"challenging step" can be a correct and usable phrase in written English.
It is typically used to describe a difficult or demanding action or decision. Here is an example: "Completing this project will require taking on several challenging steps, but the end result will be worth it."
An essential, but challenging step is the functional analysis of the resultant phenotype.
How to select appropriate polymer materials in a vast parameter space is a critical but also challenging step.
To prepare, he earned a nuclear engineering degree (a challenging step beyond a friend's suggestion that he study mechanical engineering), which enabled him to leave yachts for submarines with warheads.
I'd had my own share of family difficulties to overcome during my childhood divorced parents, challenging step families, and dysfunctional family members to name a few but I could not imagine having to face all that Bridget had experienced in her short eighteen years on earth.
This is by far the most labor intensive and intellectually challenging step in the pipeline.
Our results provide an illustration of the manner in which conformational fluctuations can play a central role in enzymatic reactions by creating low-population intermediate states that facilitate the challenging step of release of the products of the catalytic reaction.
The next most challenging step is the last 100 feet, from there to the patient's bedside.
Calibrating watershed-scale hydrologic models remains a critical but challenging step in the modeling process.
Puncture of the renal collecting system represents a challenging step in percutaneous nephrolithotomy (PCNL).
Mass cultivation of microalgae is the most overpriced and technically challenging step in microalgal biofuel generation.
