I'm 53 and my MQ score is 81 so my muscle quality is off the charts.
As a runner, your performance obviously depends on the condition and efficiency of your leg muscles. But have you ever considered whether the quality – not just the quantity – of your muscles matters? Believe it or not, studies show that muscles of equal size and volume do not necessarily have equal strength and power. In other words, you and a friend may have the same thigh circumference, but tire out after a different number of squats or leg presses. This capacity of a muscle to produce force per unit of volume is called "muscle quality," or MQ.
Although MQ was originally thought of as a medical issue, we now know that it's also important in sports and exercise. Dr. Tim Noakes, an internationally-recognized researcher and avid marathon and ultramarathon competitor, was one of the first scientists to highlight the importance of MQ for runners. In his now iconic book, "The Lore of Running," published in 1985, he stated that reduced MQ was one possible cause of the age-related fall in aerobic fitness.
U.S NEWS. "What Is Muscle Quality and Why Is It Important?"