- Email: [email protected]
In a dynamic lifting task, the relationship between cross-sectional abdominal muscle thickness and the corresponding muscle activity is affected by the combined use of a weightlifting belt and the Valsalva maneuver
Journal of Electromyography and Kinesiology 28 (2016) 99–103
Contents lists available at ScienceDirect
Journal of Electromyography and Kinesiology journal homepage: www.elsevier.com/locate/jelekin
In a dynamic lifting task, the relationship between cross-sectional abdominal muscle thickness and the corresponding muscle activity is affected by the combined use of a weightlifting belt and the Valsalva maneuver Trevor W. Blanchard, Camille Smith, Sylvain G. Grenier ⇑ Kinesiology, School of Human Kinetics, Laurentian University, Sudbury, Ontario, Canada
a r t i c l e
i n f o
Article history: Received 6 May 2015 Received in revised form 10 March 2016 Accepted 16 March 2016
Keywords: Low-back belt Valsalva Ultrasound EMG Muscle thickness
a b s t r a c t It has been shown that under isometric conditions, as the activity of the abdominal muscles increases, the thicknesses of the muscles also increase. The purpose of this experiment was to determine whether change in muscle thickness could be used as a measure of muscle activity during a deadlift as well as determining the effect of a weightlifting belt and/or the Valsalva maneuver on the muscle thicknesses. The Transversus Abdominis (TrA) and Internal Obliques (IO) muscles were analyzed at rest and during a deadlift. Muscle thickness was measured using ultrasound imaging and muscle activity was simultaneously recorded using electromyography. Each subject performed deadlift under normal conditions, while performing the Valsalva maneuver, while wearing a weightlifting belt and while both utilizing the belt and the Valsalva maneuver. There was no relationship between change in muscle thickness and muscle activity for both the TrA and IO (R2 < 0.13 for all conditions). However it was found that the Valsalva maneuver increased abdominal muscle thickness whereas the belt limited muscle expansion; each with an increase in activity. These results indicate that ultrasound cannot be used to measure muscle activity for a deadlift and that the belt affects how the IO and TrA function together. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction The Abdominal wall is composed of three muscles from deep to superficial: the Transversus Abdominis (TrA), Internal Oblique (IO), External Oblique (EO), and the Rectus Abdominis (RA) (Stevens, 2006). These muscles are tightly bound flat muscles whose fibers run at oblique angles to one another (Brown et al., 2011). This muscle group plays a crucial role in reducing the load on the spinal column as well as increasing spinal stiffness (Brown et al., 2011; John and Beith, 2007; Lee and Kang, 2002; Richardson et al., 2002; Stevens, 2006). When the abdominal wall is activated and the glottis is closed (sealing the abdominal cavity), the intraabdominal pressure (IAP) increases due to a decrease in volume of the abdominal cavity. This increase in pressure compresses the sacroiliac joints and creates tension in the thoracolumbar fascia in turn generating stiffness (Richardson et al., 2004). Additionally, the IAP allows forces on the spine, generated by a load, to be dispersed over the torso (Brown et al., 2011). ⇑ Corresponding author. E-mail address: [email protected] (S.G. Grenier). http://dx.doi.org/10.1016/j.jelekin.2016.03.006 1050-6411/Ó 2016 Elsevier Ltd. All rights reserved.
The Valsalva maneuver is a breathing pattern that involves forced exhalation against a closed glottis thereby increasing spinal stability by increasing the IAP (Hackett and Chin-Moi Chow, 2013). Free breathing (normal breathing cycle where glottis is open) generates significantly lower intra-abdominal pressures during resistance exercises compared with the intentional or unintentional use of the Valsalva maneuver (Cresswell and Grundstrom, 1992; Harman et al., 1988; McGill and Sharrat, 1990; Williams and Lind, 1987) In addition to increased intra-abdominal pressure, the Valsalva maneuver has also been shown to increase activation of the abdominal muscles (De Troyer et al., 1990; Lee and Kang, 2002). Lumbar supports in occupational settings or, weight lifting belts in sport settings, are a widely used tool believed to allow for lifting heavier weights and preventing injury. Whereas employees often use low-back belts in jobs that require frequent and/or heavy lifting to reduce symptoms, prevent and/or treat chronic low back pain, athletes may use a weightlifting belt to help them lift heavier weights. The proposed mechanism(s) by which these belts help reduce the risk of injury (if at all) varies through the literature. These mechanisms include physically restricting the range of
100
T.W. Blanchard et al. / Journal of Electromyography and Kinesiology 28 (2016) 99–103
motion, increasing proprioception, increasing the IAP and acting as a placebo (Barron and Deurstein, 1991; Calmels et al., 2009; Cholewicki et al., 1999; van Poppel et al., 2000). In order to understand how the abdominal muscles may function to create stiffness, attempts have been made to measure the activity of the three layers of muscle. To measure deep abdominal muscle activity accurately using electromyography, the use of finewire electrodes inserted into the muscle is required (Costa et al., 2009; Hodges and Richardson, 1999; Tsao, 2008). This process is costly and uncomfortable for the subject, especially if they are required to perform movements (Costa et al., 2009; Hodges and Richardson, 1999; Tsao, 2008). Recently, studies have used ultrasound imaging to measure the change in muscle thickness in order to indirectly determine muscle activity (Bunce et al., 2002; Hodges et al., 2003; McMeeken et al., 2004; Teyhen, 2006). In addition, morphological changes in muscle have been correlated with EMG measurements in low level contractions [force up to 30% of one repetition maximum (1RM) (Bakke et al., 1992; Ferreira et al., 2004; Hodges et al., 2003; McMeeken et al., 2004)], and have been found to be a reliable method to measure muscle activity (Bunce et al., 2002). More specifically, McMeeken and colleagues compared fine wire EMG data of the TrA with synchronized ultrasound motion recordings of subjects executing the abdominal hollowing maneuver. They found a linear relationship between TrA thickness and EMG activity (McMeeken et al., 2004). Moreover, Hodges et al. fit an increasing logarithmic regression to the relationship of IO muscle thickness and TrA with their respective EMG activities (Hodges et al., 2003). Based on the current literature it is clear that the relationship between the electrical activity of a muscle and its thickness has been thoroughly researched for isometric contractions. However, the relationship between morphological changes and EMG activity in the abdominal wall muscles remains unknown for dynamic conditions. The purpose of this study is to determine if measuring the change in muscle thickness can be used to measure muscle activity and observe the effects of wearing a weightlifting belt and closing the glottis on the relationship between the IO and TrA and their electrical activity. 2. Methods 2.1. Subjects Twenty-one healthy subjects were recruited from various varsity sports teams at a Canadian University. However, the data from 10 participants was not used because during the testing process, the head of the ultrasound transducer would sometimes shift on the skin and render the images unclear and unmeasurable. Subjects were excluded from the study if they had chronic low back pain, or had experienced any type of low back injury requiring surgical intervention. Out of the eleven remaining participants, three were women and the overall mean age was 20 years. Each subject signed the informed consent and the university Ethics Review Board approved the study. 2.2. Equipment A real-time ultrasound scanner was used with a 7.5 MHz linear head transducer (Rising Medical Co Ltd., RUS-9000F) to determine muscle thickness as well as the Shimmer wireless EMG system to measure electrical muscle activity. Specifications for the Shimmer EMG system can be found in Table 1. A standard 12.7 cm (5 in.) weightlifting belt and Olympic style weightlifting equipment consisting of a 20 kg bar and bumper plates of weight appropriate (30%) to the individual’s 1RM were used for the testing procedure.
Table 1 Shimmer EMG system specifications. Current draw Gain Max signal range before clipping Frequency range Ground Input protection Connections
180 lA (leads connected) 682 4.4 mV 5–482 Hz Wilson Type Driven Ground ESD and RF/EMI filtering, Current limiting Input (+), Input ( ), Reference
2.3. Pilot studies Pilot studies confirmed that the TrA, IO and EO could be viewed and measured at once while performing a deadlift with and without a weightlifting belt in both B (bright) and M (motion) modes. In B-mode (brightness mode) ultrasound, a linear array of transducers scans a plane through the body that can be viewed as a twodimensional image. Whereas In M-mode (motion mode), pulses are emitted in quick succession – each time, a B-mode image is taken. Over time, this results in a video recording. The muscle boundaries move relative to the probe and this can be used to view structural changes over a period of 4 s. The location found to show the clearest image of the three muscles together was 25 mm anterior from the midpoint between the twelfth rib and the iliac crest of the anterolateral abdominal wall. This has been the scanning point in previous studies (Critchley and Coutts, 2002).
2.4. Testing procedure Once the subject had consented to the study, the scan point was identified and resting measurements were taken of the abdominal wall with B mode at the end of a normal inspiration with the patient in a supine position. Following resting measurements, their 1RM was determined based on discussions with the athletes after their testing sessions with the varsity strength and conditioning staff. From these results, 30% was calculated which would be the weight lifted during the exercise. To prepare for EMG measurement, the skin over the anterior superior iliac spine was shaved with a disposable razor and cleaned with an alcohol swab. Subsequently, the maximum voluntary isometric contraction (MVIC) was determined for EMG measurements by asking the participant to contract their abdominal muscles as hard as possible while lying in the supine position with legs extended as in Dankaerts et al. (2004). This group found that both MVIC and sub-MVIC contractions, using this position, had excellent within-day reliability in both intra class correlation (mean = 0.91) and standard error of measurement (mean 5%). Although participants were familiar with the exercise, and performed it as a part of regular workouts, the tester demonstrated the deadlift and the subject was instructed to practice in order to ensure proper form. They were also taught how to perform the Valsalva maneuver. After this preparation phase, the test began with a series of lift presented in random order: a control lift where the subject was asked to perform a deadlift without the use of the weightlifting belt or the Valsalva maneuver; a ‘‘Valsalva” condition where the subject executed a deadlift while utilizing the Valsalva maneuver; the ‘‘Belt” condition where the participant performed the lift while wearing the 12.7 cm weight lifting belt; and the final condition involved wearing the belt and the use of the Valsalva maneuver to perform the lift. This was referred to as the ‘‘Both” condition. In order to synchronize the Ultrasound measurements with the EMG data, the participants were instructed to suddenly contract their abdominal muscles and then suddenly relax prior to performing the deadlift. This elicited a clear reaction in both datasets and
T.W. Blanchard et al. / Journal of Electromyography and Kinesiology 28 (2016) 99–103
measurements could be processed when readings returned to normal.
101
individually, however the results were not statistically significant. A plot of the mean EMG measurements under each condition is shown in Fig. 1.
2.5. Measurement 3.2. IO thickness 2.5.1. Ultrasound The Ultrasound scanner’s M mode was used to view the change in muscle thickness for the lifts under each condition. The ‘‘Freeze” function was used to capture an image that shows the entire lift as well as the relaxation phase of the synchronization contraction. Next, the ‘‘Measure” function was used to create a calibration measurement for further processing. The images were then downloaded to a computer and ImageJ software was used to analyze the images. Based on the calibration measurements the number of pixels per millimeter was determined as well as the number of pixels per second as each image represented a 4 s time frame. The TrA and IO thicknesses were measured at every 0.25 s after the relaxation phase of the contraction prior to the lift. These measurements were recorded for statistical analysis. 2.5.2. EMG The EMG was recorded with a sampling rate of 1024 Hz. Ag/AgCl disc shaped electrodes were placed horizontally over the anterior superior iliac spine 25 mm apart. The ground was directly lateral to this position. The electrode placement was according to The ABC of EMG by Konrad (2005). The raw signal was rectified and filtered using a 4th order lowpass Butterworth filter with a cut off frequency of 2.5 Hz. Once filtered, the points in the time series that corresponded to the Ultrasound measurements were selected. To account for the hypersensitivity of the electromyography measurement compared to the change in muscle shape, the 10 previous points and the 10 points after the selected activity level were selected and averaged. To clarify, electrical activity of the muscle will begin to increase prior to the initiation of the movement. Therefore, in order to accurately correlate the EMG with the muscle thickness, the average of the 10 data points before and after the point at each 0.25 s were recorded. This mean measurement was recorded in a separate data table with the muscle thickness. Furthermore, EMG data was normalized to the MVIC by expressing EMG values as a percentage of the MVIC. Resting measurements were not subtracted in the normalization equation. 2.6. Statistical analysis In order to investigate the correlation between muscle activity and TrA and IO thicknesses, the change in thickness from rest was plotted against the proportion MVIC. To determine the effects of the different conditions on TrA and IO thicknesses as well as muscle activity, one-way ANOVAs within subjects were employed. Following these tests, Tukey’s Post Hoc tests were utilized to determine where the differences were and the means of each of the conditions were plotted to further examine the differences.
For all conditions, including the control, there was no correlation (R2 < 0.11) between the change in muscle thickness from rest and the electrical activity normalized to the maximum voluntary isometric contraction (MVIC) for the IO. The one-way ANOVA and Tukey Post-Hoc tests revealed significant thickness differences between the Valsalva maneuver and all of the other conditions. This indicated an increase in thickness of the IO with the use of Valsalva and no significant change in thickness for the other conditions. A plot of the mean IO thickness measurements under each condition is shown in Fig. 2. 3.3. TrA thickness Similarly to the Internal Oblique, there was no correlation (R2 < 0.13) between the change in Transversus Abdominis thickness from rest and the proportion MVIC measurement of the EMG data for all conditions. A comparison of means for each condition demonstrated that while the subjects were wearing a belt, the TrA was significantly thinner than the control. With the Valsalva maneuver TrA exhibited a significantly higher thickness when compared with only a belt or the ‘‘Both” condition. A plot of the mean TrA thickness measurements under each condition is shown in Fig. 3. 4. Discussion The current study shows that, unlike previous similar studies for isometric tasks where the correlation coefficient was greater than 0.84 (Hodges et al., 2003; McMeeken et al., 2004), there is no relationship between electrical activity of the TrA or IO and their respective thicknesses during the dynamic lifting task. This was the case for not only the control condition, but also each of the other three conditions that were tested. Furthermore, this indicates that ultrasound cannot be used to accurately measure dynamic abdominal muscle activity. As previously mentioned these results are different than the ones found by Hodges et al. and McMeeken et al. for isometric exercises at different intensities. The differences between this research and previous studies may be due to the use of a constant weight throughout the deadlift exercise. If different weights were used, there would have been differences in intensity, which would affect the muscle activity. The greater activity differences may have also created more significant changes in thickness, which could have been correlated with the greater changes in activity. Additionally, the EMG data was
3. Results 3.1. EMG There was a significant difference (P < 0.05) in EMG data between the control lift and the condition where the Valsalva maneuver was used and the belt was worn (Both). Relative to the control condition, both the use of a belt and the Valsalva maneuver increased electrical activity of the abdominal muscles when used
Fig. 1. Mean EMG with standard error.
102
T.W. Blanchard et al. / Journal of Electromyography and Kinesiology 28 (2016) 99–103
Fig. 2. Mean IO thicknesses with standard error.
Fig. 3. Mean TrA thicknesses with standard error.
collected from the area over top of both of the muscles and measures were not taken to attempt to separate the two signals. Ideally, fine needle EMG would have been used in order to collect a separate sample for each muscle, however this capability was not available for this study. Similarly to previous research, while it did not correlate to ultrasound measurements, the use of weightlifting belt and the Valsalva maneuver increased abdominal muscle activity in terms of EMG measurement. These tools (i.e.: Belt and Valsalva), when employed independently were insignificant however when used together abdominal muscle EMG was statistically higher. This may be due to the required to activation of the abdominal muscles in order to perform the Valsalva maneuver as well as the increased proprioception caused by the belt. Current literature debates the effectiveness of a low-back belt in activating abdominal muscles. Warren et al. tested the effects of a belt on 14 females and 6 males on oblique muscle activity during a squat lift and found that all the females experienced a decrease in muscle activity whereas all but one of the men demonstrated an increase in muscle activity. This is consistent with the results of this study as most of the subjects were male and there was a general increase in EMG activity. Based on the results of this research, when an individual wears a weightlifting belt and employs the Valsalva maneuver, their abdominal muscle activity will increase significantly for a lifting task at 30% of the 1RM. This is important because increased abdominal muscle activity while lifting has been linked to decreased low back pain as well as decreased back injury (Ferreira et al., 2004). Based on the review of literature for this study, no research was found measuring relative changes in IO and TrA thicknesses during a dynamic lifting task therefore no comparison could be made. When examining the architectural changes of the IO and the TrA under the different conditions it is clear that the Valsalva maneuver plays the most significant role in increasing both of the muscle thicknesses. This corresponds to the increased muscle activity seen in EMG recording and to the theoretical stiffness requirement that the Valsalva imposes. The Valsalva maneuver requires the subject to consciously engage their abdominal
muscles, which would increase the muscle activity as well as muscle thickness. It is important to note that although an increase in mean thickness was present, there was no significant difference between the control measurement of the TrA thickness and the Valsalva condition indicating that the Valsalva plays a less significant role in affecting the geometry of the TrA muscle. In contrast, for the IO, the use of the Valsalva maneuver alone increased its thickness significantly more than any other condition. This leads to the hypothesis that the IO is more responsive to the use of the Valsalva maneuver in comparison to the TrA. Additionally, cross sectional thickness for each muscle increased in both superficial and deep directions when the Valsalva maneuver was used. Although this information was not quantified it was noted throughout the study. Wearing a weightlifting belt caused the IO and the TrA to react differently to the lift in terms of shape change compared to an overall increase in electrical activity from that area. While wearing the belt, there was a very small, non-significant, increase in the IO thickness compared to the control condition. The opposite was seen for the TrA, the use of a belt significantly decreased TrA muscle thickness. This is evidence that the use of a weightlifting changes how these two muscles interact with each other and that it has a much greater effect on the TrA compared to the IO. Moreover, when the belt was worn, both muscles seemed to favor an expansion deep to the skin. This could be due to the inability of the skin to stretch in order to allow the space for the muscle to extend toward the skin. The belt may be removing the elasticity component of the skin forcing a deep activation pattern of the TrA and the IO. When both the weightlifting belt was worn and the Valsava Maneuver was executed, there was a statistically insignificant decrease in TrA and IO thickness from the control condition combined with a significant increase in EMG activity. This may be due to the pinching of the abdominal muscles between the increased intra-abdominal pressure created by the Valsalva maneuver and the limited expansion determined by the weightlifting belt. As previously mentioned, there was only one EMG signal recorded. If these signals had been separated for the TrA and IO there may have been differences observed in the relationship between the muscle thicknesses and the EMG. This may have revealed more specific changes among the different conditions. Additionally, M mode ultrasound only allowed for the change in cross-sectional muscle thickness to be measured. If it were possible to record videos in B mode, the change in length of the muscle could also be measured and the gliding of the TrA and IO could be examined.
5. Conclusion and future directions Based on this study, the relationships previously established by Hodges et al. (2003), McMeeken et al. (2004) is not a proper fit for what is occurring during a deadlift. Therefore, measuring changes in muscle thickness using ultrasound imaging is not a reliable method for determining TrA or IO activity. The Valsalva maneuver increases muscle activity and when there are no limitations muscle thickness. Based on thickness, its effect on the IO appears to be stronger in comparison to the TrA. Furthermore, the weightlifting belt limits the expansion of both abdominal muscles with increased muscle thickness. However, it seems to have a stronger effect on the TrA, as it actually became significantly thinner compared to the control lift. The use of both the belt and the Valsalva maneuver did not produce any significant change in TrA or IO thickness compared to the control with a significant increase in EMG activity. This may possibly be due to
T.W. Blanchard et al. / Journal of Electromyography and Kinesiology 28 (2016) 99–103
the squeezing of the abdominal muscles between the increased pressure and the belt. It is clear that the belt is playing a role in changing how the TrA and IO function together however it is unknown at this time whether or not this is a positive function. Future research should be directed at examining the change in length of the muscles as well as determining any change in mechanical advantages. Acknowledgements We would like to thank Sheila Grech from Cambrian College for her assistance with the use and interpretation of the diagnostic ultrasound. References Bakke, M., Tuxen, A., Vilmann, P., Jensen, B., Vilmann, A., Toft, M., 1992. Ultrasound image of human masseter muscle related to bite force, electromyography, facial morphology and occlusal factors. Scand. J. Dent. Res. 100, 164–171. Barron, B., Deurstein, M., 1991. Industrial back belts and low back pain: mechanisms and outcomes. J. Occup. Rehabil. 4, 209–212. Brown, S.H.M., Ward, S.R., Cook, M.S., Lieber, R.L., 2011. Architectural analysis of human abdominal wall muscles: implications for mechanical function. Spine 36 (5), 355–362. http://dx.doi.org/10.1097/BRS.0b013e3181d12ed7. Bunce, S.M., Moore, A.P., Hough, A.D., 2002. M-mode ultrasound: a reliable measure of transversus abdominis thickness? Clin. Biomech. 17 (4), 315–317. http://dx. doi.org/10.1016/S0268-0033(02)00011-6. Calmels, P., Queneau, P., Hamonet, C., Le Pen, C., Maurel, F., Lerouvreur, C., et al., 2009. Effectiveness of a lumbar belt in subacute low back pain: an open, multicentric, and randomized clinical study [Miscellaneous Article]. Spine 34 (3), 215–220. http://dx.doi.org/10.1097/BRS.0b013e31819577d. Cholewicki, J., Juluru, K., Radebold, A., Panjabi, M.M., McGill, S.M., 1999. Lumbar spine stability can be augmented with an abdominal belt and/or increased intra-abdominal pressure. Eur. Spine J. 8 (5), 388–395. http://dx.doi.org/ 10.1007/s005860050192. Costa, L.O.P., Maher, C.G., Latimer, J., Smeets, R.J.E.M., 2009. Reproducibility of rehabilitative ultrasound imaging for the measurement of abdominal muscle activity: a systematic review. Phys. Ther. 89 (8), 756–769. http://dx.doi.org/ 10.2522/ptj.20080331. Cresswell, A., Grundstrom, H., 1992. Ovservations on intra-abdominal pressure and patterns of abdominal intramuscular activity in man. Acta Physiol. Scand. 144, 409–418. Critchley, D.J., Coutts, F.J., 2002. Abdominal muscle function in chronic low back pain patients: measurement with real-time ultrasound scanning. Physiotherapy 88 (6), 322–332. http://dx.doi.org/10.1016/S0031-9406(05)60745-6. Dankaerts, W., O’Sullivan, P.B., Burnett, A.F., Straker, L.M., Danneels, L.A., 2004. Reliability of EMG measurements for trunk muscles during maximal and submaximal voluntary isometric contractions in healthy controls and CLBP patients. J. Electromyogr. Kinesiol. 14 (3), 333–342. http://dx.doi.org/10.1016/ j.jelekin.2003.07.001, ISSN: 1050-6411. De Troyer, A., Estenne, M., Ninane, V., et al., 1990. Transverse abdominal muscle function in humans. J. Appl. Physiol. 68, 1010–1016. Ferreira, P., Ferreira, M., Hodges, P., 2004. Changes in recruitment of the abdominal muscles in people with low back pain: ultrasound measurement of muscle activity. Spine 29, 2560–2566. Hackett, D.A., Chow, Chin-Moi, 2013. The Valsalva maneuver: its effect on intraabdominal pressure and safety issues during resistance exercise. J. Strength Cond. Res. (Lippincott Williams & Wilkins) 27 (8), 2338–2345. Harman, E., Frykman, P., Cagett, E., Kraemer, W., 1988. Intra-abdominal and intrathroactic pressures during lifting and jumping. Med. Sci. Sports. Exerc. 20, 195– 201. Hodges, P., Richardson, C., 1999. Altered trunk muscle recruitment in people with low back pain with upper limb movement at different speeds. Arch. Phys. Med. Rehab. 80, 1005–1012. Hodges, P.W., Pengel, L.H.M., Herbert, R.D., Gandevia, S.C., 2003. Measurement of muscle contraction with ultrasound imaging. Muscle Nerve 27 (6), 682–692. http://dx.doi.org/10.1002/mus.10375. John, E.K., Beith, I.D., 2007. Can activity within the external abdominal oblique be measured using real-time ultrasound imaging? Clin. Biomech. 22 (9), 972–979. http://dx.doi.org/10.1016/j.clinbiomech.2007.07.005. Konrad, P., 2005. The ABC of EMG, first ed. Noraxcon Inc..
103
Lee, Y.-H., Kang, S.-M., 2002. Effect of belt pressure and breath held on trunk electromyography. Spine 27 (3), 282–290. McGill, S., Sharrat, M., 1990. Relationship between intra-abdominal pressure and trunk EMG. Clin. Biomech. (Bristol, Avon) 5, 59–67. McMeeken, J.M., Beith, I.D., Newham, D.J., Milligan, P., Critchley, D.J., 2004. The relationship between EMG and change in thickness of transversus abdominis. Clin. Biomech. 19 (4), 337–342. http://dx.doi.org/10.1016/ j.clinbiomech.2004.01.007. Richardson, C., Hodges, P., Hides, J., 2004. Therapeutic Exercises for Lumbo-pelvic Stabilization, second ed. Churchill Livingstone, Edinburgh. Richardson, C., Snijders, C., Hides, J., Damen, L., Pas, M., Storm, J., 2002. The relation between the transversus abdominis muscles, sacroiliac joint mechanics, and low back pain. Spine 27 (4), 399–405. Stevens, R., 2006. Gray’s Anatomy for Students. Teyhen, D., Sharrat, M., 2006. Rehabilitative ultrasound imaging symposium. J. Orthop. Sport. Phys. Ther. 36 (8), A1–3. Tsao, H., Sharrat, M., 2008. Persistence of improvements in postural strategies following motor control training in people with recurrent low back pain. J. Electromyogr. Kines. 18, 559–567. Van Poppel, M.N.M., de Looze, M.P., Koes, B.W., Smid, T., Bouter, L.M., 2000. Mechanisms of action of lumbar supports: a systematic review. Spine 25 (16), 2103–2113. Williams, C., Lind, A., 1987. The influence of straining maneuvers on the pressor response during isometric exercise. Eur. J. Appl. Physiol. O. 56, 230–237.
Trevor Blanchard has a Bachelor’s degree in Kinesiology from Laurentian University and is currently pursuing a masters in Human Kinetics. His research is primarily focused on occupational health and safety. More specifically, topics include human factors and torso loading.
Camille Smith is a human kinetics Masters student at Laurentian University in Sudbury Ontario, Canada. As a graduate of Kinesiology (BSc), she hopes to become a Registered Kinesiologist and, eventually, further her education in medicine.
Sylvain Grenier is a professor of biomechanics and ergonomics at Laurentian University in Sudbury Ontario, Canada. As a Registered Kinesiologist he prefers to keep his research work clinical and applied. Historically, his work has focused on understanding torso and spine mechanics and stability.
Contents lists available at ScienceDirect
Journal of Electromyography and Kinesiology journal homepage: www.elsevier.com/locate/jelekin
In a dynamic lifting task, the relationship between cross-sectional abdominal muscle thickness and the corresponding muscle activity is affected by the combined use of a weightlifting belt and the Valsalva maneuver Trevor W. Blanchard, Camille Smith, Sylvain G. Grenier ⇑ Kinesiology, School of Human Kinetics, Laurentian University, Sudbury, Ontario, Canada
a r t i c l e
i n f o
Article history: Received 6 May 2015 Received in revised form 10 March 2016 Accepted 16 March 2016
Keywords: Low-back belt Valsalva Ultrasound EMG Muscle thickness
a b s t r a c t It has been shown that under isometric conditions, as the activity of the abdominal muscles increases, the thicknesses of the muscles also increase. The purpose of this experiment was to determine whether change in muscle thickness could be used as a measure of muscle activity during a deadlift as well as determining the effect of a weightlifting belt and/or the Valsalva maneuver on the muscle thicknesses. The Transversus Abdominis (TrA) and Internal Obliques (IO) muscles were analyzed at rest and during a deadlift. Muscle thickness was measured using ultrasound imaging and muscle activity was simultaneously recorded using electromyography. Each subject performed deadlift under normal conditions, while performing the Valsalva maneuver, while wearing a weightlifting belt and while both utilizing the belt and the Valsalva maneuver. There was no relationship between change in muscle thickness and muscle activity for both the TrA and IO (R2 < 0.13 for all conditions). However it was found that the Valsalva maneuver increased abdominal muscle thickness whereas the belt limited muscle expansion; each with an increase in activity. These results indicate that ultrasound cannot be used to measure muscle activity for a deadlift and that the belt affects how the IO and TrA function together. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction The Abdominal wall is composed of three muscles from deep to superficial: the Transversus Abdominis (TrA), Internal Oblique (IO), External Oblique (EO), and the Rectus Abdominis (RA) (Stevens, 2006). These muscles are tightly bound flat muscles whose fibers run at oblique angles to one another (Brown et al., 2011). This muscle group plays a crucial role in reducing the load on the spinal column as well as increasing spinal stiffness (Brown et al., 2011; John and Beith, 2007; Lee and Kang, 2002; Richardson et al., 2002; Stevens, 2006). When the abdominal wall is activated and the glottis is closed (sealing the abdominal cavity), the intraabdominal pressure (IAP) increases due to a decrease in volume of the abdominal cavity. This increase in pressure compresses the sacroiliac joints and creates tension in the thoracolumbar fascia in turn generating stiffness (Richardson et al., 2004). Additionally, the IAP allows forces on the spine, generated by a load, to be dispersed over the torso (Brown et al., 2011). ⇑ Corresponding author. E-mail address: [email protected] (S.G. Grenier). http://dx.doi.org/10.1016/j.jelekin.2016.03.006 1050-6411/Ó 2016 Elsevier Ltd. All rights reserved.
The Valsalva maneuver is a breathing pattern that involves forced exhalation against a closed glottis thereby increasing spinal stability by increasing the IAP (Hackett and Chin-Moi Chow, 2013). Free breathing (normal breathing cycle where glottis is open) generates significantly lower intra-abdominal pressures during resistance exercises compared with the intentional or unintentional use of the Valsalva maneuver (Cresswell and Grundstrom, 1992; Harman et al., 1988; McGill and Sharrat, 1990; Williams and Lind, 1987) In addition to increased intra-abdominal pressure, the Valsalva maneuver has also been shown to increase activation of the abdominal muscles (De Troyer et al., 1990; Lee and Kang, 2002). Lumbar supports in occupational settings or, weight lifting belts in sport settings, are a widely used tool believed to allow for lifting heavier weights and preventing injury. Whereas employees often use low-back belts in jobs that require frequent and/or heavy lifting to reduce symptoms, prevent and/or treat chronic low back pain, athletes may use a weightlifting belt to help them lift heavier weights. The proposed mechanism(s) by which these belts help reduce the risk of injury (if at all) varies through the literature. These mechanisms include physically restricting the range of
100
T.W. Blanchard et al. / Journal of Electromyography and Kinesiology 28 (2016) 99–103
motion, increasing proprioception, increasing the IAP and acting as a placebo (Barron and Deurstein, 1991; Calmels et al., 2009; Cholewicki et al., 1999; van Poppel et al., 2000). In order to understand how the abdominal muscles may function to create stiffness, attempts have been made to measure the activity of the three layers of muscle. To measure deep abdominal muscle activity accurately using electromyography, the use of finewire electrodes inserted into the muscle is required (Costa et al., 2009; Hodges and Richardson, 1999; Tsao, 2008). This process is costly and uncomfortable for the subject, especially if they are required to perform movements (Costa et al., 2009; Hodges and Richardson, 1999; Tsao, 2008). Recently, studies have used ultrasound imaging to measure the change in muscle thickness in order to indirectly determine muscle activity (Bunce et al., 2002; Hodges et al., 2003; McMeeken et al., 2004; Teyhen, 2006). In addition, morphological changes in muscle have been correlated with EMG measurements in low level contractions [force up to 30% of one repetition maximum (1RM) (Bakke et al., 1992; Ferreira et al., 2004; Hodges et al., 2003; McMeeken et al., 2004)], and have been found to be a reliable method to measure muscle activity (Bunce et al., 2002). More specifically, McMeeken and colleagues compared fine wire EMG data of the TrA with synchronized ultrasound motion recordings of subjects executing the abdominal hollowing maneuver. They found a linear relationship between TrA thickness and EMG activity (McMeeken et al., 2004). Moreover, Hodges et al. fit an increasing logarithmic regression to the relationship of IO muscle thickness and TrA with their respective EMG activities (Hodges et al., 2003). Based on the current literature it is clear that the relationship between the electrical activity of a muscle and its thickness has been thoroughly researched for isometric contractions. However, the relationship between morphological changes and EMG activity in the abdominal wall muscles remains unknown for dynamic conditions. The purpose of this study is to determine if measuring the change in muscle thickness can be used to measure muscle activity and observe the effects of wearing a weightlifting belt and closing the glottis on the relationship between the IO and TrA and their electrical activity. 2. Methods 2.1. Subjects Twenty-one healthy subjects were recruited from various varsity sports teams at a Canadian University. However, the data from 10 participants was not used because during the testing process, the head of the ultrasound transducer would sometimes shift on the skin and render the images unclear and unmeasurable. Subjects were excluded from the study if they had chronic low back pain, or had experienced any type of low back injury requiring surgical intervention. Out of the eleven remaining participants, three were women and the overall mean age was 20 years. Each subject signed the informed consent and the university Ethics Review Board approved the study. 2.2. Equipment A real-time ultrasound scanner was used with a 7.5 MHz linear head transducer (Rising Medical Co Ltd., RUS-9000F) to determine muscle thickness as well as the Shimmer wireless EMG system to measure electrical muscle activity. Specifications for the Shimmer EMG system can be found in Table 1. A standard 12.7 cm (5 in.) weightlifting belt and Olympic style weightlifting equipment consisting of a 20 kg bar and bumper plates of weight appropriate (30%) to the individual’s 1RM were used for the testing procedure.
Table 1 Shimmer EMG system specifications. Current draw Gain Max signal range before clipping Frequency range Ground Input protection Connections
180 lA (leads connected) 682 4.4 mV 5–482 Hz Wilson Type Driven Ground ESD and RF/EMI filtering, Current limiting Input (+), Input ( ), Reference
2.3. Pilot studies Pilot studies confirmed that the TrA, IO and EO could be viewed and measured at once while performing a deadlift with and without a weightlifting belt in both B (bright) and M (motion) modes. In B-mode (brightness mode) ultrasound, a linear array of transducers scans a plane through the body that can be viewed as a twodimensional image. Whereas In M-mode (motion mode), pulses are emitted in quick succession – each time, a B-mode image is taken. Over time, this results in a video recording. The muscle boundaries move relative to the probe and this can be used to view structural changes over a period of 4 s. The location found to show the clearest image of the three muscles together was 25 mm anterior from the midpoint between the twelfth rib and the iliac crest of the anterolateral abdominal wall. This has been the scanning point in previous studies (Critchley and Coutts, 2002).
2.4. Testing procedure Once the subject had consented to the study, the scan point was identified and resting measurements were taken of the abdominal wall with B mode at the end of a normal inspiration with the patient in a supine position. Following resting measurements, their 1RM was determined based on discussions with the athletes after their testing sessions with the varsity strength and conditioning staff. From these results, 30% was calculated which would be the weight lifted during the exercise. To prepare for EMG measurement, the skin over the anterior superior iliac spine was shaved with a disposable razor and cleaned with an alcohol swab. Subsequently, the maximum voluntary isometric contraction (MVIC) was determined for EMG measurements by asking the participant to contract their abdominal muscles as hard as possible while lying in the supine position with legs extended as in Dankaerts et al. (2004). This group found that both MVIC and sub-MVIC contractions, using this position, had excellent within-day reliability in both intra class correlation (mean = 0.91) and standard error of measurement (mean 5%). Although participants were familiar with the exercise, and performed it as a part of regular workouts, the tester demonstrated the deadlift and the subject was instructed to practice in order to ensure proper form. They were also taught how to perform the Valsalva maneuver. After this preparation phase, the test began with a series of lift presented in random order: a control lift where the subject was asked to perform a deadlift without the use of the weightlifting belt or the Valsalva maneuver; a ‘‘Valsalva” condition where the subject executed a deadlift while utilizing the Valsalva maneuver; the ‘‘Belt” condition where the participant performed the lift while wearing the 12.7 cm weight lifting belt; and the final condition involved wearing the belt and the use of the Valsalva maneuver to perform the lift. This was referred to as the ‘‘Both” condition. In order to synchronize the Ultrasound measurements with the EMG data, the participants were instructed to suddenly contract their abdominal muscles and then suddenly relax prior to performing the deadlift. This elicited a clear reaction in both datasets and
T.W. Blanchard et al. / Journal of Electromyography and Kinesiology 28 (2016) 99–103
measurements could be processed when readings returned to normal.
101
individually, however the results were not statistically significant. A plot of the mean EMG measurements under each condition is shown in Fig. 1.
2.5. Measurement 3.2. IO thickness 2.5.1. Ultrasound The Ultrasound scanner’s M mode was used to view the change in muscle thickness for the lifts under each condition. The ‘‘Freeze” function was used to capture an image that shows the entire lift as well as the relaxation phase of the synchronization contraction. Next, the ‘‘Measure” function was used to create a calibration measurement for further processing. The images were then downloaded to a computer and ImageJ software was used to analyze the images. Based on the calibration measurements the number of pixels per millimeter was determined as well as the number of pixels per second as each image represented a 4 s time frame. The TrA and IO thicknesses were measured at every 0.25 s after the relaxation phase of the contraction prior to the lift. These measurements were recorded for statistical analysis. 2.5.2. EMG The EMG was recorded with a sampling rate of 1024 Hz. Ag/AgCl disc shaped electrodes were placed horizontally over the anterior superior iliac spine 25 mm apart. The ground was directly lateral to this position. The electrode placement was according to The ABC of EMG by Konrad (2005). The raw signal was rectified and filtered using a 4th order lowpass Butterworth filter with a cut off frequency of 2.5 Hz. Once filtered, the points in the time series that corresponded to the Ultrasound measurements were selected. To account for the hypersensitivity of the electromyography measurement compared to the change in muscle shape, the 10 previous points and the 10 points after the selected activity level were selected and averaged. To clarify, electrical activity of the muscle will begin to increase prior to the initiation of the movement. Therefore, in order to accurately correlate the EMG with the muscle thickness, the average of the 10 data points before and after the point at each 0.25 s were recorded. This mean measurement was recorded in a separate data table with the muscle thickness. Furthermore, EMG data was normalized to the MVIC by expressing EMG values as a percentage of the MVIC. Resting measurements were not subtracted in the normalization equation. 2.6. Statistical analysis In order to investigate the correlation between muscle activity and TrA and IO thicknesses, the change in thickness from rest was plotted against the proportion MVIC. To determine the effects of the different conditions on TrA and IO thicknesses as well as muscle activity, one-way ANOVAs within subjects were employed. Following these tests, Tukey’s Post Hoc tests were utilized to determine where the differences were and the means of each of the conditions were plotted to further examine the differences.
For all conditions, including the control, there was no correlation (R2 < 0.11) between the change in muscle thickness from rest and the electrical activity normalized to the maximum voluntary isometric contraction (MVIC) for the IO. The one-way ANOVA and Tukey Post-Hoc tests revealed significant thickness differences between the Valsalva maneuver and all of the other conditions. This indicated an increase in thickness of the IO with the use of Valsalva and no significant change in thickness for the other conditions. A plot of the mean IO thickness measurements under each condition is shown in Fig. 2. 3.3. TrA thickness Similarly to the Internal Oblique, there was no correlation (R2 < 0.13) between the change in Transversus Abdominis thickness from rest and the proportion MVIC measurement of the EMG data for all conditions. A comparison of means for each condition demonstrated that while the subjects were wearing a belt, the TrA was significantly thinner than the control. With the Valsalva maneuver TrA exhibited a significantly higher thickness when compared with only a belt or the ‘‘Both” condition. A plot of the mean TrA thickness measurements under each condition is shown in Fig. 3. 4. Discussion The current study shows that, unlike previous similar studies for isometric tasks where the correlation coefficient was greater than 0.84 (Hodges et al., 2003; McMeeken et al., 2004), there is no relationship between electrical activity of the TrA or IO and their respective thicknesses during the dynamic lifting task. This was the case for not only the control condition, but also each of the other three conditions that were tested. Furthermore, this indicates that ultrasound cannot be used to accurately measure dynamic abdominal muscle activity. As previously mentioned these results are different than the ones found by Hodges et al. and McMeeken et al. for isometric exercises at different intensities. The differences between this research and previous studies may be due to the use of a constant weight throughout the deadlift exercise. If different weights were used, there would have been differences in intensity, which would affect the muscle activity. The greater activity differences may have also created more significant changes in thickness, which could have been correlated with the greater changes in activity. Additionally, the EMG data was
3. Results 3.1. EMG There was a significant difference (P < 0.05) in EMG data between the control lift and the condition where the Valsalva maneuver was used and the belt was worn (Both). Relative to the control condition, both the use of a belt and the Valsalva maneuver increased electrical activity of the abdominal muscles when used
Fig. 1. Mean EMG with standard error.
102
T.W. Blanchard et al. / Journal of Electromyography and Kinesiology 28 (2016) 99–103
Fig. 2. Mean IO thicknesses with standard error.
Fig. 3. Mean TrA thicknesses with standard error.
collected from the area over top of both of the muscles and measures were not taken to attempt to separate the two signals. Ideally, fine needle EMG would have been used in order to collect a separate sample for each muscle, however this capability was not available for this study. Similarly to previous research, while it did not correlate to ultrasound measurements, the use of weightlifting belt and the Valsalva maneuver increased abdominal muscle activity in terms of EMG measurement. These tools (i.e.: Belt and Valsalva), when employed independently were insignificant however when used together abdominal muscle EMG was statistically higher. This may be due to the required to activation of the abdominal muscles in order to perform the Valsalva maneuver as well as the increased proprioception caused by the belt. Current literature debates the effectiveness of a low-back belt in activating abdominal muscles. Warren et al. tested the effects of a belt on 14 females and 6 males on oblique muscle activity during a squat lift and found that all the females experienced a decrease in muscle activity whereas all but one of the men demonstrated an increase in muscle activity. This is consistent with the results of this study as most of the subjects were male and there was a general increase in EMG activity. Based on the results of this research, when an individual wears a weightlifting belt and employs the Valsalva maneuver, their abdominal muscle activity will increase significantly for a lifting task at 30% of the 1RM. This is important because increased abdominal muscle activity while lifting has been linked to decreased low back pain as well as decreased back injury (Ferreira et al., 2004). Based on the review of literature for this study, no research was found measuring relative changes in IO and TrA thicknesses during a dynamic lifting task therefore no comparison could be made. When examining the architectural changes of the IO and the TrA under the different conditions it is clear that the Valsalva maneuver plays the most significant role in increasing both of the muscle thicknesses. This corresponds to the increased muscle activity seen in EMG recording and to the theoretical stiffness requirement that the Valsalva imposes. The Valsalva maneuver requires the subject to consciously engage their abdominal
muscles, which would increase the muscle activity as well as muscle thickness. It is important to note that although an increase in mean thickness was present, there was no significant difference between the control measurement of the TrA thickness and the Valsalva condition indicating that the Valsalva plays a less significant role in affecting the geometry of the TrA muscle. In contrast, for the IO, the use of the Valsalva maneuver alone increased its thickness significantly more than any other condition. This leads to the hypothesis that the IO is more responsive to the use of the Valsalva maneuver in comparison to the TrA. Additionally, cross sectional thickness for each muscle increased in both superficial and deep directions when the Valsalva maneuver was used. Although this information was not quantified it was noted throughout the study. Wearing a weightlifting belt caused the IO and the TrA to react differently to the lift in terms of shape change compared to an overall increase in electrical activity from that area. While wearing the belt, there was a very small, non-significant, increase in the IO thickness compared to the control condition. The opposite was seen for the TrA, the use of a belt significantly decreased TrA muscle thickness. This is evidence that the use of a weightlifting changes how these two muscles interact with each other and that it has a much greater effect on the TrA compared to the IO. Moreover, when the belt was worn, both muscles seemed to favor an expansion deep to the skin. This could be due to the inability of the skin to stretch in order to allow the space for the muscle to extend toward the skin. The belt may be removing the elasticity component of the skin forcing a deep activation pattern of the TrA and the IO. When both the weightlifting belt was worn and the Valsava Maneuver was executed, there was a statistically insignificant decrease in TrA and IO thickness from the control condition combined with a significant increase in EMG activity. This may be due to the pinching of the abdominal muscles between the increased intra-abdominal pressure created by the Valsalva maneuver and the limited expansion determined by the weightlifting belt. As previously mentioned, there was only one EMG signal recorded. If these signals had been separated for the TrA and IO there may have been differences observed in the relationship between the muscle thicknesses and the EMG. This may have revealed more specific changes among the different conditions. Additionally, M mode ultrasound only allowed for the change in cross-sectional muscle thickness to be measured. If it were possible to record videos in B mode, the change in length of the muscle could also be measured and the gliding of the TrA and IO could be examined.
5. Conclusion and future directions Based on this study, the relationships previously established by Hodges et al. (2003), McMeeken et al. (2004) is not a proper fit for what is occurring during a deadlift. Therefore, measuring changes in muscle thickness using ultrasound imaging is not a reliable method for determining TrA or IO activity. The Valsalva maneuver increases muscle activity and when there are no limitations muscle thickness. Based on thickness, its effect on the IO appears to be stronger in comparison to the TrA. Furthermore, the weightlifting belt limits the expansion of both abdominal muscles with increased muscle thickness. However, it seems to have a stronger effect on the TrA, as it actually became significantly thinner compared to the control lift. The use of both the belt and the Valsalva maneuver did not produce any significant change in TrA or IO thickness compared to the control with a significant increase in EMG activity. This may possibly be due to
T.W. Blanchard et al. / Journal of Electromyography and Kinesiology 28 (2016) 99–103
the squeezing of the abdominal muscles between the increased pressure and the belt. It is clear that the belt is playing a role in changing how the TrA and IO function together however it is unknown at this time whether or not this is a positive function. Future research should be directed at examining the change in length of the muscles as well as determining any change in mechanical advantages. Acknowledgements We would like to thank Sheila Grech from Cambrian College for her assistance with the use and interpretation of the diagnostic ultrasound. References Bakke, M., Tuxen, A., Vilmann, P., Jensen, B., Vilmann, A., Toft, M., 1992. Ultrasound image of human masseter muscle related to bite force, electromyography, facial morphology and occlusal factors. Scand. J. Dent. Res. 100, 164–171. Barron, B., Deurstein, M., 1991. Industrial back belts and low back pain: mechanisms and outcomes. J. Occup. Rehabil. 4, 209–212. Brown, S.H.M., Ward, S.R., Cook, M.S., Lieber, R.L., 2011. Architectural analysis of human abdominal wall muscles: implications for mechanical function. Spine 36 (5), 355–362. http://dx.doi.org/10.1097/BRS.0b013e3181d12ed7. Bunce, S.M., Moore, A.P., Hough, A.D., 2002. M-mode ultrasound: a reliable measure of transversus abdominis thickness? Clin. Biomech. 17 (4), 315–317. http://dx. doi.org/10.1016/S0268-0033(02)00011-6. Calmels, P., Queneau, P., Hamonet, C., Le Pen, C., Maurel, F., Lerouvreur, C., et al., 2009. Effectiveness of a lumbar belt in subacute low back pain: an open, multicentric, and randomized clinical study [Miscellaneous Article]. Spine 34 (3), 215–220. http://dx.doi.org/10.1097/BRS.0b013e31819577d. Cholewicki, J., Juluru, K., Radebold, A., Panjabi, M.M., McGill, S.M., 1999. Lumbar spine stability can be augmented with an abdominal belt and/or increased intra-abdominal pressure. Eur. Spine J. 8 (5), 388–395. http://dx.doi.org/ 10.1007/s005860050192. Costa, L.O.P., Maher, C.G., Latimer, J., Smeets, R.J.E.M., 2009. Reproducibility of rehabilitative ultrasound imaging for the measurement of abdominal muscle activity: a systematic review. Phys. Ther. 89 (8), 756–769. http://dx.doi.org/ 10.2522/ptj.20080331. Cresswell, A., Grundstrom, H., 1992. Ovservations on intra-abdominal pressure and patterns of abdominal intramuscular activity in man. Acta Physiol. Scand. 144, 409–418. Critchley, D.J., Coutts, F.J., 2002. Abdominal muscle function in chronic low back pain patients: measurement with real-time ultrasound scanning. Physiotherapy 88 (6), 322–332. http://dx.doi.org/10.1016/S0031-9406(05)60745-6. Dankaerts, W., O’Sullivan, P.B., Burnett, A.F., Straker, L.M., Danneels, L.A., 2004. Reliability of EMG measurements for trunk muscles during maximal and submaximal voluntary isometric contractions in healthy controls and CLBP patients. J. Electromyogr. Kinesiol. 14 (3), 333–342. http://dx.doi.org/10.1016/ j.jelekin.2003.07.001, ISSN: 1050-6411. De Troyer, A., Estenne, M., Ninane, V., et al., 1990. Transverse abdominal muscle function in humans. J. Appl. Physiol. 68, 1010–1016. Ferreira, P., Ferreira, M., Hodges, P., 2004. Changes in recruitment of the abdominal muscles in people with low back pain: ultrasound measurement of muscle activity. Spine 29, 2560–2566. Hackett, D.A., Chow, Chin-Moi, 2013. The Valsalva maneuver: its effect on intraabdominal pressure and safety issues during resistance exercise. J. Strength Cond. Res. (Lippincott Williams & Wilkins) 27 (8), 2338–2345. Harman, E., Frykman, P., Cagett, E., Kraemer, W., 1988. Intra-abdominal and intrathroactic pressures during lifting and jumping. Med. Sci. Sports. Exerc. 20, 195– 201. Hodges, P., Richardson, C., 1999. Altered trunk muscle recruitment in people with low back pain with upper limb movement at different speeds. Arch. Phys. Med. Rehab. 80, 1005–1012. Hodges, P.W., Pengel, L.H.M., Herbert, R.D., Gandevia, S.C., 2003. Measurement of muscle contraction with ultrasound imaging. Muscle Nerve 27 (6), 682–692. http://dx.doi.org/10.1002/mus.10375. John, E.K., Beith, I.D., 2007. Can activity within the external abdominal oblique be measured using real-time ultrasound imaging? Clin. Biomech. 22 (9), 972–979. http://dx.doi.org/10.1016/j.clinbiomech.2007.07.005. Konrad, P., 2005. The ABC of EMG, first ed. Noraxcon Inc..
103
Lee, Y.-H., Kang, S.-M., 2002. Effect of belt pressure and breath held on trunk electromyography. Spine 27 (3), 282–290. McGill, S., Sharrat, M., 1990. Relationship between intra-abdominal pressure and trunk EMG. Clin. Biomech. (Bristol, Avon) 5, 59–67. McMeeken, J.M., Beith, I.D., Newham, D.J., Milligan, P., Critchley, D.J., 2004. The relationship between EMG and change in thickness of transversus abdominis. Clin. Biomech. 19 (4), 337–342. http://dx.doi.org/10.1016/ j.clinbiomech.2004.01.007. Richardson, C., Hodges, P., Hides, J., 2004. Therapeutic Exercises for Lumbo-pelvic Stabilization, second ed. Churchill Livingstone, Edinburgh. Richardson, C., Snijders, C., Hides, J., Damen, L., Pas, M., Storm, J., 2002. The relation between the transversus abdominis muscles, sacroiliac joint mechanics, and low back pain. Spine 27 (4), 399–405. Stevens, R., 2006. Gray’s Anatomy for Students. Teyhen, D., Sharrat, M., 2006. Rehabilitative ultrasound imaging symposium. J. Orthop. Sport. Phys. Ther. 36 (8), A1–3. Tsao, H., Sharrat, M., 2008. Persistence of improvements in postural strategies following motor control training in people with recurrent low back pain. J. Electromyogr. Kines. 18, 559–567. Van Poppel, M.N.M., de Looze, M.P., Koes, B.W., Smid, T., Bouter, L.M., 2000. Mechanisms of action of lumbar supports: a systematic review. Spine 25 (16), 2103–2113. Williams, C., Lind, A., 1987. The influence of straining maneuvers on the pressor response during isometric exercise. Eur. J. Appl. Physiol. O. 56, 230–237.
Trevor Blanchard has a Bachelor’s degree in Kinesiology from Laurentian University and is currently pursuing a masters in Human Kinetics. His research is primarily focused on occupational health and safety. More specifically, topics include human factors and torso loading.
Camille Smith is a human kinetics Masters student at Laurentian University in Sudbury Ontario, Canada. As a graduate of Kinesiology (BSc), she hopes to become a Registered Kinesiologist and, eventually, further her education in medicine.
Sylvain Grenier is a professor of biomechanics and ergonomics at Laurentian University in Sudbury Ontario, Canada. As a Registered Kinesiologist he prefers to keep his research work clinical and applied. Historically, his work has focused on understanding torso and spine mechanics and stability.