The arms are at least 50% of running yet most triathletes let them do as they wish without conscious effort in using them to refine form. These are not my original ideas, rather my assimilation of many sessions with Bobby McGee, possibly the greatest running coach alive, and one of the smartest people I’ve been aquainted with.
There is a kinetic chain of motion that connects your upper and lower body. Right arm connected to left leg and left arm connected to right leg. What one limb does mirrors & synergistically affects the other. Shoulder and hip are connected, elbow and knee are connected, wrist and ankle are connected.
Arms swing naturally from the shoulder joints which should be loose and relaxed and respond naturally to the movement and motion of the alternate hip.
The arms are a pendulum and the total length of that pendulum should be limtied to the distance between your shoulder and the tip of your elbow. In other words, your elbows shoudl be bent at an angle that stays closed while running. Opening up the elbow angle at the rear part of the movement results in an opening up of hte knee at the front of the swing phase and results in over-striding.
Arm drills to try while running include foldign the arms across the chest to keep the arms still while letting the shoulders respond naturally to the running movement. The let your arms follow the natural movement of the shoulders in a relaxed way while keeping the elbow angle closed, rather than “pumping” the arms as some people may teach.
A second drill is to run with 1 lb weights in your hands. Begin jogging and then do 20 foot strikes as a pickup. Your natural inclination will be to hold the elbow angle fairly closed so that the weights do not swing out more than needed causing you to use more energy carrying the weights than necessary. this teaches you how to keep the elbow angle closed, which helps prvent overstriding.
If you have trouble with supination or pronation of your feet, pay attention to what your wrists are doing while you run. if you run habitually wiht your palms/wrists facing down, you may be overpronating. try turning your wrists to a neutral position (palms facing each other) and see if that helps correct some of the pronation movement. If you run with your palms/wrists facing the sky, you may be supinating more than necessary. Again, correct the wrists and see what happens with yoru feet.
Getting your leg forward under your body to “catch your next fall” requires a quick forward knee action without overstriding. Try focusing on the rearward elbow of the opposite arm to help develop a quick forward swing of the leg. Remember to keep that elbow angle closed (pretend you’re holding a weight and you dont want it to swing behind you) and this will help prevent your opposite lower leg form opening forward resulting in overstriding and exaggerated heel strikign. (heel striking is still OK, but not if you land with your foot in front of you).