Acute leg length discrepancy causes increased VO2

Oxygen consumption (VO2) is an accepted measure of an individualʹs expenditure of energy. It is frequently determined by walking or running on a treadmill at a fixed workload in which VO2 is generally constant and accurately reflects the individualʹs physical effort. Under certain conditions, however, such as with a leg length discrepancy, VO2 may be increased as well as related respiratory measures (Fb and VT). In that the increase in VO2 is subject to changes in central (Q = HR × SV) and/or peripheral (a- diff) adjustments to physical effort, it is important to determine the specific reason for the increase. In the case of an artificially created leg length discrepancy (31.8 mm) in this study, the subjectʹ HR increased with a corresponding increase in Q to match the increased need for oxygen when walking with unequal leg lengths. This central adjustment was not accommodated by a peripheral adjustment, which would have allowed for a sharing of the responsibility for increasing VO2. Moreover, the central adjustment was made specifically by the subjectsʹ HR with no change in SV. This adjustment is not as beneficial as when SV is the reason for the increase in Q. Hence, the data indicate that the acute leg length discrepancy predisposed the subjects to a slightly higher metabolic demand at the heart level (given the significant rise in HR and the correlation between HR and myocardial oxygen consumption).