Have you ever noticed how bilateral symmetry is a bit of a myth? When training parkour, how everything is easier on one side, sometimes to the point you can only do a move confidently from one side of your body? time to change this! Through our lives, we usually pick a side and stick with it. We write with it, we cook with it, we use it to jump, to land, to pull our body around. Traceurs, go have a look at your shoulders in a mirror: are they the same size and shape? probably not..
So if like me this state of things bothers you, here's a few ideas to strengthen the Weak Side. Basically, they come in three categories: forcing your brain to use the weak side (and improve its neural pathways); building up strength assymmetrically (on the weak side); training moves specifically on the weak side.
1. When sitting cross-legged, cross your legs the other way. Same for the arms.
2. Brush your teeth with the other hand. Try with shaving next.
3. Switch your computer mouse settings to the other side.
4. Reverse your hand posture when cooking, etc.
5. Work on assymmetric push-ups and pull-ups; you can start with shifting your weight to one side when doing a rep, then progress to lift part of your hand off the ground or bar; if you're really motivated go to one arm.
6. Perform unequal numbers of reps for one-sided exercises: leg raises, balancing, hopping, T push-ups, side push ups, side QMs, rolls, safety and speed vaults, tic-tacs, etc.
7. Control your footing on symmetric moves: if you do a straight vault (e.g. a kong vault), you probably jump and land almost always the same way. To force yourself to use the weak side, count two or three steps before the jump and always start from there, remembering which foot went first, so you can then use systematically the weaker of the two options.
With regular practice, you might discover that you can be symmetrical if you choose to be.