Losing strength doesn't always mean losing muscle...
When they lose strength, most people automatically assume they've
lost muscle. However, a new study has shown this isn't necessarily
the case.
Strength
Researchers from The College of William & Mary examined the effects
of 14 days of inactivity on the strength and size of several muscles
in the thigh. Although there was a drop in muscle strength, there
was no evidence of any reduction in muscle size. Instead, the decline
in strength was attributed to changes to the nervous system.
Inside your body there are billions of nerve cells. Give or take
a factor of 10, there are probably the same number of nerve cells
in your body as there are stars in our galaxy! The task of each
nerve cell is to receive a message, then pass it on to other cells.
Eventually, the signal reaches the muscle.
The nerve and the muscle fibers it activates are called a motor
unit. When a motor unit is called upon, all of the muscle fibers
in that motor unit contract. There is no such thing as a partial
contraction of a motor unit - it either contracts or it doesn't.
Instead, when you need to lift a heavy weight, your body simply
recruits more motor units.
Neural factors
In the early 1970's, researchers showed that 100 days of exercise
led to a 90% increase in muscle strength. However, there was only
a 25% increase in muscle size. In other words, you can get stronger
without getting bigger.
Untrained individuals aren't able to use all the motor units available
in a given muscle. However, when you start a training program, your
ability to recruit motor units increases. Then, as the program continues,
an increase in muscle tissue makes a greater contribution to changes
in strength. That's why someone with 20 years of training experience
under their belt won't gain strength as fast as a beginner.
While the gains in strength at the start of a training program
are due to neural factors, it also appears that the early drop
in strength when you stop training is also related to changes to
the nervous system.
The bottom line is that if you've missed training for a week or
two, don't worry too much about losing muscle tissue. Any reduction
in muscle strength is probably down to neural factors, rather than
any muscle loss.
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Reference
Deschenes, M.R., Giles, J.A., McCoy, R.W., Volek, J.S., Gomez,
A.L., & Kraemer, W.J. (2002). Neural factors account for strength
decrements observed after short-term muscle unloading. American
Journal of Physiology, 282, R578-R583
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