Marathoners, yoga instructors and other health and fitness pros say there is something for everyone hoping to rev up a workout, or trying to cool it down. "My big recommendation is one of the many popular motion sensors," said Shirley Archer, a Florida-based fitness and wellness expert. To boost or fine-tune cardio training, Dr. Mark Kelly, a California-based exercise physiologist, recommends interval training apps, such as Android's Stopwatch or Seconds Pro, which track recovery as well as exertion.



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