Ah, I think I found it. "Capacity Utilization", according to Peter Navarro, measures the extent to which a nation's "manufacturing plants are being use to produce manufacturing goods". So little "spare capacity" probably refers to a very high rate of capacity utilization, which may be inflationary because, according to Navarro, "increases in demand will outstrip the ability to produce. At higher levels of capacity bottlenecks may also emerge in the production process."
H