When I was pledging to enter my fraternity (the Black/Latino Greek hazing way-not the Rush drinking way) one of the brothers gave me a quote that left an indelible mark. My line was in trouble for not completing an assignment on time and we told him our "reason" why it couldn't be accomplished to which point he replied, "Excuses are tools used the the incompetent to build monuments of nothingness and roads to nowhere and those who use them seldom amount to anything." There was a deafening silence-later to be broken by our voices for said excuse.
The time we spend trying to explain why we couldn't do something right could be cut short by simply fixing the mistake. If you find yourself not being able to go to the gym for your regular routine, there is plenty of floor and gravity available to drop and do 20..like 20 sets of 20-pushups, situps, sprint, carry something heavy while you do it. There are plenty of fitness modalities out there to accommodate all gym rats and homebodies alike. There are experts who can teach you how to be great under the bar, powerful with a homemade sandbag, and yes even P90X (although I'd personally never do it myself). Point is-everything works if you stick with it, and if you're willing to commit to it.
You just need to ask yourself, "What's my excuse not to be great today?"