Figure 6. The number of innervated muscle fibres (A), muscle fibres per motor unit (B) and force produced per muscle fibre (C).

The average number of muscle fibres per motor unit (innervation ratio; IR) in the SOD1^G93A mouse TA muscle tended to increase by approximately 44%, compared to age-matched control SOD1^WT. Despite the relatively static IR, the force produced by each motor unit declined (Fig. 4), indicating that the contractile force producing capacity of each motor unit was reduced. Data are presented as means ± s.e.m. and statistical significance is indicated as ** for P < 0.01.