So, let's start by looking at some of the most important areas of the core and how they impact your running:
Lower back: Transverse abdomins, erector spinae
The transverse abdominis, or TVA for short, is a thin cylindrical muscle that lies underneath the abdominals. The TVA is responsible for stabilizing the spinal column and reducing lower back, hip and groin injuries. Simply speaking, a strong and healthy transverse abdominis helps the muscles prepare for movement and brace for impact by stabilizing the muscles. This results in a significant decrease in injury risk.
The erector spinae is a group of back muscles that help you lean forward and back. A forward lean when running places extra stress on the erector spinae muscles in the lower back, which causes them to fatigue and predisposes them to injury. Strengthening these muscles can help prevent excessive leaning at the waist when you get tired at the end of a race or long run.
Abdominals: rectus abdominis
The abs, despite being the most well-known muscle group of the "core," are perhaps the most unimportant when it comes to injury-free running. Sure, toned abs make you look great at the beach, but most research studies have shown that they have little actual impact on running injuries. As such, exercises, like crunches, aimed solely at strengthening the abs are likely a waste of time for runners.
Hips: Adductors, abductors gluteal and iliopsoas
The group of muscles that make up what we call the hips (adductor, abductor, gluteal and iliopsoas) are particularly important because they've been implicated in a range of running injuries. Weak hips can often be the cause of IT band pain, patella tendonitis (runner's knee), piriformis issues, sciatica and a myriad of other common running injuries.
In fact, the research on how close the connection is between hip weaknesses and running injuries is overwhelming.
A study published in the Clinical Journal of Sports Medicine in 2005 found that injured runners had weaker hip flexors and hip abductors on their injured sides compared to their healthy sides. Another more specific study published in 2003 in the Journal of Orthopaedic & Sports Physical Therapy found similar results: Injured runners had weaker hip abductors and hip external rotators on their injured legs.