Motor effort training with low exercise intensity improves muscle strength and descending command in aging

Abstract

This study explored the effect of high mental effort training (MET) and conventional strength training (CST) on increasing voluntary muscle strength and brain signal associated with producing maximal muscle force in healthy aging. Twenty-seven older adults (age: 75 ± 7.9 yr, 8 women) were assigned into 1 of 3 groups: MET group-trained with low-intensity (30% maximal voluntary contraction [MVC]) physical exercise combined with MET, CST group-trained with high-intensity muscle contractions, or control (CTRL) group-no training of any kind. MET and CST lasted for 12 weeks (5 sessions/week). The participants' elbow flexion strength of the right arm, electromyography (EMG), and motor activity-related cortical potential (MRCP) directly related to the strength production were measured before and after training. The CST group had the highest strength gain (17.6%, P <0.001), the MET group also had significant strength gain (13.8%, P <0.001), which was not statistically different from that of the CST group even though the exercise intensity for the MET group was only at 30% MVC level. The CTRL group did not have significant strength changes. Surprisingly, only the MET group demonstrated a significant augmentation in the MRCP (29.3%, P <0.001); the MRCP increase in CST group was at boarder-line significance level (12.11%, P = 0.061) and that for CTRL group was only 4.9% (P = 0.539). These results suggest that high mental effort training combined with low-intensity physical exercise is an effective method for voluntary muscle strengthening and this approach is especially beneficial for those who are physically weak and have difficulty undergoing conventional strength training.

Figure 1

Experimental setup (A) and strength testing and training schedules (B). Vertical lines in (B) indicate time in weeks, with the thin lines representing odd numbers and thick lines even numbers in the training period. Each thick vertical line also indicates a strength measurement (during-training strength measures were used to adjust training intensity). Note there were 3 strength measuremnts in the 3 week-pretraining period to obtain a truce baseline strength value.

Figure 2

Percent elbow flexion strength changes in conventional (CST), motor effort (MET), and no-training control (CTL) groups following a 12-week training program. There was no significant difference in pretraining strength among the 3 groups. Both the CST and MET groups had significant strength gains after training. The CTL group did not have significant strength increase. ^∗∗P <0.01.

Figure 3

Percent MRCP (at Cz recording site) before and after the training program. Compared with the pretraining values, the MVC-related MRCP increased significantly for the MET group at the end of the 12 weeks of training. Even though the strength gain was highest for the CST group, the MRCP increase only attained boarder-line significance (P = 0.061). ^∗∗P <0.01.

Figure 4

EEG frequency (alpha band, 8–13 Hz) power changes after versus before the 12-week training program at Cz location. Only the MET group exhibited a significant increase in the EEG power at this frequency band and recording location. ^∗P <0.05.

Figure 5

EEG frequency (alpha band, 13–35 Hz) power changes after versus before the 12-week training program at Cz location. Only the MET group exhibited a significant increase in the EEG power at this frequency band and recording location. ^∗P <0.05.

Figure 6

An example of time–frequency–power plots for a subject in the CST group before (top) and after (bottom) training at C3 (left) and Cz (right) recording locations. In each plot, the y-axis indicates EEG frequency and x-axis time points during the MVC trial with time 0 (not shown) depicting beginning of the trial, and color bar on right represents the power scales (red = greater power). Note a clear increase in power at high theta (7–8 Hz) frequency after training.