Contenders include Kirsty Dobbs, Rachel Halfpenny and Jacky O'Hagan.
Experienced runner Christine Carlton from Gisborne is favourite for the veteran women's event, Mrs Nicholson said, "but it's the veteran men where we expect to see the real struggle".
"We've finally got Graeme Butcher [of Masterton] coming in, during his training for another ultra-marathon. He tells me it's a training run but I said to him, 'You know what you're like, once you get the bit between your teeth, you don't like to have anyone in front of you'."
Rivals include Colin Rolfe of Nelson, who has only missed one race in 18 years, Kelly Holland of Palmerston North and Paul Helm of Wellington.
"Between those four it will be a bit of a tussle. They don't seem to slow down much, even though they're that year older."
Bryn Davies of Lower Hutt was the clear winner last year of the half-length Hooper Loop and is likely to have another crack at the course record.
Piriet Klade, Davies' partner, won the women's Jumbo Holdsworth last year and is doing the shorter run this year, where Mrs Nicholson says the women's course record may be under threat.
A challenger there will be Laura Rhymer of Clareville.
Robert Ruffe-Thomas, 74, of Pahiatua, is also back for another round of the Hooper Loop.