Exercise Induced Muscle Damage (EIMD)
EIMD occurs when muscles become damaged after exercise. This usually occurs when athletes take part in a new or unfamiliar sport or experience an increase in volume or intensity while learning a new technique. This may result in short-term performance degradation because Composition of muscles. These decreases in performance are often due to increased resting energy expenditure and metabolic demands, decreased force and power output generated by the muscles, and the athlete’s perception of muscle soreness. Main impact of EIMD Appears 24-48 hours after muscle damage has occurred .
EIMD has been a hot topic in exercise and exercise science research for over 30 years. It is a disorder characterized by transient ultrastructural myofibril disruption, loss of muscle strength and power, delayed onset muscle soreness (DOMS) swelling, and decreased range of motion Affected limbs have increased muscle protein release into the interstitial space and circulation as well as increased muscle temperature. 
EIMD and eccentric (i.e. lengthening) versus concentric (i.e. shortening) muscle contractions are known to recover more slowly. Concentric muscle contraction does not cause exercise-induced muscle damage, but exercise-induced muscle damage is evident after isometric contraction Long muscle length and eccentric muscle contraction, even at low intensities.
Various mechanisms may explain the loss of strength after eccentric exercise, which is considered the best indicator of exercise-induced muscle damage. The following theoretical models outline these mechanisms.
- Mechanical strain during eccentric motion can cause uneven sarcomere halves and excessive stretching of sarcomeres beyond filament overlap, resulting in “burst sarcomeres.” A sarcomere is the name for the contractile part of a muscle fiber.
- These alterations may directly reduce force production and overload the sarcolemma and T-tube structures. These events, in turn, lead to rupture of stretch-activated channel membranes and opening of excitation-contraction coupling dysfunction.
- Entry of Ca2+ into the cytosol through stretch-activated channels and/or the permeable portion of the sarcolemma may stimulate calpains to degrade contractile proteins or excitation-contraction coupling proteins, leading to long-term loss of muscle strength. 
Muscles quickly adapt to the structural damage caused by exercise and reduce further soreness and damage during later exercise events. 
Satellite Cells in EIMD
Schematic diagram of satellite cell myogenesis and typical markers of each stage
Satellite cells (SCs) play an integral role in recovery from skeletal muscle injury and in supporting muscle hypertrophy. In response to exercise, satellite cells are activated through various signaling pathways.
- SCs in men and women respond similarly to acute and chronic resistance exercise, and SC and myonuclei hyperplasia are associated with training-induced muscle fiber hypertrophy .
- Skeletal muscle regeneration is a highly synchronized process that requires muscle stem cells (satellite cells).
However, a new study (2021) found that localized injury experienced through exercise activates a mechanism of muscle fiber self-repair independent of satellite cells. .
EIMD can adversely affect performance, such as
- Endurance cyclists exhibit reduced power output during competition
- The muscle fibers of marathon runners and downhill runners show significant damage both after training and after a marathon 
Figure 5: Changes in muscle thickness after exercise-induced muscle injury.
The greatest deficits in strength speed and agility were found 48 hours after muscle damage. In sports, these margins can have a major impact on the outcome of a game.
- When muscle strength drops ≤20% immediately after exercise, it usually recovers within 2 days after exercise.
- While muscle strength drops by about 50% immediately after exercise, especially for muscle strength initially exposed to eccentric muscle contractions, it remains below pre-exercise values 7 days after exercise. 
In some cases, EIMD may be beneficial because it can increase muscle hypertrophy (increased muscle mass). This is because small tears in muscle tissue release muscle proteins that are used to build new muscle cells .
Avoiding new training techniques and increasing exercise volume and intensity for 14 days after competition can reduce the risk of EIMD. This is especially important if introducing exercises with a high eccentric component, such as plyometrics and Olympic weightlifting.
When athletes experience EIMD, recovery interventions must be maximized. Training during EIMD may not affect performance, but recovery may be delayed. This must be taken into account if the athlete is preparing for an upcoming competition. 
There is wide interindividual variability in response to EIMD. Athletes can be protected from EIMD by the ‘repeat effect’, which is the adaptation of skeletal muscle tissue after the first injurious exercise and making it less prone to injury in subsequent exercises of the same type exercise. In fact, repetitive performance of disruptive exercise has been shown to reduce inflammatory oxidative stress leukocyte infiltration and strength loss in EIMD.
Treatment for EIDM
Many treatments have been tested to see if they help restore muscle function and reduce muscle soreness after exercise. Perhaps with the exception of massaging cold water soaks and wearing tights, the treatments haven’t produced consistent results. Although There is a lack of evidence to support the physical benefit of some of these treatments, and their perceived effects may be important for motor recovery. In this regard, however, a key consideration is whether to speed up recovery by masking pain sensations or prior to structural remodeling. These treatments may actually increase the risk of further muscle damage. 
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