Further improvements in VO2max with longer periods of training are due to peripheral changes of enhanced oxygen extraction with an increased capillary density of skeletal muscle (Ekblom, 1968). In the presence of improved stroke volume, the increased filling time requirement between each heart beat selleck bio (i.e., a longer diastolic phase) results in a lower HRrest (Powers and Howley, 2012). Since a change in HRmax following training is not typical, it could be theorized that the difference between resting and maximal HR would increase after a period of chronic

endurance training. If this occurred, then a larger HRindex (i.e., HRmax – HRrest) and a greater pVO2max derived by the equation would have resulted. However, a change in the HRindex following training was not demonstrated in the current study mainly because neither the prediction variables (i.e., HRrest and HRmax) changed from pre to post. Therefore, pVO2max did not increase following the training program despite an increase in aVO2max. As noted previously, the HR is a parameter of Q that increases or decreases in response to a respective decrease or increase in stroke volume. As a result of no change in the HR parameters, we can conclude no subsequent

change in stroke volume took place in the studied sample. Therefore, perhaps the improvement in aVO2max following the training program was primarily due to an improvement in peripheral oxygen extraction (i.e., increased a-vO2diff), which was not accounted for in the HRindex equation. Though this is a reasonable explanation of the findings, it is only speculative as blood gases were not analyzed in this investigation. At any rate, the HRindex equation did not reflect improvements in observed VO2max in the group of competitive

female collegiate athletes. Another explanation of the findings may be due to how the HRrest was determined in the current study. Among the 60 studies reviewed by Wicks et al. (2011) that were used to develop Batimastat the HRindex equation, only 12 documented how the HRrest was recorded. Therefore, comparing how the HRrest was determined in the current study to all of the studies reviewed by Wicks et al. (2011) is impossible. Currently, there are no accepted standard recommendations for recording the HRrest, despite its importance as a prognostic variable related to cardiovascular disease risks (Fox et al., 2007). Standardization of methods could possibly decrease prediction error associated with the HRindex equation and enhance the utility of the HRrest for predicting VO2max. Future research in this area is needed. Although aerobic power is an important contributor to soccer performance, it should not be the exclusive focus when testing athletes from this population.