Get out a pen to jot down your answer. Got one? Great. Now please, stand up, arms relaxed at your sides. From here, lift your arm straight out to the front, palm down, up 90 degrees (that’s straight out from your shoulder).
The pop quiz question: what was the first muscle to engage in that movement? (You don’t need to know technical anatomical language for your answer to count, as in, you could say “the front of the neck.”)
Probably some muscle in the shoulder, right? Like the anterior deltoid. (That was my guess when I took this quiz.) Or, if you were being super savvy and had a sense of where this was headed, maybe you answered some part of your core, like the deep transversus abdominis.
The answer: the soleus, one of the deep muscles in your calf that connects to your Achilles tendon.
The reason: to begin the process of lifting your arm out front, and thus moving your center of weight more forward, your unimaginably intelligent body begins with an ever-so-slight movement of plantar flexion, or the ball of your foot pressing into the earth (or, if you’re driving a car, on the gas pedal).
(Another visual that might help if you’re still feeling confused: recognize that the plantar flexion, if left unchecked, would push everything above your feet backwards. And that’s where your arm moving forward comes in as a sort of balance, so only your arm actually moves.)
Can you feel it happening? (I can’t, but kudos if you can!)
Amazing, no? Now, pass your papers to the front of the class …
Liam Bowler 
I guess the brain isn’t a muscle…? that was my guess! when i held something heavy in my hand, it helped to discriminate the muscle.
that was FUN!