Number of quiescent (A) and proliferating (B) satellite cells, satellite cell progeny committed to or in the later stages of terminal differentiation (C), and intrafibre muscle nuclei per unit area in control and 21 day-stimulated rat tibialis anterior muscles (D). Statistical symbols: a, different from IRR-control; b, different from contralateral control; c, different from IRR-Stim; d, different from IRR (P < 0.05).