Friday, May 31, 2013

Basis for the Steroid Detection Calculator

The basis for the "Is He on Steroids?" calculator is pretty straightforward and based on the research done in this paper. Basically, there is a pretty clear limit in the amount of fat free body mass someone can gain naturally, and that number is generally in related to the Fat Free Mass Index (FFMI), which is the ratio of lean body mass over height squared. If your FFMI is above 25.0, there is a pretty good chance your getting some "help". Obviously, someone could be under 25.0 and still be using steroids. This calculator isn't going to detect that.

Tuesday, May 21, 2013

Muscle Force - Length Relationship

When you activate your muscle, it will not produce a constant force over time, for a variety of reasons.

One key reason is that the maximal force that a muscle can produce is dependent on the muscle length.

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Your bicep, for instance, can produce a maximal amount of force when the elbow is flexed at around 90 degrees. At more extended and flexed positions, maximum force is less.

from the wiki article: A generic example of a muscle force / length relationship

The active force component of muscle force generation is related to actin-myosin cross-bridges pulling past one-another. When they have pulled too far past each other (contracted position), their ability to produce tension reduces. Similarly  when the components are too far away from each other, limited elements are in contact and the amount of tension generated is reduced.

When you get to really stretched positions, there is an increasing "passive" contribution which is really connective tissue increasing in resistance to further strain.

The dependency of muscle force on muscle length has implications in performance and training, and will be recalled in many discussions.

The Point of This Blog

Is to aid in the conceptual understanding of how humans move and interact with their environment, with specific interest in performance / injury in sport and training. We'll discuss issues as basic as muscle force generation & body center of mass coordination, to complex tasks such as running mechanics and impact / concussion biomechanics.