adjective
strenuous
STREN-yoo-us/ˈstrenjuəs/
Requiring or showing great effort or energy.
Pushing the loaded wheelbarrow uphill is strenuous work for the man.

Etymology
Latin strenuus described someone active or vigorous. Strenuous moved from describing the energetic effort itself to describing an activity that demands such effort.
In context
It's strenuous, challenging, even dangerous. Men diagnosed with fragile nervous systems were told to do things that required physical stamina and mental acuity.
More examples
- Avoid strenuous exercise while you recover from surgery.
- Despite strenuous efforts, the crew could not repair the bridge.
- The proposal met with strenuous opposition from local residents.
Forms
strenuous · more strenuous · most strenuous
strenuously adverb — With great effort, energy, or force.