Kelley used to do three sets of squats one time per week. after three weeks she noticed she was less sore than when she started this exercise. which principle is at work?

The principle underlying this change is called progression. This principle tells us that when your fitness level improves, your body has adjusted to your regular routine; thus, you will feel less sore than when you started the squats three weeks ago. During this time, your muscles have developed and your body has adopted to the stress brought about by your exercise. 

you know that this symptom is misleading and quite often is related to: heart attack

a heart attack is a condition that occurs when the blood flow that transports oxygen to the heart muscle is damaged or cut off completely. the coronary arteries that supply the heart muscle with blood flow can be blocked by the accumulation of plaque. also, when the plaque within the heart artery breaks, it creates blood clot that can also hinder the blood flow. men that are over 45years of age and women that are over 55years of age are at risk of having a heart attack. the symptoms of a heart attack include chest discomfort, chest pain, coughing, and shortness of breath.