vigorous

Vigorous means done with strong, healthy energy. A brisk scrub, a hard walk, a plant putting out new growth.

It describes physical effort first — vigorous exercise, a vigorous shake — and it always suggests health rather than strain. Gardening uses it constantly, since a vigorous plant is one that grows fast and needs no coaxing. The word moves easily to argument, where a vigorous defence or vigorous opposition means energetic rather than angry. The noun is vigour, spelled vigor in American English, and the adverb is vigorously.