Free running is all very well, but we've all got different goals and circumstances. Some run to lose weight, others to boost their aerobic fitness, while speed is the top priority of the more experienced. Either way, there are gadgets that can help you get through the run - from tiny MP3 players, wireless headphones and the latest in running-centric trainers, armbands and backpacks - to those that help you monitor your progress. Think activity trackers, GPS watches and heart rate monitors.