DOI: https://doi.org/10.21203/rs.3.rs-16905/v1
Background: According to research, fast skating on short distances causes asymmetry in the physiology of muscle work. As has been proven in many sporting disciplines, this asymmetry can increase the risk of injury. The aim of the study was to analyze the level of right and left fatigue asymmetry of gluteus maximus muscle in elite skaters on a short track and to compare this phenomenon to a control group. The muscles were chosen deliberately, due to their influence in maintaining the right position during training on ice.
Methods: The experiment compared a group of eight members of the Polish Women’s National Team in short track with a group of eight non-training people. The subjects did the Biering-Sorensen test, in which sEMG (surface electromyography) signal frequency was measured in the gluteus maximus muscles during an isometric contraction. Fatigue slopes were analyzed with a one-way ANOVA with repeated measures.. In the skaters, the fatigue differed between the right and the left gluteus maximus muscles. All the skaters had higher fatigue in the right leg. This phenomenon was not observed in the non-training subjects, who on average had similar fatigue in both legs.
Results: The results suggest that professional short-track training leads to considerable asymmetry in fatigability of gluteus maximus muscles, thereby increasing the risk of injury in training and competition.
Conclusions: Training should thus be planned in a way that minimizes the risk of causing muscle fatigue asymmetry in skaters despite the typically asymmetrical muscle work during training on ice and competition, thus new trainign protocols should be developed or considered to decrease that asymmetry.
Trial registration: The tests were previously approved by the Bioethical Commission of the Chamber of Physicians in Opole. (Resolution No. 235 of 13 December 2016).
Much research has recently focused on the asymmetry of the human body and on lateralisation to study the diversity of the precision of movement of limbs and torsos, as well as the dominance of one eye or one ear [1–4]. Many such studies—dealing with a fatigue level during cycling, sprint runs, or jumping exercises—have used sEMG signal analysis [5–7]. Park et al. showed that, in short-track skaters, the right cerebellar hemisphere volume and vermian lobules VI–VII were larger than the left ones, a difference possibly resulting from a specific balanced training that affected muscle asymmetry [8].
Muscular asymmetry, especially in professional athletes, increases the risk of injury, as pointed out by various authors examining asymmetry of muscles in football players, basketball players, and people with spinal pains [9–12]. Surface electromyography is considered a reliable and credible tool for assessing the post-effort fatigue of muscles. In fatigue analysis, the most often used parameters of the sEMG signal are changes in amplitude scope and in the mean or median frequency of total capacity spectrum [13–15]. In some studies, however, physical effort did not decrease the sEMG signal [16].
Such studies often use the Biering-Sorensen test, in which the body is not supported and thus its position provides isometric and symmetrical tension of lower limb and spinal muscles. In this test, the gluteal muscles are simultaneously isolated to ensure the maximum symmetry of muscular work. Many authors have used this test to examine a fatigue level and determine differences in the muscular work of symmetrical muscles [17, 18]. To meet the needs of analysing muscular fatigue in different body positions, various elements of the Biering-Sorensen test have been modified, such as body position and the time of conducting the test. For instance, Champagne et al. and Larivière et al. modified the test so that it lasts 60 seconds [19, 20].
The asymmetry of gluteus maximus muscles has been described in the literature most often in the contexts of walk and isolated positions [21, 22]. In short track, previous research has dealt with the muscular work of only one limb or with asymmetry in the fatigue of muscles during skating. Felser et al. studied athletes skating in a straight line and in curves [23]. Neuromuscular activation was higher in the right leg, while with the reduction in skating speed decreased neuromuscular activity, but only when skating in a straight line. This indicates that the right leg has higher activity during skating in curves. Studying athletes skating in a straight line and in curves during the subsequent laps, Hesford et al. found considerable asymmetry in oxygen supply to the two legs. The authors did not report effects of this asymmetry, but offered suggestions for training [24]. Stoter et al. showed that the bio-electric tension of muscles of speed skaters was correlated with speed at different sections of the track, but they did not analyse whether muscular asymmetry affected this phenomenon [25].
The main research hypothesis is that intensive short-track training leads to asymmetry of the gluteus maximus muscles. Thus, the paper aims to (i) study the size of asymmetry in muscle activity and assess the difference in fatigability between the right and the left gluteus maximus muscles of the Polish Women’s National Team in short track, and (ii) to compare this fatigability with that in non-training women.
The idea behind the study was initiated by the coaches of the Polish National Team, worried about the asymmetry in the skaters and the related increased injury risk. Even though the coaches try to focus as much of the training as possible on symmetrical work, they stress that training on ice accounts for about 60% of the training volume and skating to the left is a typical asymmetrical work. Since the level of asymmetry varies from athlete to athlete, the coaches stress the importance of customised training, which would help them improve muscular symmetry in each athlete in an optimal way.
Two research groups took part in the tests. The experimental group included eight female members of the Polish National Team in short track, with a mean age of 18.7 ± 2.9 standard deviation, mean height of 162.4 ± 2.4 cm, and mean body weight of 57.2 ± 5.9 kg. The control group included eight female students actice in sports (but not in speed skating), with a mean age of 20 ± 0.9, mean height of 169.1 ± 4.1 cm, and mean body weight of 68 ± 4.2 kg. These students were randomly selected from among female students of physical education at Opole University of Technology. The research was conducted during the training cycle, after a weekend break in training, to avoid the short-term effect of fatigue accumulation due to the training. The participants were informed about the purpose and course of tests and signed a consent to participate in the tests. The tests were approved by the Bioethical Commission of the Chamber of Physicians in Opole, Poland. In interviews conducted before the tests, all the respondents declared they were right-handed and right-legged in daily and sports activities (e. g., tossing a ball, kicking a ball, supporting with a foot during swinging). Furthermore, a kick-a-ball test (with three attempts) confirmed all the participants were right-legged, while the modified Edinburgh questionnaire confirmed they were right-handed [26].
The sEMG signal frequency in the gluteus maximus muscles was examined in an isometric contraction using the position from the Biering-Sorensen test [19, 22]. To avoid too high loads for the skaters, the tests were stopped after 60 seconds of the contraction, and they were not continued until the subject was unable to hold the position because of muscle fatigue. The effectiveness of the fatigue test during a 60-second contraction was confirmed by Mutchler et al. [27]. During the test, the subjects were lying on a horizontal table on the abdomen, with the iliac crests aligned to the edge of the table and the lower limbs attached to the straps around the ankle joints. They were instructed to hold the body (head, shoulders, and torso), without support, horizontally to the ground as long as they could, with the arms crossed at the chest (Fig. 1).
[Insert Fig. 1.]
The test employed a 16-channel EMG system (produced by NORAXON DTS), thanks to which the signals were recorded with the accuracy of 16 bits at the sampling frequency of 1500 Hz. The bio-electric test of activity of the right and the left gluteus maximus muscles was carried out by the SENIAM methodology [22, 28]. To improve the adherence of the electrodes, before the test, the hair was shaved and the skin was cleaned in the place where the electrodes were to be stuck. Surface electrodes (Ag/AgCl) were placed on the muscle venter between the movement point and the tendon attachment, along the longitudinal middle line of the muscle. Signal processing and EMG analysis were performed using NORAXON MR-XP 1.07 Master Editionx software. Fatigue-related changes (frequency shift) in the frequency content were calculated for the raw EMG signal (Fig. 2) obtained during a static contraction. Unfiltered raw sEMG was analysed step-wise in 1000 ms increments over the selected portion of the measurement (60 seconds in the present test). The mean frequency was calculated for each step using values based on the frequency power spectrum (calculated by a Prime Factor Fourier Transformation). A fatigue slope (being a regression coefficient from a linear regression line between the mean frequency and time) was estimated for each participant, and for further analyses, the slopes of these lines were taken. sEMG frequency power spectrum is expected to shift to lower frequencies during fatiguing contractions, and the mean frequency analysis can be used to estimate the magnitude of that shift. This phenomenon is well established for static contractions at constant load levels and believed to reflect local fatigue (Fig. 3.).
[Insert Fig. 2.]
[Insert Fig. 3.]
Technical specification of NORAXON DTS is as follows:
The slopes representing the subjects’ fatigue were analyzed with one-way ANOVA with repeated measures. The two groups (short track and control) constituted the between-subject factor, and the two sides (left leg and right leg) constituted the within-subject factor. Since the interaction was significant, Tukey’s post hoc tests were applied for pair-wise comparisons of the four factor combinations. For the analyses, a 0.05 significance level was used. All analyses were made in Statistica v. 13.1.
In the ANOVA, the main effect of the group was non-significant (F(1, 14) = 2. 964, p = 0.107). The main effect of the side (right-left) of the muscle, however, was significant (F(1, 14) = 20.323, p < 0.001), and so was the group-by-side interaction (F = (1, 14) = 6.111, p = 0.0268) (Fig. 4). Tukey’s tests (Table 1) showed that the right and the left muscles of the skaters (i.e., the subjects in the experimental group) differed in fatigue (p = 0.001); this difference was non-significant in the control group.
The significant interaction indicates that the mean differences in the slopes between the right and the left muscles differed between the two groups; in other words, the two studied groups differed in the asymmetry of the right and the left gluteus maximus muscles. Figure 5 shows these differences for each subject. The more to the left a point lies, the greater the difference between the subject’s muscles was. We see thus that the interaction was significant because the groups differed in these differences (representing asymmetry) in the fatigue of the right and the left muscles—for most elite skaters, the asymmetry is visible in the graph (so the points lie far to the left from the zero line). Several non-training people also had this asymmetry, which proves that in addition to professional and intensive training, also other factors can affect asymmetry of gluteus maximus muscles.
While Fig. 5 shows the direct differences per subject, Fig. 6 pairs the left and right maximus gluteus muscles for each subject. This graph clarifies that the non-training subjects who had a small difference in the fatigue of the muscles had in general low fatigue of both muscles. While the subjects from the two groups did not differ in the fatigue of the left muscle, they did in the fatigue of the right muscle: the elite speed-track skaters had higher fatigue in the right muscle than the non-training subjects (p = 0.001; Table 1 and Figs. 4 and 5).
| Skaters, right muscle | Skaters, left muscle | Control, right muscle | |
|---|---|---|---|
| Skaters, left muscle | 0.001 | ||
| Control, right muscle | 0.029 | 0.234 | |
| Control, left muscle | < 0.001 | 0.955 | 0.497 |
[Insert Figs. 4–6]
The research aimed to determine differences in muscle fatigue in the left and the right maximum gluteus muscles in female short-track skaters and compare these differences with those in healthy non-training women. During the experiment, the skaters were in the middle of the training cycle, which certainly caused increased fatigue in their muscles. This circumstance itself could have directly led to the significant (and unsurprising) differences between the studied groups. Thus, one should not misinterpret the higher fatigue in the athletes than in the non-training people as a result of inefficient training. On the other hand, the tests were conducted after a weekend break in training, so the muscles were relaxed; had the tests been conducted right after training, the muscles would have been tired, which might have affected the tests.
What was surprising, however, was so high asymmetry of muscle fatigue observed in the members of the Polish Women’s National Team in short-track speed skating. In general, short-track training focuses on symmetrical movements, so it should not generate so high asymmetry between the right and the left gluteus maximus muscles. Too high asymmetry in these muscles can increase the risk of injury, so is unfavourable in high-performance athletes [9–11]. thus its importance should not be underestimated in professional sports that involve alternating limb movements.
Such high asymmetry, however, has not been observed in the non-training subjects, a result that may indicate that the asymmetry in the gluteus maximus muscles observed in the experimental group is due to the specific nature of short track training. Small asymmetry in non-training people is likely a normal phenomenon, and it should not increase the possibility of injury.
Even though experiments without the control group are difficult to interpret, most studies on muscle fatigue did not include non-training subjects. The control group was included in the experiment to analyze muscle asymmetry in skaters against the background of non-training people, which did help us draw richer conclusions about the studied phenomenon.
The studied skaters train at a skating rink in about 60% of the annual training volume, remaining 40% being focused on symmetrical training of both limbs. Various elements of their individual skating techniques—especially the technique of skating on curves—can cause asymmetry in the gluteus maximus muscles, an unfavourable phenomenon in speed skating because of the increased injury risk it poses. Unfortunately, the phenomenon of muscular asymmetry and its relation to professional training is still underdeveloped, making it difficult to design a training process that would not generate asymmetry. Asymmetry in muscle fatigability is certainly not limited to short track, however. Mastalerz et al. reported differences in fatigue between the muscles of the right and the left legs in runners, reaching from a dozen to a few dozen percentages, depending on the muscle [29]. Hartz et al. showed higher fatigue of the right arm in a 30-second tension in throwing athletes [30].
Felser et al. showed that muscle tension activity in muscles of both legs differed between the moments of skating in a straight line and in curves; greater differences occurred in the right leg muscles [23]. This result stresses the importance of the cornering technique, likely that element of the training which most strongly increases asymmetry of leg muscles. Hesford et al. also observed asymmetry in legs of professional short-track skaters—though they studied the oxygenation of the quadriceps muscle [24].
Several main conclusions follow from the present research. First of all, in speed skating, much training is symmetric, but work during competition is mainly asymmetric—which is likely why elite female speed-track skaters have significant asymmetry in fatigability of the gluteus maximus muscles. This conclusion should not be underestimated in professional sports training because strong muscular asymmetry can significantly increase the risk of injury.
Asymmetry in muscle fatigue is unlikely in healthy non-training people—thus, significant asymmetry seems to be a pathological condition. Indeed, many studies have reported that muscle diseases and faulty postures were accompanied by significant asymmetry in muscular activity and fatigue [31]. In the present research, the asymmetry observed in the healthy non-training participants was either negligible or small.
While no elite skater showed left-side asymmetry (let us recall that all the subjects were right-legged), three non-training subjects did (although small). This observation calls for new research that would answer the following question: Why some right-handed persons show left-side asymmetry in the gluteus maximus muscles?
A complex phenomenon, muscle fatigue is difficult to study, and certain aspects should be considered, such as the training cycle and the health condition of an athlete. Thus, similar studies should be conducted in various points of the training cycle, with skaters of both sexes and varying age. This research opens new avenues also for research that would aim to analyse the relation between a training process and muscular asymmetry. A related question worth exploring is whether it is possible to avoid muscular asymmetry in unilateral sports by employing appropriately structured training (including its symmetrisation).
The results offer an important lesson for the coaches of the Polish Women’s National Team in short-track skating. Professional training at this elite level is very intensive and includes a significant share of asymmetrical training on ice. Thus, to avoid generating possibly harmful muscular asymmetry, the training should involve much work increasing muscle symmetry. Employing training based on bilateral transfer might be one way of doing so.
surface electromyography
silver chloride electrode
root-mean-square
common signal rejection
The tests were previously approved by the Bioethical Commission of the Chamber of Physicians in Opole. (Resolution No. 235 of 13 December 2016).
Not applicable
The datasets generated and/or analysed during the current study are not publicly available.However, the data are available from the corresponding author on reasonable request.
Research participants have agreed in writing to the publication of the data contained in the article.
The authors declare that they have no competing interests
This study would not have been possible without our participants’ commitment, time and effort. The study was supported and funded by the statutory research of the Department of Anthropomotorics, Opole University of Technology, Opole, Poland The experiments comply with the current laws of the country in which they were performed.
MK, PP; Responsible for conception and design of the project. MK, PP; Data collection. PP, MW; Performed data analysis, interpreted the data. MK; Drafted, wrote and revised the manuscript. All authors read and approved the final version of the manuscript to be published manuscript.
Authors whose names appear on the submission have contributed sufficiently to the scientific work and, therefore, share collective responsibility and accountability for the results.