I consider this a more appropriate way to strengthen the foot intrinsics.
http://www.aptei.com/articles/pdf/IntrinsicMuscles.pdf
Some cases of chronic PF may be plantar nerve entrapment as well. They're actually fun problems to work on from my standpoint. I don't bother with the ultrasound (so much of a waste, really). To get a good clinical result, I've found that I have to do the following:
1. initial inflammation (if not a chronic problem, > 4-6 weeks) control - Plantar taping for two weeks, retaped at each treatment session
2. Biomechanical foot analysis and gait analysis, determine if orthotics are appropriate - Orthotics are often issued as a "shotgun" approach with anyone with plantar fasciitis, which is probably why the literature has shown such poor outcomes when used to treat PF.
3. Train the patient in initial weightbearing activities (slow foot circles and gradually working towards full weightbearing over a few minutes before standing/walking each morning until the symptoms come under control).
4. night sleeve - Strassburg sock - forget the plastic boots, they're impossible to sleep in.
5. Strength/endurance/balance training - the article above explains the foot end of it, but you have to work "up the chain" so to speak - hip abductor/ER training, for example - some of these cases that just don't get better aren't getting better because of poor postural/rotary control at the hip - over-pronation or prolonged pronation isn't just driven by the foot.
6. Shoes- I'm not a total minimalist freak, but I do think that the majority of trainers offer too much cushioning. The goofy thing that some do is use an orthotic device in a motion control shoe. For casual walking, I have patients wear hard-soled shoes - sounds stupid, but too much cushioning causes the foot to swim too much.
7. deep friction massage in chronic cases - trying to remodel the tissue - I use instrument assist (graston technique).
And that's about it, in a nutshell.