4 Ways To Share

Chapter 7: Your Activity

In this chapter:

  • Modify your form
  • Modify your activity

Friction is a very necessary force that helps you move with speed and efficiency. And the bones within your feet must move back and forth with every step and in all directions as part of normal function. As such, soft tissue shear within the feet is a normal and unavoidable consequence of movement.

“The foot approaches the ground at a tangential angle (not a purely vertical angle) and then pushes off in a similar tangential direction. The foot [bones] must skid to a stop and then push into the ground to propel forward. The skidding will occur in both an anterior-posterior and medial-lateral direction, depending on the activity and demands of the sport.”⁸⁸

Most blister prevention studies focus on the friction component of this equation. And quite rightly because there is a huge potential for reducing friction alone to prevent blisters. However, you can also expect some sort of blister prevention by minimising bone movement relative to the skin surface. 


MODIFY YOUR FORM

Figure 39:Blisters under heels (image credit)

Figure 39:Blisters under heels (image credit)

Changing the way you walk and run (commonly referred to as form) can reduce the magnitude of shear distortions per step. Here's an example:

The underside of the heel is not a common blister site. Hikers covering steep downhill terrain are most susceptible to these debilitating blisters. You hit the ground with your heel. The heel bone slides forward relative to the planted foot, which causes a lot of shear to the tissues under the heel bone. Compared to walking over a flat surface, there is a delay in the forefoot contacting the ground – so shear under the heel bone is prolonged. Not to mention the higher magnitude of shear; the braking forces are much higher due to the slope and forward/downhill momentum of your body weight.

Changing your form to a foot-flat strike, or even if you remain heel striking but your heel strikes closer to you, you can minimise these shear distortions. You’ll achieve this by taking smaller steps and/or by bending your hip and knee more. If this change in your form is enough to bring the shear distortions under your blister threshold, you’ll avoid these blisters. 


MODIFY YOUR ACTIVITY

Figure 40: Tennis players, netballers and other court sport players sustain a lot of this side-to-side shear (VIDEO) http://youtu.be/iuOPul7My4s 

Watch this video on the right. And imagine the bones as they roll over the skin when the foot is planted. This creates the shear that can become blister-causing. The longer you do this drill and the higher intensity you perform at, the more likely this will become blister-causing for you.

Tennis is a sport where blisters are very common and the shear distortions result from aggressive side-to-side movements, particularly under the ball of the foot and on the toes. Netball is another. Features of these court sports are sudden accelerations, decelerations and changes in direction. This video barely does these sports justice but you can image the magnitude of these side-to-side shear distortions when playing competitively!

If you’re just playing socially, you could ease up a bit, or sub off. If you’re a runner, you could not push yourself as hard (forget about your times) or cut back on your distance. And for the example of our downhill hiker, taking a different route to minimise the slope could be an option. These modifications revolve around:

  • Reducing the intensity
  • Reducing the duration
  • Reducing the frequency

These options are usually impractical – neither possible nor desired! Hopefully you've found a successful blister prevention strategy before you get to this. 

SUMMARY

  1. Aspects of form and technique may contribute to blister-causing shear.
  2. The duration, intensity and frequency of an activity can be altered to prevent blisters.
  3. Alterations to form and activity are often impractical and undesirable.