Effect Of Motor Imagery Training On Strength

It is well known that, to strengthen a muscle one should perform trainingthat involves lifting heavy loads or working against high-resistance.Also, it is widely accepted that muscle strengthgains are primarily fromneural adaptations in the early stage and from muscle hypertrophy in thelater stage of training. We have recently reported that young adults canachieve substantial voluntary strength gains in the elbow flexors withtraining involving low resistance but strong mental effort. In contrast,individuals who trained with the same low-intensity contractions but withlow mental effort had no improvement in strength. Based on thesepreliminary findings, we hypothesized that, similar to young adults,muscle strength improvements in the elderly also depend primarily on thelevel of mental effort during training, not the training intensity(resistance) per se. We also hypothesized that an increase in the centralnervous system (CNS) drive is the primary mechanism that mediatesstrength improvements induced by the low-intensity training.The purpose of the first study was to compare the effect of internal orfirst-person perspective imagery with that of external or third-personperspective imagery in increasing voluntary muscle strength. Eighteen(18) young healthy subjects were randomly assigned to one of three groups:internal mental imagery (IMI), external mental imagery (EMI), or ano-practice control (CTRL) group. Training lasted for6weeks (15min/day,5days/week). The participants’ right-elbow flexor musclestrength and motor activity-related cortical potential (MRCP) directlyrelated to the strength production were measured before and aftertraining. Only the IMI grouped showed significant strength gain (10.8±2.7%, P<.01) while the EMI (4.8±4.3%, P>.10) and CTRL (-3.0±2.6%, P>.05) group did not. Similarly, only the IMI groupdemonstrated a significant enhancement in. the MRCP (16.1%, P=0.015)but. the EMI and CTRL groups did not. These results suggest that trainingby internal Imagery of forceful muscle contractions increases brainactivation level that might translate to greater descending command fromcortical control centers to the target muscle,leading to the strengthimprovement. The purpose of the second study was to invest the mental effect inincreasing voluntary muscle strength in elderly people. Nineteen healthyelderly (age:74±6.7yr,3women) volunteers were randomly assignedinto2groups: Low-intensity (30%maximal voluntary contraction [MVC])physical exercise with high mental effort (HME) group, Low-intensity (30%maximal voluntary contraction [MVC]) physical exercise with low mentaleffort.(LME) group. Training lasted for12weeks (10min/day,5days/week).The participants’ right-elbow flexor muscle strength, surface EMG andmotor activity-related cortical potential (MRCP) directly related to thestrength production were measured before and after training. The HMEgroup had significant strength gains (13.8%, P=0.002) at the end oftraining, On the other hand, the LME group which also trained with30%MVC intensity had only5%(P=0.045) strength gain. Surprisingly, onlythe HME group demonstrated a significant enhancement in the MRCP (28.6%,P <0.005) but the LME (-2.9%, P=0.803) group did not. It is concludedthat: the level of mentaleffort related to maximal muscle activation doesindeed play a crucial role in determining voluntary strength gains inthe elderly.Tne purpose of tne third study was to explore the effect of motor imagerytraining (MIT) on increasing voluntary muscle strength and relatedcentral nervous system adaptations in elderly people. Twenty-sevenhealthy elderly (age:75±7.9yrs,8women) volunteers were randomlyassigned into3groups: Low-intensity (30%maximal voluntary contraction[MVC]); physical exercise combined with MIT group, CST group (trained withhigh-intensity muscle contractions), or a no-practice control (CTRL)group. MIT and CST lasted for12weeks (5sessions/week). Theparticipants’ right-elbow flexor muscle strength, electromyography(EMG), and motor activity-related cortical potential (MRCP) directlyrelated to the strength production were measured before and aftertraining. The CST group had the highest strength gain (17.6%, P<0.001),the MIT group also had significant strength gainst (13.8%, P<0.001), whichwas not statistically different from that of the GST group even thoughthe exercise intensity for the MIT group was only30%MVC level. Theno-practice CTRL group did not have significant strength changes.Surprisingly, only the MIT group demonstrated a significant enhancementin; the MRCP (28.6%, P<0.001); the MRCP increase in CST group was atboarder-line significance level (9.9%, P=0.061) and that for CTRL groupwas the lowest (4.9%, P=0.539). These results suggest that MIT combined with low-intensity physical exercise is an effective method for voluntarymuscle strengthening. Training of the cortical motor control centersmight translate to greater descending command to the target muscle,leading to strength gains in elderly people.This research based on these three pilot studies concluded that(1)it ispossible to gain muscle strength by mental training alone;(2)imaginedand physically executed motor actions share common neuralsubstrates;(3)A major mechanism for the increase in muscle strength inthe elderly is the excitement of the central nervous system in training.