grueling

This term describes a level of intensity that pushes a person to their absolute physical or mental limit. It carries a heavy connotation of endurance and suffering, suggesting a process that is not just difficult, but punishing and draining. While similar to words like arduous or taxing, it specifically evokes the image of being worn down or ground away. It is frequently used in the context of athletic feats, rigorous training regimes, or oppressive work schedules where the primary characteristic is the sheer exhaustion produced.