Effect of load level and muscle pain intensity on the motor control of elbow-flexion movements

Abstract

This study assessed interactions between mild/moderate muscle pain and inertial load on the control of human elbow-flexion movements. It is hypothesized that high inertial load combined with moderate muscle pain intensity affect the motor control more than for low inertial-load combined with low-intensity pain. Fifteen subjects performed horizontal pointing movements (70 degree range) under three load conditions: 0, 4, and 10 kg. Pain was induced by injection of 0.5 ml and 1.5 ml hypertonic saline into the biceps muscle. Subjects scored the muscle pain intensity on a visual analogue scale (VAS). Elbow joint position, VAS, and the electromyograms (EMG, m. biceps brachii, m. triceps brachii, m. brachioradialis, and m. trapezius) were recorded. Mild and moderate muscle pain attenuated acceleration profiles [6.1(0.9)%], effective movement amplitude [3.2 (0.7)%], peak velocity [5.8 (0.9)%] and prolonged the reaction time [21 (5)%]. No interaction between muscle pain intensity and inertial load was found for the kinematic parameters. EMG profiles from m. biceps brachii, m. triceps brachii, and m. brachioradialis were similarly attenuated [10.2 (0.80)%] by mild and moderate muscle pain in all inertial load conditions. For high inertial load, the initial agonist EMG burst activity was more attenuated [50 (5.3)%] by moderate muscle pain compared with mild muscle pain [34 (4.2)%]. These data suggest that for high effort-demanding tasks muscle pain differently affects the motor planning according to the pain-intensity level. Perturbations of motor planning lead to changes on movement strategies, which might be a potential cause of musculoskeletal problems.

Experimental muscle pain increases normalized variability of multidirectional forces during isometric contractions

“…7A, C), experimental muscle pain consistently increased force fluctuations regardless of force level, illustrating that distinct mechanisms are evoked by the different pain models. Although not supporting the third hypothesis, the current results are consistent with previous findings showing that experimental muscle pain also attenuates the kinematics of dynamic arm movements regardless of load level (Ervilha et al 2004). …”

Impact of clinical and experimental pain on muscle strength and activity

“…Other strategies might also be adopted, as individual combinations of decreased, increased, and cocontraction activity of trunk fl exors and extensors were reported during experimental low back pain [40]. Reduced activity in both the agonistic and antagonistic muscles during muscle pain has been reported without significantly impairing the movement amplitude or acceleration [41]. Specifi cally, the initial (100 ms) EMG burst recorded from the agonist muscle was decreased, illustrating the reorganized motor strategy caused by muscle pain.…”

“…Anomalous motor planning is highly important in working conditions where such a change may need compensatory activity from other muscles to fulfi l the required movement, and such a scenario may contribute to the development of musculoskeletal pain problems in occupational settings. A potential compensatory action may be the increased trapezius activity recorded during biceps muscle pain [41]. Similarly, reorganization of trapezius muscle activity during repetitive shoulder fl exion has been found as decreased activity of the upper trapezius (where pain was induced), whereas the lower trapezius showed compensatory actions by increased muscle activity [43].…”

Dissociation in changes in EMG activation during maximal isometric and submaximal low force dynamic contractions after exercise-induced muscle damage

“…Resting elbow angles, and by implication the resting length of the biceps muscle were measured with a goniometer (Lambert et al, 2002). Current pain perception was measured on a daily basis before the muscle function test with the use of a 10 cm visual analog scale (VAS) (Ervilha et al, 2004;Svensson et al, 1998).…”