If you find it hard to sit up straight without slouching, the problem might be in your hips. Here's a great way to strengthen them.
We've talked about how tight hamstrings can affect the pelvis, pulling it out of alignment, but in the case of the hips, these are muscles that aren't generally used in the range of movements we make while cycling.
That means they're not getting used, and can get rather stiff, particularly if you're not cross-training.
Road.cc yoga expert Karen Burt shows us a quick exercise to check how flexible your hips are - you can see how open hers have become through yoga, as opposed to Tony's (he wasn't previously known as a yoga bunny).
These simple exercises (they can be done sitting down!) will make you much looser in the hips, and that can only be a good thing, keeping everything balanced as you develop the muscle groups used for cycling.