Wednesday, July 8, 2015

Study Spotlight: Muscle Activity While Running at Reduced Body Weight

The amount of impacts that occur when running is astounding when you break it down.  A runner can easily achieve 3600 impacts during a 5km run.  The amount of force each contact creates is also substantial depending on the size of the runner.  Distance runners are always looking for the best way to increase their cardiovascular ability without increasing their risk for injury.  Cross-training has always been a good alternative and utilizing bikes, ellipticals, underwater running and within recent history anti-gravity treadmills has benefited countless runners.

While these types of training can help reduce injury it isn't always possible to get the physiological adaptations to transfer as well as one might hope.  Alter-G is a company that creates an anti-gravity treadmill (see picture) with the thought that you can reduce body weight while you are running for both return from injury and also to increase training load.  It has proven to be a great tool for injury and return to running but many physiologists still have the verdict out and if it can increase performance and maintain the same level of muscle activation as normal running can.

What Did They Do?
This study takes a look on how muscle activity and force change while running at a reduced body weight.  Researchers took athletes and measured through EMG both muscle activity with full body weight and then placed them on a weight reducing treadmill and measured muscle activity at reduced bodyweight's to 20%, 30%, 40%, and 50% (of normal body weight).

What Did They Find?
The data showed that there was in fact a decrease in muscle activity in key lower leg muscles when body weight was reduced on the treadmill.  What was interesting in these findings was that the decrease in muscle activity did not directly correlate with the decrease in weight.  As an example, muscles were only 36% (on average) less active when body weight was reduced by 50%.  Further numbers showed muscle activity was 43%, 51$ and 52$ less active, respectively, when body weight was reduced to 40%, 30% and then 20%

What Does it all Mean?
This non-correlating drop in body weight appears to show that their may be a ceiling effect with reduced muscle activity.  Ok great but that doesn't tell us the practical application.  Well what it all means is that runners on a treadmill that reduces bodyweight should be able to tolerate running at faster speeds at that reduced weight.  This allows runners to keep muscle activity high while absorbing less impact on their body and also running at faster paces.  

We can't comment on if that leads to a specific increase in training effect but it can allow you to replace miles that you were doing on the ground with less impact and also practice keeping a higher speed on the treadmill while also maintaining muscle activity.

These machines are great for return from injury and progressions.  This study shows some benefit to a healthy runner trying to increase their performance but more research is needed.

Muscle Activity while running at 20 to 50 percent of normal body weight
John Mercer
Research in Sports Medicine, 21: 217-228, 2013.

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