Triathlon training. The ultimate cardio combo of running, swimming and cycling, a triathlon is a super-effective way of strengthening your heart and lungs and has a profound effect on musculature, endurance and body fat.
Tennis. Improves strength, flexibility, cardiovascular fitness, and works the pecs (chest), quads (front thigh) and obliques (stomach). The short sprints, twists and lunges are great for stability and co-ordination but tough on the joints, so repetitive strain injuries are common.
Trampoline. Trampoline provides a moderate-intensity cardio exercise while protecting your ankle and knee joints. Strengthens quads, hamstrings (back of the thigh) and calves, as well as the shoulders and hip flexors.
Trail running. Trail running adds the extra challenge of hills and rocky paths to seasoned runners. It increases strength and endurance in your quads, hamstrings, calves and glutes (buttocks), and gives a moderate- to high-intensity cardio workout. The unpredictable terrain improves your "proprioception" (sense of balance and where your body is in space).
Ultimate Frisbee. Team sport in which the object is to find one of your players in the opposing end zone. Requires explosive bursts of movement to jump for the disc or sprint into free space. Also good for balance, agility, coordination and endurance.