Does resistance training lead to an increase in muscle fibre size? It appears so. 

The cross-sectional area of muscle fibres can increase by up to 70% following resistance training. Similarly, Seynnes et al. reported a 5% increase in the cross-sectional area of quadriceps (thigh) muscles after four weeks of resistance training.

It appears that a shift towards type IIa fibres is common in resistance trained athlete’s, and that type II fibres demonstrate hypertrophy following resistance training.