In-vivo measurement of muscle tension: dynamic properties of the MC sensor during isometric muscle contraction.

Srđan Đorđević,Rado Pišot,Sašo Tomažič,Marco Narici,Andrej Meglič

doi:10.3390/s140917848

Abstract

Skeletal muscle is the largest tissue structure in our body and plays an essential role for producing motion through integrated action with bones, tendons, ligaments and joints, for stabilizing body position, for generation of heat through cell respiration and for blood glucose disposal. A key function of skeletal muscle is force generation. Non-invasive and selective measurement of muscle contraction force in the field and in clinical settings has always been challenging. The aim of our work has been to develop a sensor that can overcome these difficulties and therefore enable measurement of muscle force during different contraction conditions. In this study, we tested the mechanical properties of a “Muscle Contraction” (MC) sensor during isometric muscle contraction in different length/tension conditions. The MC sensor is attached so that it indents the skin overlying a muscle group and detects varying degrees of tension during muscular contraction. We compared MC sensor readings over the biceps brachii (BB) muscle to dynamometric measurements of force of elbow flexion, together with recordings of surface EMG signal of BB during isometric contractions at 15° and 90° of elbow flexion. Statistical correlation between MC signal and force was very high at 15° (r = 0.976) and 90° (r = 0.966) across the complete time domain. Normalized SD or σN = σ/max(FMC) was used as a measure of linearity of MC signal and elbow flexion force in dynamic conditions. The average was 8.24% for an elbow angle of 90° and 10.01% for an elbow of angle 15°, which indicates high linearity and good dynamic properties of MC sensor signal when compared to elbow flexion force. The next step of testing MC sensor potential will be to measure tension of muscle-tendon complex in conditions when length and tension change simultaneously during human motion.

Highlights

Skeletal muscle system is the largest human tissue structure
The Muscle Contraction‖ (MC) measurements were performed on the biceps brachii (BB) muscle, which is the strongest elbow flexor, while the dynamometer (FD) measurements were performed simultaneously on the wrist (Figure 1)
Typical recorded signal of FD, FMC and EMG measurement of isometric contraction of BB muscle during elbow flexion of 90°is shown on Figure 1

Summary

Introduction

Skeletal muscle system is the largest human tissue structure. Our muscles are a biological force generator designed to provide the functional requirements for posture and movement.Muscle force is generated by the active (cross bridge) muscle elements and exerted via passive elastic components, such as fascia and tendon, both in series and in parallel. The earliest approximations of muscle force were based on torque measurements measured using a dynamometer and estimating the moment arm using radiographs [2], followed by MRIs [3] and in the most recent implementation, dynamic ultrasound imaging to make more precise moment arm estimations during muscle contraction and enabling more accurate muscle force calculations. These methods still share the problem of composite force measurements, limiting application [4,5]. The recovery of a specific hamstring muscle which had suffered partial strain injury can only be inferred from force measurements of knee flexion, which are due to the composite action of all three hamstring muscles, a counter-force from the quadriceps and possibly small contributions from popliteus and gastrocnemius

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