Neuroscientists face a challenge: shielded by our thick skulls and swaddled in layers of protective tissue, the human brain is extremely difficult to observe in action.

神经科学家面临着一个挑战：人类大脑被我们厚实的头骨保护并包裹在层层保护组织中，很难在活动中观察到。

At the large scale, this hamstring stretch is pulling on layers of protective tissue surrounding the muscle fibers, as well as the tendons that connect this muscle to nearby bones.

在大范围内， 这种腿筋拉伸会拉动肌肉纤维周围的保护组织层，以及将这块肌肉连接到附近骨骼的肌腱。

Sarcomere's long, fibrous proteins can relax to elongate muscle fibers or they can contract to shorten them— pulling on tendons and protective tissue to create the force propelling our athlete's body.

肌节的长纤维蛋白可以放松以拉长肌肉纤维，也可以收缩以缩短它们——拉动肌腱和保护组织以产生推动运动员身体的力量。