Count yourself lucky if you have access to indoor cardio equipment - an elliptical trainer, a treadmill or a stationary bike. It's a good way to get in some workouts without collapsing from the heat.
It does get boring, though. That's where interval training can come in handy. It makes the time go by quicker.
Here's a nice list of interval workouts, most of which can be done inside. Can't promise you'll end up looking like Blondie, there. But still. Think of the health benefits.
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