Heredity and muscle adaptation to endurance training

Area of Science:

• Exercise Physiology
• Human Genetics
• Sports Science

Background:

• Individual responses to endurance training vary considerably.
• The role of genetics in mediating these training adaptations is not fully understood.
• Monozygotic twins share identical genes, making them ideal for studying genetic influences.

Purpose of the Study:

• To investigate if muscle characteristics and aerobic performance adaptations to endurance training are genotype-dependent.
• To quantify the genetic contribution to training responses in maximal oxygen uptake and endurance performance.

Main Methods:

• Six pairs of monozygotic twins underwent a 15-week ergocycle endurance training program.
• Muscle biopsies assessed fiber type and enzyme activities (creatine kinase, hexokinase, etc.).
• Maximal oxygen uptake and endurance performance were measured before and during training.

Main Results:

• Significant increases in maximal oxygen uptake (14%) and endurance performance (31%) were observed post-training.
• Several muscle enzyme activities (hexokinase, phosphofructokinase, LDH, MDH, HAD) increased significantly.
• High intra-pair resemblances (0.65-0.83) in training responses indicated strong genetic influence.

Conclusions:

• Both maximal oxygen uptake and endurance performance adaptations to endurance training are substantially genotype-dependent.
• Genetic factors play a crucial role in determining an individual's capacity to benefit from endurance exercise.
• Specific muscle enzyme responses to training also show significant genetic heritability.