You can consider to do some exercises when you are in Singapore. There are a number of natural parks opened to public and they are well-maintained and upgraded from time to time. They are the best place to embrace the nature and to get yourself a peaceful mind. One of my favourite is MacRitchie Reservoir.
There are two main trails in MacRitchie Reservoir which are MacRitchie Trail and Lornie Trail. MacRitchie Trail is the trail at the right, winding around the reservoir and up to the entrance of TreeTop Walk. The MacRitchie Trail is around 3km long with lovely and thick tropical forest. The trail is good for walking or running and the view of the reservoir is simply breathtaking. It is always wise to reach there before 930 am as it will getting hot during the day.
TreeTop Walk is one of the attraction after MacRitchie trail ends. There is a suspension bridge of 25 meter above forest floor with great view of the forest under your feet.
Lornie trail is another trail start from the left of MacRitchie Reservoir park. There are 2 kind of trails: running trail on the hill or walking trail with wood path. You will be able to see the beautiful view of reservoir if you take the wood trail while you can enjoy the fun of running under tropical forest by taking the running trail.
There are also creatures like monkey, lizard and iguana lurking in the forest so it is a nice place to indulge yourself with the mother nature. More information regarding to the trail may refer to national park website or here.