The USDA created the food pyramid to encourage a healthy diet, but the USDA also has a mission to encourage agricultural products grown in the US. There can be a LOT of conflict between those two goals. So the food pyramid (ahem, I mean MyPlate) is not simply an objective summary of the available evidence.
The stretch reflex (myotatic reflex) is a muscle contraction in response to stretching within the muscle. It is a monosynaptic reflex which provides automatic regulation of skeletal muscle length. When a muscle lengthens, the muscle spindle is stretched and its nerve activity increases.
By sending commands to the motor neurons the brain senses and sets a muscles length. The reaction of teh stretch reflex is trying to keep the muscle at the same length by shortening the muscle. The stretch reflex is important for maintaining muscle tone and adjusting it reflexively. Patellar, (knee jerk). Or Achilles reflex.