Fix muscle mass documentation error in Umberger2010MuscleMetabolicsProbe

[mleeuwis]

Brief summary of changes

The activation and heat maintenance rate (line 317 cpp file) is multiplied by muscle mass when the total energy consumption is calculated (line 459), which was not reflected in the documentation. The documentation now correctly shows muscle mass multiplication for the activation maintenance and the shortening rate. Note that the mechanical work rate is correctly displayed without muscle mass multiplication, as this factor was divided by muscle mass upon its calculation (line 406).

Testing I've completed

Documentation change, no testing required.

CHANGELOG.md (choose one)

• updated.

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