De or het circuittraining?

The correct Dutch article is:

de circuittraining

Rule Words ending in -ing: almost always de. See the rule

How to use circuittraining

the circuittrainingde circuittraining
this circuittrainingdeze circuittraining
that circuittrainingdie circuittraining
our circuittrainingonze circuittraining
your circuittrainingjouw circuittraining
every circuittrainingelke circuittraining
which circuittraining?welke circuittraining?
a big circuittraining / the big circuittrainingeen grote circuittraining, de grote circuittraining