Runners should not just run. No, this is not some sick April fools day joke either. Start incorporating some strength exercises into your routine. Incorporating strength exercises into your routine will prevent injury and increase performance.

Try this Banded Lateral Toe Tap from Brandon at Lavack Fitness. 

Reason: Correcting Arm Swinging Across the Body

Have you ever noticed that no matter how much you focus on correcting your arms and making them move forward and backward as soon as you stop thinking about it your hands are crossing your body again?

How about if this wasn't due to a "poor form issue" and rather your body's way of trying to help off-set your hips. A lack of control of your hips in both a lateral and transverse plane could easily manifest, and often does, as a crazy arm swing issue.

The Banded Lateral Toe Tap helps to address weakness in lateral and rotational control by gaining some stability back to the outer hips in a single-leg fashion.

Cues:

1) Slight bend of the planted leg.
2) Keep the body as perpendicular to the ground as possible.
3) Shift the weight into the planted leg without moving the upper body.
4) Bring out the non-planted leg as far as possible, gently touching the foot to the floor and bringing it back.

Tips:

1) Go slow with this movement. It's not about speed, but rather control of the movement.
2) If you don't feel it in your outer hips, make sure your set-up is correct, as this movement does a great job activating these muscles.
3) While it's just demonstrated directly out to the side, you can explore different reaching positions and aim diagonally in front or backwards. Changing the stimulus provided isn't a bad idea.