The motor proteins that shorten your muscles to generate force (like the pistons in your car) can idle without creating force while still using up fuel (like your car idling at a stop sign).

When your muscles are not generating force but are idling they are relaxed, and when they stop idling they are super relaxed. If your car idled all day it would use up a lot of fuel, and when your muscles idle all day they can burn up to ~ 1000 Calories. When you activate your muscles, they keep idling for 1-60 minutes afterwards depending on how intense the activation is (compared to your maximum voluntary contraction).

Muscle idling after each brief activity is why activity breaks throughout the day are so much more beneficial than expected for stabilizing blood sugar in diabetics, and for avoiding weight gain when overeating by up to ~1000 Cal/day. Muscle can also shift towards not idling to conserve energy when the Caloric demands on the body far exceed what it needs. “Biggest Loser” television contestants have a suppressed resting metabolic rate by almost 1000 Cal per day (on average 500 Cal/day) even 6 years after being a part of the competition, consisting of intensive exercise and strict dieting.

Modulation of the super relaxed state (SRX) can therefore account for both the body’s resistance to weight gain (with regular movement when overfeeding) and to weight loss (without regular movement when underfeeding). There is no other system in the body that can fire up or shut down by 1000 Cal without disabling normal function.

Whether your muscles are idling or not while resting changes nothing for your immediate experience; either way you just feel like you are resting. However, your muscles are regulating your resting metabolic rate within a dynamic range equivalent to half your daily resting Calorie needs. We therefore now understand why inactivity is worse for us than expected, and why strict dieting can be less effective than moderate dieting. See my research paper for the scientific references of these ideas:

Published Research