Influence of Training on Oxygen Requirement, Oxygen Intake and Oxygen Debt.

The results of training may briefly be summarized as follows:

1. The oxygen requirement for a given task is diminished as a result of more efficient use of muscles and elimination of extraneous movements, and of greater mechanical efficiency of the muscles themselves.

2. The maximal oxygen intake is increased through improved capacity of the heart to pump blood, and through circulatory and respiratory adjustments.

3. The maximal oxygen debt which can be incurred is increased, probably due to an increase in the amount of buffer alkali available for neutralizing lactic acid.

Oxygen Requirement

Training increases the case with which work is performed. It is difficult to determine accurately the relative importance of increased skill and of increased mechanical efficiency of the muscles. In evaluating the influence of training on skill, it is unfair to compare athletes with nonathletes because skill is due partly to inborn aptitude. However, in a given individual, the improvement in skill with training is often striking and may be acquired early in the course of training. Thus in repeated observations on one man the improvement from training appeared to reach a maximum after only a few trial runs scattered over ten days. His net efficiency during this period rose from 17.7 to 20.6 per cent. Improvement in skill and consequent reduction in oxygen requirements are often noted in army recruits learning to march.

Improvement in the mechanical efficiency of muscles is due largely to the increase in diameter of each muscle fiber which results from continued usage. As a result, fewer fibers must contract for the development of a given amount of tension. This change takes place more gradually than does the increase in skill.