When John asked why, Chris explained that it’s a matter of practicality and what’s most effective. As humans, we pick up heavy objects symmetrically using both hands and legs. If you had a heavy object to move, you’d grab it with both arms, right? THAT is functional. Nobody would put one hand in their pocket and attempt the task with the other. This is the same way the central nervous system sees exercise. Two-armed exercises activate more muscle because your arms are designed to work together.
