I would not want anything which I said to cause you to go against
good medical advice. So this is just to share my experience with
you, particularly my experience subsequent to having chemo, in
which my level of performance in, and enjoyment of, endurance sports
is even greater than before.
I'm just a bit older than you, and had an operation, followed by chemo,
exactly four years ago. I do several activities, including running,
and have for many years, but mainly directed towards training for
cross-country ski racing. So I'm not as dedicated a runner as you, but
do go out training almost every day, about 400 hours per year recently.
My chemo was 1 week on followed by 3 weeks off, six times; so it
lasted about half a year. I was only able to do a bit of walking
during the first couple of months of that, but mainly because my
operation had caused some other difficulties which took several
months to overcome.
But for the last 2/3 of that chemo period, I decided to use cycling
to begin getting back in shape. Running wasn't possible then because
of the difficulties referred to above. I found that during the 3rd
and 4th week of each cycle, it was very enjoyable, and I suspect helped
a lot with the chemo treatments, to go out for longer and longer
bike rides. I worked my way up to 100K (60 miles or so) during that
period, as my longest single ride. I owned a HR monitor, and really
took it very easy, keeping down to about 50% to 65% maximum heartrate.
Things have gone very well subsequently. I skiied a lot right after
finishing chemo, but didn't do any real races that season. However,
I got back to it the next season, and seem to do quite a bit better
than I ever did before. I even won my age category in the major
so-called World Loppet race in Canada (Kekinada) last season, though
didn't win it this year. That's a 50K race with pretty big climbs,
about 3.5 hours. So there's no question that in reasonably short
time, it's quite possible to become just as active as before. I do
plenty of running off-season, along with using the bike and rollerskis.
I can't actually remember whether I really consulted with my doctors
that much about doing this, but if I did, they didn't object. So
with the other respondents to this thread, I'd certainly encourage
you to get advice from your oncologist. As I said above, I found
that resting the chemo week and the week after, then doing very
easy, but longer and longer workouts the other two weeks, worked
really well for me.