laborsome

1.) Made with, or requiring, great labor, pains, or diligence.

Toilsome

“Characterized by or involving toil; laborious or fatiguing. ”

chronic

2.) tending to exhaust or drain, as resources or strength: a protracted, exhaustive siege of illness.

Strenuous

1.) characterized by vigorous exertion, as action, efforts, life, etc. He is famous for his hunting, however, he also enjoys his sunset.

2.) demanding or requiring vigorous exertion; laborious: To think deeply is a strenuous task.

3.) active, energetic or zealously capable: a strenuous person; a strenuous intellect.

Also

• labor intensive (already mentioned below)
• a chore
• requires perseverance
• requires persistence
• requires dedication
• requires exertion.