This is usually most pronounced in games that aim to follow fast, precise multi-limb movement. Ubisoft's remarkable Player Projection technology only unravelled during Your Shape's quick-reflex exercises. While the player's silhouette appears on screen in UFC, there just isn't the same sense of precision or immersion.
The problems stemming from this are three-fold: first, it's very hard to get a sense of correct form, since you're either getting a move right or wrong, with only limited corrective guidance. Finding out what the game expects is often a case of trial and error.
Second, while you couldn't get away with it in Your Shape, it's very easy to cheat in UFC. During one exhausting session, I wimped out during Ice Skaters - springing from side-to-side - and found it would register perfectly if I stood still and tilted my shoulders from side-to-side.
Obviously this is not the point nor in the spirit of the game. But one of the strengths of a real personal trainer is his or her ability to stop you cutting corners and push you harder than you'd manage under your own steam: something Kinect itself was supposed to deliver.
And the third issue is, while Kinect does an admirable job for much of the time when standing, it can fall apart dramatically when you're on the floor.
Mileage varies from person to person, home to home, depending on the playing environment. What I can say about my own experience is, though my beaming green silhouette suggests I'm in the right spot, registering moves like push-ups and sit-ups is a frustrating lottery.
Not only does this disrupt the flow of your workout, it also screws up the stats. I have (as far as I'm concerned) done the reps, but thanks to Kinect's dodgy eyesight, failed the exercise to a mocking chorus of boos. It's moments like this where I'd happily see the relationship with my 'personal trainer' descend into an actual UFC fight.
Repetitive motivational and instructional dialogue from the UFC trainers - particularly during unchanging warm up/down routines - compounds the impersonal air of many of the workouts: real engagement with the game comes through the accumulation and analysis of your workout data, not the glib scripted remarks of an avatar.
To its credit, THQ has already acknowledged and is promising to fix some of these issues in an upcoming patch, including - though I've never encountered it - a freezing issue some have experienced in the lengthier programmes.
Menu navigation, by the way, is not bad as it goes, but I much prefer having a controller handy to rattle through the various options - particularly as the voice communication isn't much cop either. Is this really the future we were promised when Peter Molyneux introduced the world to Milo?
That's a lot of negatives coming after opening with more fulsome praise. And I want to finish on a more positive note as, for all its irritations, UFC Personal Trainer remains a decent training tool capable of delivering punishing, varied workouts and a palpable sense of improvement.
You get out what you put in, of course, but if you approach it with the right attitude, there's a good chance that you will have noticeably improved your fitness within a few weeks of effort.
There's a great Kinect workout waiting to be made - this isn't it. But though it is flawed, UFC Personal Trainer should still get the committed fitter faster than its current rivals - just not without frustration along the way.