<p>A) The SD of force for 5 and 30% MVC. As expected, the variability of force was greater with higher force. B) Normalized power spectrum density of force from 0–2 Hz. In this figure we present the average normalized power spectrum density because it was similar for the two force levels. The greatest power (∼75%) occurred below 0.5 Hz. C) The association between low-frequency oscillations of force and SD of force was strong (<i>R<sup>2</sup></i> = 0.82). This indicates that ∼80% of force variability is due to the oscillations in force below 0.5 Hz.</p
