So let's just for a minute forget any conversation regarding the advantages/disadvantages of running shoes for runners, and lets get into a slightly less controversial conversation; are running shoes good for general athletics?
Let's start at the beginning. Generally speaking, each sport will have a shoe (or style of shoe) that is meant for that particular sport. Baseball players have cleats, tennis players have tennis shoes, basketball players have basketball shoes, and hockey players have skates (ok, that's not a fair comparison, but you get the point). Running is no different, in that runners have running shoes. But to think that a sport-specific shoe should have carry-over to other sports is generally regarded as absurd. You would never see someone running a marathon in basketball shoes, or baseball player wearing tennis shoes. And yet the running shoe seems to have become the default athletic shoe for anything that might cause you to break a sweat.
My particular point of interest here, obviously, is the running shoe being used in the CrossFit gym as a general all-purpose fitness shoe. And if you look at just what the running shoe is designed for, you'll start to see big issues right away.
Running shoes have a soft marshmallowy cushion to them. This is apparently to help runners stay comfortable over long distances (again, don't get me started on that conversation right now...). But what is the impact of that soft cushion in the gym?
If you are already thinking critically about this, then you can probably guess the problems that this will cause. The biggest issue we will face immediately is that there will be no way to really stabilize ourselves in the gym. In weightlifting and powerlifting, creating a solid base of support with a firm connection to the ground is paramount to performing the lifts safely. There's a reason that weightlifting and powerlifting shoes have a sole that is literally made out of wood or a very hard plastic. There is no "Nike Air Romaleo" out there in the world, and for good reason. The softer the surface under our feet, the harder it is to perform any kind of heavy lift whatsoever, as our connection to the ground is shaky at best. If you've ever pulled a 1RM deadlift, think about how hard that would be if you were standing on a wobbly surface as compared to the gym floor - it would be significantly more difficult, and far less safe.
In the sport of weightlifting specifically, we run into another issue, and that's in our second pull on the clean and the snatch; the moment we drive into the ground and extend the hips aggressively. When you suddenly drive the hips up, the feet push hard into the ground. And if you're on a solid surface, there will be minimal power lost horizontally (out to the sides) because lifting shoes are so hard. But if you do the same in running shoes, the sole will simply condense and push down a bit, which actually causes a significant amount of energy to be lost, and making us unable to achieve heavier lifts.
The same is true for most other movements in the gym as well; kettlebell swings, box jumps, thrusters, wallballs, double-unders, etc... By wearing cushy running shoes, you're not allowing your body to stabilize correctly, thus putting your body at risk of injury.
The other issue that I won't touch upon too much right now, is that those big supportive marshmallow shoes actually prevent your foot from really getting strong. If you wrap your foot up in all kinds of protection and support, then you aren't letting the muscles really do their thing. The arch of the human foot is the way that it is for a very good reason, so to think that we're "outsmarting" thousands of years of evolution by putting arch support under our arch is really a crazy idea if you think about it. Let your foot get strong just like the rest of your body! No one wants weak feet!
Now, if running shoes is all you own, I'm not saying that you need to go out tomorrow and get different shoes. But as you move forward, it might be something that you think about on your next trip to Modells.
And what kind of shoe DO we want? Well, any light-weight minimalist shoe will do. There are specific CrossFit shoes if you want to go down that road (Nike MetCon, Reebok Nano,etc...), and then there are plenty of minimalist shoes designed for general fitness and athletics (Str/ke Mvmnt, Inov-8, etc..). And if you're really getting serious, then you might want to have a pair of shoes for lifting specifically. Nike, Reebok, Adidas, and many other brands make weightlifting-specific shoes (but that's an entirely different blog post!).
So if you wonder why the coach asks you to remove your running shoes next time you're in the gym lifting, now you know! We're just trying to help you become the best athlete you can be.