Weightlifting is an activity that builds up your muscles as you resist an opposing force or weight. If you use enough weight to increase your muscle size, you will typically feel a “burn” as your muscles reach their working capacity. You can also experience soreness when your muscles break down and repair themselves in the period following your workout.
When you lift heavy weights, your body gets the energy to support your activity by breaking down a substance called glucose. When glucose breaks down, it forms another substance called pyruvate. As you continue working your muscles, pyruvate turns into another substance called lactate, or lactic acid, which lets you keep lifting for a little longer. However, lactic acid also builds up rapidly in your muscles and triggers the “burn” commonly associated with weightlifting. This sensation acts a signal from your muscles to stop working and rest your body.
Building Muscle Tissue
Weightlifting triggers small-scale damage in the tissues of your affected muscles, according to Young sub Kwan and Len Kravitz of the University of New Mexico in the article “How Do Muscles Grow?” In turn, damage to your muscle fibers triggers activity in nearby cells called satellite cells. These satellite cells fuse to each other, as well as to your injured tissue. The cells that fuse to your tissues rejuvenate your existing muscle by filling in for damaged cellular structures. The cells that fuse to each other form new protein structures called myofibrils, which in turn add extra muscle tissue and muscle mass.