Why do I feel sore after exercise?

It is very common to feel sore after exercise. This feeling is called delayed onset muscle soreness, or DOMS. It occurs when we use different muscles, use our muscles in a different way, increase the intensity or length of a workout, or incorporate a new exercise.  

This type of soreness and stiffness is actually a good thing – it is a sign your muscles are strengthening and you are improving your fitness. When the muscle repairs, it gets stronger and can produce the same force without any damage.

What happens in the muscle?

Contrary to popular belief, the cause of the soreness is not a lactic acid build up. Studies have shown that the lactic acid does not stay elevated long enough after the workout to cause any soreness. 

Basically, the muscle pain occurs from small microscopic tears in the muscle, creating damage in the muscle fibres. This is called eccentric muscle contraction, in which you tense the muscle at the same time as lengthening it. 

According to the muscle damage theory of DOMS, these small ruptures are microscopic lesions at the Z-line of the muscle sarcomere. The z-line of the sarcomere are the side boundaries of a single unit of contractile muscle fibre (smallest grouping of muscle fibres that can contract). 

The soreness due to DOMS has been attributed to the increased tension force and muscle lengthening under load from eccentric exercise. This causes the parts of the muscle sarcomere (fibres) that cause contraction to separate prior to relaxation, losing the energy built up during the eccentric contraction phase and decreasing the overall strength of the muscle contractions which ultimately result in greater tension and stress on the remaining active motor units. 

This increases the risk of broadening and damage to the sarcomere. When trauma occurs to these structures, pain receptors within the muscle’s connective tissues are stimulated and cause a sensation of pain.

Another explanation for the pain associated with DOMS is the “enzyme efflux” theory. Following trauma, calcium that is normally stored in the muscle cells accumulates in the damaged muscles. The rate at which cells produce energy out of oxygen and glucose is inhibited and therefore the energy needed to actively transport calcium back into the storage area of the sarcomere is also slowed. 

This accumulation of calcium may activate proteases and phospholipases which in turn break down and degenerate muscle protein. This causes inflammation, and in turn pain due to the accumulation of histamines, prostaglandins, and potassium.

An earlier theory was that DOMS is connected to the build-up of lactic acid in the blood, which was thought to continue being produced following exercise. This build-up of lactic acid was thought to be a toxic metabolic waste product that caused the perception of pain at a delayed stage.

This theory has been largely rejected, as concentric contractions which also produce lactic acid have been unable to cause DOMS. Additionally, lactic acid is known from multiple studies to return to normal levels within one hour of exercise, and therefore cannot cause the pain that occurs much later.

Managing your soreness after exercise.

You are unlikely to be able to prevent muscle soreness, but there are many things you can do to minimise the impact. 

• • Gentle exercise – Low impact aerobic exercise brings blood flow to the muscles, some examples include walking, yoga, Pilates, swimming, or cycling. 
  • Stretch – Stretching lengthens a muscle – it can increase muscle temperature and decrease muscle stiffness

• Foam roll – Foam rolling loosens the tension in the muscle 

• Remedial or Soft Tissue Massage – This brings blood flow to the area, which helps to heal the microtraumas 

• Increase protein intake – Increased protein in your diet can increase protein synthesis in the muscle

• Cool down – Easy aerobic exercise such as jogging, or walking followed by stretching after a workout

• Cross training – Incorporating different types of exercise allows time for the muscles to rest without disrupting your training

Why it might not be a good thing.

While DOMS is typically perceived as a sign of muscle growth, if it stops you from carrying out your normal daily activities, it is too much. Muscle strength can grow without soreness, so excessive soreness can negate the benefits from exercise. 

If ignored, persistent soreness can also damage the capacity of the muscle to repair and grow strong.

At City Physiotherapy our team of professionals are here to assist you with your sports injuries and treatment for pain and stiffness. Click here to find out more about the services and treatments our physiotherapists offer.

If you have continual issues with soreness after exercise, we recommend you book an appointment with one of our highly skilled physiotherapists.

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