1. in a way that is extremely tiring, exhausting, or demanding; in a manner that causes severe hardship or suffering

Examples

• The marathon was gruellingly difficult, testing every ounce of the runners' endurance.
• She worked gruellingly long hours to meet the project deadline.
• The training regimen was gruellingly intense, pushing athletes to their physical limits.
• The cross-country journey proved gruellingly slow and uncomfortable.
• He described the experience as gruellingly painful but ultimately rewarding.
• The winter conditions made the expedition gruellingly harsh for the team.