Hubungan keaktifan mengikuti senam lansia dengan keseimbangan tubuh lansia di Panti Sosial Tresna Werdha Budi Mulia 1 Cipayung Jakarta Timur = The relationship between elderly gymnastic activity and elderly body balance in Panti Sosial Tresna Werdha Budi Mulia 1 Cipayung, East Jakarta