Hypertrophy: How do muscles grow?

Muscle growth is what many athletes want. But what exactly happens? And what are the differences?

Hypertrophy? What’s that?

Hypertrophy1, or muscle fiber hypotrophy, refers to an increase in muscle fiber volume. This means that the volume (size) of muscle fibres2 increases, regardless of whether the nuclei within these muscle fibres also multiply. This increase can occur in two ways: over the length and/or over the cross-sectional area of the muscle fibres.

What happens in hypertrophy with the same number of nuclei?

If the number of nuclei3 within the muscle fibres remains the same, the volume of a muscle fibre per nucleus increases. This can be the case if, for example, the proportion of water stored within the cells (i.e. intracellular water) is increased. This would be the case, for example, with creatine supplementation. However, it could also be because the rate of muscle protein synthesis4 has increased while the rate of degradation has remained the same. This would result in a positive muscle protein balance, which would also increase the volume.

And what happens when the nuclei multiply?

In comparison to the previous scenario, however, it is also possible that the nuclei within the muscle fibers are increased. Satellite cells5 are the starting point for this multiplication. On the basis of these satellite cells, new fibre cell nuclei can then be formed. Since the protein mass of the muscle fibres consists mainly of myofibrillary6 proteins, an increase in muscle mass will occur primarily when this myofibrillary protein mass is increased. And for this process of protein production the cell nuclei are required.

With which form of training can hypertrophy be stimulated?

In contrast to training for maximum strength, hypertrophy training in the submaximal load range involves repetition numbers of 6 to 8, and for some athletes up to 15 repetitions per set. The weights used are in the range of about 60% to 90% of the weight with which a single repetition is possible.

Of course it is also important here: The higher the weights, the more controlled the movements should be. Otherwise an increased risk of injury is to be expected.

Used terms

  1. Hypertrophy: growth in size of an organ (in our case a muscle) beyond the normal level
  2. Muscle fibre: The muscle fibres are the cells of the muscles of the cross-striped skeletal muscles and can be induced to develop strength through contraction by impulses from the connected nerves.
  3. Cell nucleus: In the nuclei of the cells, the “stamps” are created, with the help of which the cells can produce new protein for construction or other functions. In a sense, the cell nucleus is the control unit of the cell.
  4. Synthesis: In the course of synthesis, two or more units are combined to form a new unit. Muscle protein synthesis therefore means the composition of protein from several smaller building blocks (amino acids), which can then be used as a building material for muscle growth.
  5. Satellite cells (myoblasts) are precursor cells of skeletal muscle fibers and, in contrast to these, only have a single nucleus. They play a role in regeneration after muscle fibre injuries.
  6. Myofibrils are the functional units within the muscle cells that are responsible for the development of strength.

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