Representing fine-wire EMG with surface EMG in three thigh muscles during high knee flexion movements

Muscle activation and rating of perceived exertion of typically developing children during DRY and aquatic treadmill walking

Aquatic treadmill gait training is a poorly understood rehabilitation method that alters bodyweight support, increases lower limb resistance, and assists with postural stability. This training could be an attractive tool for clinical populations with balance control issues or limited weight-bearing prescriptions for the lower limb. As a first step, the purpose of this study was to quantify differences in mean muscle activity of the tibialis anterior, rectus femoris, medial gastrocnemius, and semitendinosus, and perceived exertion (RPE) in typically developing children (7:8 M:F, age = 11.3 ± 4.1 years, 1.46 ± 0.18 m, and 44.2 ± 16.8 kg) during dry and aquatic treadmill walking at 75 %, 100 %, and 125 % self-selected speed. We hypothesized that the greatest mean muscle activity, normalized to percent maximum voluntary contraction and averaged across all strides, would be observed during 125 % dry treadmill walking and that aquatic treadmill walking would produce lower RPE. Overall, aquatic treadmill walking reduced mean medial gastrocnemius activity by 50.2 % (padj < 0.001), increased mean rectus femoris activity at least 32.8 % (padj < 0.006), and produced 78.0 % (padj = 0.007) greater RPE compared to dry treadmill walking. This study provides normative pediatric data for future aquatic treadmill walking studies in clinical populations to help inform gait rehabilitation protocols.

The influence of contraction type, prior performance of a maximal voluntary contraction and measurement duration on fine-wire EMG amplitude

We aimed to investigate the impact of time on fine-wire (fw) electromyography (EMG) signal amplitude, and to determine whether any attenuation is confounded by task type. Twenty healthy participants were instrumented with fw and surface (s) EMG electrodes at the biceps brachii bilaterally. Participants held a weight statically with one arm and with the other arm either repeated the same task following a maximum voluntary contraction (MVC) or repeated dynamic elbow flexion/extension contractions. Each task was repeated for 30 s every five minutes over two hours. EMG amplitude was smoothed and normalized to time = 0. Stable median power frequency of the s-EMG ruled out the confounding influence of fatigue. Repeated-measures ANCOVAs determined the effect of electrode type and time (covariate) on EMG amplitude and the confounding impact of task type. During the isometric protocol, fw-EMG amplitude reduced over time (p = 0.002), while s-EMG amplitude (p = 0.895) and MPF (p > 0.05) did not change. Fw-EMG amplitude attenuated faster during the dynamic than the isometric protocol (p = 0.008) and there was evidence that the MVC preceding the isometric protocol impacted the rate of decline (p = 0.001). We conclude that systematic signal attenuation of fw-EMG occurs over time and is more pronounced during dynamic tasks.

The ability of surface electromyography to represent supraspinatus anterior and posterior partition activity depends on elevation angle, hand load and plane of elevation

This study examined relationships between electromyography recorded from indwelling electrodes of the anterior and posterior supraspinatus and a surface supraspinatus electrode. Twenty male and twenty female participants completed full range humeral elevations in three planes of elevation (0/40/90°) and three hand loads (unloaded/20%/40% of maximal elevation strength). EMG activation was combined with motion capture to determine activation at instantaneous activation angles, and linear regressions of anterior and posterior indwelling electrodes relative to the surface electrode determined relationships between these signals. Regressions between surface and indwelling signals were affected by plane of elevation, elevation angle, load intensity and participant sex, but no interactions existed. Surface signals underestimated activation at low elevation angles for both regions, and up to 45% in the anterior supraspinatus (p < 0.01), then overestimated activation at higher elevation angles. Surface EMG underestimated indwelling signals by up to 15% in unloaded conditions, while overestimating the posterior region by up to 17% in the 40% load condition (p < 0.01). Sex effects showed increased overestimation by surface signals in the posterior region in males by 21% (p < 0.01). Better agreement existed for the anterior region than the posterior region across postures, but postural relationships should be considered when choosing electrodes for this muscle.