Weight training increases muscle force production even if your muscles don’t grow
It makes sense that bigger muscles are stronger muscles. After all, more muscle = more force. But did you know that even if your muscles would’ve stayed the same size, weight training still would make them stronger? Your muscles ability to produce force, independent of size is known as Normalized Muscle Force (NMF). We know that NMF (often (1)) increases in response to training (2), i.e. strength per unit cross sectional area increases.
What explains this increase?
Your muscles are made up of long muscles cells called muscle fibers, which converge into a tendon which then attaches to your bones to pull them and generate movement. Muscle fibers come in many types and sizes (check earlier posts), each with different force generating capacity.
Larger muscle fibers generate more force in total, but smaller fibers generate more force compared to their cross-sectional area. The force production per cross sectional area of a fiber is called fiber specific tension (FST).
FST varies between individuals (some people have stronger muscle fibers than others) and within individuals (some of your muscles have stronger fibers compared to others). However, longitudinal observational studies show that weight training can increase FST.
We also know that muscle fibers grow in response to training, and in these fibers FST stays the same! So weight training probably makes your muscle fibers stronger by increasing their size, or keeping their size the same and increasing FST. (3, 4). FST doesn’t fully explain our increases in NMF, but we’ll cover that in another post!
Like all things, NMF increases in response to training varies between individuals. Studies show increases in 17+-11% (5), meaning some peoples’ muscles can get 28% stronger (or more) without growing in size, while others only get 6% or less.
1. Vigotsky AD. Hutchinson J, ed. PeerJ. 2015;3:e1462
2. Jones EJ. Sports Med. 2008;38(12):987-94
3. Trappe S. Journal of Applied Physiology. 1 July 2000;89(1):143-152.
4. Widrick JJ. Am J Physiol Regul Integr Comp Physiol. 2002 Aug;283(2):R408-16
5. Erskine RM. Exp Physiol. 2011 Feb;96(2):145-55.