The most common types of muscle contractions you’ll see in any gym are concentric (muscle shortening, i.e. pulling the weight toward you in a bicep curl) and eccentric (muscle lengthening, i.e. lowering the weight away from you in a bicep curl). But there’s another, often overlooked type of training; isometric, where the muscle at work is neither lengthening OR shortening. Think of carrying a bag of groceries; you aren’t moving your muscles but after a while (or rather quickly when it’s a gallon of milk!) your arms begin to fatigue. That, my friends, is an isometric contraction.
Interestingly, isometric muscle action has been shown to recruit 5% MORE motor-units/muscle fibers than concentric or eccentric actions; i.e. more bang for your buck. Try out this circuit at home and incorporate isometric training into your regular routine!