Muscle soreness following exercise is familiar to anybody who works out regularly. Thigh muscles, in particular, generate a lot of power, so they also incur a lot of damage. Physiologists don't completely understand the phenomenon of pain associated with post-exercise soreness, but its entire arc from onset to convalescence has been well documented. Most soreness will dissipate within a few days; see your doctor if the soreness in your thighs remains or worsens.
The thigh is the area of the body between the pelvis and knee. The quadriceps, a series of extensor muscles in the top of the thigh, are the largest muscle group in the thigh. The quadriceps group is made up of four separate muscles: rectus femoris, vastus lateralis, vastus intermedius and vastus medialis. Hamstring muscles are another large group. They are defined as flexor muscles on the back of the thigh comprising the biceps cruris, the semitendinosus and semimembranosus. There are also a number of other thigh muscles, including the gracilis.
Most movements require two different phases. For instance, running has a driving phase, when the leg is in contact with the ground, and a recovery phase, when the leg has left the ground. The quadriceps group is the major contracting muscle for the knee during the driving phase. The hamstrings group is a contracting force for the hip during the driving phase, and for the knee during the recovery phase. For a soccer kick, the hamstrings contract during the preparatory phase and the quadriceps contract during the kicking phase.
Muscles tend to become sore because this continuous contraction motion causes damage to the muscle fibers and motor segments of the muscle. A 2008 study by researchers at Columbia University found that, after exercise, excess calcium that would normally facilitate contractions in the muscle instead weakens it, activating enzymes that break down muscle fibers and interfere with energy production. Loss of strength, swelling and soreness in the thighs can last up to three or four days.
Delayed-Onset Muscle Soreness
Delayed-onset muscle soreness (DOMS) is a name given to a type of pain and weakness that occurs 24 to 48 hours following intense exercise. This is different from soreness that typically occurs after exercise. Experts believe DOMS is caused by lactic acid buildup in the muscles, or by an inflammatory response created by the immune system's attempt to repair structural damage in the muscles.
Sore thigh muscles can be a normal response after strenuous activity, and a healthy sign of improvement. However, soreness should always dissipate over the course of a few days. If you feel a nagging soreness that is exacerbated by exercise, rest is the best thing you can do for your muscles. Weakened muscles may suffer further damage, like a tear or strain, if pushed.