Functional training has no proven edge for cardio fitness
Workouts built around mimicking daily movements are hugely popular, but when five randomised trials were pooled, functional training showed no clear advantage over other exercise for oxygen consumption. The reviewers graded the whole evidence base very low quality.
For you: No reason to drop functional sessions if you enjoy them, and no reason to believe they build your engine better than ordinary training does.
What it shows: A reality check rather than a final verdict: only five trials existed to pool, and the reviewers rated the evidence very low quality, so the fairest reading is that a cardio advantage for functional training simply has not been shown. It may still be perfectly good exercise; it just has not proven better than anything else for fitness.Meta-analysis · Clin Physiol Funct Imaging