1
Lower Limb Muscle Activation Patterns in Ice-Hockey Skating
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and Associations with Skating Speed
2
Sami Kaartinen1, Mika Venojärvi1, Kim Lesch1, Heikki Tikkanen1, Paavo Vartiainen2, 3
Lauri Stenroth2 4
1 Institute of Biomedicine, Sports and Exercise Medicine, School of Medicine, University 5
of Eastern Finland, Kuopio, Finland; 2 Department of Applied Physics, University of 6
Eastern Finland, Kuopio, Finland 7
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ORCiDs:
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Sami Kaartinen: https://orcid.org/0000-0002-6962-1054 10
Mika Venojärvi: https://orcid.org/0000-0003-1327-9760 11
Paavo Vartiainen: https://orcid.org/0000-0003-0974-0913 12
Lauri Stenroth: https://orcid.org/0000-0002-7705-9188 13
Heikki Tikkanen: https://orcid.org/ 0000-0001-6067-4101 14
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Corresponding author:
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Sami Kaartinen 17
University of Eastern Finland 18
School of Medicine 19
PO Box 1627 20
70211 Kuopio, Finland 21
tel. +358456935233, email: [email protected] 22
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2 Abstract
24
In this study, we aimed to describe lower limb kinematic and muscle activation patterns 25
and then to examine the potential associations between those variables and skating speed 26
in highly trained ice-hockey players. Twelve players (age 18.4-22.0 years) performed five 27
maximal 30-meter forward skating sprints. Skating speeds, muscle activities from eight 28
lower limb muscles (gluteus maximus, gluteus medius, adductor magnus, rectus femoris, 29
vastus lateralis, biceps femoris, tibialis anterior, and soleus), and sagittal plane joint 30
angles from the hip and knee joint were measured. A lower activity of the gluteus 31
maximus (r=-0.651, p=0.022, β=-0.08) and a reduced gluteus maximus to rectus femoris 32
coactivity (r=-0.786, p=0.002, β=-3.26) during the recovery phase were found to be 33
associated with faster skating speed. No significant associations were observed between 34
sagittal plane hip and knee kinematics and skating speed. This study provides evidence 35
that muscle activities during the recovery phase of skating may have an important role in 36
skating performance.
37 38
Key Words: ice-hockey, recovery phase, skating cycle, biomechanics, EMG, 39
electromyography 40
3 Introduction
41
Ice-hockey is a fast team sport in which good skating skills and fast skating speed are 42
important characteristics for the players. To enhance training in ice-hockey, it would be 43
important to understand the technical determinants of fast skating performance. Lower 44
limb kinematics and muscle activity patterns can be considered as key technical 45
determinants of a motor task where lower limb kinematics represent the movement 46
pattern and muscle activity the cause of the movement pattern.
47
During the skating cycle, there is a movement of the hip joint in sagittal, frontal and 48
horizontal planes. In addition, the knee joint extends and flexes whereas the ankle joint 49
dorsiflexes and plantarflexes during different phases of the skating cycle (Haché, 2002;
50
Goudreault 2002). When the skating speed increases, greater hip abduction occurs during 51
the propulsion phase (skate is in contact with the ice, more details in Supplementary 52
material, Pearsall et al., 2000; Haché, 2002). It could be summarized that skating consists 53
of complex movement patterns, which pose special demands on motor skills (Haché, 54
2002).
55
Previous studies of muscle activity during skating in ice-hockey have indicated that the 56
gluteus maximus (Pearsall et al., 2000) and the vasti muscles are active during the 57
propulsion phase to extend, abduct and externally rotate the hip and extend the knee, 58
respectively (Chang et al., 2009; Buckeridge et al., 2015). Hamstring muscles are reported 59
to be most active during the gliding phase (isometric phase) of skating to increase the 60
stiffness of the knee joint with co-activity of knee extensors (de Boer et al., 1987).
61
Additionally, the biceps femoris shows high activity also during the propulsion phase in 62
ice-hockey skating when extension of the hip occurs (Chang et al., 2009). The activity of 63
4
the tibialis anterior is at its highest during the gliding phase to stabilize the ankle and 64
during the recovery phase to dorsiflex the ankle (Goudreault 2002).
65
Rather few studies have examined how the previously described kinematic characteristics 66
of ice-hockey skating are related to the skating speed. During the propulsion phase, 67
greater range of motion (ROM) of the hip joint (Upjohn et al., 2008), and more extended 68
knee seem to be important determinants of higher skating speed in ice-hockey players 69
(Buckeridge et al., 2015). During the recovery phase (skate is not in contact with the ice, 70
more details in Supplementary material) greater hip adduction was found to be associated 71
with a higher skating velocity (Lafontaine, 2007). Since the most above-mentioned 72
studies included players from two contrasting groups (different levels of players) one 73
needs to be careful when interpreting causality from the observed associations. However, 74
one could summarize the findings to indicate that large hip ROM during the propulsion 75
phase, may be an important determinant of fast skating speed.
76
While there is little information available on the association between the kinematic 77
characteristics of skating and skating speed in ice-hockey, it is not known if differences 78
in muscle activities between the players explain differences in skating speed between the 79
players. Overall, there has been rather little research published on skating biomechanics 80
in ice-hockey and the available data on ice-hockey originates from players with variable 81
skill and performance levels (Robbins et al., 2018; Buckeridge et al., 2015; Upjohn et al., 82
2008). Hereby it is difficult for coaches to apply evidence-based protocols in the training 83
of elite ice-hockey players. Therefore, this study aimed first to describe the lower limb 84
muscle activation and joint kinematics patterns during the maximal forward skating phase 85
in highly trained ice-hockey players. Secondly, this study aimed to examine the 86
association between the skating speed and lower limb kinematics and muscle activities 87
during the different phases of the skating cycle.
88
5
We hypothesized that muscle activities of the lower limb muscles and ROM of the hip 89
and knee joint would be associated with a faster forward skating speed. Based on previous 90
studies suggesting greater ROM at the hip and knee during the propulsion phase to be 91
associated with greater skating speed (Buckeridge et al., 2015) we hypothesized that 92
greater hip and knee extension and high muscle activity of the respective agonist muscles 93
(vastus lateralis and gluteus maximus) during the propulsion phase would enable 94
powerful propulsion and thus be associated with a higher maximal skating speed. Fast 95
lower limb flexion in addition to the high activity of the respective agonist muscles (rectus 96
femoris, biceps femoris, and tibialis anterior) during the recovery phase was hypothesized 97
to also be associated with higher skating speed as it could shorten the duration of the 98
recovery phase enabling the skater to achieve higher skating cycle frequency (Lafontaine, 99
2007; Buckeridge et al., 2015) and increase propulsion power.
100
Methods 101
Participants 102
Participants were recruited from the elite Finnish hockey league or the elite Finnish junior 103
hockey league. Inclusion criteria were male gender, age over 18 years. Players with acute 104
injury and players recovering from a previous injury were excluded. This study was aimed 105
to be a preliminary investigation and therefore we set out to detect strong correlations 106
(r<0.65) between muscle activities and lower limb kinematics with skating speed. Based 107
on a priori sample size calculation, a sample size of N=16 is needed for achieving 80%
108
statistical power to detect strong correlations with a two-tailed test (Faul et al., 2007). We 109
recruited 17 participants. All recruited participants signed an informed consent to 110
demonstrate that they were aware of the physical demands of the testing protocols and 111
were willing to participate in the study as volunteers. The ethics committee of the Hospital 112
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District of Northern Savo approved the study protocol. Four participants were not able to 113
participate due to acute injure after the recruitment, and data from one participant needed 114
to be excluded during the data analysis due to invalid data leaving us with a sample size 115
of N=12 (18.4 - 22.0 years, 81.0 ± 6.0 kg, 1.82 ± 0.03 m, and BMI 25.2 ± 1.6 kg/m2).
116
Protocol 117
The participants performed a warm-up session according to their own protocol with which 118
they had been familiarized in their training groups. After the warm-up, each participant 119
performed a 30-meter maximal sprint from a standing start at least five times. Additional 120
trials were performed if technical problems were noticed during the data collection if the 121
participant fell or stumbled during the sprint or if there was a technical error in the data 122
collection. The number of trials performed varied between five and ten. In the skating 123
test, participants wore a helmet, their own skates (which were sharped as they were used 124
to), gloves, and tracksuit. Recovery time between the skating sprints was 90 s.
125
Electromyography, acceleration and joint kinematics 126
Electromyography (EMG), acceleration, and electrogoniometer signals were collected 127
using a data logger Biomonitor ME6000 (Bittium Biosignals Oy, Finland) and sent 128
wirelessly to a laptop computer. The sampling frequency of the signals was 1000 Hz.
129
Surface EMG was used to measure muscle activity during the skating test. The electrodes 130
(measuring area 95 mm2, Ambu®, Denmark) were attached according to the guidelines 131
of the Seniam project (Hermens et al., 2000) on pre-determined muscles of the right leg 132
with a 22 mm distance between the electrodes. The selected muscles were adductor 133
magnus, rectus femoris, biceps femoris, vastus lateralis, tibialis anterior, soleus, gluteus 134
maximus, and gluteus medius. Since there are no guidelines for electrode placement on 135
the adductor magnus muscle in the Seniam guidelines, ultrasound imaging was used to 136
7
identify the most suitable electrode placement during the pilot measurements. The 137
placement was in the upper 1/3 of the thigh. An experienced researcher attached the 138
electrodes. The skin in the region of the electrodes was shaved, lightly rubbed with 139
sandpaper, and cleaned with alcohol before attachment of the electrodes, which were 140
secured using adhesive tape. After the electrodes were placed on the participant´s skin, 141
they performed maximal isometric contractions in order to collect EMG normalization 142
data. The following tasks were performed for EMG normalization: push against a wall 143
while standing on the ball of the foot, foot dorsiflexion in a seated posture with manual 144
resistance, a seated knee extension with the shank fixed, knee flexion in a prone posture 145
with manual resistance, hip flexion against manual resistance in a supine posture, hip 146
extension in a prone posture, hip abduction against manual resistance lying on the side, 147
and hip adduction in a semi-seated posture against a foam roll held between the thighs.
148
For each maximal isometric muscle testing, the participant held the maximal contraction 149
for three seconds with strong verbal encouragement by the researcher. The participants 150
executed maximum voluntary isometric contraction (MVIC) for EMG normalization and 151
each MVIC task was performed twice with a 90 s rest between the contractions. EMG 152
activities of each muscle recorded during the skating were normalized to the maximum 153
values obtained during these contractions irrespective of in which task the maximum 154
values had been obtained.
155
A triaxial accelerometer (Bittium Biosignals Oy, Finland) was attached on the lateral side 156
of the plastic part of the right foot skate using adhesive tape, to measure accelerations of 157
the skate for detecting the phases of skating cycles (Buckeridge et al., 2015).
158
During skating knee and hip joint angles were measured using electrogoniometers 159
(Bittium Biosignals Oy, Finland) which were attached to the right leg using tape and a 160
bandage. The arms of the electrogoniometers were placed over the distal part of the femur 161
8
and the proximal part of the tibia for the knee joint, the arms crossed the joint in the 162
sagittal plane. Care was taken to position the electrogoniometers on the mid-lateral aspect 163
of the leg in order to measure the sagittal plane angles. Goniometer signals were zeroed 164
to the values obtained while the participants were standing with hips and knees straight 165
(i.e. anatomical position).
166
Data analysis and reductions 167
The first five successful sprints were selected for the analysis from each participant. The 168
last two full skating cycles (occurring within the final 15 meters) of the 30-meter skating 169
were extracted from the data based on detection of the cycles from the acceleration signal 170
and voltage pulse sent to the data logger Biomonitor ME6000 (Bittium Biosignals Oy, 171
Finland) when the skater passed the photocells at the end of the 30-meter sprint. Hence, 172
a total of 10 skating cycles were extracted for analysis from each participant.
173
The 30-meter skating time, characterizing the performance of the 30-meter sprint was 174
measured using photocells (Chronojump Boscosystem®, Spain) which were placed 25 175
cm from the starting line in the direction of skating and 25 cm behind the finish line. The 176
photocells were mounted 100 cm above the ice surface to avoid interference by the ice- 177
hockey stick. The average skating speed during the final 15 meters was measured by 178
analyzing the time taken to skate the final 15 meters from a high-speed (frame rate 120 179
Hz) video (GoPro 3, GoPro Inc., USA). The calculated skating speed reflects near- 180
maximal skating speed and is later referred to as “skating speed15-30m“. The camera was 181
located in the middle of the 30-meter sprint, 16 meters from the line of skating with its 182
field of view perpendicular to the skating direction. Vertical poles were positioned 183
between the camera and the skating line to mark specific distances over the 30-meter 184
sprint. The camera parallax was considered in the location of the marks and consequently, 185
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the 30-meter mark was positioned at a distance of 29.06 meters from the starting line 186
(Figure 1).
187
Accelerometer, goniometer, and EMG data processing were performed in Matlab (v.
188
R2014a, MathWorks Inc., USA) using custom-made scripts. Skating cycle detection was 189
based on acceleration signals, which allowed the identification of time instants for the 190
start of the cycles (skate comes into contact with the ice) and the start of the recovery 191
phase (skate leaves the ice). The acceleration signals were first high-pass filtered using a 192
300 Hz bidirectional 4th order Butterworth filter to accentuate high-frequency 193
acceleration peaks in the data. Then, the time instants of the beginning of the skate cycles 194
and the beginning of the recovery phases were manually detected from the signal. EMG 195
data were first band-pass filtered between 20 and 450 Hz using bidirectional 4th order 196
Butterworth filter after which the data were full-wave rectified and low pass filtered using 197
12 Hz bidirectional 4th order Butterworth filter to create EMG envelopes (Thelen et al., 198
2005). The EMG values obtained during the skating were normalized by dividing them 199
with the maximal values obtained during the maximal isometric contractions (processed 200
similarly as data from skating). Electrogoniometer signals were low pass filtered using a 201
5 Hz bidirectional 4th order Butterworth filter.
202
The EMG envelopes and electrogoniometer data were time normalized and averaged to 203
create ensemble averages of the ten skating cycles for each participant. The ensemble 204
average cycle was divided into propulsion (i.e. ice contact) and recovery phases (i.e.
205
swing) based on the average duration of the propulsion phase across the ten cycles. The 206
propulsion phase was further divided into three equally spaced phases (beginning, middle, 207
and end) and the recovery phase was divided into two equally spaced phases (beginning 208
and end). From the ensemble averages, the mean EMG values were calculated from the 209
propulsion and recovery phases and their sub-phases. In addition, the coactivity of the 210
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agonist-antagonist pairs (gluteus maximus/rectus femoris, tibialis anterior/soleus, 211
adductor magnus/gluteus medius, and vastus lateralis/biceps femoris) was calculated as 212
the ratio of the normalised activities between the two muscles in each phase (Ervilha, 213
et.al., 2012). From the electrogoniometer data, hip and knee joint angles were extracted 214
from the beginning and the end of the propulsion and recovery phases. In addition, the 215
range of motion during both phases was calculated. Finally, the duration of each phase 216
was extracted, and the average distance traveled during the whole skating cycle and both 217
skating cycle phases were calculated based on the measured skating speed15-30m as 218
distance = velocity * duration.
219
Statistical analyses 220
Statistical analysis was performed with SPSS statistical analysis software (v. 23.0.0.2 for 221
Windows, SPSS Inc., Chicago, IL, USA). Linear regression analysis was performed to 222
examine the association between muscle activities and skating speed15-30m and between 223
joint kinematics and skating speed15-30m. Correlation coefficients were calculated using 224
Pearson product-moment correlation. The normality of the data was checked using the 225
Shapiro-Wilk test. Skating speed15-30m (dependent variable of the regression analyses) 226
was normally distributed (p=0.407) while some of the independent variables were not 227
(p<0.05). We confirmed using Spearman´s rank correlation that the conclusion of the 228
correlation analyses was not altered when the normality assumption was violated.
229
Homoscedasticity was visually confirmed and none of the associations showed clear 230
deviation from the linearity assumption. The level of statistical significance was set at 231
p<0.05.
232
11 Results
233
Mean values for skating speeds and spatio-temporal parameters of all participants are 234
presented in Table 1. At the beginning of the propulsion phase, the hip joint flexion angle 235
was on average 46.8 ± 10.0º (Figure 2). Extension of the hip continued during the 236
propulsion phase reaching 15.3 ± 6.2º hip flexion at the beginning of the recovery phase 237
with continuing extension in the early recovery phase. At the beginning of the propulsion 238
phase, the average knee joint flexion angle was 67.3 ± 21.1º. The knee joint extended 239
during the propulsion phase, reaching the minimum flexion angle shortly before the skate 240
left the ice. At the beginning of the recovery phase, the average knee joint flexion angle 241
was 18.5 ± 17.7º. The knee joint reached maximal flexion immediately after the midpoint 242
of the recovery phase, followed by a minor knee extension before the skate hit the ice 243
again (beginning of the propulsion phase).
244
Mean normalized muscle activity patterns are presented in Figure 3 and mean normalized 245
muscle activities during the propulsion and recovery phases are displayed in Table 2. The 246
soleus muscle demonstrated the highest neuromuscular activity during the propulsion 247
phase, immediately after the skate hit the ice, and at the mid-portion of the propulsion 248
phase. In contrast, the tibialis anterior was neuromuscularly active at the beginning of the 249
propulsion phase, but the highest activity occured during the recovery phase. Biceps 250
femoris showed the highest neuromuscular activity at the beginning of the propulsion 251
phase reaching the peak activity at the beginning of that phase. Vastus lateralis illustrated 252
high neuromuscular activity from the very end of the recovery phase until the second half 253
of the propulsion phase and at the very end of the recovery phase, its activity increased 254
steeply. Rectus femoris exhibited two activity peaks, the first in the mid-portion of the 255
propulsion and the second in the mid-portion of the recovery phase. Adductor magnus 256
demonstrated highest neuromuscular activity mostly at the beginning of the propulsion 257
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phase and at the time when the propulsion phase switches to the recovery phase after 258
which its activity decreased evenly until the mid-portion of the recovery phase. Gluteus 259
medius showed the highest neuromuscular activity during the first half of the propulsion 260
phase and during the mid-portion of the recovery phase.Gluteus maximus neuromuscular 261
activity was the highest at the beginning of the propulsion phase until the final parts of 262
the phase and again during the latter half of the recovery phase.
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The results of the correlation and regression coefficient analyses are presented in Tables 264
3-5. The activity of the gluteus maximus during the whole recovery phase was negatively 265
correlated with the skating speed (r=-0.651, p=0.022, β=-0.08). Additionally, a similar 266
correlation was found during the second half of the recovery phase (r=-0.701, p=0.011, 267
β=-0.05). Coactivity between gluteus maximus and rectus femoris during the recovery 268
phase correlated negatively with skating speed (r=-0.786, p=0.002, β=-3.26).
269
Discussion and Implications 270
In this study, we characterised lower limb muscle activity patterns in near maximal speed 271
ice-hockey skating in highly trained players and examined the associations between 272
muscle activities and joint kinematics with skating speed. In general, uniarticular hip, 273
knee and ankle extensors showed high neuromuscular activity during the propulsion 274
phase whereas ankle dorsiflexor showed high activity during the recovery phase. In 275
contrast to our hypothesis, no significant associations were observed between the knee or 276
hip joint sagittal plane kinematics and skating speed. Analysis of the association between 277
muscle activities and skating speed showed a negative correlation between gluteus 278
maximus activity during the recovery phase and skating speed. In support of this finding, 279
a low co-activity of gluteus maximus and rectus femoris during the recovery phase was 280
associated with faster skating speed. These findings were in line with our hypothesis of 281
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fast hip flexion during the recovery phase being beneficial for achieving fast skating speed 282
as low activity of hip flexion antagonist may facilitate fast hip flexion. However, we did 283
not observe further significant correlations between muscle activities and skating speed 284
which contradicted our hypothesis. Overall, these findings suggest that muscle activities 285
during the recovery phase may be important technical factors related to motor control 286
helping a player to achieve fast skating speed providing a potential target for training 287
interventions.
288
Muscle activity patterns during the maximal skating phase 289
In this study, muscle activity patterns were evaluated for eight major lower limb muscles 290
during the maximal skating phase in high-level players. Soleus, vastus lateralis, gluteus 291
maximus, gluteus medius, and rectus femoris were highly active during the propulsion 292
phase, a phase during which the extension of the lower limb occurs. In contrast, adductor 293
magnus and tibialis anterior were noted to be involved during the recovery phase.
294
Additionally, rectus femoris showed high levels of activity during both the propulsion 295
phase when the knee and hip were extending and during the recovery phase when the hip 296
and knee were flexing. A similar activity profile with two distinct activity periods was 297
found for the gluteus medius. The first activity period occurred during the propulsion 298
phase and the second peak occurred during the recovery phase. These two periods of 299
gluteus medius activation are probably related to the stabilization of the pelvis by 300
increasing hip joint stiffness in the frontal plane (propulsion) and positioning the leg in 301
preparation for the propulsion phase (recovery). In addition, the muscle may assist 302
propulsion by abducting the hip in the propulsion phase.
303
The timing of the adductor magnus activity suggests that adduction of the hip initiates the 304
recovery phase. Adductor magnus is known to play an important role at the beginning of 305
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the recovery phase during hip adduction. (Kiel & Kaiser, 2021) Additionally, the adductor 306
magnus seems to support the main hip flexor muscles during the hip flexion. It has been 307
reported that the activation level of the adductor magnus increases at higher skating speed 308
(Chang et al., 2009). When skating speed increases, propulsion needs to be directed more 309
laterally as compared to the acceleration phase (Pearsall et al., 2000; Haché 2002), which 310
sets higher demands on the adductor muscles to work eccentrically during the end of the 311
propulsion phase and concentrically at the beginning of the recovery phase. Proper hip 312
adduction during the recovery phase ensures the optimal length of the stride whereas 313
insufficient adduction may shorten the propulsion and limit the skating speed (Chang et 314
al., 2009). Rectus femoris may possess a double role during the skating cycle. Firstly, it 315
may take part in the propulsion phase by extending the knee. Secondly, during the 316
recovery phase, the rectus femoris can flex the hip along with other hip flexor muscles.
317
Rectus femoris is a knee extensor and a hip flexor muscle. We observed similar activation 318
of the muscle in both propulsion (knee and hip are extending) and in recovery (knee and 319
hip are flexing) phases with a decrease in activation between the phases. The finding 320
shows that rectus femoris is used for both knee extension and hip flexion in ice-hockey 321
skating. However, due to concomitant knee and hip extension and flexion, the length 322
changes in rectus femoris muscle may be limited during these activation peaks allowing 323
the muscle to operate close to isometric conditions. Similarly, to the situation with rectus 324
femoris, gluteus medius shows high activity during both the propulsion and recovery 325
phases. Gluteus medius can offer support and balance for the hip joint during the 326
propulsion phase. Furthermore, gluteus medius acts as an antagonist for the adductor 327
magnus during the hip adduction; thus eccentric activation occurs in the middle of the 328
recovery phase while controlling the hip adduction. Tibialis anterior is an ankle 329
dorsiflexor and it needs to be activated during the recovery phase. If dorsiflexion of the 330
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ankle is insufficient, the front part of the skate blade hits the ice first, which may increase 331
the friction between the skate and the ice thus limiting the skating capability and even 332
causing the skater to fall. The activity of the major hip and knee extensor muscles (vastus 333
lateralis and gluteus maximus) begins at the end of the recovery phase by pre-activity.
334
When the skate hits the ice, it can be assumed that muscles need initially to work 335
isometrically to acquire the proper gliding position while in the gliding phase (beginning 336
of the propulsion phase) there is a rapid extension of the joint.
337
Individual neuromuscular activities are presented in Figure 4. The timing of muscle 338
activity of vastus lateralis, gluteus maximus, and soleus showed small between- 339
participant variability (i.e. consistent timing of the maximum and minimum muscle 340
activation). In contrast, there was greater between-participant variability in biceps 341
femoris, rectus femoris, and gluteus medius. For instance, biceps femoris of participant 342
12 showed relatively small alterations in the activity during the cycle compared to other 343
participants. Rectus femoris of participant 1 did not show a similar increase in the activity 344
during the recovery phase than other participants. In contrast, the extensive activity of the 345
rectus femoris compared to gluteus maximus was noticed in participants 3 and 4.
346
Interestingly participant 3 had the second-worst mean time of the five 30 m skating 347
sprints. Participant 12 had the fastest average 30-meter skating time and when observing 348
Figure 4, both rectus femoris and gluteus maximus showed high activity during the 349
propulsion phase. These observations need to be put into the context of qualitative 350
observations from single participants but may suggest that motor skill and muscle 351
coordination are essential factors for ice-hockey skating performance.
352
Associations between skating speed, muscle activity, and kinematics 353
16
Lower activity of the gluteus maximus and lower coactivity of the gluteus maximus and 354
rectus femoris during the recovery phase were found to be associated with faster skating 355
speed. During the recovery phase, the hip flexes rapidly, and relaxation of the gluteus 356
maximus may enable the skater to execute greater and more rapid hip flexion, which may 357
help the skater to reach a higher skating speed. Gluteus maximus muscle is mainly a hip 358
extensor muscle and an antagonist muscle for hip flexion (Krause et al., 2020). In fact, it 359
has been found that high-level players flex the hip more quickly than their lower-level 360
counterparts (Robbins et al., 2021). Furthermore, earlier studies have shown that the 361
optimal coactivation between agonist and antagonist muscles enables a better function of 362
the muscles i.e. a more favourable muscle activation pattern and effective movement 363
(Latash, 2018).
364
Limitations and suggestions for future studies 365
As in any correlation-based study, the number of observations is critical in identifying 366
associations between variables and for accurate estimates of the strength of the 367
associations. Due to acute injuries and technical problems we were not able to include the 368
sample size that was calculated to be sufficient based on a priory sample size calculations.
369
Because of the limited number of participants and their rather homogeneous nature (all 370
were high-level ice-hockey players), we may not have observed all potentially important 371
associations between skating speed and muscle activities. On the other hand, some 372
potentially coincidental correlations were not detected. The identified statistically 373
significant correlations, therefore, reflect the strongest associations observed in this 374
dataset and serve as a starting point for future studies. In this study, kinematics were 375
available only in the sagittal plane. We do not consider this as a limitation regarding the 376
knee joint as it is common to assume the knee to function as a 1 degree of freedom hinge 377
joint as most of the movement is in the sagittal plane. However, measuring kinematics 378
17
only in the sagittal plane prevented us from examining potentially important factors 379
associated with the hip joint motion in which frontal plane movement is significant. In 380
this study, maximum voluntary isometric contractions (MVICs) were used to normalize 381
the EMG data. It is possible that some participants were not able to maximally activate 382
their muscles during these tasks and thus the results (Fig. 3) should not be viewed to 383
directly indicate the percentage of maximal muscle activation but rather the percentage 384
of activity compared to the one measured during maximal effort isometric task.
385
In the future, the results of the current study should be replicated with larger sample size 386
and with 3D kinematics measurements. In addition, the potential causality of the observed 387
associations should be investigated in an intervention study. Moreover, in the future, the 388
studies of the forward skating kinematics during fatigue as well as the muscle activations 389
and kinematics involved in backward skating, crossover skating, and different turns and 390
pivots would be beneficial to develop skating skills more comprehensively in ice-hockey 391
players. These kinds of studies would offer useful knowledge to develop ice-hockey as a 392
sport and help ice-hockey players improve their skills.
393
Practical implications 394
In this study, it was found that improper co-activity of agonist and antagonist muscles 395
may limit skating performance. Therefore, coaches need to understand the role of each 396
muscle during the different phases of the skating cycle and their function as agonists or 397
antagonists while the skater is in motion. These concepts should be also conveyed to the 398
players through specific motor skill training exercises performed either on or off the ice 399
to teach the players to activate and deactivate the muscles in the optimal order and time.
400
Here we also described muscle activity patterns of eight lower limb muscles relevant for 401
skating. The data can be useful for improving the basic understanding of the neuro- 402
18
muscular function during ice-hockey skating with potential implications on the design of 403
strength training routines or drills. For example knowing that vastus lateralis, gluteus 404
maximus, and soleus are highly active during the propulsion phase can help design a 405
functional exercise aiming to improve propulsion force. Based on the results the exercise 406
should highly activate at least vastus lateralis, gluteus maximus, and soleus in addition to 407
replicating the kinematic pattern observed during the propulsion.
408
Conclusion 409
It is concluded that muscle activity patterns (timing or magnitude) in the recovery phase 410
of the skating cycle seem to play an important role in achieving fast skating speed. The 411
novel finding in this study is that not only the powerful knee and hip extension during the 412
propulsion phase but also the ability to deactivate the gluteus maximus muscle during the 413
recovery phase appears to be important for achieving the highest possible skating speed.
414
This study provides practitioners with an overview of lower limb muscle activity patterns 415
during near-maximal speed skating and highlights the importance of considering also the 416
recovery phase muscle function, in addition to the propulsion phase, when developing 417
training methods used to develop maximal skating speed.
418
Acknowledgments 419
This work was supported by the European Regional Developments Fund and the 420
University of Eastern Finland under the project: Human measurement and analysis - 421
research and innovation laboratories (HUMEA, project identifiers: A73200 and A73241).
422
The authors thank Markku Keinänen (Tuplajäät Oy, Kuopio Finland) to offer facilities 423
for on-ice data collection and all participants for their excellent co-operation.
424
Disclosure statement 425
19
Sami Kaartinen is the co-founder and head of R&D of the company Pro Prospect that 426
provides ice-hockey coaching solutions. He is also a strength and conditioning coach for 427
the ice-hockey team KalPa Hockey (Kuopio, Finland).
428 429
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Table 1. Descriptive spatio-temporal parameters of the maximal 30-meter forward skating sprints (N=12).
Parameter (unit) Mean ± SD
30 m time (s) 4.14 ± 0.08
Skating speed15-30 m (m/s) 8.39 ± 0.12 Skating cycle frequency (cycles/s) 1.64 ± 0.14 Recovery phase proportion (% of cycle) 42 ± 4 Distance travelled during the recovery phase (m) 2.15 ± 0.27
Skating speed was measured as the average speed of the last 15 meters of the sprint. Skating cycle frequency, recovery phase proportion and distance travelled during the recovery phase were determined from skating cycles taken during the last 15 meters of the sprint.
22 Table 2. Normalized neuromuscular activity during the propulsion and recovery phases (N=12).
Muscle Propulsion phase Recovery phase
(Mean ± SD) (Mean ± SD)
Soleus 68.5 ± 26.2 18.4 ± 19.6
Tibialis anterior 25.0 ± 8.6 39.2 ± 12.9
Bicep femoris 31.9 ± 18.2 14.6 ± 6.8
Vastus lateralis 82.5 ± 28.7 15.4 ± 8.0
Rectus femoris 46.9 ± 13.9 41.9 ± 15.1
Adductor magnus 19.5 ± 27.2 17.9 ± 7.2
Gluteus medius 54.7 ± 23.6 35.3 ± 29.0
Gluteus maximus 52.3 ± 24.1 24.7 ± 13.3
The values represent mean muscle activities normalized to activities measured during maximal isometric voluntary contractions.
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Table 3. Correlation (r) and regression (β) coefficients (and their p-value) between the dependent variable (skating speed15-30 m) and the independent variables (neuromuscular activity) during the entire propulsion phase and separately for the early (0-33%), mid (33-66%) and late (66-100%) subphases of the propulsion.
Propulsion
Muscle Entire phase 0-33% 33-67% 67-100%
r p β (95% CI) r p β (95% CI) r p β (95% CI) r p β (95% CI)
SOL -0.284 0.371 -0.02 (-0.60;0.20) -0.452 0.140 -0.03 (-0.70; 0.10) -0.046 0.886 0.00 (-0.50; 0.50) -0.223 0.486 -0.01 (-0.40; 0.20) TA 0.157 0.626 0.03 (-1.00; 1.60) -0.160 0.620 0.02 (-0.70; 1.10) -0.227 0.479 0.03 (-0.60; 1.20) -0.058 0.857 -0.01 (-1.10; 0.90) RF -0.132 0.684 -0.02 (-1.00; 0.70) -0.099 0.760 -0.01 (-0.60; 0.40) -0.347 0.269 -0.03 (-0.90; 0.30) -0.153 0.635 0.01 (-0.50; 0.70) VL 0.080 0.805 0.00 (-0.40; 0.50) -0.009 0.978 0.01 (-0.30; 0.30) -0.159 0.622 0.01 (-0.30; 0.40) 0.092 0.776 0.01 (-0.40; 0.60) BF 0.199 0.536 0.02 (-0.50; 0.80) 0.165 0.609 0.01 (-0.30; 0.50) 0.189 0.556 0.01 (-0.40; 0.70) 0.218 0.496 0.04 (-0.80; 1.50) AM 0.153 0.636 0.01 (-0.03; 0.05) 0.157 0.625 0.01 (-0.03; 0.04) 0.125 0.700 0.01 (-0.04; 0.06) 0.169 0.600 0.01 (-0.03; 0.06) GlutMax 0.269 0.398 -0.02 (-0.07; 0.03) -0.378 0.226 -0.02 (-0.05; 0.01) -0.202 0.529 -0.01 (-0.05; 0.03) 0.013 0.967 0.00 (-0.09; 0.09) GlutMed 0.053 0.869 0.00 (-0.05; 0.05) -0.172 0.592 0.01 (-0.02; 0.04) -0.414 0.181 -0.03 (-0.09; 0.02) 0.230 0.471 0.02 (-0.03; 0.06) GlutMax/RF -0.065 0.840 -0.17 (-1.99; 1.65) -0,289 0.362 -0.56 (-1.88; 7.50) 0.051 0.874 0.13 (-1.67; 1.93) 0.147 0.648 0.36 (-1.34; 2.06) VL/BF -0.221 0.490 -0.21 (-0.85; 0.44) -0.200 0.532 -0.19 (-0.84; 0.46) -0.096 0.767 -0.05 (-0.40; 0.31) -0.193 0.547 -0.19 (-0.89; 0.50) TA/SOL 0.136 0.673 0.97 (-4.00; 5.94) 0.360 0.250 1.26 (-1.04; 3.55) 0.133 0.681 0.45 (-1.93; 2.84) -0.073 0.823 -0.20 (-2.15; 1.75) AM/GlutMed 0.119 0.712 0.47 (-2.31; 3.25) 0.134 0.677 0.50 (-2.09; 3.09) 0.119 0.712 0.49 (-2.41; 3.40) -0.017 0.958 -0.04 (-1.56; 1.49) SOL, soleus; TA, tibialis anterior; RF, rectus femoris; VL, vastus lateralis; BF, biceps femoris; AM, adductor magnus; GlutMax, gluteus maximus; GlutMed, gluteus medius; GlutMax/RF, activity ratio between gluteus maximus and rectus femoris; VL/BF, activity ratio between vastus lateralis and biceps femoris; TA/SOL, activity ratio between tibialis anterior and soleus;
AM/GlutMed, activity ratio between adductor magnus and gluteus medius.
24
Table 4. Correlation (r) and regression (β) coefficients (and their p-value) between the dependent variable (skating speed15-30 m) and the independent variables (neuromuscular activity) during the entire recovery phase and separately for the early (0-50%), late (51-100%) subphases of the recovery phase.
Recovery
Muscle Entire phase 0-50% 50-100%
r p β (95% CI) r p β (95% CI) r p β (95% CI)
SOL 0.105 0.745 0.02 (-1.00; 1.40) -0.091 0.779 0.01 (-0.70; 0.90) 0.105 0.745 0.03 (-1.40; 2.00) TA 0.130 0.688 0.02 (-0.70; 1.10) 0.132 0.682 0.01 (-0.60; 0.80) 0.096 0.766 0.01 (-0.90; 1.10) RF 0.320 0.310 0.04 (-0.40; 1.10) 0.270 0.396 0.02 (-0.30; 0.80) 0.210 0.512 0.02 (-0.40; 0.80) VL -0.143 0.658 -0.03 (-1.80; 1.20) -0.066 0.838 -0.03 (-3.90; 3.30) -0.144 0.655 -0.02 (-1.00; 0.60) BF 0.408 0.499 0.10 (-0.60; 2.60) 0.265 0.406 0.07 (-1.00; 2.30) 0.491 0.105 0.10 (-0.30; 2.30) AM 0.191 0.551 0.04 (-0.12; 0.21) 0.142 0.659 0.02 (-0.09; 0.13) 0.162 0.614 0.04 (-0.12; 0.20) GlutMax -0.651 0.022 -0.08 (-0.15; -0.01) -0.178 0.580 -0.03 (-0.13; 0.08) -0.701 0.011 -0.05 (-0.09; -0.01) GlutMed 0.243 0.446 0.01 (-0.03; 0.05) 0.147 0.684 0.01 (-0.03; 0.05) 0.330 0.295 0.02 (-0.02; 0.06) GlutMax/RF -0.786 0.002 -3.26 (-5.07; -1.45) -0.428 0.165 -4.63 (-11.51; 2.25) -0.620 0.032 -1.36 (-2.58; -0.15) VL/BF -0.349 0.266 -0.83 (-2.41; 0.74) -0.284 0.371 -0.98 (-3.32; 1.36) -0.268 0.400 -0.39 (-1.37; 0.59) TA/SOL 0.130 0.688 0.02 (-0.70; 1.10) -0.122 0.705 -0.13 (-0.87; 0.61) -0.217 0.498 -0.25 (-1.04; 0.54) AM/GlutMed 0.020 0.951 0.07 (-2.40; 2.54) 0.199 0.534 0.32 (-0.78; 1.41) 0.006 0.986 0.04 (-4.49; 4.56)
SOL, soleus; TA, tibialis anterior; RF, rectus femoris; VL, vastus lateralis; BF, biceps femoris; AM, adductor magnus; GlutMax, gluteus maximus; GlutMed, gluteus medius; GlutMax/RF, activity ratio between gluteus maximus and rectus femoris; VL/BF, activity ratio between vastus lateralis and biceps femoris; TA/SOL, activity ratio between tibialis anterior and soleus;
AM/GlutMed, activity ratio between adductor magnus and gluteus medius.
Table 5. Correlation (r) and regression (β) coefficients (and their p-value) between the dependent variable (skating speed15-30 m) and the independent variables (knee and hip kinematics) during different phases of the skating cycle.
Kinematic variable r p β (95% CI)
Knee flexion at start of the propulsion phase 0.067 0.845 0.00 (-0.04; 0.05) Knee flexion at start of the recovery phase -0.197 0.561 -0.01 (-0.07; 0.04) Knee ROM during the recovery phase 0.263 0.435 0.01 (-0.03; 0.05) Knee ROM during the propulsion phase 0.239 0.480 0.02 (-0.04; 0.07) Hip flexion at start of the propulsion phase -0.271 0.420 -0.05 (-0.17; 0.08) Hip flexion at start of the recovery phase 0.517 0.104 0.15 (-0.04; 0.33) Hip ROM during the recovery phase -0.409 0.211 -0.07 (-0.18; 0.05) Hip ROM during the propulsion phase -0.502 0.116 -0.08 (-0.20; 0.03)
25 Figure captions
Figure 1. Camera and split mark locations for measuring skating speed during the final 15 meters. Above, a screenshot from the video recording with 15- and 30-meter marks and photocells highlighted. Below, a schematic of the measurement setup showing the camera parallax correction considered in the location of the split time marks, The camera was located in the middle of the 30-meter sprint, 16 meters from the line of skating with its field of view perpendicular to the skating direction. The 30-meter mark was positioned at a distance of 29.06 meters from the starting line to account for cameral parallax.
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Figure 2. Average sagittal hip and knee joint angular changes during the whole skating cycle. The solid line represents the mean value of all skaters and the shaded area represents standard deviation. The area on the left side of the dotted vertical line represents the propulsion phase and on the right side the recovery phase.
Figure 3. Muscle activities during the whole skating cycle. Activities are normalized to maximal activity obtained in maximal isometric contractions. The solid line represents the mean value of all participants and the shaded area represents the standard deviation. The area which is located on the left side of the dotted vertical line represents the propulsion phase and the right side the recovery phase.
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Figure 4. Heat map of muscle activities for each participant and muscle during maximal skating phase (15-30 meters of maximal sprint). Activities were scaled individually between 0 and 100% to highlight parts of the skating cycle with high and low muscle activities relative to the range of muscle activities observed for the individual.
28