Ankle/Wrist weights

Ankle or wrist weights allow you to up the intensity of your cardio training and add some resistance training at the same time.  Any movement you do while wearing an ankle or wrist weight will be slightly harder than if you weren't which means your muscles are working harder, and if your muscles are working harder then they need more oxygen, which means your cardiovascular system has to work that little bit harder.  If you want to push yourself harder than you have been already, but you're happy with the fitness routine you have, then adding a bit of weight to your arms or legs (or both!) is a great way to achieve this.

As your hands are kept free, you could also wear them during the day, effectively turning everyday tasks like walking up stairs, driving or doing housework into a mini fitness exercise.