Previous studies have used twitch electrical stimulation and accelerometer-based mechanomyography (aMMG) to evaluate muscle function in clinical populations. However, the reproducibility and validity of the methodology has not been defined. This study evaluated the reproducibility and validity of twitch electrical stimulation and aMMG as an assessment of muscle endurance. Participants were healthy males and females 21.8±1.9 years of age. Muscle twitch acceleration was measured using an accelerometer placed over the surface of the muscle. The relationship between acceleration and torque was measured during twitch stimulation of the vastus lateralis muscle. Muscle endurance of the forearm and gastrocnemius was measured during 9 minutes of twitch electrical stimulation, in three stages (3min/stage) of increasing frequency (2Hz, 4Hz, and 6Hz). An Endurance Index (EI) was calculated as the percent of acceleration at the end of each stimulation stage relative to the peak acceleration. Oxygen saturation was measured using near-infrared spectroscopy. Results showed that acceleration correlated with torque during twitch electrical stimulation of the vastus lateralis (mean R²= 0.96±0.04; p<0.05). Measures of forearm EI reproducibility were CV= 2.5-7.4%. EI was significantly higher (12.1%) in the gastrocnemius compared to the forearm (p<0.01). Muscle oxygen saturation was not reduced during stimulation of the forearm (72.6±9.8% at 2Hz, 73.2±11.6% at 4Hz, and 71.0±12.5% at 6Hz) compared to resting baseline (74.3±15.1%) (p>0.1). This study found that EI is a reproducible measure of muscle endurance that is not influenced by declines in oxygen saturation.

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Tensiomyography (TMG) can estimate the intrinsic contractile potential of a muscle using data between 10 and 90% of the displacement-time curve. However, it is yet to be determined whether this data represents the greatest rate of displacement i.e. the most valid estimate of the maximal shortening velocity of a muscle. The aim of this secondary analysis of data gathered from 10 participants who had maximal displacement (Dm) of the rectus femoris assessed using TMG, was to compare the rate of displacement using data from 0 – 100% of Dm; 10 – 90% of Dm and the most linear phase of the displacement-time curve. One-way analysis of variance (ANOVA) indicated that rate of displacement increased as data bands narrowed towards the most linear phase of the displacement-time curve (P<0.001). Rate of displacement explained the greatest proportion of variance in total Tc when estimated from the linear phase (R²=0.601; P=0.008). Rate of displacement estimated from data points between 10 – 90% of Dm had a strong association with rate of displacement estimated from the linear phase (r=0.996; P<0.001). The most valid estimate of maximal rate of displacement comes from the linear phase of the displacement-time curve.

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Purpose: This study was designed to: a) examine the influence of elbow joint angle and contraction intensity on electromyographic (EMG) and mechanomyographic (MMG) responses using linear slope coefficients and, b) further describe these relationships utilizing polynomial regression. Methods: 14 male subjects (mean ± SD, age 22.1 ± 2.3 years) performed maximal voluntary isometric contractions (MVC) at elbow flexion angles of 60°, 90°, and 120°. Subjects then performed 35 second contractions at two MVC levels (50%, 75%) for each joint angle. EMG and MMG were recorded simultaneously from the biceps brachii. The center 30 second segment of the signal was utilized to determine the root-mean-square (RMS). Results: No significant effect of elbow joint angle was found for the EMG (p = 0.52) and MMG (p = 0.12) slope coefficient analysis, as well as contraction intensity (EMG: p = 0.61; MMG: p = 0.50). Composite polynomial regression revealed that the MMG-Time relationships were best fit with linear models at 120° (50% MVC: p = 0.025; 75% MVC: p = 0.019), while non-linear relationships best described the 60° (50% MVC, 75% MVC: p < 0.001) and 90° (50% MVC, 75% MVC: p < 0.001) joint angles. Conclusions: Results indicate that motor control strategies are not significantly different between elbow joint angles when utilizing linear regression models. However, polynomial regression revealed elbow joint angle specific MMG-Time relationships. Non-linear, MMG-Time relationships are influenced by elbow joint angle during short-term, sustained isometric contractions.

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The aim of this study was to determine the contractile properties and muscle stiffness to assess lateral symmetry in competitive female surfers. Fifteen competitive female surfers volunteered to participate in the study. Tensiomyography was used to derive maximum muscle belly displacement, and time delay duration of the Biceps Brachiis, Biceps Femoris, Deltoid, Gastrocnemius lateral head, Rectus Femoris, Tibialis Anterior, Triceps Brachii and Vastus Medialis. No significant differences between right and left limbs at in any of the tested muscles were observed (p > 0.05). Competitive female surfers showed that upper body muscles had the ability to generate force rapidly during contractions, while the lower body muscles generated force at a slower rate. Surf specific training seems to have had an influence on the contractile properties, and stiffness of these muscles. The neuromuscular profile provided here provides further normative data to this unique population.

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