Exercise system (8)
(Other definitions for aerobics that I've seen before include "Forms of exercise" , "Exercises designed to strengthen heart and lungs" , "Exercise that increases the need for oxygen" , "Strenuous exercises" , "Keep-fit exercises" .)
'exercise system' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for yoga that I've seen before include "exercise regime" , "Hindu ascetic system" , "System of physical and mental exercise" , "E.g. Lotus position" , "Hindu body work" .)
'exercise system' is the definition.
(pilates is an exercise method)
This is all the clue.
(Other definitions for pilates that I've seen before include "Set of exercises used in holistic medicine" , "regime for improved fitness" , "Exercise system" , "attributed to Biblical procurator?" , "Modern exercise" .)