To further explore the mechanism underpinning this finding, changes in RFD, contractile impulse, and rRFD were correlated (non-log transformed data, see Discussion) with changes in muscle activation parameters (i.e., RER and MAV). With regard to changes from 0–5 weeks, increases in RFD were correlated with RER measured to 50 and 75 ms,as shown in Figure 5 (RER 75 ms vs. RFD). Since increases in vastus lateralis (VL) and vastus medialis (VM) RER and MAV tended to occur simultaneously, an averaged value was used for analysis (VLVM) (e.g., Ref. 12). Changes in MAV measured in the period 0–200 ms in VL-VM were also correlated with changes in RFD measured to 30 (r 0.47, P 0.05), 50 (r 0.58, P 0.01), 100 (r 0.67, P 0.001), and 200 ms (r 0.75, P 0.001). Changes in RER and MAV were not correlated with changes in contractile impulse or rRFD in any muscle.