How to build muscle: The 7 key stages

The 7 key stages in the process of breaking down and rebuilding muscle fibres 1. The warm-up

As your heart rate increases, blood is pumped into your muscles, warming them up and allowing them to extend fully. The blood also supplies the muscle fibres with oxygen.

2. Under tension 

At the start of a rep, your muscles are under tension and stretched. As a result more blood is pumped into the protective sheaths of the muscle fibres, supplying even more oxygen and nutrients.

3. Initial spark

As you lift a weight, your central nervous system relays this to the nerves in the sheaths around the muscle fibres, telling the fibres to contract. If you do the exercise correctly your muscles will activate in a particular sequence, which your nervous system adapts to. As you repeat the workout, your nerves get more efficient, allowing you to do more. This is the first adaptation caused by weightlifting.

4. Chemical reaction 

Adenosine triphosphate (ATP) is the immediate energy source for these muscle contractions. It is broken down within the body’s cells to release energy. The cells’ creatine, phosphate and glycogen reserves are also converted into ATP. This process creates lactic acid as a by-product.

5. Feel the burn

Once the glycogen stores in your cells have been depleted and lactic acid starts to builds up the muscle can’t work efficiently, so you have to rest. As you do so, aerobic (oxygen-based) muscle respiration occurs, processing the lactic acid back into glycogen and giving you an energy source for the next set.

6. Successful failure 

As you reach failure on the last set of a given exercise, your fast-twitch muscle fibres are completely fatigued. Microscopic tears (

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