The effects of shoulder load and pinch force on electromyographic activity and blood flow in the forearm during a pinch task

Abstract

The object of the current study was to determine whether static contraction of proximal musculature has an effect on the blood flow more distally in the upper extremity. Static contractions of muscles in the neck shoulder region at three levels (relaxed, shoulders elevated and shoulders elevated loaded with 4.95 kg each) were combined with intermittent pinch forces at 0, 10 and 25% of the maximum voluntary contraction (MVC). Blood flow to the forearm was measured with Doppler ultrasound. Myoelectric activity of the forearm and neck-shoulder muscles was recorded to check for the workload levels. Across all levels of shoulder load, blood flow increased significantly with increasing pinch force (21% at 10% MVC and by 44% at 25% MVC). Blood flow was significantly affected by shoulder load, with the lowest blood flow at the highest shoulder load. Interactions of pinch force and shoulder load were not significant. The myoelectric activity of forearm muscles increased with increasing pinch force. The activation of the trapezius muscle decreased with increasing pinch force and increased with increasing shoulder load. The precise mechanisms accounting for the influence of shoulder load remains unclear. The results of this study indicate that shoulder load might influence blood flow to the forearm.

Effects of posture, movement and hand load on shoulder muscle activity

“…The small but significant effects of gripping on shoulder muscle activity appear to be dependent on function as DiDomizio (2006) found no changes in anterior or posterior deltoid activity when applying a 15% MVC hand grip in combination with a push or pull to a fixed transducer. Also, Visser et al (2003Visser et al ( , 2006 demonstrated that trapezius activity decreased when applying a pinch force of 10% MVC or higher to a hanging transducer. In both of those studies, participants did not support the transducer, which may have reduced the need to stabilize the arm compared to the current study.…”

“…Holding a 1 or 2 kg load during either shoulder flexion or abduction increased the activity of the deltoids, trapezius, and to a larger extent, supraspinatus and infraspinatus (Sigholm et al, 1984). Also, the addition of a hand grip during shoulder exertions has also been shown to influence shoulder muscle activity, even though it had no effect on the external shoulder moment (Sporrong et al, 1995(Sporrong et al, , 1996MacDonell and Keir, 2005;Visser et al, 2006). Hand grip forces of 30% and 50% maximum increased supraspinatus and infraspinatus activity by nearly 10% of maximum voluntary excitation (MVE), while middle deltoid activity decreased (Sporrong et al, 1995(Sporrong et al, , 1996.…”

Functional sensibility assessment. Part I: develop a reliable apparatus to assess momentary pinch force control

“…[25][26][27][28] Unfortunately, work-related upper extremity disorders often occur. To eliminate the risk of cumulative trauma disorder, the force dynamics that people exert on a tool or an object should be monitored, especially precision pinch force control.…”

Frequency of breaks, amount of muscular rest, and sustained muscle activity related to neck pain in a pooled dataset

“…In a preventive context, it is most of interest if such a generally increased muscle activity can be a risk factor (or mediator, i.e., a possible explanatory mechanism) for later neck pain. Cross-sectional studies and laboratory studies have not found a consistent correlation [ 5 , 13 , 14 , 63 – 68 ]. Generally, increased muscle activity does not appear to be related to concomitant pain.…”