Don't heat! Heat can be good for tight muscles, but
is generally not a good idea for inflammed tendons (which
is what tendonitis is). Use ice and take anti-
inflammatories (e.g. Advil). Try to ice a few hours
before running, and then again immediately after and
other times during the day when you can (right before bed
is also a very good time to ice). Don't ice right
before running.
You only need to ice 5-7 minutes at a time, but you can do
it a lot - every 2 or 3 hours if you have the opportunity.
For the anti-inflammatories to do much good, you need to
take them regularly (i.e. don't just pop an advil
or whatever you use when it happens to hurt) for several
days or even weeks. You can take up to 2 advil every
4-6 hours if it doesn't bother your stomach.
I am not a doctor so take all my advice with a grain
of salt and use at your own risk.
Any doctor will tell you that you should stop running
immediately and take 2-3 weeks completely off. If it's
bad, you may have no choice but to do this, but if it
is not that bad, you can treat it with ice and
anti-inflammatories if you follow the following three
rules:
1) No hills or speedwork.
2) If it starts hurting during a run and the pain increases
as you run further, stop running (be prepared to walk if
you have to) and next time don't run as far.
3) If the pain is worse from one day to the next (a good
check is doing the pinch-test in the morning), then you
need to reduce the frequency of running (e.g. every other
day instead of every day).
If you follow these rules and can find a level of running
and self-treatment that results in steady gradual
improvement, then you can probably get back to 100%
without taking a full layoff. If you ignore these rules
and just try to push through the pain as it gets worse,
be prepared to take a very long layoff and develop a
chronic condition that may require surgery down the road.
Hope this helps - good luck.