The importance of Impact training using Ground Reaction Force (GRF)

When our foot strikes the ground forces as in walking, hopping and running forces are transferred up through the bones of our feet, legs and hips like a vibration and this may help to stimulate the remodelling of the bone to the lower parts of our body as our feet hit the ground with force. 

Impact exercise can be graded as 

low (as in walking)  
moderate (as in heel drops)
high (as in   jumping)

Evidence has shown that although walking and swimming has perhaps only a small impact on bone improvement any type of appropriate movement activity is important. A word of caution though, if you have had fragility fractures it is best to avoid medium to high impact exercise such as jumping, hopping and running and instead try heel drops, marching and step ups.

Here is a chart depicting ground reaction forces with graded movements and activities. 

Ground Reaction Forces relative to body weight showing different moves and activities

Lunge	1.1 x
Walking	1.2 x
Marching	1.5 x
Jogging	2.6 x
Step up (12”)	2.7 x
Heel drops (pumps)	3.6 x
Jump Squat	3.8 x
Foot Stomp	4.6 x
Vertical jump	4.7 x

You can do 5 sets of 10 reps = 50 spread throughout your session

Aim to work between 2 and 4 of the above ground forces

We want to stimulate bone remodelling through impact exercise.

For those with spinal fractures, please confine to low impact exercise i.e. walking as medium to high impact is not recommended.

(I have extracted this information from an Australian Pilates training website Pilates HQ which is physio led).