Time course of adaptive changes and their retention Previous studies showed that functional adaptations occur rapidly after the onset of an exercise intervention and precede structural adaptations (Haram et al., 2006; Tinken et al., 2008). However, we did not detect any interplay between functional and structural adaptations, regarding their time course. An interesting finding of the present study is in relation to the time course of vascular adaptation: the change in SFA resting diameter has reached its maximum after the 3rd training week (EVE21) and did not further increase during the subsequent 3 training weeks. The steady state in luminal expansion of the SFA could not be overcome by the progressive increase in training loads by increasing weight and vibration frequency (the latter RVE only) during the study. One way of explanation would be that a functional state had been achieved at EVE21 that did not necessitate any further increase in flow capacity to accommodate the increase in exercise-related energy expenditure. In this context, it is useful to consider that the flow capacity of skeletal muscle is by far greater than could be covered by the cardiac output (Andersen & Saltin, 1985). Investigations of the retention of training effects provide helpful information about the preventive quality of a training regime. To date, only few studies investigated the retention of training interventions regarding vascular adaptation effects. We found that the BDC resting diameter of the SFA was not statistically different compared to the diameter measured at the follow-up session 70 days after intervention end. However, the difference between the BDC resting diameter and the diameter measured 90 days after the intervention failed to reach statistical significance only by a small amount (P = 006), revealing the possibility that some structural adaptation might have been maintained beyond the end of the intervention and just faded away before the follow-up testing(see Fig. 6).