The books say that you should run off the bike but often it's only towards the end of the training cycle, right before taper as you peak. Coaches will get you to run after a long bike, but they tend to tell you that a bit of jogging is all you need.
The books also say that you should take it easy until your body recovers from biking legs and switches to running legs, and to be patient about it. So thus you should not worry if you're just jogging the first mile or so.
These do work somewhat, but I don't think it's enough.
In my own experience, I take about 10 minutes to get my running legs back. And naturally, the shorter the course, the better. But running a little bit off the bike during training wasn't enough to get me speed during the run. At Ironman Brazil, it took me almost a full 30 minutes to get some of my running legs back. It was way too long a time.
In the last 3 Ironmans, I have consistently ran about a 4:51 marathon. But yet my marathon PR was 3:51. I think I should be able to run a 4:30 marathon but yet I cannot. Something else was needed.
I started asking my fast triathlon buddies on how they train for running off the bike. Their comment was that this kind of training can only be done AFTER you've put your body in a depleted state. You can't train by not being tired. The body needs to adapt to switching from biking legs to running legs while super tired. So they go out and ride 80-120 miles and then run as fast as they can for about 3 miles afterwards, just simply to get their neuromuscular systems adapted to moving their legs in a running fashion after a long bike. They also practice getting up to pace as soon as possible after transition, instead of just jogging the first mile or so, waiting for their legs to come back.
Two things going on here:
1. You need to get your neuromuscular systems to switch from biking to running as soon as possible.
2. Research has shown that your best running times are achieved by running faster than you think early on, versus holding back and then running faster later. Almost everyone slows down near the end, and negative splitting makes it harder for you to make up lost time from the early portion of the run. So inevitably, if you start out faster, you'll have a better time as long as you don't flame out later but maintain as hard as pace you can as your resources dwindle. So you better go out faster sooner if you want to get a better time.
I started biking long and then running like hell after the bike. I started with a 10 minute run and gradually increased that to a 20 minute run and inserted hills into my run path. How funny was this.
The first time I went out my legs felt like bricks and really floppy. I basically just tried to move my legs as fast as possible and it was really tough. They did not want to move like that at all. I felt like I was pounding the pavement and didn't have much form at all.
The second and third times got progressively better. As soon as I went out, it was hugely uncomfortable and my legs felt like big floppy duck feet. But according to my GPS, I was doing 7:30-9:00 minute miles. Much better! And I was maintaining strength up and down hills as well.
The fourth time I went out, my legs didn't feel like bricks but definitely very floppy. Now I was definitely maintaining 7:00-8:30 minute miles but my HR was jumping to LT very fast and I had to walk a bit. My body was adapting to the stress and now my next step is to determine pacing so I don't flame out.
Like many things, this training was taking time and was HUGELY uncomfortable, but thankfully with no pain. You gotta put up with some discomfort and over the next few weeks you'll see results. I hope to draw out my after-bike run up to 30 minutes with some hour long runs inserted.