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Abstract

BACKGROUND:

Information regarding the relationship between methods for assessment of voluntary and involuntary muscle contractile properties is of importance in sport science and medicine.

OBJECTIVE:

To appraise the concurrent and predictive validity of isokinetic dynamometry and tensiomyography (TMG) in differently trained men and women.

METHODS:

Fifty men and 45 women were divided into three groups: physically inactive, physically active and athletes. Isokinetic testing was performed on knee muscles in concentric mode at 60 and 180 ${}^{\circ}$ s while tensiomyographic measurements were obtained from the rectus and the biceps femoris muscles.

RESULTS:

A small, statistically significant correlation was detected between the peak moment and tensiomyography parameters relating to contraction time and maximal displacement (Adj. R ${}^{2}=$ 0.086, $p=$ 0.028).

CONCLUSION:

In general, isokinetic dynamometry and tensiomyography are not related and represent different technologies that measure different contractile properties of muscles. A hierarchical structure of predictive validity at the level of individual variables was detected as a function of gender and training level.

Keywords

Voluntary contraction involuntary contraction peak moment contraction time maximal displacement

1. Introduction

One of the basic properties of muscle tissue is the ability to contract, that is, react to stimuli by increasing tension and changing its length [1]. Muscle contraction can be voluntary or involuntary.

Voluntary muscle contractions are characteristic of skeletal muscles, are generated by cerebral cortex in response to perceived need, and play a central role in human movement [2, 3]. On the other hand, involuntary muscle contractions are controlled by the autonomic nervous system, are exerted by smooth muscles, but may also occur in skeletal muscles due to various factors (reflexes, neuromuscular conditions, electrical stimulation) [4, 5, 6]. Involuntary muscular contractions of skeletal muscles evoked by electrical stimulation have a particular role both in sports and clinical practice and are extensively investigated. In addition to being used in rehabilitation and training process, electrically-induced contractions enables the acquisition of meaningful information about the contractile and mechanical properties of muscles as well as the conductivity of the nervous system [7, 8].

A number of methods are available for assessing muscle contractile and mechanical properties. Among these, isokinetic dynamometry and tensiomyography (TMG) are currently employed. Isokinetic dynamometry is considered the gold-standard method for measuring muscle strength at constant angular velocities [9, 10, 11]. TMG is a relatively new tool for assessing the morpho-functional potential of skeletal muscles to determine the involuntary mechanical response to a single electrical stimulus under isometric conditions. This mechanical response is expressed by transverse muscle belly displacement [12].

To-date no studies have attempted to examine the relationships between isokinetic dynamometry and TMG for the assessment of voluntary and involuntary muscle contractile and mechanical properties. Therefore, the aim of the present study was to appraise the concurrent and predictive validity of isokinetic dynamometry and TMG in differently trained men and women and to compare these methods according to the gender and training level. Based on the findings of some previous studies which indicated a certain significant correlation between TMG and various methods for assessment of muscle strength (isometric and isotonic/isoinertial dynamometry) [13, 14, 15], it was hypothesized that there would be significant correlation between these methods and that these methods have some predictive values.

2. Methods

2.1 Participants

The sample of participants consisted of 95 individuals (50 men: age $=$ 24.5 $\pm$ 3.8 years; body height $=$ 180.7 $\pm$ 7.08 cm; body weight $=$ 81.2 $\pm$ 10.2 kg; and 45 women: age $=$ 22.6 $\pm$ 2.6 years; body height $=$ 168.7 $\pm$ 7.07 cm; body weight $=$ 61.7 $\pm$ 8.6 kg) divided into three groups: the physically inactive (PI group, 15 men and 15 women), the physically active (PA group, 17 men and 15 women), and athletes (AT group, 18 men and 15 women).

The PI group consisted of sedentary adults who did not take part in regular and systematic physical activity. The PA group consisted of adults who took part in physical activities 2 or 3 times per week but did not take part in daily, systematically planned physical or training activities. The level of physical activity in PI and PA group was determined by a valid questionnaire on eating habits, physical activity and lifestyle [16]. AT group consisted of athletes from strength and power sports (judokas, wrestlers, karatekas, boxers, kick-boxers, sprinters – swimmers, cyclists and runners) regularly engaging in sports training, who had competitive experience in their sport of choice of no less than 5 years and who actively competed in higher league ranks of the sports they participated in.

All the participants were made acquainted with the goals and procedures of the research and the testing included individuals who had voluntarily agreed in written form to participate in the research. All the study procedures were carried out in accordance with the Declaration of Helsinki and the rules of the Ethics Committee of the Faculty of sport and physical education University of Belgrade (IRB: 484-2, 2011–2018, project number III47015 – Ministry of science of Republic of Serbia). Testing was carried out from May to September 2016.

2.2 Procedures

The participants were tested by randomized cross measurement method, where, using the random sample method, in one group of subjects measurements on TMG were carried out first, and after a break of half an hour, measurements on the isokinetic dynamometer were performed, while in other group measurements were made in reverse order (participants arrival is arranged individually according to their free time and training schedule of athletes). All measurements were performed under the same conditions. The participants were tested in the morning, they were well rested, not practicing physical activity in the 24 hours preceding the testing, and all tests were performed by the team of researches which included three experienced personnel. All measurements were performed in the Methodology-research laboratory of the Faculty of Sport and Physical Education at the University of Belgrade, Serbia.

The isokinetic evaluation of voluntary muscle contractile properties was carried out on an Kin-Com AP125 isokinetic dynamometer (Chattecx Corp., Chattanooga, TN, USA). Measurements were done on the dominant knee flexors and extensors in concentric mode at 60 and 180 ${}^{\circ}$ /s [17, 18]. These velocities were chosen as they were the most widely used in research and practice representing high (180 ${}^{\circ}$ /s) and low (60 ${}^{\circ}$ /s) movement conditions. Prior to the measurement, the participants were made acquainted with the testing procedures and were required to warm up for a period of approximately 10 minutes (5 minutes on a stationary bicycle and 5 minutes of static leg muscle stretching – 7 exercises, 1 repetition of 30 s duration with rest between exercises of 10 s) to prevent musculoskeletal injury [19, 20, 21]. The participants were seated in an upright position and fixed to the testing apparatus with the straps around the pelvis, thigh and malleoli [22]. From that position they performed the near maximum extension in the knee joint, starting with the flexed knee at an angle of 90 ${}^{\circ}$ and then reverse flexion to the initial position (movement amplitude was approximately 80 ${}^{\circ}$ ) according to previously established protocols [17]. Participants were instructed to repeat it at maximal intensity. Each participant performed 5 repetitions at both speeds, with the first testing carried out at a lower speed (60 ${}^{\circ}$ /s) (testing was done with gravity compensation) [20, 23]. The rest between the sets was 3 minutes [23]. During task completion, the participants received verbal encouragement [24]. A custom-made Lab View application was used for data acquisition and processing of the muscle strength tests. The representative isokinetic parameter was the peak moment (PM) [17, 25, 26].

Figure 1.

Correlation between peak moment of quadriceps muscles measured at speed of 60 and 180 ${}^{\circ}$ /s and TMG parameters (Tc and Dm) of rectus femoris muscle in women expressed as a standardized multidimensional score – centroid (generally).

The measurement of involuntary muscle contractile properties was carried out using the method of tensiomyography (TMG-BMC Ltd, Ljubljana, Slovenia). The testing was carried on the rectus femoris (RF) and biceps femoris (BF) muscles [27]. Measurements were performed in standardized position, static and relaxed conditions, with the subject in the supine and prone position, to assess RF and BF muscles, respectively, while the knee joint was fixed at an angle of 120 ${}^{\circ}$ [27]. The measuring location was carefully determined as a point of maximal muscle belly displacement during voluntary contraction [28]. After defining the location, the point was marked, and two adhesive electrodes (5 cm ${}^{2}$ ) were positioned (Pals Platinum, model 895220 with a multi-stick gel, Axelgaard Manufacturing Co. Ltd), both of which emitted an electric impulse, in the proximal and distal position, at a standardized distance of 55 to 60 mm from the marked point (Fig. 3) [27, 29]. Between the electrodes a sensor was positioned (GK40, Panoptik, Ljubljana, Slovenia) which detected changes in the muscle belly caused by electrical stimulations, based on which data are obtained on the involuntary muscle contractile properties. The electrical impulse of 1 ms duration was realized by an electrostimulator TMG-100 (TMG-BMC, Ljubljana, Slovenia), while the initial impulse was set at an intensity of 20 mA, then proportionally increased by 10 mA steps until the maximal value was achieved namely until the moment when any muscle reaction to the increase in the electrostimulation ceased [30, 31]. The interval between impulses was approximately 10 s, to minimize the effects of fatigue and potentiation (increase in muscle force after repetitive evoked contractions) [32, 33]. The maximum amplitude ranged from 60 to 110 mA. Two of the best results (the lowest values of Tc for the highest possible value of Dm) were recorded and based on them the TMG software calculated the average. Parameters of TMG which were used in the study were contraction time (Tc) – time between 10% and 90% of the maximum value of the muscle response, and maximal displacement (Dm) – maximal radial displacement of muscle belly, which have been previously reported as the most valid, reliable and established TMG parameters in research studies [34].

Table 1

Descriptive statistics (Mean $\pm$ SD) of isokinetic dynamometry and TMG parameters

		PM				Tc		Dm
		Q60	H60	Q180	H180	RF	BF	RF	BF
PI	M	158.5 $\pm$ 22.5	103.4 $\pm$ 15.9	115.6 $\pm$ 19.4	79.3 $\pm$ 13.7	31.7 $\pm$ 6.2	33.8 $\pm$ 10.4	5.4 $\pm$ 2.1	4.5 $\pm$ 2.1
	W	90.3 $\pm$ 22.2	55.1 $\pm$ 10.3	62.1 $\pm$ 15.03	41.8 $\pm$ 9.1	30.7 $\pm$ 5.06	37.7 $\pm$ 7.02	5.5 $\pm$ 1.6	7.7 $\pm$ 1.8
PA	M	182.1 $\pm$ 27.1	120.7 $\pm$ 19.04	126.1 $\pm$ 19.02	93.08 $\pm$ 13.3	32.5 $\pm$ 4.6	32.4 $\pm$ 7.5	6.1 $\pm$ 2.05	5.5 $\pm$ 1.9
	W	107.1 $\pm$ 18.3	69 $\pm$ 10.05	73.1 $\pm$ 11.4	52.4 $\pm$ 6.5	29.5 $\pm$ 5.8	39.5 $\pm$ 9.9	5.3 $\pm$ 2.02	5.5 $\pm$ 2.1
AT	M	192.1 $\pm$ 42.1	116.8 $\pm$ 19.2	128.5 $\pm$ 24.4	89.7 $\pm$ 19.1	26.6 $\pm$ 3.4	34.5 $\pm$ 12.9	5.9 $\pm$ 1.9	4.8 $\pm$ 1.3
	W	120.6 $\pm$ 29.9	76 $\pm$ 24.9	79.2 $\pm$ 21.6	59.02 $\pm$ 20.2	27.1 $\pm$ 5.9	37.8 $\pm$ 9.2	4.8 $\pm$ 1.6	6.07 $\pm$ 1.7

PI – Physically inactive, PA – Physically active, AT – Athletes, M – Men, F– Women, PM (Nm) – Peak moment, Tc (ms) – Contraction time, Dm (mm) – Maximal displacement, Q – Quadriceps muscles, H – Hamstring muscles, 60 – Angular speed of 60 ${}^{\circ}$ /s, 180 – Angular speed of 180 ${}^{\circ}$ /s, RF – Rectus femoris, BF – Biceps femoris.

Table 2

Correlation between parameters of isokinetic dynamometry and TMG according to gender

		RFtc	RFdm	BFtc	BFdm
Men	Q60	$-$ 0.153 ( $p=$ 0.290)	$-$ 0.195 ( $p=$ 0.175)	$-$ 0.174 ( $p=$ 0.228)	$-$ 0.241 ( $p=$ 0.910)
	H60	$-$ 0.027 ( $p=$ 0.850)	0.039 ( $p=$ 0.788)	$-$ 0.246 ( $p=$ 0.085)	$-$ 0.117 ( $p=$ 0.420)
	Q180	$-$ 0.100 ( $p=$ 0.490)	$-$ 0.140 ( $p=$ 0.333)	$-$ 0.266 ( $p=$ 0.062)	$-$ 0.289 ( $p=$ 0.042)
	H180	0.024 ( $p=$ 0.868)	$-$ 0.037 ( $p=$ 0.797)	$-$ 0.231 ( $p=$ 0.106)	$-$ 0.163 ( $p=$ 0.257)
Women	Q60	$-$ 0.176 ( $p=$ 0.247)	$-$ 0.089 ( $p=$ 0.560)	$-$ 0.092 ( $p=$ 0.547)	$-$ 0.390 ( $p=$ 0.008)
	H60	$-$ 0.017 ( $p=$ 0.911)	0.025 ( $p=$ 0.872)	0.031 ( $p=$ 0.842)	$-$ 0.372 ( $p=$ 0.012)
	Q180	$-$ 0.112 ( $p=$ 0.462)	$-$ 0.081 ( $p=$ 0.598)	$-$ 0.072 ( $p=$ 0.641)	$-$ 0.320 ( $p=$ 0.032)
	H180	$-$ 0.052 ( $p=$ 0.735)	$-$ 0.058 ( $p=$ 0.707)	0.067 ( $p=$ 0.663)	$-$ 0.305 ( $p=$ 0.041)

Q – Quadriceps muscles, H – Hamstring muscles, 60 – Angular speed of 60 ${}^{\circ}$ /s, 180 – Angular speed of 180 ${}^{\circ}$ /s, RF – Rectus femoris, BF – Biceps femoris, tc – contraction time, dm – maximal displacement.

2.3 Statistical analyses

Of the statistical procedures in the study we used the descriptive analysis to describe the measured variables (Mean, SD). Pearson correlation coefficient and linear regression analysis were applied to define concurrent and predictive validity of examined methods, where for each correlation between measured variables the prediction equation is defined using mathematical modeling. For additional confirmation of the initial hypothesis, factor analysis and ANOVA with Bonferroni post hoc test were used. Factor analysis was used to determine standardized multidimensional scores (Z scores – centroides) of all isokinetic dynamometry and TMG parameters of flexor/extensor muscles in differently trained men and women. After determining mutually Z score, linear regression was used for purpose of obtaining general correlations between methods and to compare these methods generally (according to gender) and partially (according to training level). ANOVA was used to determine the differences in isokinetic and TMG parameters between the groups. The level of statistical significance was calculated at 95% with $p<$ 0.05 [35], while all the statistical procedures were performed on the SPSS19 (IBM) program.

3. Results

Table 2 presents the results of the linear correlation analyses between the parameters of isokinetic dynamometry and TMG. A statistically significant negative correlation was detected between the PM of the quadriceps and hamstring measured at both speeds and Dm ( $r=$ $-$ 0.335. $p=$ 0.027 on average) of the BF muscle. These correlations were generally higher in women ( $r=$ $-$ 0.346, $p=$ 0.023 on average level) than in men ( $r=$ $-$ 0.289, $p=$ 0.042).

Based on the results presented in Table 3, the highest correlation coefficients between the two methods’ parameters were observed in the PI group ( $r=$ $-$ 0.550, $p=$ 0.037 on average), followed by the PA ( $r=$ $-$ 0.527, $p=$ 0.044), and the AT group ( $r=$ $-$ 0.490, $p=$ 0.039).

Table 3
Correlations between parameters of isokinetic dynamometry and TMG in differently trained subjects according to the gender

		Men				Women
		RFtc	RFdm	BFtc	BFdm	RFtc	RFdm	BFtc	BFdm
PI	Q60	0.266	$-$ 0.367	$-$ 0.450	$-$ 0.531 ${}^{\ast}$	$-$ 0.448	0.110	$-$ 0.514 ${}^{\ast}$	$-$ 0.489
	H60	0.203	0.129	$-$ 0.411	$-$ 0.380	$-$ 0.144	0.425	$-$ 0.167	$-$ 0.403
	Q180	0.244	$-$ 0.253	$-$ 0.388	$-$ 0.559 ${}^{\ast}$	$-$ 0.541 ${}^{\ast}$	0.111	$-$ 0.544 ${}^{\ast}$	$-$ 0.510
	H180	0.312	0.027	$-$ 0.466	$-$ 0.654 ${}^{\ast\ast}$	0.002	0.236	$-$ 0.195	$-$ 0.489
PA	Q60	0.229	$-$ 0.033	$-$ 0.205	$-$ 0.432	$-$ 0.055	$-$ 0.201	$-$ 0.248	$-$ 0.527 ${}^{\ast}$
	H60	$-$ 0.047	$-$ 0.030	$-$ 0.221	$-$ 0.331	0.176	$-$ 0.312	0.042	$-$ 0.336
	Q180	0.053	$-$ 0.075	$-$ 0.301	$-$ 0.409	0.298	$-$ 0.256	$-$ 0.111	$-$ 0.362
	H180	0.123	$-$ 0.126	$-$ 0.191	$-$ 0.446	0.287	$-$ 0.425	0.184	$-$ 0.298
AT	Q60	$-$ 0.490 ${}^{\ast}$	$-$ 0.344	$-$ 0.109	$-$ 0.177	0.171	0.125	0.200	0.013
	H60	$-$ 0.174	$-$ 0.090	$-$ 0.199	0.094	0.207	0.242	0.079	$-$ 0.202
	Q180	$-$ 0.464	$-$ 0.182	$-$ 0.213	$-$ 0.110	0.138	0.058	0.158	0.079
	H180	$-$ 0.254	$-$ 0.139	$-$ 0.143	0.235	0.064	0.124	0.131	$-$ 0.016

${}^{*}p<$ 0.05, ${}^{**}p<$ 0.01, PI – Physically inactive, PA – Physically active, AT – Athletes, Q – Quadriceps muscles, H – Hamstring muscles, 60 – Angular speed of 60 ${}^{\circ}$ /s, 180 – Angular speed of 180 ${}^{\circ}$ /s, RF – Rectus femoris, BF – Biceps femoris, tc – contraction time, dm – maximal displacement.

Table 4 presents the results of the regression analysis and prediction equation model for those parameters which showed a significant correlation. The coefficient of determination (R ${}^{2}$ ) ranged from 0.227 to 0.427, while the SEM ranged from 4.41 Nm to 37.8 Nm, that is, 7.1% to 21.9%.

Table 4

Single partial level relation: Regression analysis and predictive equation model

Group	Relation	Equation model	R ${}^{2}$	P value	Std. Err. (Nm)	Std. Err. (%)
PI men	Q60 vs BFdm	Q60 (PM) $=$ $-$ 5.5523BFdm $+$ 183.57	0.281	0.041	19.7	12.4
	Q180 vs BFdm	Q180 (PM) $=$ $-$ 5.0523BFdm $+$ 138.36	0.312	0.030	16.7	14.4
	H180 vs BFdm	H180 (PM) $=$ $-$ 4.1758BFdm $+$ 98.156	0.427	0.008	10.7	13.5
PI women	Q60 vs BFtc	Q60 (PM) $=$ $-$ 1.6293BFtc $+$ 151.91	0.264	0.049	19.8	21.9
	Q180 vs BFtc	Q180 (PM) $=$ $-$ 1.163BFtc $+$ 106.05	0.295	0.036	13.09	21.07
	Q180 vs RFtc	Q180 (PM) $=$ $-$ 1.6083RFtc $+$ 111.62	0.293	0.037	4.41	7.1
PA women	Q60 vs BFdm	Q60 (PM) $=$ $-$ 4.4731BFdm $+$ 132.14	0.227	0.043	16.1	15.03
AT men	Q60 vs RFtc	Q60 (PM) $=$ $-$ 6.0241RFtc $+$ 352.46	0.239	0.039	37.8	19.6

PI – Physically inactive, PA – Physically active, AT – Athletes, Q – Quadriceps muscles, H – Hamstring muscles, 60 – Angular speed of 60 ${}^{\circ}$ /s, 180 – Angular speed of 180 ${}^{\circ}$ /s, PM – Peak moment RF – Rectus femoris, BF – Biceps femoris, tc – contraction time, dm – maximal displacement.

Table 5 reports the results for the regression analysis of standardized multidimensional scores of all the isokinetic dynamometry and TMG parameters in differently trained men and women obtained by factor analysis. A significant correlation was found only between the PM of quadriceps and the TMG parameters of rectus femoris in women on a general level (Adj. $R^{2}=$ 0.086, $F=$ 5.145, $p=$ 0.028, Fig. 1) and the PM of hamstring and the TMG of the BF on partial level in the male PI group (Adj. $R^{2}=$ 0.276, $F=$ 6.326, $p=$ 0.026, Fig. 2).

Table 5

General and partial level relations: Regression analysis between two methods (IsoDyn vs TMG) by use of standardized multidimensional scores (centroides) method

			R	R square	Adjusted R square	F	Sig.
Pooled	M	PMQ vs TMGRF	0.166	0.028	0.007	1.331	0.254
		PMH vs TMGBF	0.241	0.058	0.038	2.839	0.096
	F	PMQ vs TMGRF	0.327	0.107	0.086	5.145	0.028
		PMH vs TMGBF	0.192	0.037	0.015	1.650	0.206
PI	M	PMQ vs TMGRF	0.016	0.000	$-$ 0.077	0.003	0.955
		PMH vs TMGBF	0.572	0.327	0.276	6.326	0.026
	F	PMQ vs TMGRF	0.309	0.096	0.026	1.376	0.262
		PMH vs TMGBF	0.404	0.163	0.099	2.532	0.136
PA	M	PMQ vs TMGRF	0.048	0.002	$-$ 0.064	0.035	0.854
		PMH vs TMGBF	0.374	0.140	0.083	2.441	0.139
	F	PMQ vs TMGRF	0.112	0.013	$-$ 0.063	0.165	0.691
		PMH vs TMGBF	0.147	0.022	$-$ 0.054	0.287	0.601
AT	M	PMQ vs TMGRF	0.427	0.182	0.128	3.345	0.087
		PMH vs TMGBF	0.059	0.004	$-$ 0.063	0.053	0.821
	F	PMQ vs TMGRF	0.203	0.041	$-$ 0.033	0.557	0.469
		PMH vs TMGBF	0.047	0.002	$-$ 0.075	0.029	0.868

PI – Physically inactive, PA – Physically active, AT – Athletes, M – Men, F – Women, Q – Quadriceps muscles, H – Hamstring muscles, RF – Rectus femoris, BF – Biceps femoris, PM – Peak moment (PM) measured at speed of 60 ${}^{\circ}$ /s and 180 ${}^{\circ}$ /s expressed as a standardized multidimensional score (centroid), TMG – Tc and Dm expressed as a standardized multidimensional score (centroid).

Figure 2.

Correlation between peak moment of hamstring muscles measured at speed of 60 and 180 ${}^{\circ}$ /s and TMG parameters (Tc and Dm) of biceps femoris muscle in physically inactive men expressed as a standardized multidimensional score – centroid (partially).

Based on the results of ANOVA post hoc tests (Table 6) the differences in the isokinetic and TMG parameters between differently trained men and women were relatively small and inconsistent.

Table 6

Results of ANOVA post hoc test – differences in isokinetic and TMG parameters between differently trained men and women

			Men		Women
			Mean	Sig.	Mean	Sig.
			difference		difference
Q60	PI	PA	$-$ 23.5	0.030	$-$ 16.7	0.081
		AT	$-$ 32.4	0.031	$-$ 31.7	0.015
	PA	AT	$-$ 8.9	0.755	$-$ 15.0	0.306
H60	PI	PA	$-$ 17.3	0.023	$-$ 13.8	0.002
		AT	$-$ 13.1	0.114	$-$ 19.4	0.011
	PA	AT	4.3	0.799	$-$ 5.6	0.631
Q180	PI	PA	$-$ 10.5	0.286	$-$ 11.0	0.080
		AT	$-$ 12.3	0.276	$-$ 17.7	0.052
	PA	AT	$-$ 1.8	0.969	$-$ 6.6	0.587
H180	PI	PA	$-$ 13.7	0.020	$-$ 10.6	0.003
		AT	$-$ 8.8	0.288	$-$ 17.1	0.020
	PA	AT	4.9	0.653	$-$ 6.5	0.476
BFtc	PI	PA	1.370	0.907	$-$ 1.796	0.836
		AT	$-$ 1.085	0.964	0.019	1.000
	PA	AT	$-$ 2.455	0.785	1.815	0.864
BFdm	PI	PA	$-$ 1.058	0.337	2.120	0.020
		AT	$-$ 0.308	0.885	1.607	0.055
	PA	AT	0.750	0.426	$-$ 0.513	0.756
RFtc	PI	PA	$-$ 0.807	0.912	1.255	0.805
		AT	4.864	0.036	4.267	0.106
	PA	AT	5.672	0.001	3.012	0.357
RFdm	PI	PA	$-$ 0.712	0.611	0.233	0.936
		AT	$-$ 0.359	0.870	0.954	0.279
	PA	AT	0.352	0.860	0.721	0.553

PI – Physically inactive, PA – Physically active, AT – Athletes, Q – Quadriceps muscles, H – Hamstring muscles, 60 – Angular speed of 60 ${}^{\circ}$ /s, 180 – Angular speed of 180 ${}^{\circ}$ /s, RF – Rectus femoris, BF – Biceps femoris, tc – contraction time, dm – maximal displacement.

Figure 3.

TMG method of installation of electrodes and sensors.

4. Discussion

This study examined the concurrent and predictive validity of isokinetic dynamometry and TMG for the assessment of voluntary and involuntary muscle contractile properties in a sample of 95 differently trained men and women. To the best of our knowledge, this is the first investigation that dealt with this issue.

We expected a significant correlation between the two methods, in the light of the findings of some previous studies which indicated a significant correlation between TMG and various methods for assessment of muscle strength. For confirmation of our hypothesis, a significant correlation between measured parameters should exist as well as the differences in these parameters between differently trained men and women. However, in view of the correlation between certain parameters of isokinetic dynamometry and TMG (Tables 2 and 3) their magnitude (Table 5), and the low differences in the two sets of parameters between the groups (only 25% of all possible significant differences) and inconsistency (Table 6), we can conclude that the hypothesis is only partially confirmed.

A significant correlation was detected between the PM and the TMG-based, Tc and Dm. The Tc (contraction time) parameter is an indicator of the muscle ability to contract at fast rates, and has been shown to be associated with fatigue and type of muscle fibers, with higher values indicating a high level of fatigue or predominance of slow muscle fibers, and vice versa [36, 37, 38]. The Dm (maximal displacement) parameter comprehensively expresses muscle tension, muscle stiffness, tendon mechanical properties, muscle mass and fatigue [27, 33, 39]. The decrease in Dm is an indicator of increased muscular stiffness, whereas high scores indicate a lack of muscle tone.

The results of this study outlined a relationship between maximal isokinetic strength, muscle contraction speed and muscle stiffness. These correlations were negative in nature, which indicates that people with higher values of isokinetic muscle strength might be capable of for faster muscle contraction (increased power). Also, the results showed the same relation between strength and muscle stiffness, which means that people with higher values of isokinetic muscle strength would have increased muscle stiffness. The observed results also indicate that maximal isokinetic strength depends to a certain extent on muscle contraction speed and muscle stiffness, and that muscle contraction speed and muscle stiffness can influence isokinetic muscle strength (from 22.7% to 42.7%, Table 4). This finding is in accord with previous studies which showed that there is a significant correlation between Tc, Dm and voluntary muscle contractile properties measured at various movement conditions (isometric, isotonic/isoinertial) [13, 14, 15].

These correlations are generally higher in women (Tables 2, 3 and 5; Fig. 1). This result is somewhat expected, as previous studies indicated that the correlation between TMG parameters and voluntary contractions were higher in women [13] and can be explained by specificities of muscle neuromechanical contractile properties of men and women. It is generally known that there are gender differences in muscle contractile properties, especially in muscle strength [40, 41, 42]. However, other reports found no gender differences in muscle contraction speed and stiffness [43, 44, 45]. Thus muscle contraction speed and muscle stiffness may influence isokinetic strength manifestation in women, while in men other factors, such as muscle mass and testosterone level, may play a more prominent role.

Regarding the training factor, the findings indicate that the highest degree of correlation between parameters of isokinetic dynamometry and tensiomyography is detected in the PI group while the lowest is in the AT group (Tables 3 and 5; Fig. 2). Therefore, the degree of correlation between PM, Tc, and Dm tends to decrease as the level of physical activity increases. However, it may not be concluded that the correlation between these parameters decrease as the level of isokinetic muscle strength increases as the differences in strength between groups were not consistent (Table 6).

These findings can be explained by several factors. First of all, it can be assumed that the training process in the AT group is primarily focused on increasing muscle strength, while the goal of increasing muscle contraction speed is generally neglected, and vice versa. Secondly, data from previous studies indicate that, compared to non-athletes, athletes have higher level of voluntary muscle activation and voluntary effort, which to a certain extent can influence the muscle strength manifestation [46, 47]. Thus, because of high level of voluntary muscle activation/effort, in the AT and PA group there were inconsistent changes in voluntary and involuntary muscle contractile properties, unlike the PI group. Finally, although it has been shown that isokinetic muscle strength, to a certain extent, depends on muscle stiffness, we assume that further increase in muscle stiffness with increase in muscle strength is not possible due to morphological limitations.

The degree of correlation between PM and the TMG parameters (Tables 2 and 3) is generally higher for Dm ( $r=$ $-$ 0.476, $p=$ 0.018 on average level) than Tc parameter ( $r=$ $-$ 0.414, $p=$ 0.023 on average level). Hence, isokinetic strength likely depends to a greater extent on muscle stiffness (Adj. $R^{2}$ , 31.1% on average) than on muscle contraction speed (Adj. $R^{2}$ , 27.2% on average) (Table 4). On the other hand, the correlation between the observed TMG and isokinetic parameters is slightly higher when muscle strength is measured on lower speeds (60 ${}^{\circ}$ /s rather than 180 ${}^{\circ}$ /s) (Tables 2 and 3), where a higher effort is required due to the greater external load. This possibly indicates that the relationship between voluntary and involuntary muscle contractions is higher when voluntary contractile properties are tested in conditions of dominant manifestation of higher muscle force level than in conditions of dominant manifestation of higher movement velocity level.

The correlation between isokinetic and TMG parameters proved higher for the hamstring muscle BF (Tables 2, 3 and 5; Fig. 2). Given the functional role of the BF muscle as agonist and coactivator, this finding is in line with previous studies [48, 49] and emphasizes the importance of BF in the neuromechanical function of knee joint muscles.

The results of this study may be of utility both for research and practice. Isokinetic dynamometry and TMG, as previously mentioned, may be used for injury prevention in sports training, physical therapy and rehabilitation, as methods for the assessment of muscle strength, speed of muscle contraction, muscle stiffness, muscle fiber types, functional and lateral symmetry.

The results obtained in this study indicate that these methods generally do not have valuable relations and that there is no scientifically valuable prediction power between the methods (Table 5). However, at a single partial level (level of individual variables) there is a moderate but significant predictive linear relationship between isokinetic dynamometry and TMG and its parameters, peak moment (PM), contraction time (Tc), and maximal displacement (Dm) (Table 4). The coefficients in Table 4 suggest some agreement between the two methods in the description of contractile muscle properties, that is, a certain amount of variability in isokinetic strength can be explained by a certain amount of variability in Dm and/or Tc (from 22.7% to 42.7%).

The main limitation of this study is the sample of participant structure. This study dealt with physically inactive/active individuals and athletes from strength and power sports only. Future studies should include participants from other sports, such as endurance and team sports athletes. Also, this research did not take into consideration the athletes’ training phase (preparation, competition, transition), which may influence the correlation between examined methods. The current investigation has focused on the knee joint and future research should point at confirming these data in other regions.

5. Conclusion

It can be concluded that at the general level, isokinetic dynamometry and TMG are not statistically associated, and represent different technologies that measure different contractile properties of muscles. However, a hierarchical structure of predictive validity at the single partial level (level of individual variables) was detected as a function of gender and training level.

We have to especially emphasize the negative relations between measured strength characteristics and TMG muscle stiffness variable in women. This means that if women have an increased muscle stiffness, especially biceps femoris muscle, they might have the potential for a higher strength level performance. Also, the inverse proportional relation between the training level and the applied methods was observed (the greater the training level, the smaller the relationship between the methods).

The results of this study render a whole new perspective in the use of isokinetic dynamometry and TMG method especially, as a relatively new and undiscovered method for assessment of muscle involuntary neuromechanical contractile properties

Footnotes

Acknowledgments

The paper is a part of the project Effects of applied physical activity on the locomotive, metabolic, psychosocial and educational status of the population of Republic of Serbia, number III47015, funded by the Ministry of Education and Science of the Republic of Serbia – Research Projects Cycle 2011-2018.

Conflict of interest

The authors declare no conflict of interest.

References

Abernethy

Kippers

Hanrahan

Pandy

McManus

Mackinnon,

. Biophysical foundations of human movement. Champaing IL: Human Kinetics; 2013.

Enoka

. Neuromechanics of human movement. Champaign IL: Human Kinetics; 2008.

Frontera

Ochala

. Skeletal muscle: a brief review of structure and function. Calcif Tissue Int. 2015; 96(3): 183-195.

Miller

Layzer

. Muscle cramps. Muscle Nerve. 2005; 32(4): 431-442.

Webb

. Smooth muscle contraction and relaxation. Adv Physiol Educ. 2003; 27(4): 201-206.

Zhou

Lawson

Morrison

Fairweather

. Electromechanical delay in isometric muscle contractions evoked by voluntary, reflex and electrical stimulation. Eur J Appl Physiol Occup Physiol. 1995; 70(2): 138-145.

Gardiner

. Advanced neuromuscular exercise. Champaign IL: Human Kinetics; 2011.

Maffiuletti

. Physiological and methodological considerations for the use of neuromuscular electrical stimulation. Eur J Appl Physiol. 2010; 110(2): 223-234.

Baltzopoulos

Brodie

. Isokinetic dynamometry. Sports Med. 1989; 8(2): 101-116.

10.

Abernethy

Wilson

Logan

. Strength and power assessment. Sports Med. 1995; 19(6): 401-417.

11.

Caruso

Brown

Tufano

. The reproducibility of isokinetic dynamometry data. Isokineti Exerc Sci. 2012; 20(4): 239-253.

12.

Neamţu

Neam tu

Marin

Bieru

Rusu

. Prediction of motor disorders in multiple sclerosis using muscle change structure assessment. Rom J Morphol Embryol. 2016; 57(4): 1331-1335.

13.

Dopsaj

Ivanovic

Ćopić

. Voluntary vs non-voluntary muscle contraction explosivity: RFD vs RMTD as a possible new TMG parameter. In: Srdjan Djordjevic editor. TMG: Today and Future – ISOT 2014; 2014 Oct 24; Rome (Italy). Romania: Universitaria Craiova; 2014. pp. 5-10.

14.

de Paula Simola

RÁ

Harms

Raeder

Kellmann

Meyer

Pfeiffer

, et al. Assessment of neuromuscular function after different strength training protocols using tensiomyography. J Strength Cond Res. 2015; 29(5): 1339-1348.

15.

Gil

Loturco

Tricoli

Ugrinowitsch

Kobal

Cal Abad

, et al. Tensiomyography parameters and jumping and sprinting performance in Brazilian elite soccer players. Sports Biomech. 2015; 14(3): 340-350.

16.

Turconi

Guarcello

Cignoli

Setti

Bazzano

Roggi

. Eating behaviors, physical activity, nutritional and food safety knowledge and beliefs in an adolescent Italian population. J Am Coll Nutr. 2008; 27(1): 31-43.

17.

Perrin

. Reliability of isokinetic measures. J Athl Train. 1986; 21(4): 319-321.

18.

Pincivero

Lephart

Karunakara

. Reliability and precision of isokinetic strength and muscular endurance for the quadriceps and hamstrings. Int J Sports Med. 1997; 18(2): 113-117.

19.

Papadopoulos

Siatras

Kellis

. The effect of static and dynamic stretching exercises on the maximal isokinetic strength of the knee extensors and flexors. Isokineti Exerc Sci. 2005; 13(4): 285-291.

20.

Knezevic

Mirkov

Kadija

Milovanovic

Jaric

. Evaluation of isokinetic and isometric strength measures for monitoring muscle function recovery after anterior cruciate ligament reconstruction. J Strength Cond Res. 2014; 28(6): 1722-1731.

21.

Nugent

Snodgrass

Callister

. The effect of velocity and familiarisation on the reproducibility of isokinetic dynamometry. Isokineti Exerc Sci. 2015; 23(3): 205-214.

22.

Mirkov

Knezevic

Maffiuletti

Kadija

Nedeljkovic

Jaric

. Contralateral limb deficit after ACL-reconstruction: an analysis of early and late phase of rate of force development. J Sports Sci. 2017; 35(5): 435-440.

23.

Wilhite

Cohen

Wilhite

. Reliability of concentric and eccentric measurements of quadriceps performance using the KIN-COM dynamometer: the effect of testing order for three different speeds. J Orthop Sports Phys Ther. 1992; 15(4): 175-182.

24.

McNair

Depledge

Brettkelly

Stanley

. Verbal encouragement: effects on maximum effort voluntary muscle action. Br J Sports Med. 1996; 30(3): 243-245.

25.

Kannus

. Isokinetic evaluation of muscular performance. Int J Sports Med. 1994; 15(1): 11-18.

26.

Dvir

. Isokinetics: muscle testing, interpretation, and clinical applications. Churchill Livingstone: Elsevier Health Sciences; 2004.

27.

Rey

Lago-Peñas

Lago-Ballestero

. Tensiomyography of selected lower-limb muscles in professional soccer players. J Electromyogr Kinesiol. 2012; 22(6): 866-872.

28.

de Paula Simola

RÁ

Raeder

Wiewelhove

Kellmann

Meyer

Pfeiffer

, et al. Muscle mechanical properties of strength and endurance athletes and changes after one week of intensive training. J Electromyogr Kinesiol. 2016; 30: 73-80.

29.

Loturco

Gil

de Souza Laurino

Roschel

Kobal

Abad

CCC

, et al. Differences in muscle mechanical properties between elite power and endurance athletes: A comparative study. J Strength Cond Res. 2015; 29(6): 1723-1728.

30.

Tous-Fajardo

Moras

Rodríguez-Jiménez

Usach

Doutres

Maffiuletti

. Inter-rater reliability of muscle contractile property measurements using non-invasive tensiomyography. J Electromyogr Kinesiol. 2010; 20(4): 761-766.

31.

Toskić

Dopsaj

Koropanovski

Jeknić

. The neuromechanical functional contractile properties of the thigh muscles measured using tensiomyography in male athletes and non-athletes. Phys Cult. 2016; 70(1): 34-45.

32.

Binder-Macleod

Dean

Ding

. Electrical stimulation factors in potentiation of human quadriceps femoris. Muscle Nerve. 2009; 25(2): 271-279.

33.

Križaj

Šimunič

Žagar

. Short-term repeatability of parameters extracted from radial displacement of muscle belly. J Electromyogr Kinesiol. 2008; 18(4): 645-651.

34.

Martín-Rodríguez

Loturco

Hunter

Rodríguez-Ruiz

Munguia-Izquierdo

. Reliability and measurement error of tensiomyography to assess mechanical muscle function: A systematic review. J Strength Cond Res. 2017; 31(12): 3524-3526.

35.

Hair

Anderson

Tatham

Black

. Multivariate data analysis. 5th ed. New Jersey, USA: Prentice-Hall. Inc.; 1998.

36.

Dahmane

Djordjevič

Šimunič

Valenčič

. Spatial fiber type distribution in normal human muscle: histochemical and tensiomyographical evaluation. J Biomech. 2005; 38(12): 2451-2459.

37.

Dahmane

Valenčič

Knez

Eržen

. Evaluation of the ability to make non-invasive estimation of muscle contractile properties on the basis of the muscle belly response. Med Biol Eng Comput. 2001; 39(1): 51-55.

38.

Šimunič

Degens

Rittweger

Narici

Mekjavic

Pišot

. Noninvasive estimation of myosin heavy chain composition in human skeletal muscle. Med Sci Sports Exerc. 2011; 43(9): 1619-1625.

39.

García-Manso

Rodríguez-Matoso

Sarmiento

de Saa,

Vaamonde

Rodríguez-Ruiz

Da Silva-Grigoletto

. Effect of high-load and high-volume resistance exercise on the tensiomyographic twitch response of biceps brachii. J Electromyogr Kinesiol. 2012; 22(4): 612-619.

40.

Wüst

Morse

De Haan

Jones

Degens

. Sex differences in contractile properties and fatigue resistance of human skeletal muscle. Exp Physiol. 2008; 93(7): 843-850.

41.

Miller

AEJ

MacDougal

Tarnopolsky

Sale

. Gender differences in strength and muscle fiber characteristics. Eur J Appl Physiol Occup Physiol. 1993; 66(3): 254-262.

42.

Clark

Collier

Manini

Ploutz-Snyder

. Sex differences in muscle fatigability and activation patterns of the human quadriceps femoris. Eur J Appl Physiol. 2005; 94(1-2): 196-206.

43.

Padua

Carcia

Arnold

Granata

. Gender differences in leg stiffness and stiffness recruitment strategy during two-legged hopping. J Mot Behav. 2005; 37(2): 111-126.

44.

Krivickas

Suh

Wilkins

Hughes

Roubenoff,

Frontera

. Age-and gender-related differences in maximum shortening velocity of skeletal muscle fibers. Am J Phys Med Rehabil. 2001; 80(6): 447-455.

45.

Blackburn

Riemann

Padua

Guskiewicz

. Sex comparison of extensibility, passive, and active stiffness of the knee flexors. Clin Biomech. 2004; 19(1): 36-43.

46.

Ahtiainen

Häkkinen

. Strength athletes are capable to produce greater muscle activation and neural fatigue during high-intensity resistance exercise than nonathletes. J Strength Cond Res. 2009; 23(4): 1129-1134.

47.

Young

Bilby

. The Effect of Voluntary Effort to Influence Speed of Contraction on Strength, Muscular Power, and Hypertrophy Development. J Strength Cond Res. 1993; 7(3): 172-178.

48.

Kubo

Tsunoda

Kanehisa

Fukunaga

. Activation of agonist and antagonist muscles at different joint angles during maximal isometric efforts. Eur J Appl Physiol. 2004; 91(2-3): 349-352.

49.

Dahmane

Djordjevič

Smerdu

. Adaptive potential of human biceps femoris muscle demonstrated by histochemical, immunohistochemical and mechanomyographical methods. Med Biol Eng Comput. 2006; 44(11):

Concurrent and predictive validity of isokinetic dynamometry and tensiomyography in differently trained women and men

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSION:

Keywords

1. Introduction

2. Methods

2.1 Participants

2.2 Procedures

3. Results

Table 3 Correlations between parameters of isokinetic dynamometry and TMG in differently trained subjects according to the gender

5. Conclusion

Footnotes

Acknowledgments

Conflict of interest

References

Table 3
Correlations between parameters of isokinetic dynamometry and TMG in differently trained subjects according to the gender