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Sensor location affects skeletal muscle contractility parameters measured by tensiomyography

Cite this dataset

Schwiete, Carsten et al. (2023). Sensor location affects skeletal muscle contractility parameters measured by tensiomyography [Dataset]. Dryad. https://doi.org/10.5061/dryad.63xsj3v6b

Abstract

Tensiomyography (TMG) is a non-invasive method for measuring contractile properties of skeletal muscle that is increasingly being used in research and practice. However, the lack of standardization in measurement protocols mitigates the systematic use in sports medical settings. Therefore, this study aimed to investigate the effects of lower leg fixation and sensor location on TMG-derived parameters. Twenty-two male participants underwent TMG measurements on the m. biceps femoris (BF) in randomized order with and without lower leg fixation (fixed vs. non-fixed). Measurements were conducted at 50% of the muscle’s length (BF-mid) and 10 cm distal to this (BF-distal). The sensor location affected the contractile properties significantly, both with and without fixation. Delay time (Td) was greater at BF-mid compared to BF-distal (fixed: 23.2 ± 3.2 ms vs. 21.2 ± 2.7 ms, p = 0.002; non-fixed: 24.03 ± 4.2 ms vs. 21.8 ± 2.7 ms, p = 0.008), as were maximum displacement (Dm) (fixed: 5.3 ± 2.7 mm vs. 3.5 ± 1.7 mm, p = 0.005; non-fixed: 5.4 ± 2.5 mm vs. 4.0 ± 2.0 mm, p = 0.03), and contraction velocity (Vc) (fixed: 76.7 ±  25.1 mm/s vs. 57.2 ± 24.3 mm/s, p = 0.02). No significant differences were revealed for lower leg fixation (all p > 0.05). In summary, sensor location affects the TMG-derived parameters on the BF. Our findings help researchers to create tailored measurement procedures in compliance with the individual goals of the TMG measurements and allow adequate interpretation of TMG parameters.

Methods

A single-group randomized-crossover design was used for this study, which was approved by the local ethics committee (#) and conducted in accordance with the ethical standards set by the declaration of Helsinki. Skeletal muscle contractility of the biceps femoris (BF) of the dominant leg was assessed using tensiomyography (TMG; TMG-BMC Ltd., Ljubljana, Slovenia). The participants lay in a prone position with their ankles placed on the TMG cushion for lower leg measurements, so that the measurement was performed with a knee flexion of about 5°. The TMG measurements were performed at two measurement sites and conditions on the BF. The first measurement site was at 50% of the length between the origin (ischial tuberosity) and the insertion (head of the fibula) (BF-mid); the site was marked with a water-resistant pen. To ensure that the mark was correctly placed on the BF, each participant was instructed to perform an isometric contraction with the hamstrings at 90° knee flexion against the arm of the investigator. The second measurement site was 10 cm distal of BF-mid and was also marked (BF-distal). For BF-distal, the proximal electrode of BF-mid was placed 5 cm below the distal electrode from BF-mid. Hence, the distal BF-mid electrode turned into the proximal electrode for BF-distal, again allowing for an inter-electrode distance of 5 cm. The TMG measurements at both measurement sites (BF-mid and BF-distal) were performed under two conditions: in one condition, measurements were performed without fixation of the lower leg (non-fixed), while the second condition was performed with the participant’s lower leg strapped to the TMG pad using a 25 mm 2 m non-elastic adjustable strap (fixed). Each participant underwent each of the two conditions in a randomized order, as determined by randomizer.org. Ultimately, our study included four measurements in a randomized order per participant, e.g., 1. BF-mid/fixed, 2. BF-mid/non-fixed, 3. BF-distal/fixed, 4. BF-distal/non-fixed.

The TMG measurement itself was performed as follows: starting at 50 mA, the intensity was progressively increased by 10 mA every 30 seconds until maximal displacement or maximal output was reached. Thus, the participants had a maximum of seven stimuli per measurement site. The electrical stimulation consisted of single, monophasic, square wave stimuli, with a duration of 1 ms each. Between each measurement site, a resting interval of 2–3 minutes was included to provide muscle relaxation between measurements. For statistical analysis, the measurement curve with the highest Dm was used. All other parameters were derived from the same measurement curve. Vc was calculated as the mean velocity until 90% Dm (Vc = 0.9 Dm/ [Td + Tc]*1000) was reached.

Statistical analysis

Prior to statistical analyses, all data were checked for outliers and normal distribution using Boxplots and Shapiro-Wilk’s test of normality, respectively. A two-way repeated measures ANOVA using planned simple contrasts was performed to check for differences between the measurement sites (BF-mid vs. BF-distal) and conditions (fixed vs. non-fixed). Bonferroni correction was applied to impede alpha error accumulation. Given their poor within-subject reliability, Ts and Tr were only presented using descriptive statistics. Pearson’s correlation was carried out to investigate the strength of the relationship between the variables, while Bland and Altman’s limits of agreement (LOA) were calculated to determine the degree of agreement (bias and LOA) between conditions. Linear regression was employed to detect proportional bias. All tests were based on a 5% level of significance. Data are presented as means ± standard deviations, including Cohen’s dz if adequate.

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