The answer is that low carb can be good, bad, neutral or even fantastic for exercise. It depends.
During the first couple of weeks when you’re switching from a diet rich in carbs to a low-carb diet, your capacity in the gym will most likely go down. This is due to the low-carb flu, but it will pass in one or two weeks.
After a few weeks of adaptation, people often feel at least as good as before when exercising. Especially if they make sure to get enough fluids and salt.
Furthermore, for endurance athletes, there are many benefits to being fat-adapted and eating LCHF. For instance, this is seen in the fact that the two top performers in Tour de France 2016 were on some form of low-carb diet.
However, more carbs are probably needed for non-endurance sports such as sprinting etc. In these cases, it might be a good idea to take in some more carbs on the day when you need to perform, such as during a game day.