Literature Review: Changes in Muscle Size and MHC Composition in Response to Resistance Exercise with Heavy and Light Loading Intensity, Journal of Applied Physiology, September 2008.


Here is a brief summary of the study from the Journal of Applied Physiology.  We kept it simple and to the point, but it is definitely a good article to read if you have the time and desire!

The study conducted examined the different responses to heavy vs light load training. In this study, researchers identified heavy load training (HL) as working at 70% of the individuals 1RM and light load training (LL) as working at 15.5% of the 1RM.  During the study, participants completed a total number of 36 repetitions, performed every 5 seconds for 3 minutes.  Test subjects worked one leg HL and the other LL for a period of 12 weeks at 3x/week. Researchers used MRI images and muscle biopsy results before and after the test period. The goal of the study conducted was to ¨compare adaptive changes in muscle size, contractile strength and MHC (Myosin heavy chain) composition evoked by resistance training performed at either low or high contraction intensity while equalized for total volume¨.

After the 12 week study, both the HL and LL showed improvements in muscle size and 1RM strength (though the LL was significantly less compared to HL).

Why is this important

 Whether you are a coach, athlete or simply someone interested in improving their fitness, it is important to understand what HL and LL training does to your body (and how you can use that to improve your performance).  Age, training history, chronic or acute injuries or other factors can inhibit the ability to train with heavy loads.  This does not mean that you can not improve your fitness.  Light load training, as shown by this study, can still have positive effects on muscle gain and strength improvement.

This does not mean that you should only do light load training.  Heavy load training has been shown to be superior in muscle growth and performance improvements.

As with all resistance training, the load % used by the athlete should be adjusted based on current abilities.

If you are just starting out, consult your physician and then a certified strength coach!


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