When you lift weights, you expose your active muscles to repetitive stress loads that increase their size over time. However, the amount of effort required during your workout can also trigger a form of temporary soreness called delayed onset muscle soreness, or DOMS. When DOMS is present, your muscles rest, rebuild and grow larger.
Pain Leading to Gain
In order to gain muscle strength, endurance or size, you must lift enough weight — or perform enough exercise repetitions — to temporarily fatigue or overload your muscles. The effort required to produce muscle fatigue can easily trigger the onset of DOMS, especially if you’re new to weightlifting or make adjustments in the weight amount or frequency of your established weightlifting routine. Although researchers don’t know exactly what causes DOMS, current theories emphasize the combined effects of microscopic tearing in your muscle tissue and inflammation inside your muscle tissue fibers.
The Muscle Building Process
Improvements in muscle size in strength actually stem from trauma to muscle tissue stemming from overload. Overload is the deliberate process of exercising beyond your current level of comfort to elicit a training adaptation. According to Len Kravitz, exercise scientist with the University of New Mexico, when you overload your muscles, microtears in the muscle fiber set off an inflammatory immune response that triggers the release of hormones and growth factors involved in the repair and rebuilding of muscle tissue. The end result is an increase in muscle fiber cross-sectional area and strength. During the healing process, inflammation and tissue damage irritate nerve endings in the muscles, causing DOMS.
The soreness associated with DOMS peaks within 24 to 48 hours and typically fades on its own within three to seven days. Although you usually can’t decrease this healing period, you can take several steps to ease the discomfort of your condition. First, make sure that you give you affected muscles plenty of time to rest during healing. If necessary, you can also apply a cold source such as ice, compress your affected muscle with bandages and/or elevate your muscle above the level of your heart. In addition, you can stretch or massage your muscles, increase blood flow to your muscles with low-intensity aerobics and use prescription or over-the-counter, nonsteroidal anti-inflammatory medications such as ibuprofen or aspirin.
When to Worry
DOMS is different from acute types of soreness that occur either during or immediately after the major exertion of weightlifting or other heavy exercise. In some cases, persistent severe debilitating pain and swelling of muscle tissues, accompanied with dark brown urine, can signal rhabdomyolysis, nicknamed "rhabdo". Rhabdo is a severe breakdown of muscle fibers that causes myoglobin to leak into your bloodstream. When left untreated, excessive myoglobin can cause serious kidney damage leading to kidney failure or death. If you suspect you have rhabdo, seek immediate medical intervention.