By STEPHEN REGENOLD

New Balance enlisted top ultra runners Kyle Skaggs and Anton Krupicka for assistance in designing the MT100, a trail-running race shoe new this month. As such, the company touts the shoe as “designed for the most dedicated ultra-trail runners.”

After three weeks of testing this lithe shoe, I have discovered that despite my calendar of more than a dozen trail races a year, I may not fit in that “most dedicated” class.

In my test runs so far, the MT100s have had hits and misses. Dubbed as “an extremely lightweight racing comp,” the shoes are indeed “extremely” light. They weigh a scant seven ounces per foot in a men’s size nine — almost half as heavy as shoes other companies might market as light.

The women’s version, the WT100 model, weigh six ounces per shoe (in a size seven).

But the minimal build comes with minimal support. The uppers are made of mesh and foam. There is almost no midsole. Your feet are separated from the ground by a low-profile treaded sole and a thin forefoot plate.

The MT100s have a fast, bare-bones design that keeps you on your midfoot and forefoot for maximum speed. Elite runners might crank a long run off in a shoe like the MT100. Some could run an ultra.

Average trail runners should consider a 10K in them, but nothing more.

As the company cites, the MT100s are a running flat made for racing, not training. I would add that most serious, competitive runners will find this shoe too minimal even in a race. Your calves — maybe your knees, ankles, and back, too — will be sore after a hard run in these speedsters.

On the trail, the MT100s do feel fast. Each foot fall is light. But to me the “barefoot” feeling is compromised by the MT100s’ stiff sole. Compared to a lightweight Inov-8 shoe — a brand I often run in — the New Balance WT100s were unforgiving and plank-like.

Hold a MT100 in your hand and try and torque its sole. It takes considerable pressure to flex the forefoot. Plus, there is almost zero lateral flex.

On soft terrain, including grass and dirt trails, New Balance’s unforgiving outsole bites in for grip and serves as a fine platform for sprinting. It is a flat-footed feel — just like any other racing-flat shoe — that promotes a fast, staccato stride.

On hard-pack trails and pavement, I found the MT100s to be painful. There is no support. Further, the stiff sole hinders natural foot-flex biomechanics, creating a sharp foot-fall with almost no anatomical absorption.

At $75, the New Balance MT100s are a specialized shoe you might consider keeping in your quiver for the right venue. I will use them on sprints where speed trumps comfort and support. Ultra-race stallions the likes of Skaggs and Krupicka might lace them up for long runs. For the rest of us, the airy and starved shoe will prove too pared-back in all but our “most dedicated” of moments.

—Stephen Regenold writes about outdoors gear at www.gearjunkie.com.