The barrier might be repeated or prolonged sicknesses that derail our training. Or perhaps our jobs take up too much time and energy, so that the last thing we feel like doing is training. Or maybe you're hit with an injury, or you're hitting some speed bumps in your personal life. How do we handle all of this?
First, don't let the wheels come off. While it might seem that all is lost, don't believe it for a second. It is easy to fall off the edge and into the abyss of depression about your waning fitness, your inability to train/race, and so on. We are used to pushing ourselves hard and training day in/day out. So, when this freedom is taken away from us, it's hard not to let it get us down. The best thing you can do here is focus on what you CAN do rather than what you can't do.
Let's say you're a cyclist, but an injury is keeping you from biking. You have a choice to make— and believe me, you always have a choice. You can either: 1) Do nothing since you cannot do your primary sport. This is what starts you down the slippery slope of losing motivation, getting depressed, gaining weight, etc.; or 2) You can find a way to maintain your fitness or at least minimize the loss of fitness so that when you are back on the bike, you are ready to get back at it. This approach can leave you excited to finally get back on the bike. And your day-to- day routine is minimally disrupted, so you won't feel like you're floating in space. Instead of cycling, you can try swimming, water running, StairMaster, elliptical trainer, or rowing machine . . . anything that does not aggravate the injury further. Doing something, even at a very baseline, recovery level of effort, is better than doing nothing.
Any of the above examples are great ways to keep the heart pumping and your fitness growing. And, since you would be exercising in a way you are unaccustomed to, when you get back to cycling you might find your fitness is actually better than before. The short rest from cycling and the use of your body in a completely different way can help to rejuvenate you and build you up in new ways, effectively making you stronger all-around. This is just one simple example. As athletes, we are creatures of habit. We are used to juggling many responsibilities and being in certain places at certain times. Our training, work, and family require this so that we can properly attend to each facet of our lives appropriately. When one of these facets falls out of whack, it can send our entire lives into tailspins.... if we allow that to happen. But we don't have to! We CAN stay in control.
And that's the crux of it all. As I stated earlier, we always have a choice to make. If you end up gaining 10-20 pounds while you are nursing an injury, you have to ask yourself whether it is because the injury completely took you out (like getting hit by a car while biking) or if you simply decided to wallow in the misery that can accompany a niggling injury (such as an Achilles tendon strain or patellar tendinitis). In the former case, there is nothing you can do about your inactivity. Yes, you can fight to rehab ASAP, but the road to recovery is long. So, your motivation should be to get back in the saddle more quickly than any doctor tells you is possible. In the latter example, your blinders and lack of personal flexibility are what is keeping you from looking at alternatives to stay fit.
Each of us hits both expected and unexpected roadblocks along the road of fitness improvement. It is how we handle these roadblocks—emotionally, mentally, physically—that will help shape the athletes we are and the athletes we are becoming.