It could be envisaged that the correlation between spindle abundance and muscle mass may be true for postural muscles, but high spindle density was also found in some intrinsic hand muscles [ 15].
This suggests that smaller muscles show a higher spindle density if compared to larger ones [ 2, 8, 9].
Unpaired t-test with Welch's correction showed a significant difference in spindle density between digastric muscle and mylohyoideus (P < 0.001)) and between digastric muscle and mylohyoideus with plantaris muscles (P < 0.001 for both comparison)).
In these studies, the presence of spindles in skeletal muscles has been quantified by spindle density.
Finally, spindle density was evaluated as the spindle number per gram of wet muscle tissue for each muscle sample.
In fact, as Banks shows, despite the common use of spindle density in comparative studies, it has never been demonstrated that muscle mass is an appropriate reference for spindle number.
The measurement of spindle density was 0.7/g (range 0.4 9.7, standard deviation 0.2) for digastric muscle and 0.1/g (range 0 0.4, standard deviation 0.2) for mylohyoideus.
As can be depicted from Figure 3, also by this method, in agreement to spindle density, there is a decrease in relative abundance in digastric muscles and mylohyoideus compared to plantaris ones.
The following parameters were then considered: spindle duration, spindle density and ISAs.
(a) Computer simulations of muscle spindle feedback circuit dynamics.
