Reader Mark writes “I had no idea that plantar fasciitis and achilles tendonitis were related. I’ve also been told that rolling your foot on a tennis ball while seated is good for stretching the plantar fascia. Is this a good idea, or is it doing damage? I’ve found it really relieves the pain for a while. Also I am wondering if shoes that are too loose or tight might be a factor.”
Mark asks great questions and ones I get every day. First lets talk about rolling your arch over a tennis ball…I’m not a fan. I know that many physical therapists and other sports medicine specialists will recommend this but in my experience agressive stretching of the plantar fascia can lead to tearing or even rupture of the plantar fascia. Athletes in general do things in a big way and stretching with a tennis ball is no different. In this case, experiencing a stretch so good it hurts, can actually be doing harm. Better off to make an appointment with your local sports medicine podiatrist for evaluation and treatment.
In general, shoes that are too loose are worse than too tight and shoes that are too short are worse than too long. The more loose your shoe, the more your foot will pronate which can cause plantar fasciitis. If your shoe is too is too short, particularly heel-to-ball, your plantar fascia won’t be properly supported as this image shows.
Dr. Jenny Sanders Shoe Blog 
A simple image comparison explanation can give detail information. Thanks for sharing this valuable info.