DOI: 10.5061/dryad.63xsj3v6b
title: Sensor location affects skeletal muscle contractility parameters measured by tensiomyography

description: 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 &gt; 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.
description: 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%
 D<sub>m</sub> (V<sub>c</sub> = 0.9
 D<sub>m</sub>/ [T<sub>d</sub> +
 T<sub>c</sub>]*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, T<sub>s</sub> and T<sub>r</sub> 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 d<sub>z</sub> if
 adequate.
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