The Role Of Exercise Intensity In Cell Signaling: Is There A Repeated-bout Effect?

Abstract

PURPOSE: Acute exercise elicits a temporary change in redox balance resulting in activation of antioxidant related gene expression and enzymes. We have previously shown in men that the type of acute exercise stimulus, constant workload (CW) vs. high intensity interval protocol (HIIP) results in different redox responses despite no differences in mean VO2. The present study tested whether these results translate to women. In addition, we asked whether the responses are amplified through a repeated bout effect, by comparing the responses after 1 bout to those after 3 bouts. It was hypothesized that HIIP would render greater cell signaling response compared to CW and that differences would be amplified after 3 sessions. METHODS: Healthy women ages 30-45y participated in this study in a randomized, cross-over design (n=12, projected) with a 2-week washout period between trials. Each participant completed a VO2max on a cycle ergometer to establish the workload for the exercise trials. Subjects were randomized to complete either CW or HIIP sessions first. Each trial occurred every other day for 5 days. A second VO2max was performed prior to the second trial to ascertain that VO2 max had not changed from baseline. CW consisted of 30-min of cycling at 70% VO2max. HIIP consisted of a 9-min ramp-up, 7 intervals of 1-min “all out” intervals at 90-100% VO2max followed by 2-min recovery for a total of 30-min of cycling. Blood draws were taken pre-, and 10- 30-, and 60-min post exercise during the first and third exercise session of each trial. Cell signaling was measured by nuclear localization of Nrf2 as well as protein abundance of GCLC and GSR in PBMCs. GR enzyme activity was measured in erythrocyte lysate. RESULTS: To date, 5 women have enrolled in the study and testing is still underway. The average intensity of the CW trial is 70.3% and the average intensity of the HIIP intervals is 91.7% VO2max. The early data show a trend for increased nuclear Nrf2 and GSR protein abundance HIIP compared to CW, and an amplification of the response after 3 sessions. CONCLUSION: These preliminary data suggest that delivering an exercise stimulus in short “pulses” of high intensity such as the HIIP elicits a greater protective signaling response as compared to a block of moderate CW exercise, and furthermore that these effects are amplified by a repeated bout effect.