© 2015 John Wiley & Sons A/S.
Scand J Med Sci Sports 2015: ••: ••–•• doi: 10.1111/sms.12429
Published by John Wiley & Sons Ltd
Relationship between strength qualities and short track speed skating performance in young athletes S. Felser1, M. Behrens1, S. Fischer1, S. Heise1, M. Bäumler2, R. Salomon3, S. Bruhn1 Department of Exercise Science, University of Rostock, Rostock, Germany, 2Olympic Training Center M-V, Rostock, Germany, Institute of Applied Microelectronics and Computer Engineering, University of Rostock, Rostock, Germany Corresponding author: Martin Behrens, PhD, Department of Exercise Science, University of Rostock, Ulmenstraße 69, Rostock 18057, Germany. Tel: +49381/498 2744, Fax: +49381/498 2738, E-mail: [email protected]
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Accepted for publication 13 January 2015
This study analyzed the relationships between isometric as well as concentric maximum voluntary contraction (MVC) strength of the leg muscles and the times as well as speeds over different distances in 17 young short track speed skaters. Isometric as well as concentric single-joint MVC strength and multi-joint MVC strength in a stable (without skates) and unstable (with skates) condition were tested. Furthermore, time during maximum skating performances on ice was measured. Results indicate that maximum torques during eversion and dorsal flexion have a significant influence on skating speed. Concentric MVC strength of the knee extensors was higher corre-
lated with times as well as speeds over the different distances than isometric MVC strength. Multi-joint MVC testing revealed that the force loss between measurements without and with skates amounts to 25%, while biceps femoris and soleus showed decreased muscle activity and peroneus longus, tibialis anterior, as well as rectus femoris exhibited increased muscle activity. The results of this study depict evidence that the skating times and speeds are primarily influenced by concentric MVC strength of the leg extensors. To be able to transfer the strength onto ice in an optimal way, it is necessary to stabilize the knee and ankle joints.
Short track speed skating is characterized by high demands on dynamic stability of the ankle and knee joints. In order to achieve speeds up to 12.5 m/s, high propulsive forces have to be effectively transferred via the skates onto the ice (Quinn et al., 2003). Some studies suggested that the short-distance performance is determined by the start, and thereby by the maximum force of the leg extensor muscles (Kwon et al., 1997; Felser et al., 2012; Felser, 2013). On the basis of her investigations for clarifying the performance structure in short track speed skating, Felser (2013) concluded that the isometric maximum voluntary force (iMVF) of the leg extensor muscles explains 27% of differences in the time over 500 and 1000 m. In that study, the quantification of iMVF was done on the basis of multi-joint measurements in a leg press. However, by means of these measurements, it was not possible to detect relationships between singlejoint maximum voluntary contraction (MVC) strength of different knee muscles as well as ankle muscles and the short track speed skating performance. In addition, several studies have shown that increasing the external degrees of freedom during a force production task results in decreased muscle force and increased muscle activity of the stabilizing muscles (Kornecki & Zschorlich, 1994; Kornecki et al., 2001; Behm & Anderson, 2006; Seo & Armstrong, 2009; Wübbenhorst & Zschorlich, 2012). Behm and Anderson (2006)
suggested that the inherently greater instability of mechanically unstable movements challenges the neuromuscular system to a greater extent than movements that are performed under stable environmental conditions. Because of the locomotion on skates, short track speed skating is characterized by increased degrees of freedom compared with the barefoot condition and sets high demands on joint stabilization. Therefore, the aim of this study was to analyze the relationship between isometric as well as concentric MVC (cMVC) strength of the lower leg muscles and the times as well as speeds over different distances in young short track speed skaters. In addition, forces and muscle activities during isometric MVCs on a leg press with and without skates were analyzed. These parameters were correlated with the times and speeds over different distances. Materials and methods Subjects Seventeen young short track speed skaters (14 males, 3 females, age: 13.2 ± 1.1 years, weight: 55.7 ± 11.3 kg, height: 162 ± 10 cm) participated in this study. At the time of the investigation, all athletes have exercised short track speed skating between 1 and 10 years at the Olympic Training Center M-V. We tried to constitute a homogenous sample with regard to the age of the participants. However, because of poor availability of subjects, we have investigated a heterogeneous sample with regard to expertise. Before testing, all athletes were informed of the procedures to
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Felser et al. be utilized and signed informed consent. The study was conducted according to the Declaration of Helsinki and was approved by the university’s ethics committee.
Experimental procedure All athletes participated in two experimental sessions separated by at least 48 h. During the first session, MVC strength measurements were performed in the laboratory. Prior to the laboratory tests, the athletes had to perform a warm-up on bicycle for 10 min. The second session was devoted to maximum on ice skating performance tests (i.e., time measurements). Prior to the measurements, the athletes performed the warm-up on an individual basis.
based program (IMAGO, Pfitec, Endingen, Germany). The measurements of the iMVF were made unilaterally right and left with a knee angle of 120°. Prior to the tests, the athletes completed up to three MVC familiarization trials. During the tests, they were asked to perform two MVC trials. The athletes were instructed to fold their arms across their chests and to exert iMVF against the force plate for 3 s. These measurements were performed with and without skates. The athletes were provided with verbal encouragement to act as forcefully as possible during the execution of MVC tasks. Care was taken that the movement was executed without any countermovement. The time between the trials was 30 s. The best trial was taken for further analysis.
Electromyography (EMG) recordings Skating performance All athletes completed explosive starts over 5 and 30 m on the straight as well as over half a lap for quantifying the acceleration capability. The skating time was measured by photoelectric barriers (transmitter: DRL F02, receiver: TS 01-R04, mobile digital-timer DT800+, sportronic®, Sportronic, WinnendenHertmannsweiler, Germany). The maximum skating speeds were determined as follows: The athletes first accelerated over a distance of their choice. They then passed a short test distance of 10 or 25.13 m, respectively. The duration of that test distance was used to determine the individual maximum skating speed. All athletes performed two trials, from which the better was taken for further analyses. In addition, all athletes completed a 1000 m skating trial for determining their average lap speeds.
The surface EMGs were recorded using bipolar EMG Ambu® Blue Sensor N electrodes (Ambu GmbH, Bad Nauheim, Germany) (2 cm diameter). The electrodes were applied to the shaved, abraded, and cleaned skin over the middle of the muscle bellies of rectus femoris, biceps femoris, soleus, peroneus longus, medial gastrocnemius, and tibialis anterior of the right leg. The reference electrode was attached to the tibia. The resistance between electrodes was measured with a digital multimeter (MY-68, McVoice, Braunschweig, Germany) and was kept below 5 kΩ. Signals were amplified (1000×) and recorded with a sampling frequency of 1500 Hz by an 8-channel telemetry EMG system “PowerPack” (Pfitec). Data were transmitted by wireless LAN (Netgear WNDR3700) and were stored on a hard drive for later analysis with a custom-built LABVIEW®-based program.
Data analysis Torque recordings Torque signals were measured under isometric and concentric conditions using a CYBEX NORM dynamometer (Computer Sports Medicine®, Inc., Stoughton, Massachusetts, USA). The athletes were instructed to fold their arms across their chests. The isometric MVC tests for the ankle and knee joint muscles were performed with joint angles of 90 and 80° (0° = full extension), respectively. The axis of the dynamometer was aligned with the anatomical flexion-extension axis. The athletes were fixed to the dynamometer as described previously (Behrens et al., 2013, 2014, 2015). The isometric maximum voluntary torque (iMVT) was measured during the following isometric MVC tasks: eversion, plantar flexion, dorsal flexion, knee flexion, and knee extension. Three MVC trials were performed for each side of the body as well as direction of movement with at least a 30-s break between the trials. The concentric tests were performed with a velocity of 150°/s. The cMVC trials included: eversion, inversion, plantar flexion, dorsal flexion, knee flexion, and knee extension. Before the tests, the athletes completed up to three MVC familiarization trials. During the tests, they performed five MVCs. All athletes were thoroughly instructed to act as forcefully and as fast as possible. The torque signals were sampled with 100 Hz and recorded with the Humac® software (Computer Sports Medicine®, Inc., Stoughton, Massachusetts, USA ) (version 4.5.3).
Force recordings The measurement of iMVF was carried out on a custom-made force measurement system. It is designed according to the principle of a seated leg press with two vertically inserted force plates (Digimax®, DigiMax Systems, Hamm, Germany). It allows the seated position to be individually adjusted according to the anthropometry of the athletes. The force signals were sampled at 1500 Hz and stored on a hard drive for later analysis with a custom-built LABVIEW®-
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The intra-session reliability for the majority of the measurements was assessed. Statistical procedures were performed using a spreadsheet for calculating reliability (Hopkins, 2011). The results are presented in Table 1. Every athlete’s highest MVC trial, i.e., the attempt with the highest iMVT or concentric MVT (cMVT), was taken for further analyses. The torque was normalized to body weight. The root mean square of the EMG signal (RMS-EMG) for the different muscles was calculated over a 200 ms time period at iMVT and cMVT (100 ms prior to and 100 ms following the iMVT and cMVT, respectively). The highest iMVF was retained for further analyses. The following parameters were calculated on the basis of the force-time curves: iMVF without skate and iMVFSkate with skate. The parameters were normalized with respect to the athlete’s body weight. RMS-EMG was calculated to assess the muscle activity during the MVC trials. RMS-EMG was calculated over a 200 ms time interval at iMVF and iMVFSkate, i.e., 100 ms preceding and 100 ms following the iMVF and iMVFSkate. The calculated RMS-EMG values are stated in relation to the reference values obtained during the single-joint isometric MVC trials for the respective muscles.
Statistical analysis Data were visually inspected for extreme values and outliers using box-whisker plots. All extreme values and outliers were removed. Thereafter, data were checked for normal distribution considering skewness and kurtosis. As cutoff criteria, a skewness |>2| and a kurtosis |>7| were used (West et al., 1995). In addition, linearity was checked using scatter plots. Pearson’s correlation was used to analyze linear connections between the variables. The level of significance was established at P < 0.05. All data were analyzed using the SPSS statistical package 19 (SPSS Inc., Chicago, Illinois, USA). Data are presented as mean ± standard deviation in the tables.
0.95 (0.79 to 0.99) 0.92 (0.65 to 0.98) 0.98 (0.94 to 1.00) 0.98 (0.95 to 0.99) 0.83 (0.60 to 0.93) 0.97 (0.93 to 0.99) 0.96 (0.90 to 0.98) 0.97 (0.94 to 0.99) 0.96 (0.92 to 0.98)
Table 2. Mean and standard deviation (SD) of the relevant parameters
Parameter
Mean ± SD
Time over 5 m (s) 1.38 ± 0.12 Time over 30 m (s) 5.21 ± 0.35 Time over half a lap (s) 8.23 ± 0.59 Maximum speed straight 9.21 ± 0.76 (m/s) Maximum speed curve 8.09 ± 0.55 (m/s) Time over 1000 m (s) 128.91 ± 11.32 7.81 ± 0.71 Average speed 1000 m (m/s) Leg press iMVF right (N/kg) 48.33 ± 11.93 iMVFSkate right (N/kg) 35.95 ± 7.95 iMVF left (N/kg) 43.20 ± 8.89 iMVFSkate left (N/kg) 33.58 ± 7.06 Isometric and concentric iMVT knee extension 3.03 ± 0.50 MVT right leg (Nm/kg) cMVT knee extension 1.69 ± 0.28 iMVT knee flexion 1.63 ± 0.33 cMVT knee flexion 1.35 ± 0.19 cMVT ankle inversion 0.39 ± 0.09 iMVT ankle eversion 0.33 ± 0.06 cMVT ankle eversion 0.27 ± 0.06 iMVT plantar flexion 2.20 ± 0.34 cMVT plantar flexion 0.72 ± 0.10 iMVT dorsal flexion 0.37 ± 0.12 cMVT dorsal flexion 0.30 ± 0.06 Isometric and concentric iMVT knee extension 3.03 ± 0.48 MVT left leg (Nm/kg) cMVT knee extension 1.67 ± 0.25 iMVT knee flexion 1.49 ± 0.30 cMVT knee flexion 1.40 ± 0.21 cMVT ankle inversion 0.40 ± 0.09 iMVT ankle eversion 0.35 ± 0.07 cMVT ankle eversion 0.29 ± 0.09 iMVT plantar flexion 2.13 ± 0.29 cMVT plantar flexion 0.76 ± 0.15 iMVT dorsal flexion 0.33 ± 0.10 cMVT dorsal flexion 0.30 ± 0.08 Parameters on ice
SDDiff, SD of the difference between trial 1 and 2; TE, typical error; CV%, coefficient of variation; ICC, intraclass correlation coefficient.
3.4 (2.3 to 7.2) 2.4 (1.6 to 5.2) 1.4 (1.0 to 2.6) 1.4 (1.0 to 2.2) 3.4 (2.5 to 5.1) 9.2 (7.1 to 13.3) 11.2 (8.7 to 16.3) 7.4 (5.8 to 10.7) 7.6 (5.9 to 11.0) 0.35 (0.24 to 0.74) 0.13 (0.09 to 0.27) 0.17 (0.12 to 0.30) 0.15 (0.12 to 0.24) 0.50 (0.37 to 0.75) 176.6 (137.8 to 250.3) 184.7 (144.1 to 261.9) 122.8 (95.8 to 174.1) 125.9 (98.2 to 178.5) 0.06 0.18 0.17 0.18 0.38 249.7 261.2 173.6 178.1 1.38 (0.16) 5.25 (0.37) 8.14 (0.76) 9.26 (0.84) 8.05 (0.65) 2509.2 (954.1) 2280.5 (847.5) 1848.2 (736.9) 1768.8 (651.9) 5m 30 m Half a lap Maximum speed straight Maximum speed curve iMVF right iMVF left iMVFSkate right iMVFSkate left
1.43 (0.11) 5.31 (0.24) 8.23 (0.66) 9.20 (0.82) 8.03 (0.54) 2388.7 (899.7) 2239.8 (822.9) 1710.9 (668.1) 1646.0 (560.3)
−0.05 (−0.10 to 0.00) −0.06 (−0.21 to 0.09) −0.09 (−0.20 to 0.02) 0.07 (−0.03 to 0.16) 0.02 (−0.17 to 0.20) 120.5 (14.8 to 226.3) 40.7 (−69.9 to 151.3) 137.3 (63.8 to 210.8) 122.8 (47.4 to 198.2)
TE (95% CI) SDDiff Mean difference (95% CI) Trial 2 Mean (SD) Trial 1 Mean (SD)
Table 1. Intra-session reliability for the starts (s), maximum speeds (m/s), and the isometric maximal voluntary forces (N) on the leg press
CV% (95% CI)
ICC (95% CI)
Strength and short track speed skating
cMVT, concentric maximum voluntary torque; iMVT, isometric maximum voluntary torque.
Results Skating performance The mean times and speeds achieved over the different distances are summarized in Table 2. The maximum skating speed in the curve was on average 11.9% (P = 0.000) below the maximum skating speed on the straight. Over a distance of 1000 m, 75% of the athletes attained their maximum lap speed in lap 2, whereas the remaining 25% attained it in lap 3. iMVT and cMVT The results of the iMVT and cMVT measurements are presented in Table 2. The analysis did not indicate any significant differences regarding iMVT and cMVT between the right and the left leg. iMVF and neuromuscular activation on the leg press The iMVF values measured on the leg press are shown in Table 2. The data show that the iMVF values were about 25% higher than the iMVFSkate values.
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Felser et al. Table 3. Mean and standard deviation (SD) of RMS-EMG of the different muscles during strength testing on the leg press with and without skate. Data are normalized to RMS-EMG during iMVT
Mean ± SD (%) Without skate
With skate
Biceps femoris Rectus femoris Soleus Peroneus Gastrocnemius Tibialis Biceps femoris Rectus femoris Soleus Peroneus Gastrocnemius Tibialis
60.5 ± 38.0 40.5 ± 19.1 52.3 ± 21.6 41.0 ± 22.3 49.4 ± 23.6 27.8 ± 16.2 40.4 ± 18.0 47.4 ± 20.7 49.6 ± 24.9 57.3 ± 20.0 46.7 ± 16.9 39.6 ± 20.1
RMS-EMG, root mean square of the EMG signal; iMVT, isometric maximum voluntary torque. Table 4. Percentage change in RMS-EMG of the relevant muscles during strength testing on the leg press between the execution of the MVCs with and without skate
Mean ± SD (%) Biceps femoris Rectus femoris Soleus Peroneus Medial gastrocnemius Tibialis anterior
−13.5 ± 16.2 (P = 0.415) 11.6 ± 25.3 (P = 0.484) −6.5 ± 19.9 (P = 0.626) 16.3 ± 22.4* (P = 0.027) 3.3 ± 17.4 (P = 0.967) 11.8 ± 25.4 (P = 0.092)
Asterisks denote a significant difference. *P ≤ 0.05. RMS-EMG, root mean square of the EMG signal; MVC, maximum voluntary contraction.
Table 3 shows the normalized EMG data of the different muscles during the MVCs with and without skates. It becomes apparent that some muscles exhibit a reduced activation whereas one muscle shows a stronger contraction (Table 4). The biceps femoris, a knee flexor and hip extensor, showed the highest activity on the leg press when no skates were worn. This muscle activation was reduced in the measurement with skate. The muscular activation of the soleus muscle was reduced by 6.5% during MVC strength testing with skates. In contrast to this, the muscular activation of the rectus femoris, peroneus longus, and tibialis anterior increased between 11.6% and 16.3%. The t-test has shown that the RMSEMG of the peroneus longus was significantly higher in the trials with skate (P = 0.027). Correlation analysis The results of the correlation analyses suggest that the time over 5 m is not an appropriate indicator to provide valid statements about the times over 30 m, half a lap, and 1000 m, as well as about the different skating speeds. The other parameters on ice were significantly correlated (Table 5).
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There were some significant correlations between the MVT of the knee extensors as well as knee flexors and the times as well as speeds over the different distances. Especially cMVT of the knee extensors showed significant correlations with the time over 5 and 1000 m as well as the maximum skating speed in the curve and in lap 2. With regard to the importance of MVC strength of knee flexors, it seems that iMVT has a larger influence on the skating times or speeds than cMVT (Table 6). There were no significant correlations between MVT of the ankle muscles and the time over 30 m and half a lap. The maximum speed in the curve showed significant correlations with cMVT during ankle eversion and cMVT of the dorsal flexors of the right leg. The iMVT and cMVT during the right leg’s ankle eversion significantly correlated with the skating speed in lap 2. By contrast, the correlations between iMVT of the plantar flexors and dorsal flexors of the left leg and the maximum skating speed on the straight were rather low. The cMVT during ankle eversion of the left leg was significantly correlated with the skating speed in lap 2. The same was the case for iMVT of the dorsal flexors of the left leg (Table 6). Correlation analysis between iMVF as well as iMVFSkate on the leg press and the skating times as well as speeds revealed that more and higher relationships exist for iMVFSkate and the short track speed skating performance than for iMVF and the short track speed skating performance variables (Table 6). Discussion The present study investigated relationships between strength qualities of the lower leg muscles and the short track speed skating performance in young athletes. Therefore, isometric and concentric single-joint MVC strength measurements for relevant knee and ankle muscles have been conducted using a dynamometer. In addition, multi-joint MVC strength of the lower extremity with and without skates was tested using a leg press. The strength parameters were correlated with the times over 5 m, 30 m, half a lap, and 1000 m, as well as the speeds on the straight, in the curve, and in lap 2 during a 1000 m time trial. The results of the study have shown that the maximum speed in the curve is on average 11.9% lower than the maximum skating speed on the straight. This can be explained by the fact that there are centrifugal forces in the curve. Moreover, skating through the curves is more complex than skating on the straight because of the curve technique required (Letzelter & Letzelter, 1983). The results of the correlation analysis show that there is a correlation between the maximum skating speed on the straight and in the curve which is highly significant [r = 0.802, i.e., explained variance (r2) is 65%]. Because of that, it is assumed that the skating speed which can be achieved and maintained in the curve has a major
Strength and short track speed skating Table 5. Correlation analysis between the different parameters measured on ice
1. 2. 3. 4. 5. 6. 7.
Time over 5 m Time over 30 m Time over half a lap Maximum speed straight Maximum speed curve Time over 1000 m Average speed 1000 m
1
2
3
4
5
6
1 0.423 0.275 −0.176 −0.494* 0.290 −0.437
1 0.851** −0.866** −0.794** 0.801** −0.836**
1 −0.821** −0.739** 0.682** −0.676**
1 0.802** −0.876** 0.839**
1 −0.877** 0.901**
1 −0.936**
Asterisks denote a significant correlation. *P ≤ 0.05; **P ≤ 0.01. Table 6. Correlation analysis between strength parameters and the times as well as speeds
iMVT knee extension right cMVT knee extension right iMVT knee flexion right cMVT knee flexion right cMVT ankle inversion right iMVT ankle eversion right cMVT ankle eversion right iMVT plantar flexion right cMVT plantar flexion right iMVT dorsal flexion right cMVT dorsal flexion right iMVT knee extension left cMVT knee extension left iMVT knee flexion left cMVT knee flexion left cMVT ankle inversion left iMVT ankle eversion left cMVT ankle eversion left iMVT plantar flexion left cMVT plantar flexion left iMVT dorsal flexion left cMVT dorsal flexion left iMVF right iMVFSkate right iMVF left iMVFSkate left
Time over 5m
Time over 30 m
Time over half a lap
Maximum speed straight
Maximum speed curve
Speed in lap 2
Time over 1000 m
−0.465* −0.713** −0.468* −0.398 0.055 −0.182 −0.330 −0.018 −0.517* −0.344 −0.351 −0.591** −0.554* −0.306 −0.197 −0.227 −0.177 −0.375 0.066 0.132 −0.360 −0.291 −0.467* −0.437* −0.241 −0.390
−0.109 −0.450* −0.368 −0.310 0.007 −0.084 −0.404 0.214 −0.200 −0.110 −0.381 −0.461* −0.379 −0.424* −0.068 −0.057 0.064 −0.183 0.391 0.341 −0.392 −0.268 −0.170 −0.174 −0.148 −0.308
−0.174 −0.333 −0.330 −0.077 0.028 −0.138 −0.332 0.125 −0.100 −0.151 −0.372 −0.284 −0.201 −0.348 0.155 0.143 0.216 −0.141 0.287 0.211 −0.322 −0.029 −0.105 −0.168 −0.086 −0.285
0.161 0.405 0.450* 0.255 −0.046 0.290 0.385 −0.337 0.096 0.213 0.374 0.304 0.345 0.535* 0.136 −0.081 −0.054 0.167 −0.423* −0.219 0.498* 0.204 0.060 0.251 0.173 0.351
0.253 0.628** 0.431* 0.382 −0.106 0.299 0.576** −0.160 0.109 0.111 0.423* 0.490* 0.565** 0.558** 0.079 −0.097 −0.115 0.384 −0.273 −0.246 0.309 0.103 0.278 0.411 0.295 0.528*
0.561* 0.750** 0.683** 0.630** 0.034 0.536* 0.573* −0.225 0.205 0.323 0.348 0.597** 0.642** 0.720** 0.355 −0.034 0.216 0.456* −0.341 −0.003 0.486* 0.253 0.396 0.616** 0.425 0.593**
−0.334 −0.648** −0.680** −0.619** 0.155 −0.483* −0.437 0.325 −0.093 −0.320 −0.359 −0.452* −0.708** −0.620** −0.416 0.048 −0.092 −0.273 0.332 0.034 −0.410 −0.131 −0.596** −0.679** −0.643** −0.621**
Asterisks denote a significant correlation. *P ≤ 0.05; **P ≤ 0.01. cMVT, concentric maximum voluntary torque; iMVT, isometric maximum voluntary torque.
influence on the speed skating performance. Therefore, the speed in the curve seems to be a crucial factor for a good performance in short track speed skating. Since a good time over 500 , 1000, or 1500 m depends on several factors, among others on speed endurance (Felser, 2013), it seems more important to find out which of the measured parameters has a positive influence on time and speed in the curve, respectively. One can conclude from the results of this study that the strength of the knee extensors and knee flexors has a major influence on skating times and speeds, respectively. With regard to knee extension strength, we found higher significant correlations between the times as well as speeds and cMVT than for the times as well as speeds and iMVT. In contrast, for the knee flexion MVC strength, we found more significant correlations between the iMVT and the skating times as well as speeds. This can be explained by the fact
that the knee extensors are responsible for producing the propulsion force during mid-stance, whereas the knee flexors work predominantly static or eccentric because of the low position of the body. At the same time, the results of the correlation analysis show that the maximum torques during eversion and dorsal flexion have a significant influence on the speed in the curve and lap 2, respectively. The dorsal flexion is mainly performed by the tibialis anterior and the eversion by the peroneus longus. These two muscles are responsible for stabilizing the ankle joint. Furthermore, we found moderate significant correlations between the speed in lap 2 and iMVFSkate as well as between the maximum skating speed in the curve and iMVFSkate. These parameters were not significantly correlated with iMVF measured without skates. This can be explained by the fact that in short track speed skating, the
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Felser et al. movement is performed on skates, i.e., the force has to be transferred to the ice before it can develop its performance-enhancing effect. In short track speed skating, there are specific requirements concerning the stabilization of the knee and ankle joint as well as the force development during mid-stance. According to Quinn et al. (2003), high forces of the ankle joint muscles are required during short track speed skating. Consequently, the conditions at the leg press with skates in the present study are quite similar to the conditions on the ice. The tests on the leg press have shown that the loss of force between the measurements without and with skates amounts to 25%. At the same time, biceps femoris and soleus showed 13.5% and 6.5% less activity during measurements with skates. In contrast, the muscle activities of peroneus longus, tibialis anterior, and rectus femoris were increased. According to Kornecki et al. (2001), the rectus femoris, which is part of the quadriceps femoris muscle, belongs to the muscles with mainly motor function. In the present study, the rectus femoris showed an increase in activity under unstable test conditions, i.e., during measurement with skates. This increase in activity might be due to the stabilization requirements to which this muscle contributes as has been described earlier (Anderson & Behm, 2004; Behm & Anderson, 2006; MCGowan et al., 2009; Wübbenhorst & Zschorlich, 2012). The significant activity increase of both peroneus longus and tibialis anterior by 11.8% might also be due to their function as joint stabilizers (Wübbenhorst & Zschorlich, 2011). The loss of force in the unstable condition compared with the stable condition during the execution of the same motor task can be defined as the lack of functional force. In case of a high functional force deficit, balance training can be used to enhance joint stability and to optimize the transfer of force in unstable environmental conditions. If the lack of functional force is low, resistance training is suitable to increase overall strength. Therefore, for athletes whose sport imposes high requirements on maximum forces, active joint stabilization, and postural control, for instance, a combined training of balance and strength is advisable. It has been shown that a combination of balance training and strength training is suitable to improve MVC strength, neuromuscular activation, jump height, and time in the curve in young short track speed skaters (Behrens et al., 2010; Felser et al., 2012). The results of this study depict evidence that not only isometric MVC strength of the leg muscles has a
tremendous influence on short track speed skating performance (Kwon et al., 1997; Felser, 2013), but that the skating times and speeds are primarily influenced by cMVC strength of the leg extensors as well. To be able to transfer the strength onto ice in an optimal way, it is necessary to stabilize the knee joints and ankle joints. The present study analyzed the relationship between strength qualities and short track speed skating performance without the consideration of technical aspects of the short track speed skating performance. The skating technique is one of the main components that contribute to performance (Allinger & Van den Bogert, 1997). Therefore, our study is the first step in clarifying crucial factors for an optimal short track speed skating performance. Thus, further studies are required in this respect. Furthermore, our sample was heterogeneous with regard to their training history. This was due to the poor availability of subjects that are engaged in short track speed skating. Perspectives The results of the present study have clearly shown that depending on single muscles or groups of muscles, different forms of contraction are very important for short track speed skating. Concentric forces are crucial regarding the leg extensors, whereas mainly high-static forces are required from the hamstring muscles. Because of the necessary stabilization of the knee and ankle joints, (strength) training should additionally focus on the tibialis anterior and peroneus longus muscles. Future studies on this topic should find out to which extent the forces produced by the athletes under laboratory conditions correlate with the actual propulsion force produced by the athletes on the ice. Key words: Short track speed skating, neuromuscular activation, joint stabilization, maximum voluntary contraction strength.
Acknowledgements The authors gratefully thank all the staff and athletes of ESV Turbine Rostock team without whom the present study would not have been possible. Special thanks are due to Ivonne Bolt who did a terrific organization job. This study was supported in part by a grant of the Federal Institute of Sports Science (BISp IIA1-071504 12-14). Conflicts of interest: The authors have disclosed any financial and personal relationship with other people or organizations that could inappropriately influence their work.
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Strength and short track speed skating and mechanical properties of the knee extensor muscles. Int J Sports Med 2014: 35: 101–119. Behrens M, Mau-Moeller A, Heise S, Skripitz R, Bader R, Bruhn S. Alteration in neuromuscular function of the plantar flexors following caffeine ingestion. Scand J Med Sci Sports 2015: 25 (1): e50–e58. Behrens M, Mau-Moeller A, Wassermann F, Bruhn S. Effect of fatigue on hamstring reflex responses and posterior-anterior tibial translation in men and women. PLoS ONE 2013: 8: e56988. Behrens M, Mau-Möller A, Laabs H, Felser S, Bruhn S. Combined sensorimotor and resistance training for young short track speed skaters. A case study. Isokinet Exerc Sci 2010: 18: 193–200. Felser S. Modellierung einer Leistungsstruktur am Beispiel der Sportart Short Track. Rostock: Universität Rostock, 2013. Felser S, Mau-Möller A, Behrens M, Bäumler M, Bruhn S. Adaptationen der Kraftfähigkeiten, der neuromuskulären Aktivierung und der Kurvenlaufzeit
infolge eines kombinierten Balanceund Krafttrainings bei Short-Track-Kaderathleten. Leistungssport 2012: 42: 53–56. Hopkins WG. “Precision of measurement,” in A New View of Statistics. 2011, http://sportsci.org/ resource/stats/precision.html. Kornecki S, Kebel A, Siemienski A. Muscular co-operation during joint stabilisation, as reflected by EMG. Eur J Appl Physiol 2001: 84: 453–461. Kornecki S, Zschorlich V. The nature of the stabilizing functions of skeletal muscles. J Biomech 1994: 27: 215–225. Kwon YH, Cho SG, Lee DG, Jun MK. The effects of short-term power training on the starting technique of Korean elite female short-track speed skaters. Korean J Sport Sci 1997: 9: 45–57. Letzelter H, Letzelter M. Leistungsdiagnostik. Beispiel Eisschnelllauf. Niedernhausen/Taunus: Schors, 1983. MCGowan CP, Kram R, Neptune RR. Modulation of leg muscle function in response to altered demand for body
support and forward propulsion during walking. J Biomech 2009: 42: 850–856. Quinn A, Lun V, McCall J, Overend T. Injuries in short track speed skating. Am J Sports Med 2003: 31: 507–510. Seo NJ, Armstrong TJ. Biomechanical analysis for handle stability during maximum push and pull exertions. Ergonomics 2009: 52: 1568–1575. West SG, Finch JF, Curran PJ. Structural equation models with nonnormal variables: Problems and remedies. In: Hoyle RH, ed. Structural equation modeling: concepts, issues and applications. Thousand Oaks, CA: Sage Publications, 1995: 56–75. Wübbenhorst K, Zschorlich V. Effects of muscular activation patterns on the ankle joint stabilization: an investigation under different degrees of freedom. J Electromyogr Kinesiol 2011: 21: 340–347. Wübbenhorst K, Zschorlich V. The effect of increasing external degrees of freedom on force production and neuromuscular stabilisation. J Sports Sci 2012: 30: 1561–1569.
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Scand J Med Sci Sports 2015: ••: ••–•• doi: 10.1111/sms.12429
Published by John Wiley & Sons Ltd
Relationship between strength qualities and short track speed skating performance in young athletes S. Felser1, M. Behrens1, S. Fischer1, S. Heise1, M. Bäumler2, R. Salomon3, S. Bruhn1 Department of Exercise Science, University of Rostock, Rostock, Germany, 2Olympic Training Center M-V, Rostock, Germany, Institute of Applied Microelectronics and Computer Engineering, University of Rostock, Rostock, Germany Corresponding author: Martin Behrens, PhD, Department of Exercise Science, University of Rostock, Ulmenstraße 69, Rostock 18057, Germany. Tel: +49381/498 2744, Fax: +49381/498 2738, E-mail: [email protected]
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Accepted for publication 13 January 2015
This study analyzed the relationships between isometric as well as concentric maximum voluntary contraction (MVC) strength of the leg muscles and the times as well as speeds over different distances in 17 young short track speed skaters. Isometric as well as concentric single-joint MVC strength and multi-joint MVC strength in a stable (without skates) and unstable (with skates) condition were tested. Furthermore, time during maximum skating performances on ice was measured. Results indicate that maximum torques during eversion and dorsal flexion have a significant influence on skating speed. Concentric MVC strength of the knee extensors was higher corre-
lated with times as well as speeds over the different distances than isometric MVC strength. Multi-joint MVC testing revealed that the force loss between measurements without and with skates amounts to 25%, while biceps femoris and soleus showed decreased muscle activity and peroneus longus, tibialis anterior, as well as rectus femoris exhibited increased muscle activity. The results of this study depict evidence that the skating times and speeds are primarily influenced by concentric MVC strength of the leg extensors. To be able to transfer the strength onto ice in an optimal way, it is necessary to stabilize the knee and ankle joints.
Short track speed skating is characterized by high demands on dynamic stability of the ankle and knee joints. In order to achieve speeds up to 12.5 m/s, high propulsive forces have to be effectively transferred via the skates onto the ice (Quinn et al., 2003). Some studies suggested that the short-distance performance is determined by the start, and thereby by the maximum force of the leg extensor muscles (Kwon et al., 1997; Felser et al., 2012; Felser, 2013). On the basis of her investigations for clarifying the performance structure in short track speed skating, Felser (2013) concluded that the isometric maximum voluntary force (iMVF) of the leg extensor muscles explains 27% of differences in the time over 500 and 1000 m. In that study, the quantification of iMVF was done on the basis of multi-joint measurements in a leg press. However, by means of these measurements, it was not possible to detect relationships between singlejoint maximum voluntary contraction (MVC) strength of different knee muscles as well as ankle muscles and the short track speed skating performance. In addition, several studies have shown that increasing the external degrees of freedom during a force production task results in decreased muscle force and increased muscle activity of the stabilizing muscles (Kornecki & Zschorlich, 1994; Kornecki et al., 2001; Behm & Anderson, 2006; Seo & Armstrong, 2009; Wübbenhorst & Zschorlich, 2012). Behm and Anderson (2006)
suggested that the inherently greater instability of mechanically unstable movements challenges the neuromuscular system to a greater extent than movements that are performed under stable environmental conditions. Because of the locomotion on skates, short track speed skating is characterized by increased degrees of freedom compared with the barefoot condition and sets high demands on joint stabilization. Therefore, the aim of this study was to analyze the relationship between isometric as well as concentric MVC (cMVC) strength of the lower leg muscles and the times as well as speeds over different distances in young short track speed skaters. In addition, forces and muscle activities during isometric MVCs on a leg press with and without skates were analyzed. These parameters were correlated with the times and speeds over different distances. Materials and methods Subjects Seventeen young short track speed skaters (14 males, 3 females, age: 13.2 ± 1.1 years, weight: 55.7 ± 11.3 kg, height: 162 ± 10 cm) participated in this study. At the time of the investigation, all athletes have exercised short track speed skating between 1 and 10 years at the Olympic Training Center M-V. We tried to constitute a homogenous sample with regard to the age of the participants. However, because of poor availability of subjects, we have investigated a heterogeneous sample with regard to expertise. Before testing, all athletes were informed of the procedures to
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Felser et al. be utilized and signed informed consent. The study was conducted according to the Declaration of Helsinki and was approved by the university’s ethics committee.
Experimental procedure All athletes participated in two experimental sessions separated by at least 48 h. During the first session, MVC strength measurements were performed in the laboratory. Prior to the laboratory tests, the athletes had to perform a warm-up on bicycle for 10 min. The second session was devoted to maximum on ice skating performance tests (i.e., time measurements). Prior to the measurements, the athletes performed the warm-up on an individual basis.
based program (IMAGO, Pfitec, Endingen, Germany). The measurements of the iMVF were made unilaterally right and left with a knee angle of 120°. Prior to the tests, the athletes completed up to three MVC familiarization trials. During the tests, they were asked to perform two MVC trials. The athletes were instructed to fold their arms across their chests and to exert iMVF against the force plate for 3 s. These measurements were performed with and without skates. The athletes were provided with verbal encouragement to act as forcefully as possible during the execution of MVC tasks. Care was taken that the movement was executed without any countermovement. The time between the trials was 30 s. The best trial was taken for further analysis.
Electromyography (EMG) recordings Skating performance All athletes completed explosive starts over 5 and 30 m on the straight as well as over half a lap for quantifying the acceleration capability. The skating time was measured by photoelectric barriers (transmitter: DRL F02, receiver: TS 01-R04, mobile digital-timer DT800+, sportronic®, Sportronic, WinnendenHertmannsweiler, Germany). The maximum skating speeds were determined as follows: The athletes first accelerated over a distance of their choice. They then passed a short test distance of 10 or 25.13 m, respectively. The duration of that test distance was used to determine the individual maximum skating speed. All athletes performed two trials, from which the better was taken for further analyses. In addition, all athletes completed a 1000 m skating trial for determining their average lap speeds.
The surface EMGs were recorded using bipolar EMG Ambu® Blue Sensor N electrodes (Ambu GmbH, Bad Nauheim, Germany) (2 cm diameter). The electrodes were applied to the shaved, abraded, and cleaned skin over the middle of the muscle bellies of rectus femoris, biceps femoris, soleus, peroneus longus, medial gastrocnemius, and tibialis anterior of the right leg. The reference electrode was attached to the tibia. The resistance between electrodes was measured with a digital multimeter (MY-68, McVoice, Braunschweig, Germany) and was kept below 5 kΩ. Signals were amplified (1000×) and recorded with a sampling frequency of 1500 Hz by an 8-channel telemetry EMG system “PowerPack” (Pfitec). Data were transmitted by wireless LAN (Netgear WNDR3700) and were stored on a hard drive for later analysis with a custom-built LABVIEW®-based program.
Data analysis Torque recordings Torque signals were measured under isometric and concentric conditions using a CYBEX NORM dynamometer (Computer Sports Medicine®, Inc., Stoughton, Massachusetts, USA). The athletes were instructed to fold their arms across their chests. The isometric MVC tests for the ankle and knee joint muscles were performed with joint angles of 90 and 80° (0° = full extension), respectively. The axis of the dynamometer was aligned with the anatomical flexion-extension axis. The athletes were fixed to the dynamometer as described previously (Behrens et al., 2013, 2014, 2015). The isometric maximum voluntary torque (iMVT) was measured during the following isometric MVC tasks: eversion, plantar flexion, dorsal flexion, knee flexion, and knee extension. Three MVC trials were performed for each side of the body as well as direction of movement with at least a 30-s break between the trials. The concentric tests were performed with a velocity of 150°/s. The cMVC trials included: eversion, inversion, plantar flexion, dorsal flexion, knee flexion, and knee extension. Before the tests, the athletes completed up to three MVC familiarization trials. During the tests, they performed five MVCs. All athletes were thoroughly instructed to act as forcefully and as fast as possible. The torque signals were sampled with 100 Hz and recorded with the Humac® software (Computer Sports Medicine®, Inc., Stoughton, Massachusetts, USA ) (version 4.5.3).
Force recordings The measurement of iMVF was carried out on a custom-made force measurement system. It is designed according to the principle of a seated leg press with two vertically inserted force plates (Digimax®, DigiMax Systems, Hamm, Germany). It allows the seated position to be individually adjusted according to the anthropometry of the athletes. The force signals were sampled at 1500 Hz and stored on a hard drive for later analysis with a custom-built LABVIEW®-
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The intra-session reliability for the majority of the measurements was assessed. Statistical procedures were performed using a spreadsheet for calculating reliability (Hopkins, 2011). The results are presented in Table 1. Every athlete’s highest MVC trial, i.e., the attempt with the highest iMVT or concentric MVT (cMVT), was taken for further analyses. The torque was normalized to body weight. The root mean square of the EMG signal (RMS-EMG) for the different muscles was calculated over a 200 ms time period at iMVT and cMVT (100 ms prior to and 100 ms following the iMVT and cMVT, respectively). The highest iMVF was retained for further analyses. The following parameters were calculated on the basis of the force-time curves: iMVF without skate and iMVFSkate with skate. The parameters were normalized with respect to the athlete’s body weight. RMS-EMG was calculated to assess the muscle activity during the MVC trials. RMS-EMG was calculated over a 200 ms time interval at iMVF and iMVFSkate, i.e., 100 ms preceding and 100 ms following the iMVF and iMVFSkate. The calculated RMS-EMG values are stated in relation to the reference values obtained during the single-joint isometric MVC trials for the respective muscles.
Statistical analysis Data were visually inspected for extreme values and outliers using box-whisker plots. All extreme values and outliers were removed. Thereafter, data were checked for normal distribution considering skewness and kurtosis. As cutoff criteria, a skewness |>2| and a kurtosis |>7| were used (West et al., 1995). In addition, linearity was checked using scatter plots. Pearson’s correlation was used to analyze linear connections between the variables. The level of significance was established at P < 0.05. All data were analyzed using the SPSS statistical package 19 (SPSS Inc., Chicago, Illinois, USA). Data are presented as mean ± standard deviation in the tables.
0.95 (0.79 to 0.99) 0.92 (0.65 to 0.98) 0.98 (0.94 to 1.00) 0.98 (0.95 to 0.99) 0.83 (0.60 to 0.93) 0.97 (0.93 to 0.99) 0.96 (0.90 to 0.98) 0.97 (0.94 to 0.99) 0.96 (0.92 to 0.98)
Table 2. Mean and standard deviation (SD) of the relevant parameters
Parameter
Mean ± SD
Time over 5 m (s) 1.38 ± 0.12 Time over 30 m (s) 5.21 ± 0.35 Time over half a lap (s) 8.23 ± 0.59 Maximum speed straight 9.21 ± 0.76 (m/s) Maximum speed curve 8.09 ± 0.55 (m/s) Time over 1000 m (s) 128.91 ± 11.32 7.81 ± 0.71 Average speed 1000 m (m/s) Leg press iMVF right (N/kg) 48.33 ± 11.93 iMVFSkate right (N/kg) 35.95 ± 7.95 iMVF left (N/kg) 43.20 ± 8.89 iMVFSkate left (N/kg) 33.58 ± 7.06 Isometric and concentric iMVT knee extension 3.03 ± 0.50 MVT right leg (Nm/kg) cMVT knee extension 1.69 ± 0.28 iMVT knee flexion 1.63 ± 0.33 cMVT knee flexion 1.35 ± 0.19 cMVT ankle inversion 0.39 ± 0.09 iMVT ankle eversion 0.33 ± 0.06 cMVT ankle eversion 0.27 ± 0.06 iMVT plantar flexion 2.20 ± 0.34 cMVT plantar flexion 0.72 ± 0.10 iMVT dorsal flexion 0.37 ± 0.12 cMVT dorsal flexion 0.30 ± 0.06 Isometric and concentric iMVT knee extension 3.03 ± 0.48 MVT left leg (Nm/kg) cMVT knee extension 1.67 ± 0.25 iMVT knee flexion 1.49 ± 0.30 cMVT knee flexion 1.40 ± 0.21 cMVT ankle inversion 0.40 ± 0.09 iMVT ankle eversion 0.35 ± 0.07 cMVT ankle eversion 0.29 ± 0.09 iMVT plantar flexion 2.13 ± 0.29 cMVT plantar flexion 0.76 ± 0.15 iMVT dorsal flexion 0.33 ± 0.10 cMVT dorsal flexion 0.30 ± 0.08 Parameters on ice
SDDiff, SD of the difference between trial 1 and 2; TE, typical error; CV%, coefficient of variation; ICC, intraclass correlation coefficient.
3.4 (2.3 to 7.2) 2.4 (1.6 to 5.2) 1.4 (1.0 to 2.6) 1.4 (1.0 to 2.2) 3.4 (2.5 to 5.1) 9.2 (7.1 to 13.3) 11.2 (8.7 to 16.3) 7.4 (5.8 to 10.7) 7.6 (5.9 to 11.0) 0.35 (0.24 to 0.74) 0.13 (0.09 to 0.27) 0.17 (0.12 to 0.30) 0.15 (0.12 to 0.24) 0.50 (0.37 to 0.75) 176.6 (137.8 to 250.3) 184.7 (144.1 to 261.9) 122.8 (95.8 to 174.1) 125.9 (98.2 to 178.5) 0.06 0.18 0.17 0.18 0.38 249.7 261.2 173.6 178.1 1.38 (0.16) 5.25 (0.37) 8.14 (0.76) 9.26 (0.84) 8.05 (0.65) 2509.2 (954.1) 2280.5 (847.5) 1848.2 (736.9) 1768.8 (651.9) 5m 30 m Half a lap Maximum speed straight Maximum speed curve iMVF right iMVF left iMVFSkate right iMVFSkate left
1.43 (0.11) 5.31 (0.24) 8.23 (0.66) 9.20 (0.82) 8.03 (0.54) 2388.7 (899.7) 2239.8 (822.9) 1710.9 (668.1) 1646.0 (560.3)
−0.05 (−0.10 to 0.00) −0.06 (−0.21 to 0.09) −0.09 (−0.20 to 0.02) 0.07 (−0.03 to 0.16) 0.02 (−0.17 to 0.20) 120.5 (14.8 to 226.3) 40.7 (−69.9 to 151.3) 137.3 (63.8 to 210.8) 122.8 (47.4 to 198.2)
TE (95% CI) SDDiff Mean difference (95% CI) Trial 2 Mean (SD) Trial 1 Mean (SD)
Table 1. Intra-session reliability for the starts (s), maximum speeds (m/s), and the isometric maximal voluntary forces (N) on the leg press
CV% (95% CI)
ICC (95% CI)
Strength and short track speed skating
cMVT, concentric maximum voluntary torque; iMVT, isometric maximum voluntary torque.
Results Skating performance The mean times and speeds achieved over the different distances are summarized in Table 2. The maximum skating speed in the curve was on average 11.9% (P = 0.000) below the maximum skating speed on the straight. Over a distance of 1000 m, 75% of the athletes attained their maximum lap speed in lap 2, whereas the remaining 25% attained it in lap 3. iMVT and cMVT The results of the iMVT and cMVT measurements are presented in Table 2. The analysis did not indicate any significant differences regarding iMVT and cMVT between the right and the left leg. iMVF and neuromuscular activation on the leg press The iMVF values measured on the leg press are shown in Table 2. The data show that the iMVF values were about 25% higher than the iMVFSkate values.
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Felser et al. Table 3. Mean and standard deviation (SD) of RMS-EMG of the different muscles during strength testing on the leg press with and without skate. Data are normalized to RMS-EMG during iMVT
Mean ± SD (%) Without skate
With skate
Biceps femoris Rectus femoris Soleus Peroneus Gastrocnemius Tibialis Biceps femoris Rectus femoris Soleus Peroneus Gastrocnemius Tibialis
60.5 ± 38.0 40.5 ± 19.1 52.3 ± 21.6 41.0 ± 22.3 49.4 ± 23.6 27.8 ± 16.2 40.4 ± 18.0 47.4 ± 20.7 49.6 ± 24.9 57.3 ± 20.0 46.7 ± 16.9 39.6 ± 20.1
RMS-EMG, root mean square of the EMG signal; iMVT, isometric maximum voluntary torque. Table 4. Percentage change in RMS-EMG of the relevant muscles during strength testing on the leg press between the execution of the MVCs with and without skate
Mean ± SD (%) Biceps femoris Rectus femoris Soleus Peroneus Medial gastrocnemius Tibialis anterior
−13.5 ± 16.2 (P = 0.415) 11.6 ± 25.3 (P = 0.484) −6.5 ± 19.9 (P = 0.626) 16.3 ± 22.4* (P = 0.027) 3.3 ± 17.4 (P = 0.967) 11.8 ± 25.4 (P = 0.092)
Asterisks denote a significant difference. *P ≤ 0.05. RMS-EMG, root mean square of the EMG signal; MVC, maximum voluntary contraction.
Table 3 shows the normalized EMG data of the different muscles during the MVCs with and without skates. It becomes apparent that some muscles exhibit a reduced activation whereas one muscle shows a stronger contraction (Table 4). The biceps femoris, a knee flexor and hip extensor, showed the highest activity on the leg press when no skates were worn. This muscle activation was reduced in the measurement with skate. The muscular activation of the soleus muscle was reduced by 6.5% during MVC strength testing with skates. In contrast to this, the muscular activation of the rectus femoris, peroneus longus, and tibialis anterior increased between 11.6% and 16.3%. The t-test has shown that the RMSEMG of the peroneus longus was significantly higher in the trials with skate (P = 0.027). Correlation analysis The results of the correlation analyses suggest that the time over 5 m is not an appropriate indicator to provide valid statements about the times over 30 m, half a lap, and 1000 m, as well as about the different skating speeds. The other parameters on ice were significantly correlated (Table 5).
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There were some significant correlations between the MVT of the knee extensors as well as knee flexors and the times as well as speeds over the different distances. Especially cMVT of the knee extensors showed significant correlations with the time over 5 and 1000 m as well as the maximum skating speed in the curve and in lap 2. With regard to the importance of MVC strength of knee flexors, it seems that iMVT has a larger influence on the skating times or speeds than cMVT (Table 6). There were no significant correlations between MVT of the ankle muscles and the time over 30 m and half a lap. The maximum speed in the curve showed significant correlations with cMVT during ankle eversion and cMVT of the dorsal flexors of the right leg. The iMVT and cMVT during the right leg’s ankle eversion significantly correlated with the skating speed in lap 2. By contrast, the correlations between iMVT of the plantar flexors and dorsal flexors of the left leg and the maximum skating speed on the straight were rather low. The cMVT during ankle eversion of the left leg was significantly correlated with the skating speed in lap 2. The same was the case for iMVT of the dorsal flexors of the left leg (Table 6). Correlation analysis between iMVF as well as iMVFSkate on the leg press and the skating times as well as speeds revealed that more and higher relationships exist for iMVFSkate and the short track speed skating performance than for iMVF and the short track speed skating performance variables (Table 6). Discussion The present study investigated relationships between strength qualities of the lower leg muscles and the short track speed skating performance in young athletes. Therefore, isometric and concentric single-joint MVC strength measurements for relevant knee and ankle muscles have been conducted using a dynamometer. In addition, multi-joint MVC strength of the lower extremity with and without skates was tested using a leg press. The strength parameters were correlated with the times over 5 m, 30 m, half a lap, and 1000 m, as well as the speeds on the straight, in the curve, and in lap 2 during a 1000 m time trial. The results of the study have shown that the maximum speed in the curve is on average 11.9% lower than the maximum skating speed on the straight. This can be explained by the fact that there are centrifugal forces in the curve. Moreover, skating through the curves is more complex than skating on the straight because of the curve technique required (Letzelter & Letzelter, 1983). The results of the correlation analysis show that there is a correlation between the maximum skating speed on the straight and in the curve which is highly significant [r = 0.802, i.e., explained variance (r2) is 65%]. Because of that, it is assumed that the skating speed which can be achieved and maintained in the curve has a major
Strength and short track speed skating Table 5. Correlation analysis between the different parameters measured on ice
1. 2. 3. 4. 5. 6. 7.
Time over 5 m Time over 30 m Time over half a lap Maximum speed straight Maximum speed curve Time over 1000 m Average speed 1000 m
1
2
3
4
5
6
1 0.423 0.275 −0.176 −0.494* 0.290 −0.437
1 0.851** −0.866** −0.794** 0.801** −0.836**
1 −0.821** −0.739** 0.682** −0.676**
1 0.802** −0.876** 0.839**
1 −0.877** 0.901**
1 −0.936**
Asterisks denote a significant correlation. *P ≤ 0.05; **P ≤ 0.01. Table 6. Correlation analysis between strength parameters and the times as well as speeds
iMVT knee extension right cMVT knee extension right iMVT knee flexion right cMVT knee flexion right cMVT ankle inversion right iMVT ankle eversion right cMVT ankle eversion right iMVT plantar flexion right cMVT plantar flexion right iMVT dorsal flexion right cMVT dorsal flexion right iMVT knee extension left cMVT knee extension left iMVT knee flexion left cMVT knee flexion left cMVT ankle inversion left iMVT ankle eversion left cMVT ankle eversion left iMVT plantar flexion left cMVT plantar flexion left iMVT dorsal flexion left cMVT dorsal flexion left iMVF right iMVFSkate right iMVF left iMVFSkate left
Time over 5m
Time over 30 m
Time over half a lap
Maximum speed straight
Maximum speed curve
Speed in lap 2
Time over 1000 m
−0.465* −0.713** −0.468* −0.398 0.055 −0.182 −0.330 −0.018 −0.517* −0.344 −0.351 −0.591** −0.554* −0.306 −0.197 −0.227 −0.177 −0.375 0.066 0.132 −0.360 −0.291 −0.467* −0.437* −0.241 −0.390
−0.109 −0.450* −0.368 −0.310 0.007 −0.084 −0.404 0.214 −0.200 −0.110 −0.381 −0.461* −0.379 −0.424* −0.068 −0.057 0.064 −0.183 0.391 0.341 −0.392 −0.268 −0.170 −0.174 −0.148 −0.308
−0.174 −0.333 −0.330 −0.077 0.028 −0.138 −0.332 0.125 −0.100 −0.151 −0.372 −0.284 −0.201 −0.348 0.155 0.143 0.216 −0.141 0.287 0.211 −0.322 −0.029 −0.105 −0.168 −0.086 −0.285
0.161 0.405 0.450* 0.255 −0.046 0.290 0.385 −0.337 0.096 0.213 0.374 0.304 0.345 0.535* 0.136 −0.081 −0.054 0.167 −0.423* −0.219 0.498* 0.204 0.060 0.251 0.173 0.351
0.253 0.628** 0.431* 0.382 −0.106 0.299 0.576** −0.160 0.109 0.111 0.423* 0.490* 0.565** 0.558** 0.079 −0.097 −0.115 0.384 −0.273 −0.246 0.309 0.103 0.278 0.411 0.295 0.528*
0.561* 0.750** 0.683** 0.630** 0.034 0.536* 0.573* −0.225 0.205 0.323 0.348 0.597** 0.642** 0.720** 0.355 −0.034 0.216 0.456* −0.341 −0.003 0.486* 0.253 0.396 0.616** 0.425 0.593**
−0.334 −0.648** −0.680** −0.619** 0.155 −0.483* −0.437 0.325 −0.093 −0.320 −0.359 −0.452* −0.708** −0.620** −0.416 0.048 −0.092 −0.273 0.332 0.034 −0.410 −0.131 −0.596** −0.679** −0.643** −0.621**
Asterisks denote a significant correlation. *P ≤ 0.05; **P ≤ 0.01. cMVT, concentric maximum voluntary torque; iMVT, isometric maximum voluntary torque.
influence on the speed skating performance. Therefore, the speed in the curve seems to be a crucial factor for a good performance in short track speed skating. Since a good time over 500 , 1000, or 1500 m depends on several factors, among others on speed endurance (Felser, 2013), it seems more important to find out which of the measured parameters has a positive influence on time and speed in the curve, respectively. One can conclude from the results of this study that the strength of the knee extensors and knee flexors has a major influence on skating times and speeds, respectively. With regard to knee extension strength, we found higher significant correlations between the times as well as speeds and cMVT than for the times as well as speeds and iMVT. In contrast, for the knee flexion MVC strength, we found more significant correlations between the iMVT and the skating times as well as speeds. This can be explained by the fact
that the knee extensors are responsible for producing the propulsion force during mid-stance, whereas the knee flexors work predominantly static or eccentric because of the low position of the body. At the same time, the results of the correlation analysis show that the maximum torques during eversion and dorsal flexion have a significant influence on the speed in the curve and lap 2, respectively. The dorsal flexion is mainly performed by the tibialis anterior and the eversion by the peroneus longus. These two muscles are responsible for stabilizing the ankle joint. Furthermore, we found moderate significant correlations between the speed in lap 2 and iMVFSkate as well as between the maximum skating speed in the curve and iMVFSkate. These parameters were not significantly correlated with iMVF measured without skates. This can be explained by the fact that in short track speed skating, the
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Felser et al. movement is performed on skates, i.e., the force has to be transferred to the ice before it can develop its performance-enhancing effect. In short track speed skating, there are specific requirements concerning the stabilization of the knee and ankle joint as well as the force development during mid-stance. According to Quinn et al. (2003), high forces of the ankle joint muscles are required during short track speed skating. Consequently, the conditions at the leg press with skates in the present study are quite similar to the conditions on the ice. The tests on the leg press have shown that the loss of force between the measurements without and with skates amounts to 25%. At the same time, biceps femoris and soleus showed 13.5% and 6.5% less activity during measurements with skates. In contrast, the muscle activities of peroneus longus, tibialis anterior, and rectus femoris were increased. According to Kornecki et al. (2001), the rectus femoris, which is part of the quadriceps femoris muscle, belongs to the muscles with mainly motor function. In the present study, the rectus femoris showed an increase in activity under unstable test conditions, i.e., during measurement with skates. This increase in activity might be due to the stabilization requirements to which this muscle contributes as has been described earlier (Anderson & Behm, 2004; Behm & Anderson, 2006; MCGowan et al., 2009; Wübbenhorst & Zschorlich, 2012). The significant activity increase of both peroneus longus and tibialis anterior by 11.8% might also be due to their function as joint stabilizers (Wübbenhorst & Zschorlich, 2011). The loss of force in the unstable condition compared with the stable condition during the execution of the same motor task can be defined as the lack of functional force. In case of a high functional force deficit, balance training can be used to enhance joint stability and to optimize the transfer of force in unstable environmental conditions. If the lack of functional force is low, resistance training is suitable to increase overall strength. Therefore, for athletes whose sport imposes high requirements on maximum forces, active joint stabilization, and postural control, for instance, a combined training of balance and strength is advisable. It has been shown that a combination of balance training and strength training is suitable to improve MVC strength, neuromuscular activation, jump height, and time in the curve in young short track speed skaters (Behrens et al., 2010; Felser et al., 2012). The results of this study depict evidence that not only isometric MVC strength of the leg muscles has a
tremendous influence on short track speed skating performance (Kwon et al., 1997; Felser, 2013), but that the skating times and speeds are primarily influenced by cMVC strength of the leg extensors as well. To be able to transfer the strength onto ice in an optimal way, it is necessary to stabilize the knee joints and ankle joints. The present study analyzed the relationship between strength qualities and short track speed skating performance without the consideration of technical aspects of the short track speed skating performance. The skating technique is one of the main components that contribute to performance (Allinger & Van den Bogert, 1997). Therefore, our study is the first step in clarifying crucial factors for an optimal short track speed skating performance. Thus, further studies are required in this respect. Furthermore, our sample was heterogeneous with regard to their training history. This was due to the poor availability of subjects that are engaged in short track speed skating. Perspectives The results of the present study have clearly shown that depending on single muscles or groups of muscles, different forms of contraction are very important for short track speed skating. Concentric forces are crucial regarding the leg extensors, whereas mainly high-static forces are required from the hamstring muscles. Because of the necessary stabilization of the knee and ankle joints, (strength) training should additionally focus on the tibialis anterior and peroneus longus muscles. Future studies on this topic should find out to which extent the forces produced by the athletes under laboratory conditions correlate with the actual propulsion force produced by the athletes on the ice. Key words: Short track speed skating, neuromuscular activation, joint stabilization, maximum voluntary contraction strength.
Acknowledgements The authors gratefully thank all the staff and athletes of ESV Turbine Rostock team without whom the present study would not have been possible. Special thanks are due to Ivonne Bolt who did a terrific organization job. This study was supported in part by a grant of the Federal Institute of Sports Science (BISp IIA1-071504 12-14). Conflicts of interest: The authors have disclosed any financial and personal relationship with other people or organizations that could inappropriately influence their work.
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