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21

Original scientific article                                   UDC: 612.741:796.012.13
received: 2016-04-18

LOWER CORRELATION BETWEEN BICEPS FEMORIS 
CONTRACTION TIME AND MAXIMAL RUNNING SPEED IN 
CHILDREN THAN IN ADULTS: A LONGITUDINAL STUDY IN 

9- TO 14-YEAR OLD CHILDREN*

Jernej ZAVRŠNIK1, Rado PIŠOT2, Tadeja VOLMUT2, Katja KOREN2, 
Helena BLAŽUN VOŠNER3, Peter KOKOL4, Janez VOŠNER4, Boštjan ŠIMUNIČ2

1Dr. Adolf Drolc Healthcare Center, Maribor, Slovenia
2University of Primorska, Science and Research Centre, Institute for Kinesiology Research, 

Koper, Slovenia
3University of Maribor, Faculty of Health Sciences, Center for International Cooperation, 

Maribor, Slovenia
4University of Maribor, Faculty of Electrical Engineering and Computer Sciences, Maribor 

Slovenia

Corresponding author:
Boštjan ŠIMUNIČ

University of Primorska, Science and Research Centre, Institute for Kinesiology Research
Garibaldijeva 1, 6000 Koper, Slovenia

phone: +386 31 832 016
e-mail: bostjan.simunic@zrs.upr.si

ABSTRACT

Biceps femoris is a major propulsor muscle in sprinting and its contraction time 
negatively correlates to the running speeds of adults. Our aim was to compare age- and 
gender-related correlations between vastus lateralis and biceps femoris contraction 
times and running speeds during a longitudinal study of 9- to 14-year old children. On 
a yearly basis, we conducted vastus lateralis and biceps femoris tensiomyographic me-
asurements of muscle contraction time and maximal running speeds measured during 
7-metre sprints with flying starts using photocells in 107 children (of which 53 boys). 
Vastus lateralis contraction time was not correlated with the running speed. Howe-
ver, biceps femoris contraction time was negatively correlated with the running speed 
only in boys after the age of 12.9 years (Pearson r ranges from -0.391 to -0.426; p < 

* The paper has been previously published in the hijacked journal Wulfenia (Vol. 22(1): pp. 
233–252, January 2015). The editor has been notified and he fully agrees with the publication in 
Annales Kinesiologiae. The paper has been modified, double-blind peer reviewed and only then 
accepted for publication.



22

Jernej ZAVRŠNIK, Rado PIŠOT, Tadeja VOLMUT, Katja KOREN, Helena BLAŽUN VOŠNER, Peter KOKOL, Janez VOŠNER, Boštjan ŠIMUNIČ, 21–42

ANNALES KINESIOLOGIAE • 7 • 2016 • 1

0.002). It was concluded that biceps femoris contraction time is far less correlated with 
running speed than in adult athletes (Pearson r = -0.60); however, the correlation is 
gender- and age-specific. It seems that the knee flexor and hip extensor, biceps femoris, 
is not as yet the major determinant of running speed in 9- to 14-year old children at 
that age.

Keywords: skeletal muscle, biceps femoris, vastus lateralis, tensiomyography, 
pediatrics.

KORELACIJA MED ČASOM KRČENJA MIŠICE BICEPS FEMORIS 
IN HITROSTJO ŠPRINTA JE PRI OTROCIH NIŽJA KOT PRI 
ODRASLIH: LONGITUDINALNA ŠTUDIJA 9- DO 14-LETNIH 

OTROK

IZVLEČEK

Skeletna mišica biceps femoris je pomembna za propulzijo v fazi odriva med tekom 
in vemo, da je njen čas krčenja negativno povezan z maksimalno hitrostjo teka pri od-
raslih moških. Zato smo si za cilj zastavili, da preverimo povezavo med časom krčenja 
mišic vastus lateralis in biceps femoris pri otrocih, glede na spol in starost. V longitu-
dinalni 5-letni študiji smo spremljali 107 otrok (53 dečkov) s periodično letnimi meri-
tvami telesnih značilnosti, maksimalne hitrosti teka in kontraktilnih lastnosti omenjenih 
mišic z uporabo Tenziomiografije. Otroci so bili na začetku stari 9 let in na koncu 14 let. 
Ugotovili smo, da čas krčenja mišice vastus lateralis ni povezan z maksimalno hitrostjo 
teka. Medtem, ko je bil čas krčenja mišice biceps femoris negativno povezan z maksi-
malno hitrostjo teka, a le pri dečkih po 12.9 letu starosti (Pearsonov r med -0.391 in 
-0.426; p < 0.002). Zaključimo lahko, da je čas krčenja mišice biceps femoris bistveno 
manj povezan z maksimalno hitrostjo teka pri otrocih, kot pri odraslih (Pearsonov r = 
-0.60). Sklepamo lahko, da mišica biceps femoris pri tej starosti otrok še ni poglaviten 
dejavnik maksimalne hitrosti teka.

Ključne besede: skeletna mišica, biceps femoris, vastus lateralis, tenziomiografija, 
pediatrija



ANNALES KINESIOLOGIAE • 7 • 2016 • 1

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Jernej ZAVRŠNIK, Rado PIŠOT, Tadeja VOLMUT, Katja KOREN, Helena BLAŽUN VOŠNER, Peter KOKOL, Janez VOŠNER, Boštjan ŠIMUNIČ, 21–42

INTRODUCTION

Nowadays, we are faced with fast lifestyle as a society, which influences indivi-
duals’ health, social, cultural, and physical statuses. Children are one of the more vul-
nerable groups within a society. Therefore, we should pay special attention to their 
development. Childhood is a very sensitive period and is, in general, characterized by 
various dynamic changes in physiological and psychological development, as well as 
the establishment of healthy or unhealthy behaviour (Faigenbaum & Myer, 2012). As a 
result of global health trends, there is a growing interest in children’s physical exercise; 
and, thus, consequently in their body growth and development.

Tensiomyography (TMG) is a non-invasive tool for the assessment of skeletal mu-
scle contractile properties (Valenčič & Knez, 1997) which are related to muscle com-
position (Dahmane, Valenčič, Knez, & Eržen, 2001; Šimunič et al., 2011). Rodríguez 
Ruiz, et al. (2011) performed a study amongst 84 males who were divided into four 
age groups; teenagers, undergraduate students, adults and the elderly, and discovered 
a decline in Vm (tensiomyographicaly determined normalized muscle twitch response 
velocity, contraction time / amplitude of radial displacement) in the vastus lateralis in 
relation to age. In contrast, Vm values in biceps femoris (BF) did not change between 
age groups; although, the value was slightly reduced in the older age group. Further-
more, the researchers noted that changes in muscle composition are associated with the 
physical activity levels of individuals and, therefore, the changes in muscle response 
may not only depend on age but also on the amounts and types of physical activity 
(Rodríguez Ruiz et al. 2011).

There is great interest in muscle composition; however, it is more than evident that 
the invasiveness of the approach used in this research field is the main drawback for 
obtaining data on muscle composition as a representative sample. Further, the more 
common muscle to be observed by its composition is the vastus lateralis. Additionally, 
there is also a huge interest in other muscles that are even more important in childho-
od for children’s health, posture, and motor development. However, sample sizes are 
rather small and longitudinal studies are very rare. Valenčič and Knez (1997) proposed 
a non-invasive and selective TMG where several TMG contractile parameters were 
defined (Valenčič & Knez, 1997), and where contraction time was later correlated to a 
proportion of slow-twitch muscle fibers within skeletal muscle (Dahmane et al., 2001; 
Dahmane, Djordjević, Šimunič, & Valenčič, 2005; Šimunič et al. 2011). The TMG 
contractile parameters were found to be highly reliable (ICC r > 0.85; Šimunič, 2012).

Oliver, Lloyd, and Rumpf (2013) claimed that sprinting speed is one of the dis-
tinguishing indicators of successful motor performance in children and is developed 
throughout childhood and adolescence, as children grow and mature. Indeed, a failure 
to master sprinting may be an enormous barrier preventing children from gaining more 
complex physical activity skills. These authors also suggest that speed during this peri-
od is developed in a nonlinear manner due to the large maturational influence associa-
ted with increases in limb lengths, increased muscle mass, and changes in intrinsic mu-
scle-tendon properties. Additionally, gender differences in speed development become 



24

Jernej ZAVRŠNIK, Rado PIŠOT, Tadeja VOLMUT, Katja KOREN, Helena BLAŽUN VOŠNER, Peter KOKOL, Janez VOŠNER, Boštjan ŠIMUNIČ, 21–42

ANNALES KINESIOLOGIAE • 7 • 2016 • 1

apparent at the onset of puberty, with girls making limited gains in speed throughout 
adolescence, contrary to boys for whom large gains in speed could be observed. These 
authors also noted paucity of research studies on speed and muscle development for the 
above pediatric population (Oliver et al., 2013).

Therefore, we aimed at analysing the correlation between vastus lateralis and biceps 
femoris contraction time with maximal running speed and, furthermore, at establishing 
how contraction times of both abovementioned muscles are related to standard anthro-
pometric measures (body height and mass, ROHR index) at different ages and sexes.

METHODS

Participants

Recruitment of participants started in September 2001 in three different Slovenian 
regions: Ljubljana region, Maribor region, and the Primorska region. Primary schools 
in these regions were randomly selected. Therefore, the participants come from five 
different Slovenian towns (Table 1), two of which are major cities covering central and 
northeast Slovenia, and three small towns covering the coastal region. In this way, we 
ensured that the sample covered the whole of Slovenia.

Table 1. Selection of regions, primary schools and towns included in the 5-year longi-
tudinal study.

City Primary School Town

Ljubljana region

Tone Čufar Ljubljana

Valentin Vodnik Ljubljana

Dr. Vito Kraigher Ljubljana

Maribor region

Prežihov Voranc Maribor

Slava Klavora Maribor

Tone Čufar Maribor

Primorska region

Anton Ukmar Koper

Vojka Šmuc Izola

Ciril Kosmač Piran



ANNALES KINESIOLOGIAE • 7 • 2016 • 1

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Jernej ZAVRŠNIK, Rado PIŠOT, Tadeja VOLMUT, Katja KOREN, Helena BLAŽUN VOŠNER, Peter KOKOL, Janez VOŠNER, Boštjan ŠIMUNIČ, 21–42

Researchers organized short workshops for the school head teachers, physical edu-
cation teachers, the children, and their parents, with the aim of presenting the purpose 
and the aims of the research study, the research design, to present the measurement 
protocols and tools, and to invite potential participants. Throughout the workshop exe-
cution, the researchers were available for answering any questions which might occur 
during the session in order to clarify any dilemmas regarding the study.

In regard to the recruitment process, 300 children in total were selected (100 children 
from each region), of which 265 children participated in the baseline study (138 boys, 
127 girls). In the first follow-up study, 263 children (125 boys, 138 girls) participated, 
in the second follow-up study 252 children (127 boys, 125 girls), in the third follow-up 
study 179 children (98 boys, 81 girls), in the fourth follow-up study  175 children (98 
boys, 77 girls), and in the last, the fifth follow-up study, there were 176 children (96 
boys, 80 girls). To summarize, 107 children (53 boys, 54 girls) (initial measurement 
average age 9.1 ± 0.5 years) who had completed all six longitudinal measurements 
were selected for the analysis. At the baseline, the study participants attended the third 
grade of primary school and at the last follow-up study they attended the eighth grade.

The selection process was performed by researchers with the support of teachers 
in a manner which prevented any possible bias (i.e. gender, geographical distribution, 
anthropometrical characteristics). However, children eligible to participate in this study 
had to be in good health. None of the children had had any history of neuromuscular 
disorders or muscle diseases. During the recruitment process and before carrying out 
any research study at the baseline or follow-ups, the participants and their parents were 
informed that any participation in the study was strictly on voluntary basis. Additio-
nally, they were informed that the participants could withdraw from the study at any 
time and for any reason, and that the collected data would only be used for the research 
purposes. Therefore, the parents of the children gave their written consent for them to 
participate in the study. Moreover, all procedures conformed to the 1964 Declaration of 
Helsinki and were approved by the National Medical Ethics Committee of the Republic 
of Slovenia.

The organizational settings of the conducted longitudinal study were the same wi-
thin all three regions.

Procedures

The 5-year-long research was conducted once per school year from 2001 till 2006, 
and it included single-point quantitative research studies and the following measure-
ments of:

 – anthropometrical characteristics;
 – contractile properties of skeletal muscles; and
 – running speed.



26

Jernej ZAVRŠNIK, Rado PIŠOT, Tadeja VOLMUT, Katja KOREN, Helena BLAŽUN VOŠNER, Peter KOKOL, Janez VOŠNER, Boštjan ŠIMUNIČ, 21–42

ANNALES KINESIOLOGIAE • 7 • 2016 • 1

Measurements of Anthropometrical Characteristics
Participants’ body masses and heights were measured by using standard tools. The 

body mass was measured to an accuracy of 0.1 kilograms, while the height was me-
asured to an accuracy of 0.5 centimetres. All participants were barefoot and wearing 
their sportswear during the measurements. On the basis of the measured variables, each 
body mass index (ROHR’s index) was calculated. ROHR’s anthropometric index is a 
statistical data, which combines a participant’s height and mass into a metrical form. 
Actually, both ROHR’s as well as the body mass index (BMI), serve the purpose of 
classifying individuals into categories of underweight, normal, and obese. BMI measu-
rement projects a two-dimensional square state by measuring the mass per square unit 
of surface area, while ROHR’s index assumes that the body is a three-dimensional cube 
and, therefore, measures the mass per cubic unit of volume. ROHR’s index takes into 
account both the width and circumference, unlike BMI which projects that the breadth 
and scope of an individual is proportional to his / her height. ROHR’s index was, there-
fore, chosen as a better indicator of the children’s and adolescents’ nutritional statuses 
(Foster, Voors, Webber, Frerichs, & Berenson, 1977; Kokol et al., 1992; Omura, Zinno, 
Harada, & Inoue, 1993; Freedman & Perry, 2000). The measurements of anthropome-
trical characteristics were performed on three sport science students.

Measurements of Contractile Properties of Skeletal Muscles
The contractile properties of their skeletal muscles were measured using the TMG 

method. TMG detects radial displacement of the skeletal muscle belly during maximal 
isometric twitch contraction (Valenčič, 1990), and has been developed in the Labora-
tory for Skeletal Muscles and Biomedical Imaging (LBM) at the Faculty of Electrical 
Engineering, University of Ljubljana, Slovenia. Measurements were performed on two 
muscles vastus lateralis and biceps femoris of leg-dominant sites. Measurements on 
the vastus lateralis were performed in supine positions at knee angles set at 30° knee 
flexion, where 0° represents the extended joint. Measurements on the biceps femoris 
were performed in prone positions at a knee angles set at 5° knee flexion. A measured 
muscle was in a relaxed predefined position and muscle contraction was evoked by bri-
ef electrical stimulus. To this end, we used a pair of self-adhesive stimulation electrodes 
(AxelGaard, Pals) within this study with a diameter of 50 millimetres. The muscle was 
measured in a bipolar way in that we installed the negative electrode (cathode) 5 cm 
distal, and the positive electrode (anode) 5 cm proximal to the measurement point. The 
measuring point was selected at a place where the belly muscle was the largest and 
additionally ensured that the selected place was between the two electrodes. In doing 
so, we used the experimental measurements, palpation and re-installing the electrodes 
and sensors if needed. Due to the fact that each muscle has its own specific anatomic 
structure, we had to make adjustments according to the locations of the measuring 
equipment. The sensor was set perpendicular to the skin overlying the muscle belly: 
in vastus lateralis at 30 % of the femur length above the patella on the lateral side; 
in biceps femoris at the midpoint of the line between the fibula head and the ischial 



ANNALES KINESIOLOGIAE • 7 • 2016 • 1

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Jernej ZAVRŠNIK, Rado PIŠOT, Tadeja VOLMUT, Katja KOREN, Helena BLAŽUN VOŠNER, Peter KOKOL, Janez VOŠNER, Boštjan ŠIMUNIČ, 21–42

tuberosity. In order to elicit twitch contraction, we used a single one-millisecond pulse 
applied through the cathode and the anode. The stimulation current at the start was just 
above the contraction threshold and then it was gradually increased until the response 
amplitude did not increase any further. Two maximal twitch responses were recorded 
and saved.

The maximal displacement amplitude and the contraction times were calculated 
from each twitch response, as proposed by Valenčič (1990) and Valenčič and Knez 
(1997). Maximal displacement amplitude (Dm, in millimeters) was defined as the peak 
amplitude on the displacement-time curve of the TMG twitch response. The contrac-
tion time (Tc, in milliseconds) was the time from 10 % to 90 % of Dm being reached. 
The average value of these parameters, extracted from two twitch responses, was used 
for further analysis. TMG measurements were performed by an expert from the field 
of electrical engineering and computer science, four physical education teachers, and 
five undergraduate sport sciences students. The measurements were supervised by a 
medical doctor.

Measurement of the Running Speed
Prior to testing the maximal running speed, all the children were appropriately war-

med up, which lasted approximately 20 minutes. The warm-up process was composed 
of running (5 minutes), stretching (5 minutes), and warm-up running practices (10 mi-
nutes). The children’s warming-up process was always conducted by the same person 
and by using the same procedure. Each participant had the opportunity of two experi-
mental sprints. Maximal running speed was measured at a distance of 7 meters from a 
flying start. During the measurement process, the participants performed preliminary 
runs, then followed the first photocell checkpoint, and after 7 meters the second pho-
tocell checkpoint.

We divided up the running distance of 7 meters to include a sprint time from which 
we calculated the sprint speed. Each participant repeated the sprint twice and the better 
result was used in the further analysis. Maximum running speed was measured by using 
a wireless Brower measurement system (Brower Timing Systems Ltd., USA).

Design and Measures

Detailed description of all study procedures and design are presented in Figure 1. 
We performed six repeated measurements of the children’s progress from the third to 
the eighth grade of their primary schools. Every measurement was performed using the 
same procedure. A week before the study, each school was notified to follow a specific 
protocol prior to the measurement, namely, that all major physical or sport activities 
were discouraged two days before the measurement. All the recruited participants were 
invited to participate at each study / measurement. A detailed description of the recruit-
ment and data collection is presented in Figure 1.



28

Jernej ZAVRŠNIK, Rado PIŠOT, Tadeja VOLMUT, Katja KOREN, Helena BLAŽUN VOŠNER, Peter KOKOL, Janez VOŠNER, Boštjan ŠIMUNIČ, 21–42

ANNALES KINESIOLOGIAE • 7 • 2016 • 1

Figure 1. Flowchart of recruitment and data collection procedure 



ANNALES KINESIOLOGIAE • 7 • 2016 • 1

29

Jernej ZAVRŠNIK, Rado PIŠOT, Tadeja VOLMUT, Katja KOREN, Helena BLAŽUN VOŠNER, Peter KOKOL, Janez VOŠNER, Boštjan ŠIMUNIČ, 21–42

Data Analysis

All data are expressed as means ± standard deviations. For all variables, the hypothe-
sis of a normal distribution was tested and confirmed using visual inspection suppor-
ted by D’Agostino’s normality procedure and Kolmogorov-Smirnov test. Morpholo-
gic growth was analyzed by 2-way RM ANOVA, with age as a repeated measure and 
gender as a fixed group. For correlating vastus lateralis and biceps femoris Tc with 
running speed, a Pearson correlation coefficient was calculated. Statistical significance 
was accepted at p<0.05 level.

RESULTS

Background of the Participants

In all six-measurement points in total, 107 participants being included; their average 
age, body height and body mass is shown in Table 2.

Table 2. Longitudinal descriptive anthropometrical data of 53 boys and 54 girls at dif-
ferent age.

Age / 
years Body height / cm P Body mass / kg P ROHR’s index / 

kg / m3 P

Boys Girls Boys Girls Boys Girls
9.1±0.5 139.6±6.5 139.5±7.2 0.905 34.9±7.2 32.7±6.8 0.110 12.7±1.78 12.0±1.66 0.025

9.9±0.5 143.4±6.9 143.5±7.5 0.962 37.8±8.2 36.1±7.5 0.257 12.7±1.96 12.1±1.70 0.097

10.6±0.5 147.6±7.2 148.4±7.6 0.602 39.5±8.8 37.4±7.8 0.188 12.2±1.88 11.3±1.54 0.015

12.0±0.5 156.5±7.9 158.4±7.5 0.215 48.5±10.8 45.8±9.0 0.160 12.5±1.92 11.4±1.59 0.002

12.9±0.5 162.6±8.1 162.4±6.9 0.883 53.5±11.6 50.7±9.3 0.166 12.4±2.12 11.8±1.68 0.109

13.6±0.5 167.2±8.0 164.5±6.5 0.058 56.8±11.7 54.3±8.7 0.016 12.1±1.96 11.6±1.49 0.162

Child anthropometrical growth could be classified as normal, following gen-
eral trends. There was a significant age effect on body height (p<0.001), body mass 
(p<0.001) and ROHR’s index (p<0.001) with a significant age × gender interaction 
effect on body height (p<0.001), body mass (p=0.028), and ROHR’s index (p=0.026).



30

Jernej ZAVRŠNIK, Rado PIŠOT, Tadeja VOLMUT, Katja KOREN, Helena BLAŽUN VOŠNER, Peter KOKOL, Janez VOŠNER, Boštjan ŠIMUNIČ, 21–42

ANNALES KINESIOLOGIAE • 7 • 2016 • 1

Vastus lateralis and biceps femoris Tc and running speed correlation analysis

In Figure 2, a descriptive data for vastus lateralis and biceps femoris Tc is presented, 
as well as for maximal running speed for both muscles and genders. In Tables 3 and 4, 
a correlation analysis is presented for both muscles and genders. We found sex-related 
differences only after the age of 12.9 years in all three presented variables. Furthermo-
re, a longitudinal trend reveals that there was no significant correlation between run-
ning speed and vastus lateralis Tc; however, significant negative correlation for biceps 
femoris Tc and running speed could be confirmed in boys after the age of 12.9 years 
(Figure 3).

* p<0.05 between sexes

Figure 2: Longitudinal descriptive analysis for vastus lateralis and biceps femoris con-
traction time (Tc) and maximal running speed.



ANNALES KINESIOLOGIAE • 7 • 2016 • 1

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Jernej ZAVRŠNIK, Rado PIŠOT, Tadeja VOLMUT, Katja KOREN, Helena BLAŽUN VOŠNER, Peter KOKOL, Janez VOŠNER, Boštjan ŠIMUNIČ, 21–42

Table 3. Pearson correlation between vastus lateralis contraction time and running 
speed.

Boys Girls

Age / years Pearson r p Pearson r P

9.1 ± 0.5 -0.048 0.367 -0.033 0.408

9.9 ± 0.5 -0.062 0.331 -0.053 0.352

10.6 ± 0.5 -0.118 0.201 -0.070 0.309

12.0 ± 0.5 -0.167 0.115 0.037 0.396

12.9 ± 0.5 -0.170 0.112 0.351 0.399

13.6 ± 0.5 -0.172 0.109 0.043 0.380

Table 4. Pearson correlation between biceps femoris contraction time and running 
speed.

Boys Girls

Age / years Pearson r p Pearson r P

9.1 ± 0.5 0.118 0.200 0.130 0.175

9.9 ± 0.5 -0.021 0.441 -0.020 0.390

10.6 ± 0.5 -0.195 0.081 0.085 0.270

12.0 ± 0.5 -0.177 0.097 0.128 0.178

12.9 ± 0.5 -0.426 0.001 0.117 0.200

13.6 ± 0.5 -0.391 0.002 0.125 0.182



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Jernej ZAVRŠNIK, Rado PIŠOT, Tadeja VOLMUT, Katja KOREN, Helena BLAŽUN VOŠNER, Peter KOKOL, Janez VOŠNER, Boštjan ŠIMUNIČ, 21–42

ANNALES KINESIOLOGIAE • 7 • 2016 • 1

Figure 3: Pearson correlation for biceps femoris contraction time (Tc) and maximal 
running speed at age 12.9 (left) and 13.6 (right) years.

Correlation between body mass, height, ROHR index, and Tc of vastus lateralis 
and biceps femoris

While the TMG measurement tool or running speed measurement equipment are 
not readily available to parents, average school sports teachers or sport club trainers, 
we decided to analyse how simple anthropometrical measures like mass, height and 
ROHR’s index are correlated to Tc of vastus lateralis and biceps femoris muscles to 
enable them to have some indicators for predicting the muscle developments and sport 
talents of young adolescents. Table 5 presents the correlations between body mass, 
height, and the ROHR index and the Tc of biceps femoris and vastus lateralis muscles 
for all six measurement points (baseline and 5 follow-up studies). It is evident, that 
the correlations between the contraction times of the vastus lateralis muscle and the 
anthropometrical measurements is more frequent than for the BL muscle. To be precise, 
at least one anthropometrical measurement correlated with the contraction time of the 
vastus lateralis muscle for the 4th till 6th measurement points. On the contrary, the biceps 
femoris muscles contraction times are more correlated with anthropometrical measures 



ANNALES KINESIOLOGIAE • 7 • 2016 • 1

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Jernej ZAVRŠNIK, Rado PIŠOT, Tadeja VOLMUT, Katja KOREN, Helena BLAŽUN VOŠNER, Peter KOKOL, Janez VOŠNER, Boštjan ŠIMUNIČ, 21–42

at the baseline and the first and the second follow-up compared to the  third, the fourth 
and the fifth follow-up studies.

Table 5. Significant correlations between body mass, height, ROHR index, and contrac-
tion time of biceps femoris (BF) and vastus lateralis (VL) muscles.

A v e r a g e 
age / years

9.1 ± 
0.5

9.9 ± 
0.5

10.6 ± 
0.5

12.0 ± 
0.5

12.9 ± 
0.5

13.6 ± 
0.5

Anthropome-
trical measu-
rements

9.1 ± 0.5

Body mass -BF +VL +VL +VL

Body height +VL +VL +VL

ROHR index -BF -BF

9.9 ± 0.5

Body mass +VL +VL +VL

Body height +VL +VL +VL

ROHR index -BF -BF -BF

10.6 ± 0.5

Body mass +VL +VL +VL

Body height +VL +VL +VL +VL

ROHR index -BF -BF -BF

12.0 ± 0.5

Body mass +VL +VL +VL

Body height +VL +VL +VL

ROHR index -BF -BF

12.9 ± 0.5

Body mass -BF -BF +VL -BF, 
+VL

Body height +VL +VL +VL +VL

ROHR index -BF -BF

13.6 ± 0.5

Body mass -BF +VL +VL +VL -BF, 
+VL

Body height +VL +VL +VL +VL +VL

ROHR index -BF -BF -BF



34

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Interestingly, the ROHR’s index is obviously a better predictor of contraction times 
for biceps femoris muscles compared to mass and height, indeed, it only correlates 
with biceps femoris muscles and not in any instance to vastus lateralis muscles. On the 
other hand, the height is a better predictor for the vastus lateralis muscle contraction 
time than the mass.

DISCUSSION

Our longitudinal study contributed with an insight into children’s skeletal muscle 
development, focusing on skeletal muscle composition. Using a non-invasive TMG, we 
assessed muscle composition related to the contractile parameter (Tc) in two skeletal 
muscles. Although there were initially 263 children included in the study, representa-
tive subsamples of 107 children (42 %) were present in all six measurements. TMG 
assessment requires electrical stimulus to evoke muscle contraction and some of the 
children found this as being less appropriate for them and so they were not forced to 
cooperate during the measurement. This was also the main reason for not performing 
the TMG assessment. Other reasons were illness or injury, absence from school, chan-
ging schools, etc. Skeletal muscle composition is very difficult, if not even ethically im-
possible, to measure in healthy children. Therefore, using a non-invasive approach we 
presented age- and gender-related longitudinal trends in Tc in the two skeletal muscles.

There are numerous data about vastus lateralis composition in adults but only few in 
children (Bell, MacDougal, Billeter, & Howald, 1980) and in adolescents (Glenmark, 
Hedberg, & Jansson, 1992). Johnson, Polgar, Weightman, and Appleton (1973) repor-
ted 37.8 % and 46.9 % at muscle surface and deep site, respectively. In a longitudinal 
study, Glenmark et al. (1992) found different developments of fibre type composition 
with increased age from 16 to 27 in women and men: the type I percentage tended to 
increase in the women from 51 % to 55 % and decrease significantly in the men from 
55 % to 48 %. Fibre cross-sectional areas remained unchanged in both genders. They 
suggested gender-related fibre type 1 adapted during increased age. In children, Bell et 
al. (1980) found 58.8 % type1 fibers and concluded that the distribution patterns and 
ultra-structures of skeletal muscles in six-year-old children was not different from nor-
mal adult tissues. However, this study showed no correlation between vastus lateralis 
contraction time and running speed in both sexes at any age, which is rather logical 
since the fact that vastus lateralis muscle is not the most important muscle for maximal 
running speed (Praprotnik, Valenčič, Čoh, & Šimunič, 2002). However, from this study 
we also found positive proportional correlations between the contraction time of the va-
stus lateralis muscle and anthropometrical measurements (i.e. body mass, body height) 
in children older than 12.0 ± 0.5 years; meaning that heavier and taller participants have 
shorter contraction times for the vastus lateralis muscle.



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Jernej ZAVRŠNIK, Rado PIŠOT, Tadeja VOLMUT, Katja KOREN, Helena BLAŽUN VOŠNER, Peter KOKOL, Janez VOŠNER, Boštjan ŠIMUNIČ, 21–42

Vastus lateralis muscle

In the lateral muscle of the knee extensors on the dominant side, we found that the 
contraction time changes with age, in boys faster than in girls. In boys, according to 
the third grade results (at the baseline) we found significantly lower contraction times 
in the fourth and the fifth grades, while in girls we measured significantly lower con-
traction times in the sixth and the seventh grades. A short contraction time means that 
the muscle is faster in younger boys than in girls. Differences between correlations ac-
cording to sex showed significant deviations; meaning that the girls in the seventh and 
eighth grade had shorter contraction times, due to the fact that their outer knee extensor 
muscles on the dominant side were faster during this period of time.

Vastus lateralis muscle is an anti-gravitational muscle and as such receives a lot of 
mechanical stimuli for its adaptation − hypertrophy. Shorter contraction times in the 
fourth and the fifth grades were witnesses to increasing in physiological cross-section 
of the rapid muscle fibres, which may be the answer to the intense movement triggered 
by muscles in the legs. However, the subsequent extension of Tc does not confirm the 
long age-range. One of the possible causes for an extension of the period Tc in the 6th 
grade can be with age and physical habits associated with an increase of the pennation 
angle of the muscle fibres and, thus, less effective transfer of forces to the tendons or 
bone. In the more pennant muscles, the forces are transferred slower to the attachment 
of the bone. We assume also that the cause of the extension of Tc in the period from the 
6th to 8th grades could be a less active lifestyle at this age. Differences in girls during 
this period of age could be explained by developmental delay, which is also identified 
in the speed of sprint.

Biceps femoris muscle

Analysis of the biceps femoris muscles on the dominant side of the body showed 
that the times of contractions varied with the ages of the children. However, post hoc 
analysis did not show significant variations in the boys belonging to the third grade. 
The girls belonging to the third grade did have significant longer contraction times in 
the fifth, sixth, seventh and eighth grades. Analysis by sex showed significant deviati-
ons, namely that the girls had longer contraction times in the seventh and eighth grades, 
which means that girls compared with boys have slower biceps femoris during the 
second half of elementary school.

Biceps femoris is not an anti-gravitational muscle and, therefore, there has lit-
tle everyday mechanical stimuli. This alone can explain the longer Tc versus vastus 
lateralis muscle. It is interesting that the Tc observed in girls extends through this 
period, while in boys only to the sixth grade and then it decreases again. This finding 
coincides with the kind of changes in muscle biceps femoris, which can be confirmed 
by the characteristics of the life-style, since boys use their legs more from a certain 
age, while the girls use their hands more. The biceps femoris muscle is used mainly 



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during various high-speed runs, changing directions, jumps, the trends of which are 
more typical of boys.

The relation between the contractile properties of the vastus lateralis and biceps 
femoris skeletal muscles and the maximum running speed

In order to see the connection between the contractile properties of the skeletal mu-
scle and the maximal running speed, we first present the development of the maximal 
running speeds and the contraction times of the vastus lateralis and the biceps femoris, 
by age:

 – maximal running speed of the boys over the whole measurement period grew, 
while for the girls it only grew up to the seventh grade;

 – the contraction times of the vastus lateralis first declined to the fourth grade and 
later went upwards, significantly more in boys than in girls;

 – the contraction times of the biceps femoral increased over the whole measure-
ment period.

Analysis of the results showed that there was a significant negative correlation be-
tween the maximal running speeds and the contraction times of the biceps femoris in 
boys. This relationship was characterized only from the sixth to the eighth grade and 
amounted to between -0.21 and -0.29. Regression analysis of the variance showed that 
the correlation was relatively low, as it was represented by only 8.4 % of the explained 
variance. As for the girls, the correlation was not determined during any of the measure-
ment period. There was also no evidence found of any correlation between the maximal 
running speeds and the contraction times of the vastus lateralis, neither in boys nor in 
girls.

A negative correlation was found confirming that there was a significant correlation 
between the biceps femoris and the maximum running speed. It is known that the peri-
od between the ages 6 to 11 years, or the early school period, as we like to call it, is the 
most suitable period for the development of children’s motor potentials and the learning 
of movement patterns. The child learns new movement techniques very quickly and 
without much effort (Shaffer & Kipp, 2009; Koffka, 2002). When children develop 
coordination, they also change their ways of running. It seems that boys run technically 
more correctly and they do include a biceps femoris during the running process. The 
correlation though was only -0.29 but this was the result of poor technique just at the 
start of a proper running process. In the study (Praprotnik et al., 2002), the correlation 
between the femoral biceps muscle and the maximum speeds of the adult athletes was 
studied, specifically male sprinters. They found a correlation of -0.60. A greater cohe-
rence was the result of optimal running using a proper technique and by taking advan-
tage of the biceps femoris muscle. In the girls, we did not detect correlations, which 
can be attributed to their later motor development. Dolenec and Pistotnik (2001) found 
that in most tests of coordination boys perform better than girls. At the age of 8 or 9, 
the only statistically significant differences between sexes occur in their capacities to 



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Jernej ZAVRŠNIK, Rado PIŠOT, Tadeja VOLMUT, Katja KOREN, Helena BLAŽUN VOŠNER, Peter KOKOL, Janez VOŠNER, Boštjan ŠIMUNIČ, 21–42

carry out rhythmic structures, namely, in the benefit of girls, meaning that during this 
period the girls are not using the biceps femoris as much as boys. It is also true that to 
date there is no known correlation with adult female sprinting events.

Gender differences in the contraction times of vastus lateralis and biceps femoris 
skeletal muscles and the maximal running speeds

After identifying the impact of regular sporting activity on the maximal running 
speed and to the biceps femoris, we checked if the contraction time of the skeletal mu-
scle and maximal running speed differed between the sexes. We found that:

 – contraction times of the skeletal muscle were significantly different between the 
sexes. Throughout the period of the measurements, the following were discove-
red: vastus lateralis contraction time is shorter in girls, while contraction time of 
the biceps femoris is shorter in boys;

 – maximum running speed differs between sexes where boys reach a higher maxi-
mum speed of running than girls. Significant differences were not confirmed 
only at the age of 10 to 12 year olds.

The vastus lateralis muscle has shorter contraction time in girls during the period 
of the seventh and eighth grade. In reviewing the periods in which the muscles in girls 
are faster than in boys, the question appears as to the impact of growth and maturing of 
the nervous system. It is known that the myelination of the nervous system is crucial 
for the responsiveness of the muscles, significant differences in the speed of muscle 
coincides with the so-called blast growth in the middle and late childhood and adole-
scence (Tomazo-Ravnik, 2004). The period of late childhood, which is from the age of 
7 to 10 for girls and from the age of 7 to 12 for boys, is characterized by rapid linear 
growth of the limbs. The following growth surge occurs during adolescence, beginning 
with pre-puberty and lasts for about two years, from 11 to 13 years of age in girls and 
from 12 to 14 years of age in boys. At this stage, a rapid increase occurs in some of the 
dimensions of the body. Faster growing and maturing of girls could have an impact on 
their faster muscle responses.

Boys had higher maximal running speed, significantly in the seventh and eighth 
grade. The exception was in the fifth and sixth grades, where girls were faster but it was 
not significant.

The previous study (Praprotnik et al., 2002) that was also confirmed by our findings, 
reported that the biceps femoris muscle was correlated to the maximal running speed 
(r = -0.60). Furthermore, they reported also significant correlation for gastrocnemius 
lateralis Tc with a maximal running speed (r = -0,39) and even bigger correlation was 
found between half relaxation time of biceps femoris with a maximal running speed 
(r = -0.66). It seems that time-based contractile parameters assessed using TMG are 
negatively related to maximal running speed. The study of Praprotnik et al. (2002) 
was conducted on twenty-seven Slovenian adult sprinters and confirmed the primary 



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Jernej ZAVRŠNIK, Rado PIŠOT, Tadeja VOLMUT, Katja KOREN, Helena BLAŽUN VOŠNER, Peter KOKOL, Janez VOŠNER, Boštjan ŠIMUNIČ, 21–42

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importance of the biceps femoris muscle when implementing the propulsive phase of 
sprint running.

In the analysis of the results, several questions were raised, why the biceps femoris 
muscle contraction time appears equal for both sexes, and why boys experience higher 
maximum running speeds than the girls. The answer could be sought in the differences 
in the muscle masses of children. It is well known that the key biomechanical para-
meter that affects the speed of running is muscle power, which is the product of force 
and speed. Using the contraction times of muscles, we measured the rate of shortening, 
however, this did not cover the muscle mass which affects the maximum force. Šimu-
nič, Volmut, and Pišot (2010) presented that overall muscle mass in boys is higher than 
in girls by 13 % to 17 % between the ages of 8 to 13. This may explain the higher run-
ning speed of boys, although the contraction times of the biceps femoris are the same.

It is known that the biceps femoris can be trained to a greater extent, because it 
contains the largest number of fibers of type IIc or satellite-based fibers which can 
be, depending on the functional requirements of the body, transformed into fibers of 
type I or II.

Djordjević, et al. (2000) measured biceps femoris contraction time in two groups: in 
non-athletes and sprinters. The difference in the biceps femoris contraction time betwe-
en both groups was 35.5 %, which confirms the correlation between muscle contractile 
property and maximum running speed. Differences between athletes and non-athletes 
were also found by Šimunič, Pišot, and Rittweger (2009), who measured the contractile 
properties of biceps femoris and vastus lateralis in master athletes and comparable con-
trols. These findings suggest that regular exercise affects muscle properties and were 
also confirmed by our results.

Undoubtedly, the maximum running speed is affected by the development of the 
child and, consequently, in the correct technique of running the maximum running spe-
ed is also affected by the proper integration of the biceps femoris muscles during the 
process of running. Among other determinants of the maximal running speed (body 
dimensions, muscle power, stiffness, etc.) described by Åstrand et al. (2003), Schepens 
et al. (1998) found also significant increase in step frequency after the age of 12 years, 
where strengthening of the muscles has a decisive impact on the run, however, differs 
by gender. In a number of conducted studies, a difference was found in the choice of 
discipline. Men are more often involved in team sports, while girls prefer to engage in 
individual sports disciplines (Pears Dawes, Vest, & Simpkins, 2013). When choosing 
a discipline, it is also important considering their popularity. Boys are often involved 
in football, basketball, and athletics, while the girls engage in gymnastics, swimming, 
and athletics (Volmut, Pišot, & Šimunič, 2013). A possible answer would be different 
muscle compositions by gender but research to date does not support such a hypothesis. 
Significant differences in the percentage of fibre types between the sexes do not exist 
(Drinkwater, 1984; Staron et al., 2000). Although women have a smaller cross-section 
of muscle fibres than men (Always, Grumbt, Gonyea, & Stray-Gundersen, 1989), a 
possible explanation of shorter contraction time in women can also be in a smaller 
weight of the body in which the muscles work.



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Jernej ZAVRŠNIK, Rado PIŠOT, Tadeja VOLMUT, Katja KOREN, Helena BLAŽUN VOŠNER, Peter KOKOL, Janez VOŠNER, Boštjan ŠIMUNIČ, 21–42

Study Limitations

The limitations of the study are in the selection of the research environment, na-
mely, only three of twelve Slovenian regions were selected for performing this study. 
Although instructions and test sprinting trials were clearly stated, we did not check for 
achievement of maximal sprinting speed using redundant photocells setup.

CONCLUSION

The research focuses on studying children’s motor development, specifically the 
biomechanical properties of skeletal muscles in relation to the physical development 
and growth (anthropometrical characteristics). After the age of 12.9, girls have shorter 
Tc in vastus lateralis but boys have shorter Tc in biceps femoris. Furthermore, shorter 
Tc in biceps femoris was found to correlate with higher running speed; however, the 
correlation was much lower than in adults. Non-invasive and selective assessment of 
muscle’s contractile parameters in two skeletal muscles contributed to some important 
understanding of children’s skeletal muscle development.

Acknowledgement

This study was funded by the Slovenian Research Agency through two three-year 
projects and performed by the Institute for Kinesiology Research, Science and Rese-
arch Centre, University of Primorska in cooperation with Dr. Adolf Drolc Healthcare 
Center Maribor. The authors would like to thank the research group of the TMG-BMC 
Company and the research group of the Department of Muscle Biomechanics at the 
Faculty of Electrical Engineering, University of Ljubljana. Finally, we are thankful to 
school head teachers, their physical education teachers, all the participants in the study, 
and the parents for their willingness to participate in a study of such magnitude.

Funding

The presented longitudinal research study was a part of two national projects finan-
ced by the Ministry of Education, Science and Sport of the Republic of Slovenia: the 
applicative project with the title “The role of the biomechanical skeletal muscle proper-
ties in children’s motor development” and the basic project with the title “Monitoring 
the biomechanical properties of skeletal muscles in childhood and adolescence” per-
formed by the Institute for Kinesiology Research, Science and Research Centre, Uni-
versity of Primorska in cooperation with Dr. Adolf Drolc Healthcare Centre Maribor.



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