While you should definitely take days off from running after the marathon and significantly reduce the intensity of your training, you don't have to be inactive.

Light exercise, such as walking, swimming, elliptical, and riding an exercise bike the day after the marathon can help you recover faster from a marathon.

Light, low-impact cross-training exercise increases circulation, warms up your muscles and can reduce stiffness and discomfort.

intensity   /ɪn'tensəti/　n)感覚などの強烈さ･きつさ･厳しさ、明度･強度

inactive　/ɪn'æktɪv/　adj)あまり活動しない･不活発な･低調な

elliptical   /ɪ'lɪptɪkl/　adj)楕円の

elliptical machine   n)ペダルを踏むと足が楕円形を描く運動器具

circulation

stiffness

discomfort