Originally Posted by OBoile

When you consume an excess of calories, your body will build both muscle and fat with the leftover calories. If you don't lift weights (or something similar) your body will build mostly fat. Lifting weights will signal to your body that you need build more muscle, so the ratio of muscle to fat built becomes more favourable (similarly when you diet, you lose both, but again lifting will signal your body to preserve as much muscle as possible). However, as someone else said, there is a limit to how much muscle you can build no matter what, so you don't want to consume too many excess calories as beyond a certain point, everything extra becomes fat.

Just curious, what was your routine? I saw you mention 3 sets of 8 to failure but what actual exercises were you doing? Were you training your legs? If not, you really should be. That is where most of your muscle mass is, so if you want to build muscle that is the key. Cycling is good, but it doesn't really provide the same muscle building stimulus that heavy squats do (unless you're doing something like track sprints). Also, training to failure is probably not a good idea. 1. At that point, your form breaks down and you have increased risk of injury. 2. It is much harder to recover from a set to failure than it is from a set where you stop 2 reps short of failure, but the benefits aren't all that different (so essentially the cost/benefit ratio isn't all that good from a recovery perspective). That doesn't mean you don't train hard, just that you don't push every set as hard as you possibly can (just like you don't ride as hard as you can every time on the bike).