Introduction: Lumbar spine stability programs have been advocated to prevent and rehabilitate low back injury. Specifically, abdominal ‘drawing in’ has been used to train motor control deficits in individuals with low back pain. This technique requires differential activity within deep and superficial lumbar multifidus fibres, yet the ability of these fibres to act differentially has not been extensively examined. Deep fibres are hypothesized to act as spinal stabilizers while superficial fibres are hypothesized to act as global movers of the trunk. Objective: To investigate differential excitation of deep and superficial lumbar multifidus fibres during segmental indentation loads to the lumbar spine. Methods: Posterior-anterior indentation loads were applied to individual lumbar spinous processes of prone participants at three different velocities and three different indentation displacements. Indentations consisted of an initial downward displacement that was subsequently held for 500 milliseconds. Intramuscular electromyography (EMG) of deep and superficial lumbar multifidus fibres at L3, L4 and L5 was recorded. EMG was quantified by “average” root mean square (RMS), peak RMS of a sliding RMS window and time-to-peak RMS over the indentation phase and 500 millisecond hold phase. Results: Increased indentation displacement at the slowest velocity resulted in increased “average” RMS of only the L5 superficial multifidus fibres. Increased indentation velocity produced differential effects in deep and superficial multifidus fibres. “Average” RMS and peak RIVIS significantly increased with increasing indentation velocity in most deep fibre recording sites, yet superficial fibre excitation did not significantly increase. In most EMG recording sites, the time-to-peak RMS increased with increasing indentation displacement and decreased with increasing indentation velocity. Conclusion: Differential excitation of superficial and deep multifidus fibres was found with increasing indentation velocity; however, the result was opposite to that hypothesized. This result is clinically relevant because it suggests deep multifidus fibre excitation may increase in response to increased perturbation magnitude, possibly to restore vertebral body position. Differential excitation effects may also be related to different mechanical stimuli experienced by deep and superficial fibres due to vertebral body movement during indentation loads. 11

Introduction: Lumbar spine stability programs have been advocated to prevent and rehabilitate low back injury. Specifically, abdominal ‘drawing in’ has been used to train motor control deficits in individuals with low back pain. This technique requires differential activity within deep and superficial lumbar multifidus fibres, yet the ability of these fibres to act differentially has not been extensively examined. Deep fibres are hypothesized to act as spinal stabilizers while superficial fibres are hypothesized to act as global movers of the trunk. Objective: To investigate differential excitation of deep and superficial lumbar multifidus fibres during segmental indentation loads to the lumbar spine. Methods: Posterior-anterior indentation loads were applied to individual lumbar spinous processes of prone participants at three different velocities and three different indentation displacements. Indentations consisted of an initial downward displacement that was subsequently held for 500 milliseconds. Intramuscular electromyography (EMG) of deep and superficial lumbar multifidus fibres at L3, L4 and L5 was recorded. EMG was quantified by “average” root mean square (RMS), peak RMS of a sliding RMS window and time-to-peak RMS over the indentation phase and 500 millisecond hold phase. Results: Increased indentation displacement at the slowest velocity resulted in increased “average” RMS of only the L5 superficial multifidus fibres. Increased indentation velocity produced differential effects in deep and superficial multifidus fibres. “Average” RMS and peak RIVIS significantly increased with increasing indentation velocity in most deep fibre recording sites, yet superficial fibre excitation did not significantly increase. In most EMG recording sites, the time-to-peak RMS increased with increasing indentation displacement and decreased with increasing indentation velocity. Conclusion: Differential excitation of superficial and deep multifidus fibres was found with increasing indentation velocity; however, the result was opposite to that hypothesized. This result is clinically relevant because it suggests deep multifidus fibre excitation may increase in response to increased perturbation magnitude, possibly to restore vertebral body position. Differential excitation effects may also be related to different mechanical stimuli experienced by deep and superficial fibres due to vertebral body movement during indentation loads. 11

Introduction: Lumbar spine stability programs have been advocated to prevent and rehabilitate low back injury. Specifically, abdominal ‘drawing in’ has been used to train motor control deficits in individuals with low back pain. This technique requires differential activity within deep and superficial lumbar multifidus fibres, yet the ability of these fibres to act differentially has not been extensively examined. Deep fibres are hypothesized to act as spinal stabilizers while superficial fibres are hypothesized to act as global movers of the trunk. Objective: To investigate differential excitation of deep and superficial lumbar multifidus fibres during segmental indentation loads to the lumbar spine. Methods: Posterior-anterior indentation loads were applied to individual lumbar spinous processes of prone participants at three different velocities and three different indentation displacements. Indentations consisted of an initial downward displacement that was subsequently held for 500 milliseconds. Intramuscular electromyography (EMG) of deep and superficial lumbar multifidus fibres at L3, L4 and L5 was recorded. EMG was quantified by “average” root mean square (RMS), peak RMS of a sliding RMS window and time-to-peak RMS over the indentation phase and 500 millisecond hold phase. Results: Increased indentation displacement at the slowest velocity resulted in increased “average” RMS of only the L5 superficial multifidus fibres. Increased indentation velocity produced differential effects in deep and superficial multifidus fibres. “Average” RMS and peak RIVIS significantly increased with increasing indentation velocity in most deep fibre recording sites, yet superficial fibre excitation did not significantly increase. In most EMG recording sites, the time-to-peak RMS increased with increasing indentation displacement and decreased with increasing indentation velocity. Conclusion: Differential excitation of superficial and deep multifidus fibres was found with increasing indentation velocity; however, the result was opposite to that hypothesized. This result is clinically relevant because it suggests deep multifidus fibre excitation may increase in response to increased perturbation magnitude, possibly to restore vertebral body position. Differential excitation effects may also be related to different mechanical stimuli experienced by deep and superficial fibres due to vertebral body movement during indentation loads. 11 / Education, Faculty of / Kinesiology, School of / Graduate

Lesões em coluna vertebral estão intimamente relacionadas a alterações neuromusculares, de modo que pela sensibilidade dolorosa e restrição da movimentação podem levar a alterações musculares como assimetrias e atrofias. Por outro lado, a musculatura enfraquecida pode predispor a lesões vertebrais. Esse trabalho buscou investigar ultrassonograficamente a presença de alterações musculoesqueléticas em cães com suspeita clínica de alterações nos segmentos toracolombar e lombar da coluna vertebral, confirmada ou não, pelo exame radiográfico. Além da análise descritiva, o grau de atrofia muscular foi quantificado através da mensuração da espessura e área da secção transversal do músculo Multifidus dorsi no nível de cada vértebra entre T13 e L7. Análises descritivas e quantitativas foram realizadas para 30 cães hígidos e 30 sintomáticos, levando em conta a presença de lesões, escore de condição corporal e tempo de evolução do quadro (para animais com histórico de lesão). O exame ultrassonográfico possibilitou a avaliação qualitativa de superfícies ósseas dos processos articulares e espinhosos, ligamentos supraespinhoso, interespinhoso e flavo e grupos musculares que envolvem o Multifidus dorsi e Longissimus dorsi, bem como alterações de ecogenicidade e irregularidades em superfícies ósseas e fibras musculares. Para análise dos dados foi utilizado um modelo com três fatores, considerando presença de lesão, cronicidade e escore como efeitos fixos e o bloco idade-sexo-porte como efeito aleatório. A espessura do Multifidus dorsi foi menor em animais com lesão do que em cães hígidos e naqueles cães que apresentaram lesão crônica, quando comparado com animais sem histórico de lesão, não variando entre cães com escore adequado ou obesos. Houve menores valores de área da secção transversal para animais com lesão crônica e uma correlação forte entre mensurações de área dos lados direito e esquerdo para uma mesma vértebra. A ultrassonografia mostrouse um método interessante para estimativa da atrofia muscular com base na espessura do Multifidus dorsi, sobretudo no nível de T13, L1 e L3. A utilização da ultrassonografia musculoesquelética da coluna vertebral neste trabalho apresentou impacto positivo em 45% dos casos, seja por concomitantemente contribuir para o diagnóstico diferencial e influenciar na conduta em 17% dos casos ou por exclusivamente influenciar na conduta em 28% deles. O emprego deste método não afetou o diagnóstico em 55% dos casos. Portanto, é um método promissor para ser empregado na investigação musculoesquelética da coluna vertebral toracolombar e lombar, em casos específicos. / Spinal injuries are closely related to neuromuscular changes, so that pain and movement impairment can lead to muscle changes such as asymmetries and atrophies. On the other hand, the weakened muscles may predispose to vertebral injuries. This work used the ultrasound to investigate the presence of musculoskeletal alterations in the thoracolumbar and lumbar segments of the canine spine, associated or not to radiographic findings. In addition to the descriptive analysis, the muscle atrophy was quantified by measuring the thickness and crosssectional area (CSA) of the Multifidus dorsi muscle at the level of each vertebra between T13 and L7. Descriptive and quantitative analyzes were performed for 30 healthy and 30 symptomatic dogs, taking into account the presence of lesions, body condition score and chronicity (for animals with a history of injury). Ultrasound examination allowed the qualitative evaluation of bone surfaces of articular and spinal processes, supraspinatus, interspinous and flavum ligaments and paraspinal muscle groups involving Multifidus dorsi and Longissimus dorsi, as well as changes in echogenicity and irregularities in bone surfaces and muscle fibers. For data analysis a model with three factors was used, considering presence of injury, chronicity and score as fixed effects and the block age-sex-size as random effect. Multifidus dorsi thickness was lower in animals with lesions than in healthy dogs and in dogs with chronic lesions when compared to animals with no lesion history. This parameter did not vary between dogs with adequate score or obese dogs. There were lower CSA values for animals with chronic lesions and a strong correlation between CSA measurements on the right and left sides for the same vertebra. Ultrasonography was an interesting method to estimate muscle atrophy based on the Multifidus dorsi thickness, especially at the level of T13, L1 and L3. The use of the musculoskeletal ultrasonography in this study had a positive impact in 45% of the cases, either by contributing to the differential diagnosis and influencing the conduct in 17% of the cases or by exclusively influencing the conduct in 28%. The use of this method did not affect the diagnosis in 55% of the cases. Therefore, it is a promising method to be used in musculoskeletal investigation of the spine in specific cases.

Lesões em coluna vertebral estão intimamente relacionadas a alterações neuromusculares, de modo que pela sensibilidade dolorosa e restrição da movimentação podem levar a alterações musculares como assimetrias e atrofias. Por outro lado, a musculatura enfraquecida pode predispor a lesões vertebrais. Esse trabalho buscou investigar ultrassonograficamente a presença de alterações musculoesqueléticas em cães com suspeita clínica de alterações nos segmentos toracolombar e lombar da coluna vertebral, confirmada ou não, pelo exame radiográfico. Além da análise descritiva, o grau de atrofia muscular foi quantificado através da mensuração da espessura e área da secção transversal do músculo Multifidus dorsi no nível de cada vértebra entre T13 e L7. Análises descritivas e quantitativas foram realizadas para 30 cães hígidos e 30 sintomáticos, levando em conta a presença de lesões, escore de condição corporal e tempo de evolução do quadro (para animais com histórico de lesão). O exame ultrassonográfico possibilitou a avaliação qualitativa de superfícies ósseas dos processos articulares e espinhosos, ligamentos supraespinhoso, interespinhoso e flavo e grupos musculares que envolvem o Multifidus dorsi e Longissimus dorsi, bem como alterações de ecogenicidade e irregularidades em superfícies ósseas e fibras musculares. Para análise dos dados foi utilizado um modelo com três fatores, considerando presença de lesão, cronicidade e escore como efeitos fixos e o bloco idade-sexo-porte como efeito aleatório. A espessura do Multifidus dorsi foi menor em animais com lesão do que em cães hígidos e naqueles cães que apresentaram lesão crônica, quando comparado com animais sem histórico de lesão, não variando entre cães com escore adequado ou obesos. Houve menores valores de área da secção transversal para animais com lesão crônica e uma correlação forte entre mensurações de área dos lados direito e esquerdo para uma mesma vértebra. A ultrassonografia mostrouse um método interessante para estimativa da atrofia muscular com base na espessura do Multifidus dorsi, sobretudo no nível de T13, L1 e L3. A utilização da ultrassonografia musculoesquelética da coluna vertebral neste trabalho apresentou impacto positivo em 45% dos casos, seja por concomitantemente contribuir para o diagnóstico diferencial e influenciar na conduta em 17% dos casos ou por exclusivamente influenciar na conduta em 28% deles. O emprego deste método não afetou o diagnóstico em 55% dos casos. Portanto, é um método promissor para ser empregado na investigação musculoesquelética da coluna vertebral toracolombar e lombar, em casos específicos. / Spinal injuries are closely related to neuromuscular changes, so that pain and movement impairment can lead to muscle changes such as asymmetries and atrophies. On the other hand, the weakened muscles may predispose to vertebral injuries. This work used the ultrasound to investigate the presence of musculoskeletal alterations in the thoracolumbar and lumbar segments of the canine spine, associated or not to radiographic findings. In addition to the descriptive analysis, the muscle atrophy was quantified by measuring the thickness and crosssectional area (CSA) of the Multifidus dorsi muscle at the level of each vertebra between T13 and L7. Descriptive and quantitative analyzes were performed for 30 healthy and 30 symptomatic dogs, taking into account the presence of lesions, body condition score and chronicity (for animals with a history of injury). Ultrasound examination allowed the qualitative evaluation of bone surfaces of articular and spinal processes, supraspinatus, interspinous and flavum ligaments and paraspinal muscle groups involving Multifidus dorsi and Longissimus dorsi, as well as changes in echogenicity and irregularities in bone surfaces and muscle fibers. For data analysis a model with three factors was used, considering presence of injury, chronicity and score as fixed effects and the block age-sex-size as random effect. Multifidus dorsi thickness was lower in animals with lesions than in healthy dogs and in dogs with chronic lesions when compared to animals with no lesion history. This parameter did not vary between dogs with adequate score or obese dogs. There were lower CSA values for animals with chronic lesions and a strong correlation between CSA measurements on the right and left sides for the same vertebra. Ultrasonography was an interesting method to estimate muscle atrophy based on the Multifidus dorsi thickness, especially at the level of T13, L1 and L3. The use of the musculoskeletal ultrasonography in this study had a positive impact in 45% of the cases, either by contributing to the differential diagnosis and influencing the conduct in 17% of the cases or by exclusively influencing the conduct in 28%. The use of this method did not affect the diagnosis in 55% of the cases. Therefore, it is a promising method to be used in musculoskeletal investigation of the spine in specific cases.

<p><strong>Sammanfattning</strong></p><p>Inom vården är det idag vanligt med bland annat ryggproblem. Risken är stor att värken blir långvarig. En Australiensk studie visade att en tredjedel av dem som hade besvär från ländryggen fortfarande hade det ett år senare.</p><p>Styrkan i bålmuskulaturen är central för alla typer av rörelser som vi utför funktionellt i det dagliga livet, i arbetssituationen och på fritiden. Har man en bra styrka i magmuskulaturen och i ryggmuskulaturen förebygger man skador och överbelastningsproblem bland annat i ländryggen.</p><p>Syftet med studien har varit att visa om vårdpersonal kan få minskade problem i ländryggen av att bygga upp sin bålstabilitet genom övningar som stärker m.transversus abdominis och m.multifidus. Går det att förbättra förutsättningarna för att personalen ska kunna orka jobba inom vårdyrket, som är ett mycket tungt arbete med många osymmetriska lyft. Vårdyrket har idag en överrepresentation av kvinnor.</p><p>Studien är en kvantitativ undersökning av 12 kvinnor mellan 20 och 55 år. Dessa kvinnor gick igenom en hållningsanalys för att vi skulle få en uppfattning om hur deras fysiska förutsättningar såg ut. Därefter har vi testat balansförmågan genom Elphinstons enbenstest. Som tredje test har vi mätt av styrkan i magmuskulaturen genom att använda oss av Kendalls nedre abdominala muskeltest. Slutligen testas Biering Sörensens ryggtest, som mäter styrkan i ryggmuskulaturen.</p><p>Resultatet av balanstestet visar att 83 % hade förbättrat vänster ben medan 66 % har förbättrat sin balans på höger ben. Kendalls magtest visade en 100 %-ig förbättring för alla, där ursprungsstyrkan var mycket dålig. Sist testades Biering Sörensens ryggtest. Även detta visade en stor svaghet i ryggmuskulaturen från början. Resultatet var även här en 100 %-ig förbättring.</p><p>Slutsatsen är att vårdpersonal som vi har undersökt har generellt en mycket svag muskulatur, främst i magmuskulaturen men även i ryggmuskulaturen. En dålig hållning kan vara ett resultat av en dålig bålstabilitet, vilket var uppenbart i våra testresultat. Dock har testpersonerna varit entusiastiska och tagit åt sig vår information, vilket har lett till en stor förändring av attityden till träning. Alla har under resans gång fått ett större medvetande för hur viktigt det är med en god hållning och en bra bålstabilitet.</p><p> </p><p><em>Nyckelord: bålstabilitet, core, multifidus, ländryggsbesvär, transversus abdominis, motion.</em></p>

Sammanfattning Inom vården är det idag vanligt med bland annat ryggproblem. Risken är stor att värken blir långvarig. En Australiensk studie visade att en tredjedel av dem som hade besvär från ländryggen fortfarande hade det ett år senare. Styrkan i bålmuskulaturen är central för alla typer av rörelser som vi utför funktionellt i det dagliga livet, i arbetssituationen och på fritiden. Har man en bra styrka i magmuskulaturen och i ryggmuskulaturen förebygger man skador och överbelastningsproblem bland annat i ländryggen. Syftet med studien har varit att visa om vårdpersonal kan få minskade problem i ländryggen av att bygga upp sin bålstabilitet genom övningar som stärker m.transversus abdominis och m.multifidus. Går det att förbättra förutsättningarna för att personalen ska kunna orka jobba inom vårdyrket, som är ett mycket tungt arbete med många osymmetriska lyft. Vårdyrket har idag en överrepresentation av kvinnor. Studien är en kvantitativ undersökning av 12 kvinnor mellan 20 och 55 år. Dessa kvinnor gick igenom en hållningsanalys för att vi skulle få en uppfattning om hur deras fysiska förutsättningar såg ut. Därefter har vi testat balansförmågan genom Elphinstons enbenstest. Som tredje test har vi mätt av styrkan i magmuskulaturen genom att använda oss av Kendalls nedre abdominala muskeltest. Slutligen testas Biering Sörensens ryggtest, som mäter styrkan i ryggmuskulaturen. Resultatet av balanstestet visar att 83 % hade förbättrat vänster ben medan 66 % har förbättrat sin balans på höger ben. Kendalls magtest visade en 100 %-ig förbättring för alla, där ursprungsstyrkan var mycket dålig. Sist testades Biering Sörensens ryggtest. Även detta visade en stor svaghet i ryggmuskulaturen från början. Resultatet var även här en 100 %-ig förbättring. Slutsatsen är att vårdpersonal som vi har undersökt har generellt en mycket svag muskulatur, främst i magmuskulaturen men även i ryggmuskulaturen. En dålig hållning kan vara ett resultat av en dålig bålstabilitet, vilket var uppenbart i våra testresultat. Dock har testpersonerna varit entusiastiska och tagit åt sig vår information, vilket har lett till en stor förändring av attityden till träning. Alla har under resans gång fått ett större medvetande för hur viktigt det är med en god hållning och en bra bålstabilitet.   Nyckelord: bålstabilitet, core, multifidus, ländryggsbesvär, transversus abdominis, motion.

The purposes of this dissertation were to determine: 1) the relationship betweenmuscle thickness change (MTC) as measured by rehabilitative ultrasound imaging(RUSI) and EMG activity in the lumbar multifidus (LM), 2) if motor control changesproduced by experimentally induced pain are measurable with RUSI, 3) if a differenceexists in MTC between subjects with low back pain (LBP) classified in the treatmentbasedclassification system (TBC) system and controls, 4) if MTC improves followingintervention.Current literature suggests sub-groups of patients with LBP exist and responddifferently to treatment, challenging whether the majority of LBP is "nonspecific". TheTBC system categorizes subjects into one of four categories (stabilization, mobilization,direction specific exercise, or traction). Currently, only stabilization subjects receive anintervention emphasizing stability. Because recent research has demonstrated that motorcontrol impairments of lumbar stabilizing muscles are present in most subjects with LBP,it is hypothesized that impairments may be present across the TBC classifications.Study 1: Established the relationship between MTC as measured by RUSI andEMG in the LM. Study 2: Assessed MTC of the LM during control and painfulconditions to determine if induced pain changes in LM and transverse abdominis (TrA)are measurable with RUSI. Study 3: Measured MTC of the LM and TrA in subjects withLBP classified in the TBC system and 20 controls. Subjects completed a stabilizationprogram and were re-tested.The inter-tester reliability of the RUSI measurements was excellent (ICC3,3 =.91,SEM=3.2%). There was a curvilinear relationship (r = .79) between thickness changeand EMG activity. There was a significant difference (p andlt; .01) between control andpainful conditions on 4 of the 5 LM tasks tested and on the TrA task. There was adifference in MTC between subjects and controls on the loaded LM test which varied bylevel and category. All categories were different from control on the TrA. Followingintervention the TrA MTC improved (p andlt; .01). The LM MTC did not (p values from .13-.86).These findings suggest MTC can be clinically measured and that deficits existwithin TBC system. Significant disability and pain reduction were measured.

BACKGROUND: Healthcare workers are among the most injured workers in the United States. This is due to the high rate of patient handling. The low back is the most injured in this population. This study observed biomechanical factors and how these factors affect low back and ground reaction forces. This study further investigated pain and its relationship to low back force, multifidus cross-sectional area, and multifidus activation in healthcare workers. METHODS: The 45 participants included 10 healthy subjects in the preliminary study and 35 active healthcare workers in the main study. Subjects filled out the VAS to determine current pain level. Ultrasound images of the multifidus muscles were taken. The participants were fitted with reflective markers and surface EMG sensors. A series of patient transfers at various bed heights using three different transfer devices was undertaken. The transfer devices included a Cotton sheet, a Skil-Care™ Transfer Sling, and an AirPal® device. RESULTS: There was a downward trend in resultant low back force when comparing lower bed heights to higher. Therefore, the highest bed position was determined to be optimal. There were significant differences in low back force between self-chosen and optimal bed heights among healthcare workers. There was no significant difference between peak low back or ground reaction forces between pain and nonpain groups. There was a significant difference in multifidus cross-sectional area between these groups at S1, a trend toward significance at L5, and no difference at L4. There was a trend toward significance when comparing multifidus activation between these groups as recorded by surface EMG. CONCLUSIONS: Healthcare workers should choose higher bed heights and appropriate equipment to reduce low back force and those who have smaller multifidus have more pain.

The objective of this study was to evaluate effects of extracorporeal shockwave therapy (ESWT) on spinal mechanical nociceptive threshold (MNT) and multifidus muscle cross-sectional area (CSA) in horses with thoracolumbar pain. We hypothesized that ESWT would increase MNT and multifidus CSA. Twelve horses with thoracolumbar pain were included. Prior to treatment, each thoracolumbar spine was radiographed to document existing pathology. Horses received 3 ESWT treatments, 2 weeks apart (days 0, 14, 28). Palpation scores were documented (days 0, 45, 65) and ultrasonographic CSA of left and right multifidus was recorded at T12, T14, T16, T18, L3 and L5 (days 0, 45, 65). MNT was measured at T12, T14, T16, T18, L3 and L5 every 7 days (day 0-56). Change in MNT in 10/12 horses was significant at each timepoint compared to day 0 (P<0.05). MNT increased at all timepoints at 6 sites in 2/12, at 5 sites in 3/12, at 4 sites in 4/12 and at 1 site in 1/12 (P<0.05). MNT average percent increase from day 0-56 was 64% for T12-T18 and 29% for L3-L5. There was no statistical difference in MNT from day 35-56 (P=0.25). A bimodal analgesic trend was observed following ESWT. Degree of radiographic change was not associated with response to treatment and no significant change in multifidus CSA was observed. In conclusion, 3 treatments of ESWT 2 weeks apart raised MNT over a 56-day period in horses with back pain, but did not influence change in CSA of the multifidus. / Master of Science / Back pain in the horse is a frequently diagnosed and treated cause of back stiffness, lameness, poor performance and/or avoidance behavior under saddle. Treatment is focused on reducing pain and inflammation and on strengthening and promoting proper muscle development to maintain long term results. Recently, rehabilitation of the deep spinal stabilizer multifidus muscle, particularly with regard to increased cross-sectional area (CSA), has become a focus of targeted physiotherapy. Assessment of the degree of pain is subjective due to individual interpretation and palpation technique. In an attempt to standardize quantification of pain, pressure algometry has become a validated, objective and repeatable measure of axial skeleton mechanical nociceptive threshold (MNT), which is defined as the minimum pressure required to induce a pain response. Although many treatment options for back pain exist, there is limited research documenting the efficacy of these treatments in horses. Extracorporeal shockwave therapy (ESWT), which consists of focused, high velocity acoustic waves, is one type of non-invasive, well-tolerated treatment for back pain. Despite its popularity, there is no research documenting the effects of ESWT on equine spinal MNT or multifidus muscle CSA. This is the first study to document the effects of ESWT on spinal MNT and multifidus muscle CSA in horses with back pain. We hope that the results of this study will help guide treatment decisions for horses with back pain.