Apart from gait retraining, one of the most compelling aspects of using the new TgForce3D sensor is to compare the level of impact (PPA, Peak positive acceleration) sustained by the lower leg when running on various surfaces. Since the sensor is directly attached to the body, it is possible to obtain the actual peak positive acceleration of the leg when hitting the running surface.

For this blog post, we are comparing the impact felt at the tibia for an occasional 18 years old runner when running on a treadmill (Healthrider 500sel) and when running outside on pavement (asphalt). The treadmill includes a fairly standard ‘cushioning system’ to reduce impact. The objective was to demonstrate how significant the difference in impact can be between two running surfaces.

Treadmill running:

  • The treadmill was set at 10km/h
  • The runner is wearing ‘Trainer’ shoes with limited cushioning (Adidas Cloudfoam super flex shoes).
  • TgForce 3D sensor on the lower left leg (tibia).
  • Running at a low cadence of 155-160.
  • Impact data was transmitted live on an iPad and was also recorded in the sensor memory.
  • In the video, the TgForce App on the iPad displays the 3D resultant acceleration vector.

Asphalt pavement running:

  • For the pavement running, our runner is using the same ‘trainer’ shoes, and the running speed is roughly the same at 10km/h.
  • Cadence at around 160-165 in the same range as the treadmill running.
  • To effectively display the impact results, the camera and the iPhone were mounted on a bicycle which is following the runner.
  • Typically, the runner can use the audio feedback to get real-time updates. The sensor is also recording all steps for evaluation after the running session.

In the video, we can see the cushioning effect of the treadmill. For our runner, the average 3D impact recorded on the treadmill was 5.3g (5.1g at the end of the running session). On the asphalt pavement, the average impact was significantly higher at 12.6g (3D)

For this particular runner, a significant portion of the increase came from the Z-axis (from 4.2g to 10.0g), while the X-axis (frontal plane) acceleration increased almost threefold from 2.2g average to 6.3g.

As demonstrated by the accompanying charts, the TgForce App let you review all axis of acceleration.

The safe level of impact is a subject of debate, but the TgForce sensor helps in removing the guessing when it comes time to evaluate potential training options. In any case, the consensus is usually to proceed gradually with any transition.

In a future blog post, I will evaluate impact when running with a different type of shoes and on other types of surface (grass, trail, athletic tracks).

Data recorded for the treadmill session on the iPad mini

Treadmill, 3D, 5.1g

Treadmill, X, 2.2g

Treadmill, Y, 1.8g

Treadmill, Z, 4.2g

Data recorded for the pavement running session on the iPhone SE

Pavement, 3D, 12.6g

Pavement, X, 6.3g

Pavement, Y, 4.1g

Pavement, Z, 10.0g