Her knees sagged, and for a moment she rested weakly against him.

His knees sagged, and Rick just caught him before he fell.

His knees sagged; he sat down cross-legged on the ground.

He took another step toward them, and his knees sagged.

"It seemed like a better idea," she said, and her knees sagged.

Someone else moved beside him and held him as his knees sagged.

Her knees sagged to either side and she closed her eyes.

Shaking off the image, he let his knees sag on to the chair's plump arms.

The man's knees sagged; his body plunked back against the wall.

Waves of heat flooded away the fatigue and her knees sagged.