Introduction and Background
|Comparison of filtered and unfiltered FMG (top traces) to EMG for isometric extension (left) and flexion (right) tasks.|
FMG consists of an array of pressure sensors mounted to a cuff and worn on the leg. Theses sensors record the outward pressure exerted on the skin, which changes at different locations along the leg as muscles contract and relax. FMG works on the principle that as limb muscles contract, certain regions on the muscle bellies bulge outward, while others recede inward from the surface, resulting in positive or negative pressure changes below the surface of the skin. These pressures are detected by sensors within the sleeve which register the pressures as activation and cessation of muscle activity, which can be displayed in real-time and recorded for post-hoc analysis.
Comparison to ElectromyographyEnhanced Repeatability & Compatibility
|Comparison of filtered FMG (left) and filtered & rectified EMG (right) for ambulatory tasks (v=1.3m/s, n=8). Traces normalized temporally and for magnitude.|
Results show that FMG records temporal landmarks of muscle activity with as much fidelity as EMG, but with less waveform variability from stride to stride and from trial to trial: mean variance ratios were calculated to be an order of magnitude greater for that of EMG as compared to FMG. Intraclass correlation coefficients of temporal landmarks typically exceeded 0.8 for the inter-rater comparison of FMG to EMG.
Additionally, a single male subject, 53 years old, and with no significant limitations, participated in a single session of isometric protocols. Seated ina Biodex Dynamometer and using the right (dominant) leg, 10-15 seconds of isometric flexion and extension tasks were recorded simultaneously by EMG and FMG. Data was smoothed and processed for evaluation of temporal landmarks and waveform fidelity.
During isometric contractions, FMG and EMG waveforms were highly correlated, with r>0.8 for flexion and r>0.95 for extension. These results, together with those of the ambulatory data, suggest the utility of FMG as a simpler alternative to EMG for some applications.