will find many other exercises on the web by searching glute medius exercises, do them after you run you don’t want to go out for 5k with a tired ass. Starting at the source and strengthening those 2 glute muscles may help cure a whole plethora of leg issues, as well as wake your dead butt up.