In today's high speed culture, multitasking is a highly prized and sought after skill. The advent of smart phones has made it so that at all times, we can be accomplishing another task, whether it be while driving, standing in line, or on the toilet. Those who cannot multitask are viewed as slow, incompetent weak and undesirable, whereas those that can aren't particularly rewarded for their ability, as it's become somewhat expected. Yet, just like those people texting and driving, if you try to multitask when it comes to your training, you're just going to crash and burn.
And you're probably an asshole, plus your blinker has been on for miles
As appealing as it may be to be awesome at everything, you have to take a realistic look at yourself when it comes to training. How great of an athlete are you? Is it possible you have the genetic makeup to be great at many activities, or is it more probable that, if you have the capability to be great at all, it's only going to be at one thing?
Go through your mental rolodex and think of how many athletes you know of that were ever at the professional level in two sports? Right now, the only thing that comes to mind for me is Bo Jackson.
Yes, I made a reference to Rolodex and Bo Jackson, I swear I am writing this in 2013
Don't get me wrong though. I still wouldn't fight him
Brian Siders, one of the strongest men in the world by powerlifting standards, had a very lackluster peformance in his World's Strongest Man debut as well. And these are sports that value similar attributes in their respective athletes. It gets even worse as you attempt to deviate to odder extremes.
Think about it. Professional athletes are genetic supermen that have trained their whole lives to excel athletically, yet these individuals still need to specialize. Why is that? Because very few people have the capacity to be great at many things, and the reality is, if you want to be great at anything, it's going to come at the expense of pursuing other physical goals.
From a personal example, growing up, I wanted to be big and strong, and I also wanted to be a fighter. In my mind, the two were equated, in that being big and strong would surely make me a great fighter, and being a great fighter would be the purest expression of strength. In reality though, the goals contrasted. My lifting would negatively impact my recovery from fight training, whereas my fight training would make me skinny from the energy I expended. After years of training both goals, I was terrible at both of them. Once I finally hung up the gloves and pursued strength training full time, my lifts took off, with me adding 140lbs to my deadlift and 30lbs to my bodyweight in a year.
This isn't to say that you can't pursue multiple goals as an athlete, it just means you have to pick and choose the time to chase these goals. If you try to train for powerlifting while engaging in boxing training and HIIT on your "off days", you're going to burn out quick and have no progress to show for it. But if you periodize your training so that you have a phase where you are 100% dedicated to strength, then conditioning, then your sport, you will make massive gains in each endeavor.