I've always been susceptible to lower leg aches and pains, especially my achilles. I've recently started using this innovative new cross-training device, the Elliptigo! It helps me to keep my aerobic volume up, making it so that I never have to miss days because of the impact running places on my body. Using my heart rate monitor, I've been amazed at how easily I can get my heart rate up to the threshold effort that I have previously only been able to achieve through tempo runs. My motivation to cross train using the Elliptigo is much higher than other forms of cross training because I'm outside covering distance like an actual run and it's less of a mental struggle to stay engaged and push the envelope. Plus, the mechanics are different from an indoor Elliptical machine, because you're actively engaging core muscles to balance while riding. I am loving the Elliptigo and incorporating it into my training, here's some more information off their website:

  

TheElliptigo Website: http://www.elliptigo.com

The Elliptigo Project Website: http://theelliptigoproject.com