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Research in Sports Medicine: An International Journal Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gspm20
The Effect of Unilateral Hockey Bag Carriage on the Muscle Activities of the Trunk and Lower Limb of Young Healthy Males During Gait a
a
Liam Patrick Corrigan & Jing Xian Li a
School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada Published online: 06 Jan 2014.
To cite this article: Liam Patrick Corrigan & Jing Xian Li (2014) The Effect of Unilateral Hockey Bag Carriage on the Muscle Activities of the Trunk and Lower Limb of Young Healthy Males During Gait, Research in Sports Medicine: An International Journal, 22:1, 23-35, DOI: 10.1080/15438627.2013.852094 To link to this article: http://dx.doi.org/10.1080/15438627.2013.852094
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions
Research in Sports Medicine, 22:23–35, 2014 Copyright © Taylor & Francis Group, LLC ISSN: 1543-8627 print/1543-8635 online DOI: 10.1080/15438627.2013.852094
The Effect of Unilateral Hockey Bag Carriage on the Muscle Activities of the Trunk and Lower Limb of Young Healthy Males During Gait
Downloaded by [Uppsala universitetsbibliotek] at 14:08 18 November 2014
LIAM PATRICK CORRIGAN and JING XIAN LI School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
This study explored the trunk and lower limb muscle activity of 15 males during unilateral hockey bag carriage of 10%, 20%, and 30% of one’s body weight (BW) compared with without a load during walking. The electromyography (EMG) activities of the left and right erector spinae, rectus abdominis, gluteus maximus, rectus femoris, vastus medialis, biceps femoris, semitendinosus, and the medial gastrocnemius were studied. A 2-way repeated measures analysis of variance (ANOVA) was used to examine the differences between the load weight and muscle side. Results showed significant increase in peak EMG and iEMG in the carrying side vastus medialis, rectus abdominis, semitendinosus, and gastrocnemii ( p < 0.05) at the 30% BW load. The noncarrying side showed a greater peak EMG in the semitendinosus and rectus femoris at the 30% BW load when compared with the carrying side ( p < 0.05). It was concluded that unilateral hockey bag carriage is similar to both backpack and side-pack carriage styles. KEYWORDS EMG, unilateral, load carriage, asymmetrical load carriage, walking
INTRODUCTION Load carrying with backpack, side-packs, and front packs have been found to alter the gait, posture, trunk and lower limb biomechanics, and muscle activities of the human body (Cook & Neumann, 1987; Knapik, Harman, &
Received 14 January 2013; accepted 30 July 2013. Address correspondence to Jing Xian Li, School of Human Kinetics, University of Ottawa, 75 Laurier Avenue East, Ottawa, Ontario K1S 5S9, Canada. E-mail: [email protected] 23
Downloaded by [Uppsala universitetsbibliotek] at 14:08 18 November 2014
24
L. P. Corrigan and J. X. Li
Reynolds, 1996; Motmans, Tomlow, & Vissers, 2006; Smith, Ashton, Bohl, Clark, Metheny, & Klassen, 2006). Many studies indicate that the more drastic and perhaps the more injury prone method of load carriage is unilateral (side-pack) carrying (DeVita, Hong, & Hamill, 1991; Fowler, Rodacki, & Rodacki, 2006; Motmans et al., 2006). Sports such as golf, football, soccer, baseball, and ice hockey all require participants to carry their equipment to the field of play for the recreational athlete. The hockey bag, when full of equipment, is large in volume and weight. Its weight is considerably more than the bags of other sports. A survey of 33 participants at the University of Ottawa’s Sports Complex arena conducted by our research team showed that male and female, university-aged students between 19 and 23 yrs. (avg. = 20.63 ± 1.53) carry hockey bags with an average of 18.77 ± 5.13% body weight (BW) over one shoulder and walk distances of average 641.67 m ± 687.67 m. In the same survey, the maximum weight of a hockey bag recorded was by a 21-year-old male goaltender with a weight that equaled 33.29% of his total body weight (Corrigan, Law, & Law, 2010). Unilateral load carriage is commonly found in ice-hockey players carrying their equipment. It was also found that during play in hockey, participants perform repetitive or continuous forward trunk flexion. This particular movement in addition to the chronic and repetitive forward flexion with load carriage may lead to injury involving the spinal column (Baranto, Hellström, Cederlund, Nyman, & Swärd, 2009; Mountain, 2002). Biomechanical study of the unilateral load carriage use loads up to 20% of one’s BW (Crosbie, Flynn, & Rutter, 1994; DeVita et al., 1991; Fowler et al., 2006; Gillette, Stevermer, Miller, Meardon, & Schwab, 2010; Lee & Li, in press; Motmans et al., 2006). Muscle activity of the trunk and the lower limb, however, during walking while unilaterally carrying a load more than 20% of carrier’s BW is unknown. Therefore, a comprehensive study on temporospatial kinematics and muscle activities of the trunk and lower limb during walking with a hockey bag of different weight will add to our understanding of the impact of unilateral load carrying on the biomechanical responses. The purpose of the study was to investigate the trunk and lower limb muscle activity during heavy unilateral load carriage. After examining previous EMG studies on load carriage, it was hypothesized that the muscle activity of the trunk and lower limb would be increased with the added load. It was also hypothesized that the muscle activity would be higher in the noncarrying side as the body adjusts to the one-sided load in an effort to maintain balance.
METHODOLOGY Hockey Bag One standard, Reebok hockey bag (0.11 m3 ) was used in this study. Insulation was placed in the hockey bag to allow for a full volume, and
Downloaded by [Uppsala universitetsbibliotek] at 14:08 18 November 2014
Effect of Unilateral Hockey Bag Carriage
25
FIGURE 1 The hockey bag is shown with styrofoam and designated sections along the center for the placement of metal weights. (Color figure available online).
metal weights were positioned into the hockey bag to account for the load weight of 10%, 20%, and 30% of the subject’s BW. The insulation and metal weights allowed for an equal distribution of weight and to limit any shifting or movement of the weights during walking (Figure 1).
Walking Path The walking path was located in a laboratory and had smooth rubber flooring. It was 8 m in length and was surrounded by infrared motion analysis cameras that made up a volume to capture two gait cycles (right and left). In the middle of the pathway were four force plates, placed in a staggered position.
Instrumentation The instruments used to capture temporospatial kinematic data included 10 infrared, high speed, Vicon optical cameras, recording at 100Hz (Vicon MX-13, Oxford Metrics, Oxford, UK). Four force plates were used to aid in the detection of foot contact (two models 9286AA, Kistler Instruments Corp., Winterthur, Switzerland; two models FP 4060-08, Bertec Corporation, Columbus, OH, USA). A 16-channel EMG system (DS-B04, BagnoliTM 16 Desktop EMG system, DelsysInc., Boston, MA, USA) was used to record muscle activity in 16 muscles at 1000 Hz.
Participants The participants were 15 male hockey players (23.4 ± 2.63 years) with an average of 16.56 ± 4.92 years of ice hockey experience and, therefore, hockey bag carriage experience. All but one of the participants carried the bag on their dominant right shoulder (Figure 2). For the one participant who
Downloaded by [Uppsala universitetsbibliotek] at 14:08 18 November 2014
26
L. P. Corrigan and J. X. Li
FIGURE 2 A display of the style (posterior-lateral) during hockey bag carriage. (Color figure available online).
carried his bag on his dominant left, the left gait cycle and left muscles were used for analysis and pooled in with the right of the others. It is in this way that the “right” muscles will be defined as the carrying side.
Data Collection The participants were asked to come to the biomechanics lab at the University of Ottawa campus once for data collection. The participant read and signed a consent form approved by the University of Ottawa Health Sciences and Science Research Ethics Board. A questionnaire regarding the subject’s experience with hockey bag load carriage was completed at this time. Participants wore their own gym shorts and gym shirt, with regular running shoes. Participants warmed up on a stationary bicycle and stretched before executing the trials in the experiment. For EMG sensor placement, the skin overlying the following muscle bellies (left and right) were shaven and cleaned with alcohol wipes: erector spinae (ES; located at the level of the L4–L5 interspace and 2 cm away from the midline), rectus abdominis (RA; located on the belly of the muscle just below the umbilicus), rectus femoris (RF), vastus medialis (VM), biceps femoris (BF), semitendinosus (ST), medial gastrocnemius (GAS), and gluteus maximus (GM), with the reference electrode placed on the skin overlying the left olecranon. Retroreflective markers were attached to the anatomical landmarks of the toe, heel, and lateral and medial malleoli of both feet. This allowed for the measuring of stride length, stride width, and single and double support time. The participant performed 3–5 practice trials of each condition to maintain a normal gait unaffected by the increased attention. The participant
Effect of Unilateral Hockey Bag Carriage
27
was asked to carry the hockey bag over his self-chosen, dominant shoulder in a manner that he would carry his own hockey bag and to walk the 8 m through the testing area. The walking speed of the participants was self-determined and at a natural pace. Motion was captured by 10 VICON MX-13 cameras during four trials of each condition of 0% BW (no load), 10% BW load, 20% BW, and 30% BW. The total number of trials was 16. The condition order for each participant was randomly selected from one of the scenarios in a Latin Square design.
Downloaded by [Uppsala universitetsbibliotek] at 14:08 18 November 2014
Data Processing Movement was analyzed for one gait cycle and averaged from subject’s four trials of each condition. All subjects were then averaged to give representations of a normal population. Data were expressed as percent of the dominant side gait cycle. Foot contact was identified visually while inspecting the labeled markers of the heel, toe, and malleoli on VICON Nexus software (v1.3) and through force plate data signals. Measurements included stride length, stride width, single leg support, and double support phase. These measurements were determined through formulas on SMART Analyzer (BTS Software, Italy). The EMG data were processed with a cut-off frequency of 4 Hz, rectified using the temporal mean, and filtered using a single, low-pass Butterworth filter. The filtered EMG data were then normalized to 100% of the gait cycle and plotted as a percentage of the peak amplitude in the average of the control condition. As a result, data for the peak EMG activity are shown as a percentage. Integrated EMG (iEMG) was also examined. The iEMG were calculated using the normalized EMG with the following formula in Microsoft Excel (2011): area = (xi+1 − xi ) × 1/2[f (xi+1 ) + f (xi )], where xi represents an initial percent value in the gait cycle and xi+1 represents the following percent value. The f (x) are the y-values or the normalized peak EMG value for the given x coordinate. The formula is an adaptation of the sum of area = base × height/2.
Statistical Analysis A two-way repeated measures ANOVA was used to examine the differences between the repeated factor of hockey bag load weight and muscle side. When significance was found, a Bonferroni post-hoc test was performed using repeated measures of t tests for load and independent t tests for differences between left and right muscles. The probability of error in all
28
L. P. Corrigan and J. X. Li
tests is presented with a p < 0.05. All analyses were performed using the statistical software package SPSS 20.0 for Macintosh (SPSS Inc., Chicago, IL, USA).
RESULTS All measurements and results are expressed as a mean with standard error (SE).
Downloaded by [Uppsala universitetsbibliotek] at 14:08 18 November 2014
Temporospatial Variables The carrying side is defined as the right side, while the noncarrying side is defined as the left in this study. No differences in the measurements were observed between left and right gait cycle in the study. As a result, only the right gait cycle was used for analysis (Table 1). The stride length had shown to decrease as the load increased, with significance in the 30% BW condition when compared to the control (p = 0.002). The stride width had shown to increase as load increased, with significance in the 30% BW condition when compared to the control (p = 0.001). Finally, the double support duration increased and single support decreased as load weight was increased, with the largest significant difference being from the control to 30% BW (p < 0.001).
Peak Magnitude of EMG and iEMG The results of the peak EMG and the iEMG are illustrated in Figure 3. The peak EMG of the right RA significantly increased by 1.86 times in 30% BW condition compared with no load condition (p ≤ 0.05). Similar increases were found in the right RA for the iEMG, being significantly greater in the 30% BW load compared with all other conditions (p ≤ 0.05). The right VM was significantly larger in peak EMG for the 30% BW condition (2.08 ± 0.27) when compared with all other conditions (p ≤ 0.05). TABLE 1 Mean and Standard Error of the Tempospatial Variables During Walking With a Unilateral Hockey Bag. Measurements are Compared With the Control Condition of No Load. Load % BW 0 10 20 30 ∗
Stride length (m)
p-value
± ± ± ±
– 0.211 0.117 0.002
1.51 1.46 1.45 1.39
0.03 0.03 0.03 0.03∗
Stride width (cm) 10.6 11.2 13.1 16.3
p < 0.05, vs 0% BW load condition.
± ± ± ±
Single Double support (% of support (% of p-value a gait cycle) p-value a gait cycle) p-value
0.5 – 0.7 1.0 0.9 0.053 1.1∗
Research in Sports Medicine: An International Journal Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gspm20
The Effect of Unilateral Hockey Bag Carriage on the Muscle Activities of the Trunk and Lower Limb of Young Healthy Males During Gait a
a
Liam Patrick Corrigan & Jing Xian Li a
School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada Published online: 06 Jan 2014.
To cite this article: Liam Patrick Corrigan & Jing Xian Li (2014) The Effect of Unilateral Hockey Bag Carriage on the Muscle Activities of the Trunk and Lower Limb of Young Healthy Males During Gait, Research in Sports Medicine: An International Journal, 22:1, 23-35, DOI: 10.1080/15438627.2013.852094 To link to this article: http://dx.doi.org/10.1080/15438627.2013.852094
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions
Research in Sports Medicine, 22:23–35, 2014 Copyright © Taylor & Francis Group, LLC ISSN: 1543-8627 print/1543-8635 online DOI: 10.1080/15438627.2013.852094
The Effect of Unilateral Hockey Bag Carriage on the Muscle Activities of the Trunk and Lower Limb of Young Healthy Males During Gait
Downloaded by [Uppsala universitetsbibliotek] at 14:08 18 November 2014
LIAM PATRICK CORRIGAN and JING XIAN LI School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
This study explored the trunk and lower limb muscle activity of 15 males during unilateral hockey bag carriage of 10%, 20%, and 30% of one’s body weight (BW) compared with without a load during walking. The electromyography (EMG) activities of the left and right erector spinae, rectus abdominis, gluteus maximus, rectus femoris, vastus medialis, biceps femoris, semitendinosus, and the medial gastrocnemius were studied. A 2-way repeated measures analysis of variance (ANOVA) was used to examine the differences between the load weight and muscle side. Results showed significant increase in peak EMG and iEMG in the carrying side vastus medialis, rectus abdominis, semitendinosus, and gastrocnemii ( p < 0.05) at the 30% BW load. The noncarrying side showed a greater peak EMG in the semitendinosus and rectus femoris at the 30% BW load when compared with the carrying side ( p < 0.05). It was concluded that unilateral hockey bag carriage is similar to both backpack and side-pack carriage styles. KEYWORDS EMG, unilateral, load carriage, asymmetrical load carriage, walking
INTRODUCTION Load carrying with backpack, side-packs, and front packs have been found to alter the gait, posture, trunk and lower limb biomechanics, and muscle activities of the human body (Cook & Neumann, 1987; Knapik, Harman, &
Received 14 January 2013; accepted 30 July 2013. Address correspondence to Jing Xian Li, School of Human Kinetics, University of Ottawa, 75 Laurier Avenue East, Ottawa, Ontario K1S 5S9, Canada. E-mail: [email protected] 23
Downloaded by [Uppsala universitetsbibliotek] at 14:08 18 November 2014
24
L. P. Corrigan and J. X. Li
Reynolds, 1996; Motmans, Tomlow, & Vissers, 2006; Smith, Ashton, Bohl, Clark, Metheny, & Klassen, 2006). Many studies indicate that the more drastic and perhaps the more injury prone method of load carriage is unilateral (side-pack) carrying (DeVita, Hong, & Hamill, 1991; Fowler, Rodacki, & Rodacki, 2006; Motmans et al., 2006). Sports such as golf, football, soccer, baseball, and ice hockey all require participants to carry their equipment to the field of play for the recreational athlete. The hockey bag, when full of equipment, is large in volume and weight. Its weight is considerably more than the bags of other sports. A survey of 33 participants at the University of Ottawa’s Sports Complex arena conducted by our research team showed that male and female, university-aged students between 19 and 23 yrs. (avg. = 20.63 ± 1.53) carry hockey bags with an average of 18.77 ± 5.13% body weight (BW) over one shoulder and walk distances of average 641.67 m ± 687.67 m. In the same survey, the maximum weight of a hockey bag recorded was by a 21-year-old male goaltender with a weight that equaled 33.29% of his total body weight (Corrigan, Law, & Law, 2010). Unilateral load carriage is commonly found in ice-hockey players carrying their equipment. It was also found that during play in hockey, participants perform repetitive or continuous forward trunk flexion. This particular movement in addition to the chronic and repetitive forward flexion with load carriage may lead to injury involving the spinal column (Baranto, Hellström, Cederlund, Nyman, & Swärd, 2009; Mountain, 2002). Biomechanical study of the unilateral load carriage use loads up to 20% of one’s BW (Crosbie, Flynn, & Rutter, 1994; DeVita et al., 1991; Fowler et al., 2006; Gillette, Stevermer, Miller, Meardon, & Schwab, 2010; Lee & Li, in press; Motmans et al., 2006). Muscle activity of the trunk and the lower limb, however, during walking while unilaterally carrying a load more than 20% of carrier’s BW is unknown. Therefore, a comprehensive study on temporospatial kinematics and muscle activities of the trunk and lower limb during walking with a hockey bag of different weight will add to our understanding of the impact of unilateral load carrying on the biomechanical responses. The purpose of the study was to investigate the trunk and lower limb muscle activity during heavy unilateral load carriage. After examining previous EMG studies on load carriage, it was hypothesized that the muscle activity of the trunk and lower limb would be increased with the added load. It was also hypothesized that the muscle activity would be higher in the noncarrying side as the body adjusts to the one-sided load in an effort to maintain balance.
METHODOLOGY Hockey Bag One standard, Reebok hockey bag (0.11 m3 ) was used in this study. Insulation was placed in the hockey bag to allow for a full volume, and
Downloaded by [Uppsala universitetsbibliotek] at 14:08 18 November 2014
Effect of Unilateral Hockey Bag Carriage
25
FIGURE 1 The hockey bag is shown with styrofoam and designated sections along the center for the placement of metal weights. (Color figure available online).
metal weights were positioned into the hockey bag to account for the load weight of 10%, 20%, and 30% of the subject’s BW. The insulation and metal weights allowed for an equal distribution of weight and to limit any shifting or movement of the weights during walking (Figure 1).
Walking Path The walking path was located in a laboratory and had smooth rubber flooring. It was 8 m in length and was surrounded by infrared motion analysis cameras that made up a volume to capture two gait cycles (right and left). In the middle of the pathway were four force plates, placed in a staggered position.
Instrumentation The instruments used to capture temporospatial kinematic data included 10 infrared, high speed, Vicon optical cameras, recording at 100Hz (Vicon MX-13, Oxford Metrics, Oxford, UK). Four force plates were used to aid in the detection of foot contact (two models 9286AA, Kistler Instruments Corp., Winterthur, Switzerland; two models FP 4060-08, Bertec Corporation, Columbus, OH, USA). A 16-channel EMG system (DS-B04, BagnoliTM 16 Desktop EMG system, DelsysInc., Boston, MA, USA) was used to record muscle activity in 16 muscles at 1000 Hz.
Participants The participants were 15 male hockey players (23.4 ± 2.63 years) with an average of 16.56 ± 4.92 years of ice hockey experience and, therefore, hockey bag carriage experience. All but one of the participants carried the bag on their dominant right shoulder (Figure 2). For the one participant who
Downloaded by [Uppsala universitetsbibliotek] at 14:08 18 November 2014
26
L. P. Corrigan and J. X. Li
FIGURE 2 A display of the style (posterior-lateral) during hockey bag carriage. (Color figure available online).
carried his bag on his dominant left, the left gait cycle and left muscles were used for analysis and pooled in with the right of the others. It is in this way that the “right” muscles will be defined as the carrying side.
Data Collection The participants were asked to come to the biomechanics lab at the University of Ottawa campus once for data collection. The participant read and signed a consent form approved by the University of Ottawa Health Sciences and Science Research Ethics Board. A questionnaire regarding the subject’s experience with hockey bag load carriage was completed at this time. Participants wore their own gym shorts and gym shirt, with regular running shoes. Participants warmed up on a stationary bicycle and stretched before executing the trials in the experiment. For EMG sensor placement, the skin overlying the following muscle bellies (left and right) were shaven and cleaned with alcohol wipes: erector spinae (ES; located at the level of the L4–L5 interspace and 2 cm away from the midline), rectus abdominis (RA; located on the belly of the muscle just below the umbilicus), rectus femoris (RF), vastus medialis (VM), biceps femoris (BF), semitendinosus (ST), medial gastrocnemius (GAS), and gluteus maximus (GM), with the reference electrode placed on the skin overlying the left olecranon. Retroreflective markers were attached to the anatomical landmarks of the toe, heel, and lateral and medial malleoli of both feet. This allowed for the measuring of stride length, stride width, and single and double support time. The participant performed 3–5 practice trials of each condition to maintain a normal gait unaffected by the increased attention. The participant
Effect of Unilateral Hockey Bag Carriage
27
was asked to carry the hockey bag over his self-chosen, dominant shoulder in a manner that he would carry his own hockey bag and to walk the 8 m through the testing area. The walking speed of the participants was self-determined and at a natural pace. Motion was captured by 10 VICON MX-13 cameras during four trials of each condition of 0% BW (no load), 10% BW load, 20% BW, and 30% BW. The total number of trials was 16. The condition order for each participant was randomly selected from one of the scenarios in a Latin Square design.
Downloaded by [Uppsala universitetsbibliotek] at 14:08 18 November 2014
Data Processing Movement was analyzed for one gait cycle and averaged from subject’s four trials of each condition. All subjects were then averaged to give representations of a normal population. Data were expressed as percent of the dominant side gait cycle. Foot contact was identified visually while inspecting the labeled markers of the heel, toe, and malleoli on VICON Nexus software (v1.3) and through force plate data signals. Measurements included stride length, stride width, single leg support, and double support phase. These measurements were determined through formulas on SMART Analyzer (BTS Software, Italy). The EMG data were processed with a cut-off frequency of 4 Hz, rectified using the temporal mean, and filtered using a single, low-pass Butterworth filter. The filtered EMG data were then normalized to 100% of the gait cycle and plotted as a percentage of the peak amplitude in the average of the control condition. As a result, data for the peak EMG activity are shown as a percentage. Integrated EMG (iEMG) was also examined. The iEMG were calculated using the normalized EMG with the following formula in Microsoft Excel (2011): area = (xi+1 − xi ) × 1/2[f (xi+1 ) + f (xi )], where xi represents an initial percent value in the gait cycle and xi+1 represents the following percent value. The f (x) are the y-values or the normalized peak EMG value for the given x coordinate. The formula is an adaptation of the sum of area = base × height/2.
Statistical Analysis A two-way repeated measures ANOVA was used to examine the differences between the repeated factor of hockey bag load weight and muscle side. When significance was found, a Bonferroni post-hoc test was performed using repeated measures of t tests for load and independent t tests for differences between left and right muscles. The probability of error in all
28
L. P. Corrigan and J. X. Li
tests is presented with a p < 0.05. All analyses were performed using the statistical software package SPSS 20.0 for Macintosh (SPSS Inc., Chicago, IL, USA).
RESULTS All measurements and results are expressed as a mean with standard error (SE).
Downloaded by [Uppsala universitetsbibliotek] at 14:08 18 November 2014
Temporospatial Variables The carrying side is defined as the right side, while the noncarrying side is defined as the left in this study. No differences in the measurements were observed between left and right gait cycle in the study. As a result, only the right gait cycle was used for analysis (Table 1). The stride length had shown to decrease as the load increased, with significance in the 30% BW condition when compared to the control (p = 0.002). The stride width had shown to increase as load increased, with significance in the 30% BW condition when compared to the control (p = 0.001). Finally, the double support duration increased and single support decreased as load weight was increased, with the largest significant difference being from the control to 30% BW (p < 0.001).
Peak Magnitude of EMG and iEMG The results of the peak EMG and the iEMG are illustrated in Figure 3. The peak EMG of the right RA significantly increased by 1.86 times in 30% BW condition compared with no load condition (p ≤ 0.05). Similar increases were found in the right RA for the iEMG, being significantly greater in the 30% BW load compared with all other conditions (p ≤ 0.05). The right VM was significantly larger in peak EMG for the 30% BW condition (2.08 ± 0.27) when compared with all other conditions (p ≤ 0.05). TABLE 1 Mean and Standard Error of the Tempospatial Variables During Walking With a Unilateral Hockey Bag. Measurements are Compared With the Control Condition of No Load. Load % BW 0 10 20 30 ∗
Stride length (m)
p-value
± ± ± ±
– 0.211 0.117 0.002
1.51 1.46 1.45 1.39
0.03 0.03 0.03 0.03∗
Stride width (cm) 10.6 11.2 13.1 16.3
p < 0.05, vs 0% BW load condition.
± ± ± ±
Single Double support (% of support (% of p-value a gait cycle) p-value a gait cycle) p-value
0.5 – 0.7 1.0 0.9 0.053 1.1∗
