。
Even after finishing, my legs felt light.
Literal
Ended after [also-も] legs [subject-が] light feeling [subject-が] did [polite-past-ました].
Post-exercise wellness observation. 足が軽い ('legs are light') describes the physical sensation of feeling springy and agile. 感じがする ('it feels like, has a feeling of') is a fixed expression for subjective impressions. 終わったあとも uses the ~た+あと+も pattern — 'even after X-ing.' Reads like a fitness/yoga review.