In order to have a better understanding of the basic metabolic changes the take place in response to endurance and anaerobic training, you first need to know the different ways ATP or adenosine triphosphate is generated. Also, the principle of sports specificity helps give a “real world” understanding of how specialized the biochemical adaptations are that occur with different types of training.
Energy Metabolism 101
Energy in the form of ATP is needed to fuel metabolic processes at rest and physical activity. There are different energy-yielding pathways by which ATP can be produced. These individual pathways are not exclusive as all are ongoing at any given moment during physical activity. However, it is the intensity and duration of the physical activity that determines to which degree each pathway contributes energy.
The energy-yielding pathways can be classified into 3 groups:
- Anaerobic phosphagen system (a.k.a. ATP-PCr system)
- Anaerobic (glycolytic) pathway (a.k.a. substrate-level phosphorylation)
- Aerobic pathway (a.k.a. oxidative phosphorylation)
The Principle of Specificity
To increase performance in a certain sport or event, the individual must train specifically to stress the particular energy pathway that is predominant in his/her respective sport. This is referred to as metabolic training and is part of the training principle of specificity. Not only is it important to train at a similar or higher intensity (overload), training has to involve closely related modalities and movements that emulate actual kinesthetics/biomechanics of competition. Basically, the same muscle groups have to be stressed in a manner similar to that used in sport. For example, research has demonstrated that the effects of swim training elicited a significant increase in swimming VO2max with no improvement in running VO2max. Therefore, no translation of increased performance took place in running from swim training.
Anaerobic Training: Metabolic Adaptations
Anaerobic power training will produce metabolic adaptations specific to this energy system. The adaptations here occur mostly in the type IIx muscle fibers, which are predominantly used during anaerobic activity. Three major physiological changes occur in response to anaerobic training:
↑ concentration of anaerobic substrates (ATP, PCr, creatine, glycogen)
↑ concentration and activity of enzymes involved with anaerobic glycolysis
↑ concentration of blood lactate during all-out exercise and concomitant tolerance to plasma induced acidity
Endurance Training: Metabolic Adaptations
Effect on Mitochondria
Similarly, endurance or aerobic training elicits adaptations specific to the aerobic pathway. These metabolic changes occur mostly in type I muscle fibers that are primarily stimulated in aerobic activity. However, research has shown that oxidative capacity of type IIa fibers can nearly match that of the type I’s with high-intensity aerobic training.
↑ size of mitochondria
↑ number of mitochondria
↑ concentration of oxidative enzymes (as a result of increased mitochondria number and size)
Effect on Fat and Carbohydrate Metabolism
Furthermore, endurance training involves changes in the way primary aerobic pathway substrates (fat and carbohydrate) are metabolized. Lipolysis and fat oxidation during submaximal exercise increases as a result of endurance training.
The factors contributing to this effect are:
↑ blood flow in trained muscle
↑ concentration of fat-metabolizing enzymes
↑ muscle respiratory capacity due to mitochdrial improvement
↓ catecholamine release (catecholamines increase glycolysis)
Concerning changes to carbohydrate metabolism:
↑ capacity to oxidize carbohydrate during maximal exercise
↑ glycogen storage
↓ use of glycogen at submaximal exercise due to increased fat oxidation
