There’s been a debate for some time over whether single-sided strength training has and advantage over double-sided (doing a one-armed chest press vs doing a conventional barbell bench-press, for example). There are reasons to expect it to be better, such as getting your obliques involved in a one-armed chest press, and the fact that the total load lifted by the two sides individually is more than the total load in a double-sided lift. That is because one side is usually stronger than the other, and the double-sided exercise can be limited by the weaker side. But as discussed in a recent article in Alex Hutchinson’s Sweat Science column, studies have shown mixed results until now.
He goes on to review a recent study that showed a pronounced advantage for single-legged vs. double-legged leg presses and endurance performance, however. The protocol was to alternate legs in a single leg press, vs. lift with both legs simultaneously. The alternate legs led to significant more improvement in time to exhaustion in a cycling endurance test. This makes sense based on the principle of specificity- it helps if the training you do matches the actual movement in your chosen sport. Alternate legs while pushing obviously is closer to the actual cycling motion that double-leg presses.
I was already doing this because I enjoy it. I do “on-bike” leg strength training, like standing up to pedal in a big gear up hill, which is close to alternating single-leg presses. I also like to do single arm presses, which are close to a jab in boxing, and the canoe paddling motion which alternates sides. In all these cases I enjoy the motion because it simulates an actual sport movement. But that’s just me. If you enjoy double-side movements better, by all means do them. I agree with Alex’s concluding remarks that you should do whatever type of strength training feels better for you.
[update 09/09/21: please see the very helpful suggestions in the comments by UltraIan below]