Interlimb transfer of load compensation during rapid elbow joint movements

Abstract

Previous research has shown that training of a novel task can improve subsequent performance in the opposite arm owing to anticipation of the previously learned task conditions. Interestingly, we recently reported preliminary evidence that such transfer might also include modulation of feedback-mediated responses. We now test interlimb transfer of load compensation responses, measured through kinematic and EMG recordings during rapid 20 degrees elbow flexion movements. Two subject groups, LR and RL, each comprising six right-handed subjects, first performed using either the left (LR) or right (RL) arm, followed by opposite arm performance. After 30 trials of consistent performance, five random trials within a background of 50 trials were loaded with a 2-kg mass prior to the "go" signal. We compared load compensation responses for naive performance with those following opposite arm exposure. Under naive conditions, the resulting load compensation responses began about 50 ms following movement onset, and were substantially more effective for the nondominant arm. Opposite arm exposure substantially improved the accuracy of only dominant arm responses. This, however, did not occur through changes in the short latency components of the load compensation response. Instead, changes in muscle activities, associated with interlimb transfer, began some 150 ms following movement onset. We expect that these changes represent transfer in the "volitional" component of the load compensation response. Because the shorter latency response was unaffected by opposite arm exposure, modulation of this component likely requires prior experience with limb specific effectors.

Fig. 1

EMG timing analysis procedure. P value time series. Baseline and loaded averaged EMG recordings (five trials each condition) for biceps and anconeus. Data were synchronized to elbow peak acceleration. Data were normalized to the maximum muscle activity

Fig. 2

Two representative profiles from the nondominant (left) and dominant (right) arm groups under naïve performances. Averaged elbow displacement. The insets depict the respective elbow velocity profiles. Data were synchronized to elbow peak acceleration. Bar graphs: Kinematic comparisons: elbow displacement error and time of zero crossing (elbow velocity) for dominant and nondominant arm groups across subjects and conditions. *Results from statistical analysis were significant

Fig. 3

EMG recordings (individual trials) for biceps brachii and anconeus for the nondominant (left) and the dominant (right) arm under naïve performances. Data were synchronized to elbow peak acceleration. Data were normalized to the maximum muscle activity. Bar graphs: EMG impulse comparisons for dominant and nondominant arm groups for all recorded muscles. *Results from statistical analysis were significant

Fig. 4

Two representative profiles from the nondominant (left) and dominant (right) arm groups after opposite arm performances. Averaged elbow displacement. The insets depict the respective elbow velocity profiles. Data were synchronized to elbow peak acceleration. Bar graphs: Kinematic comparisons: elbow displacement error and time of zero crossing (elbow velocity) for dominant and nondominant arm groups across subjects and conditions

Fig. 5

Maximum and final elbow displacement angles across subjects for the dominant arm, under naïve performance and after opposite arm performance (AOAP). *Results from statistical analysis were significant

Fig. 6

EMG recordings (individual trials) for biceps brachii and anconeus for nondominant (left) and dominant (right) arm after opposite arm performances. Data were synchronized to elbow peak acceleration. Data were normalized to the maximum muscle activity. Bar graphs: EMG impulse comparisons for dominant and nondominant arm groups for all recorded muscles. *Results from statistical analysis were significant

Fig. 7

Dominant arm EMG impulse comparisons for all recorded muscles for two time intervals: 0 (A_max) to 100 ms (left) and 100–200 ms (right). *Results from statistical analysis were significant