Mechanomyographic and electromyographic responses during fatigue in humans: influence of muscle length

Abstract

Mechanomyography (MMG) provides a measure of muscle mechanical changes during contractions. The purpose of this study was to quantify alterations in MMG signals during fatigue at two muscle lengths. Comparisons with electromyographic (EMG) recordings were made. A group of 13 subjects performed isometric dorsiflexions (50% of maximum for 60 s) at 40 degrees of plantarflexion (long, l(l)) and 5 degrees of dorsiflexion (short, l(s)). The mean power frequency of the EMG (f(EMG)) and MMG (f(MMG)) signals and the mean rectified MMG (rMMG) and EMG (rEMG) were determined over each 1-s period, normalized to the respective maximal value, regressed against time, and the resulting slopes (units = %max. s(-1)) were analyzed. The slopes were larger (P = 0.007) at l(l) compared to l(s) [mean l(l) 0.50 (SD 0.26), mean l(s) 0.27 (SD 0.16)], however there were no differences (P = 0.24) between mean fMMG slopes [l(l) -0.10 (SD 0.16), l(s) -0.16 (SD 0.11)]. Similarly, slopes were larger (P = 0.001) at l(l) versus l(s) [l(l) 0.26 (SD 0.13), l(s) 0.08 (SD 0.15)] and there were no differences (P=0.89) between mean fEMG slopes [l(l) -0.15 (SD 0.14), l(s) -0.14 (SD 0.12)]. At 5 s following the exercise to fatigue mean MVC (units = %max) were not significantly different between l(l) and l(s) [P = 0.08; l(l) 78.8 (SD 9.1), l(s) 85.2 (SD 6. 0)]. These results showed that during fatiguing contractions, MMG and EMG amplitudes increased while frequency characteristics decreased at both muscle lengths. The change in and was greater at l(l) but no differences in fMMG or fEMG slopes occurred between lengths. These results would suggest that larger increases in motor unit recruitment occur with time during fatigue at l(l) compared to l(s).

Optimal Elbow Angle for MMG Signal Classification of Biceps Brachii during Dynamic Fatiguing Contraction

“…Various studies have linked fatigue occurrence to muscle length (which is dependent upon the joint angle) based on force loss in the muscle [4,5]. In addition, other researchers have found that the rate of fatigue in long muscles is dependent upon the rate of changes in the signal for both sEMG [6,7] and in the MMG signal [8].…”

Dynamic monitoring of forearm muscles using one-dimensional sonomyography system

“…For example, MMG is the sound generated by a muscle during its contraction and is used as a measure of mechanical muscle changes during contraction [17]. Recently, it has been widely analyzed along with EMG for different purposes [18][19][20], such as control of a prosthesis with 2 degrees of freedom [21]. However, MMG can be affected by many factors, such as muscle temperature [22], skinfold thickness [23], and external mechanical noise [24].…”

Changes in Surface EMG and Acoustic myogram Parameters During Static Fatiguing Contractions until Exhaustion: Influence of Elbow Joint Angles.

“…1); our findings were in good agreement with those of previous investigations (Basmajian and De Luca, 1985;De Luca, 1984). With respect to EMG, the well-documented increase in amplitude during fatigue at different force levels has often been attributed to increase in MU recruitment and firing rate (Moritani et al, 1986;Weir et al, 2000). The decreases in MPF of EMG have been suggested to result from a decrease in muscle fiber conduction velocity (Sadoyama et al, 1983;Eberstein and Beattie, 1985), and possibly from an increase in MU synchronization (Weir et al, 2000).…”

“…With respect to EMG, the well-documented increase in amplitude during fatigue at different force levels has often been attributed to increase in MU recruitment and firing rate (Moritani et al, 1986;Weir et al, 2000). The decreases in MPF of EMG have been suggested to result from a decrease in muscle fiber conduction velocity (Sadoyama et al, 1983;Eberstein and Beattie, 1985), and possibly from an increase in MU synchronization (Weir et al, 2000). However, synchronization, i.e., the tendency for MUs to discharge at, or nearly at, the same time, has often been cited as the cause for both frequency shift and amplitude increase (De Luca, 1984).…”

“…This phenomenon might have been due to the occurrence of changes in muscle length that at different elbow angles. It was suggested that differences in MU recruitment rates might have been involved in the lengthdependent fatigue rates reported by Weir et al (2000). Future investigation of this phenomenon could clarify the role of the mechanical properties of the muscle itself in determining the muscle's sound characteristics.…”