ttPR-05-2000 703 7b? 9244 DT1C-ÜC 09=49 P.0^/02 DEFENSE TECHNICAL INFORMATION CENTER REQUEST FOR SCIENTIFIC AND TECHNICAL REPORTS 'The ßfLfr-ho^shif) &E-Kss,£sS LouijJL fWvefyr»^ S^^^ßih <xnd ShouidzA Ovyiuse^ S^/nß4cvn-s-., A (!CL9M.k..§tllE9.„od... P°^'°. §LL^v,vofL'Si 1. Report Availability (Please check one box) [5J This report is available. Complete sections 2a - 2f. 2a. Number of Copies Forwarded 2b. Forwarding Date / Q This report is not available. Complete section 3. y-5'2ooo 2c. Distribution Statement (Please check ONE box) DoD Directive S230.M, "Distribution Statements on Technical Documents," 18 Mar 81, contains seven distribution statements, as described briefly below. Technical documents MUST be assigned a distribution statement. ® DISTRIBUTION STATEMENT A: Approved for public release. Distribution is unlimited D DISTRIBUTION STATEMENT 6: Distribution authorized to U.S. Government /Agencies only. 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(Pleaso check appropriate box) G if was previously forwarded to OTIC on ft*»»/ and the AD number is D It will be published at o later date. Enter approximate date if known. 5n accordance with the provisions of DoD Directive 3200.12, the requested document 13 not. supplied because: print or Type Warm© /rwv,,,j<w. Ph-oTetepfaOKM SikjjtKjKiisra • >/or OTIC i'sx Only I ÄÖ Ktambw TOTAL P.02 DTTC QUALITY INSPECTED 3 ' / The Relationship Between Lower Extremity Strength and Shoulder Overuse Symptoms: A Model Based on Polio Survivors Mary G. Klein, PhD;1 John Whyte, MD PhD;2'5 Mary Ann Keenan, MD;1'5 Alberto Esquenazi, MD;3'5 Marcia Polansky, ScD4 Philadelphia, PA 8 1) Albert Einstein Medical Center; 2) Moss Rehabilitation Research Institute; 9 3) MossRehab Hospital; 4) MCP-Hahnemann University; jo 5) Temple University School of Medicine ll 12 Supported by grant DAMD17-95-1-5079 from the U.S. Department of the Army. 13 14 15 Reprint requests to Mary G. Klein, Korman 204-B, Moss Rehabilitation Research 16 Institute, 1200 West Tabor Road, Philadelphia, PA 19141; Phone: 215-456-7864, 17 FAX: 215-456-9514. 18 19 20 21 22 23 Footline: Leg Weakness and Shoulder Overuse 24 25 ABSTRACT Objective: To determine the relationship between lower extremity weakness and shoulder 26 overuse symptoms among polio survivors. We predicted that individuals with moderate 27 weakness in their leg extensor muscles use their arms to help compensate for this weakness and 28 would be at high risk for developing symptoms of shoulder overuse. 29 30 Design: A cohort study of polio survivors recruited from the Einstein-Moss Post-Polio Management Program, the community and the surrounding tri-state area. 31 Setting: A research laboratory at Moss Rehabilitation Research Institute. 32 Participants: One hundred ninety-four polio survivors were studied; demographic and 33 34 medical history data, symptom data, and strength data were obtained for each. Main Outcome Measures: Presence or absence of shoulder symptoms and ratings of pain by 35 visual analogue scale (VAS) were recorded. Strength was measured using a hand-held 36 dynamometer and manual muscle testing (MMT). 37 Results: Shoulder symptoms could be grouped into two distinct clusters based on the type of 38 testing used for assessment. Symptoms elicited by palpation were present in 26% of the subjects 39 and were strongly related to knee extensor strength and weight. These symptoms were more 40 common among females than males (42% vs. 10%). Symptoms elicited by resistance tests were 41 present in 33% of the subjects and were seen with equal frequency in both genders. These 42 symptoms were also related to lower extremity strength, however the specific relationship was 43 not as clear as for the palpation-related symptoms. 44 Conclusions: Lower extremity weakness predisposes individuals to shoulder overuse 45 symptoms. Gender and body weight are contributing factors. These results may generalize to 46 other populations with lower extremity weakness, including the elderly. Footline: Leg Weakness and Shoulder Overuse 2 47 48 INTRODUCTION The relationship between muscle weakness, overuse and injury is thought to be both a 49 cyclical and a reciprocal one. Muscle weakness can produce overuse, overuse can lead to further 50 weakness, and both can predispose to injury.1 Overuse can occur directly when weakened 51 muscles need to work harder to maintain a certain force or indirectly when alternate muscles are 52 recruited to compensate for weak ones. Individuals can enter this weakness--overuse--injury 53 cycle at different points and at different levels of weakness. 54 There are various etiologies of muscle weakness, but each may lead to overuse. Muscle 55 weakness can occur as a result of lack of exercise (disuse), after an injury or illness, or as the 56 result of a disease, such as polio. The resulting muscle weakness may be severe or mild. Often, 57 individuals may not even be aware of mild muscle weakness. They may function and feel normal 58 during their daily activities but might actually be overusing muscles to compensate for 59 undetected "subclinical" weakness. 60 Because the muscle weakness experienced by many polio survivors is often quite 61 significant, this population is susceptible to an accelerated pattern of overuse. Theoretically, this 62 would allow the symptoms of overuse to be readily observed in a small population over a short 63 period of time. For this reason, we hypothesize that the post-polio population provides an 64 excellent model for the study of overuse disorders in the general population. 65 There are over one million polio survivors in the United States.2 After recovering from 66 the acute infection, survivors were left with varying degrees of muscle strength. As time passed, 67 they became very adept at compensating for weakened muscles, with the end result being a 68 higher risk of overuse and trauma to the compensating muscles as well as those muscles 69 weakened by the initial polio. Footline: Leg Weakness and Shoulder Overuse 3 70 Although the muscle weakness of the polio survivor is often more pronounced than that 71 noted in the general population, polio is not a primary muscle disease. Normal muscle 72 physiology, sensation and motor control are preserved.3 It is thus a "pure" model for studying 73 the effects of muscle weakness on the remainder of the musculoskeletal system. 74 Polio affected the lower extremities with twice the frequency of the upper extremities.4 75 As a result, the most common complaints of polio survivors are related to issues of mobility.5 76 For example, individuals with knee or hip extensor weakness may have difficulty with activities 77 like climbing stairs or rising from a chair and often use their arms to assist with weight-bearing 78 (e.g. to push off the armrests of a chair or pull up on a stair railing). We hypothesized that this 79 behavior would lead to increased susceptibility to shoulder overuse and there would be an 80 association between leg extensor weakness and shoulder overuse symptoms. 81 Previous studies have looked at the relationship of lower extremity weakness to various 82 gait parameters and overuse of compensatory muscles in the legs among polio survivors.3'6 There 83 have also been studies on upper extremity overuse in individuals with paraplegia who must rely 84 exclusively on their upper extremities for mobility.7'8 However, to date, there have not been any 85 studies which explored the potential relationship between lower extremity weakness and upper 86 extremity overuse in an ambulatory population. 87 Therefore, the objective of this study was to explore the relationship between lower 88 extremity weakness and upper extremity overuse among polio survivors, focusing specifically on 89 shoulder symptoms and leg extensor strength. We predicted a curvilinear relationship between 90 symptoms and strength (i.e. that the proportion of subjects with shoulder symptoms would be 91 highest in the mid-range of leg extensor strength). These individuals would be more active than 92 those with severe weakness and would put more stress on their arms during everyday activities Footline: Leg Weakness and Shoulder Overuse 4 93 than those with mild or no noticeable weakness. We also predicted that shoulder symptoms 94 would increase with age, weight and activity level and that the duration of time since the original 95 polio infection would also be an important factor. 96 97 METHOD 98 Subjects 99 A total of 290 polio survivors were recruited from the Einstein-Moss Post-Polio 100 Management Program and the community at large, including the surrounding four-state area: 101 Pennsylvania, New Jersey, Delaware, and southern New York. The inclusion criteria were as 102 follows: 1) a history of polio, 2) no major disabilities unrelated to polio that could cause 103 weakness or overuse problems (e.g. stroke, amputation, inflammatory arthritis, peripheral 104 neuropathy, muscular dystrophy, or congenital malformation), 3) no serious illnesses such as 105 heart or lung disease which would make it unsafe for them to exert themselves in a strength test 106 (e.g. severe emphysema, poorly controlled asthma, resting angina, recent heart attack, or recent 107 treatment of an uncontrolled heart condition), and 4) no fractures or surgeries within the 108 previous six months. 109 Of the 290 polio survivors initially screened, 194 participated in the study. Thirty-one 110 individuals were excluded because they did not meet the inclusion criteria. The remaining 65 111 individuals did not participate because of personal reasons (transportation problems, job 112 conflicts, illness/death in family, etc.) or simply did not show up for one or more scheduled 113 appointments. Ultimately, 98 men and 96 women were enrolled in the study. All subjects 114 provided written informed consent prior to testing. 115 Footline: Leg Weakness and Shoulder Overuse 5 116 117 Procedure The following protocol was approved by our Institutional Review Board. A brief clinical 118 interview was conducted to review a standardized medical history questionnaire and a polio 119 history form in which subjects specified their age at the time of the initial polio infection and 120 identified any sites where they were left with residual weakness or paralysis. There were seven 121 possible sites given: neck, back, abdomen, left arm, left leg, right arm, and right leg. 122 Each subject also completed a self-administered activity assessment survey, which was 123 developed based on a questionnaire designed to measure habitual physical activity.9 The survey 124 included specific activities that might predispose to overuse symptoms and were divided into 125 household, occupational, and recreational tasks. Under each heading, the tasks were broken 126 down into upper limb activities (e.g. reaching, typing, sewing), lower limb activities (e.g. 127 standing, walking, climbing stairs) and transfer activities (moving from sit to stand). For each 128 activity, the subjects chose one of four levels that gave the best estimate of the frequency with 129 which they performed that activity. Upper limb, lower limb, and transfer activity levels were 130 then calculated by summing the frequency scores in each category. 131 After the forms were completed, height (cm) and weight (kg) were measured using a 132 standard scale. A nurse then performed a symptom assessment, which included a combination of 133 palpation and resistance tests of the biceps and supraspinatus. For the biceps palpation test, the 134 shoulder was in neutral rotation, the elbow flexed at 90 degrees and the forearm supinated. 135 Pressure was applied in the bicipital groove on the anterior shoulder. The arm was positioned in 136 a similar way for the biceps resistance test, except the palm was down. The nurse then attempted 137 to supinate the forearm while the subject resisted. For the supraspinatus palpation test, the arm 138 was relaxed at the side and pressure was then applied on the tendon insertion site, just proximal Footline: Leg Weakness and Shoulder Overuse 139 to the greater tuberosity of the humerus. Finally, for the supraspinatus resistance (impingement) 140 test, the arm was held straight out at the side with the thumb pointing towards the floor. The 141 nurse pushed on the arm above the elbow while the subject resisted. 142 If subjects reported feeling shoulder pain during a symptom test, they were asked if they 143 had experienced pain in that area before and if they could identify the estimated date of onset 144 (EDO) of the pain. They were also asked to specify activities that caused pain in the same area. 145 Pain or tenderness identified as being related to the exam only (i.e. "It only hurts when you push 146 there.") was not considered a potential overuse symptom and was not included in any of the 147 analyses. 148 A manual strength examination was then performed by a physical therapist using a hand- 149 held dynamometer (Empi Microfet2, St. Paul, MN). The physical therapist was masked from the 150 results of the symptom assessment to prevent any potential bias. The bilateral hip extensor and 151 knee extensor muscle groups were tested in gravity-eliminated postures. Bilateral shoulder 152 flexion and abduction strength was also measured to account for the possibility that shoulder 153 symptoms might be related to shoulder rather than leg weakness. The postures, placement of the 154 dynamometer, and stabilization points were standardized (Table 1), along with the verbal 155 encouragement used during the testing. 156 For each strength test, the subject pushed against the padded dynamometer force plate, 157 which the physical therapist held stationary. The peak force was measured in pounds, and the 158 range of the dynamometer was 0 to 100 lbs. Two measurements of peak force were taken for 159 each muscle group. Additional measurements were taken only if the first two varied by more 160 than 10% or by more than 1 lb. for strengths less than 10 lbs. The maximum number of 161 Footline: Leg Weakness and Shoulder Overuse 7 162 " Insert Table 1 about here. 163 164 — 165 measurements for a single muscle group was four to prevent fatigue. If a subject reported pain 166 during testing, those trials were considered invalid. For each muscle group, the average of the 167 valid trials was used for analysis. However, any muscle groups that did not have two trials that 168 met the 10% or lib. criteria after four attempts were not included in any analyses. 169 — In order for individuals to use their arms effectively to help push themselves out of a 170 chair, they must have gravity-resistant strength in their elbow extensor muscles. Therefore, once 171 the dynamometer testing was completed, the physical therapist performed manual muscle testing 172 (MMT) on both elbow extensors using a standardized protocol as described by Kendall, and the 173 Lovett grading system.10'11 If the strength was equal to or greater than grade 3, it was specified 174 using a plus (+) or a minus (-) sign to designate intermediary levels. If the strength was less than 175 a grade 3, a muscle grade of <3 was recorded. Only subjects who had a minimum of grade 3 176 strength in both elbow extensors were included in the symptom and strength analyses 177 178 179 Reliability Two nurses and three physical therapists were involved in data collection for this study. 180 Therefore, it was necessary to get a measure of inter-rater reliability for both the symptom and 181 strength assessments. 182 Sixteen polio survivors were tested to determine symptom interrater reliability. Nurse #1 183 performed the initial assessment for 10 of the subjects and Nurse #2 performed the initial 184 assessment for the remaining 6 subjects. A period of one to five days separated the two Footline: Leg Weakness and Shoulder Overuse 8 185 assessments for each subject. All assessments were done at the same time of day.. For 186 symptom reliability, p0 or the proportion of observed agreement was calculated by taking the 187 number of assessments when both nurses agreed divided by the total number of assessments for 188 each of the four symptom tests. All values for p0 were above 93% except for the supraspinatus 189 (impingement) test, which was 87%. 190 To determine the interrater reliability of the strength measurements, six subjects (2 polio 191 survivors and 4 individuals with no history of polio) had their hip extensor, knee extensor, 192 shoulder flexion, and shoulder abduction strength tested bilaterally by each of the three physical 193 therapists. For each subject, all strength assessments were performed at the same time of day 194 within a one month period. Intraclass correlation coefficients (ICC[3,1]12) were used as indices 195 of reliability for the strength measurements. All ICC values were above 0.910 except hip 196 extension on the dominant side, which was 0.787 197 198 Statistical Analysis 199 Data were analyzed using the SYSTAT7 software package. Subjects were classified 200 based on whether they had a positive or negative response to each symptom test. In order to 201 determine whether certain symptom tests were linked in their occurrence either by structure 202 (biceps vs. supraspinatus) or type of test (palpation vs. resistance test), a correspondence analysis 203 was performed. The results revealed two distinct clusters that were arbitrarily identified as 204 Cluster 1 and Cluster 2. Subjects were then reclassified based on whether or not they had any 205 Cluster 1 or Cluster 2 symptoms. 206 Biomechanically, there was no reason to believe that the symmetric/assymmetric use of 207 the lower extremities was relevant to the production of shoulder symptoms. The knee extensors Footline: Leg Weakness and Shoulder Overuse 9 208 work together to help lift a person off a chair, and the hip extensors work together to help the 209 body straighten to a standing position. Therefore, we felt it was appropriate to consider 210 combinations of the strengths of similar types of muscles in our analyses, including KNEES (the 211 combined strength of both knee extensors), HIPS (the combined strength of both hip extensors), 212 and ALL (the combined strength of both knee extensors and both hip extensors). 213 In order to determine the nature of the relationship between symptom status and the 214 various independent variables (age, time since polio, weight, activity scores and the various 215 strength measures), we converted the independent variables to quintiles (i.e. sorted each from 216 smallest to largest and separated them into five bins with approximately the same number of 217 subjects in each bin). The proportion of subjects in each quintile with either Cluster 1 or Cluster 218 2 symptoms was then calculated. Plots of the proportion of subj ects in each symptom cluster 219 against the various independent variables (in quintiles) revealed neither a linear pattern nor a 220 good fit to a polynomial equation. Therefore, the quintiles were treated as categorical variables 221 (1 -5). The only exception was weight. In the plot of the proportion of subj ects with Cluster 1 222 symptoms versus weight, we observed an increasing pattern. Therefore, this variable was 223 treated as quantitative instead of categorical in the analyses for this symptom cluster. A Chi- 224 square analysis was used to evaluate the effect of gender. 225 Because of the relatively large number of potential predictor variables, univariate logistic 226 regression was performed to eliminate some terms prior to doing a multivariate stepwise logistic 227 analysis. A cutoff value of 0.15 was used. In the multivariate analysis, the p-values were 228 calculated relative to the highest level or quintile 5 for each independent variable. Odds ratios 229 were calculated as a measure of the difference in the proportion of shoulder symptoms between 230 quintile 5 and the other quintiles. Footline: Leg Weakness and Shoulder Overuse 10 231 RESULTS 232 Subject Characteristics 233 The range in age for the study population was 32 to 81 years (mean age: 57 ± 10 yr.). 234 The median age at onset of polio was 5 years, and the median number of years since polio was 235 48, ranging from 29 to 80 years. As expected, the most common sites for residual weakness 236 were the legs (left (57%) and right (55%)). All of the remaining sites had values below 25%. 237 Approximately 7% of the subjects stated that they had no residual weakness or paralysis. 238 A total of 15 (8%) of the subjects enrolled in the study did not meet the minimum 239 requirements for elbow extensor strength (grade 3 or better in both arms). Therefore, their data 240 were excluded from the strength and symptom analyses. 241 242 243 Shoulder Symptoms Overall, 90 (46%) of the subjects had one or more shoulder symptoms. The 244 correspondence analysis showed that there were two distinct symptom clusters. Cluster 1 245 consisted of the four palpation tests (left and right biceps palpation and left and right 246 supraspinatus palpation). Cluster 2 consisted of the four resistance tests (left and right 247 supraspinatus (impingement) tests and left and right biceps tests). Replication of the 248 correspondence analysis separately for each gender gave similar results. In both cases, the 249 palpation-provoked symptoms formed one cluster and the resistance-provoked symptoms formed 250 another. 251 252 There was no significant association between symptom clusters (Chi-square value = 0.060,1 d.f, p = 0.806). Overall, 30 (17%) subjects had palpation-provoked symptoms only, 43 Footline: Leg Weakness and Shoulder Overuse 253 (24%) subjects had resistance-provoked symptoms only, and 17 (9%) subjects had both types of 254 symptoms. 255 256 Palpation Symptom Analysis 257 There was a significant association between gender and the presence of palpation 258 symptoms (Chi-square value = 15.552,1 d.f, p-value < 0.001). A total of 38 (42%) females had 259 palpation symptoms compared to only 9 (10%) males. Because of the relatively low number of 260 males with these symptoms, the remaining analyses were performed with females only. 261 The results of the univariate logistic regression analysis with presence or absence of 262 palpation symptoms as the dependent variable, showed that weight, age, shoulder flexion 263 strength, upper limb activity score, KNEES and ALL had p-values below the 0.15 cutoff. When 264 these variables were put into a stepwise multivariate logistic regression analysis, the results 265 showed that KNEES and weight were the best predictors of the presence of palpation symptoms 266 among females. The p-values and odds ratios for the model are listed in Table 2. 267 A plot of the proportion of females with palpation symptoms versus KNEES (in 268 quintiles) showed evidence of a threshold effect (Figure 1). The proportion of females with 269 palpation symptoms was significantly higher when bilateral knee extensor strength was less than 270 79 lb. than when it was greater than 79 lb. A plot of the proportion of females with palpation 271 symptoms versus weight (in quintiles) revealed that as weight increased, the proportion of 272 females with shoulder symptoms also increased (Figure 2). 273 274 275 Insert Table 2 about here. ~ Footline: Leg Weakness and Shoulder Overuse " 12 276 Insert Figure 1 about here. 277 278 279 Insert Figure 2 about here. 280 281 282 283 284 Resistance Symptom Analysis A Chi-square analysis showed no significant association between gender and presence of 285 resistance symptoms (Chi-square value = 0.025, p - 0.999), with an approximately equal 286 proportion of symptomatic subjects for each gender (males: 33% and females: 34%). Therefore, 287 we initially performed the logistic analyses with both genders combined. 288 The results of the univariate analysis, with presence or absence of resistance symptoms as 289 the dependent variable, showed that HIPS, KNEES, ALL, and age all had p-values that were less 290 than the cutoff level of 0.15. The results of the stepwise multivariate analysis showed that the 291 model containing ALL and age best predicted the presence of resistance symptoms. The p- 292 values and odds ratios for the model are summarized in Table 3. 293 A plot of the proportion of subjects with resistance symptoms versus ALL (in quintiles) 294 showed that the highest proportion of symptomatic subjects was found in the mid-range for 295 overall leg extensor strength (Figure 3). The plot of the proportion of subjects with resistance 296 297 Insert Table 3 about here. 298 Footline: Leg Weakness and Shoulder Overuse 299 symptoms versus age (in quintiles) showed that subjects between the ages of 50 and 54 years, 300 had the highest proportion of symptoms (Figure 4). 30i Because of concern that gender was possibly confounding the results, the analysis was 302 repeated on each gender separately. The results of the univariate analysis for males showed that 303 KNEES and age were the only predictors with p-values less than 0.15. The stepwise multivariate 304 analysis resulted in a model containing both variables. Plots of the proportion of males with 305 resistance symptoms revealed that the highest proportion of symptomatic males were in the mid- 306 range for both bilateral knee extensor strength and age. For females, the results of the univariate 307 analysis showed that HIPS, ALL, and age had p-values less than 0.15. The stepwise multivariate 308 analysis produced a model containing HIPS and age. The highest proportion of symptomatic 309 females was on the low end for both bilateral hip extensor strength and age. 310 The odds ratios, sensitivity, and specificity values for the KNEES model and the HIPS 311 model for both genders were compared (Table 4). For males, the KNEES model appeared to be 312 the best predictor, with larger, more significant odds ratios and a higher sensitivity value model 313 than the HIPS model. However, the HIPS model for males had a higher value for specificity 314 than the KNEES model. For females, the odds ratios for both the knee and hip models show 315 similar patterns, and the sensitivity and specificity values for both models are comparable. 316 — 317 Insert Figure 3 about here. 318 319 320 —— Insert Figure 4 about here. 321 Footline: Leg Weakness and Shoulder Overuse 14 322 _____ 323 Insert Table 4 about here. 324 325 326 DISCUSSION The purpose of this study was to determine if there was a systematic relationship between 327 leg extensor weakness and the presence of pain potentially attributable to shoulder overuse. The 328 results showed that the shoulder symptom tests could be divided into two distinct clusters based 329 on the type of testing used for assessment. The results of the multivariate analyses appear to 330 support the theory that these are two different symptom complexes. 331 Palpation-provoked symptoms were more common among females, as are many overuse 332 injuries.13,14 This may be due to differences in pain perception and report. Previous studies have 333 suggested men have a higher pain tolerance than women, especially in tests involving pressure 334 pain.15,16'17 These differences in pain sensitivity have been attributed to a variety of factors 335 including differences in body size and skin thickness, sex-role expectations, and hormones. This 336 may explain why we did not see a significant gender effect for resistance symptoms, which were 337 assessed with an active motion test as opposed to someone applying pressure to a particular area. 338 In order to determine if gender differences might simply be related to greater stoicism among 339 men, we assessed the severity ratings for the resistance symptoms and found no significant 340 differences (i.e.women did not rate their pain intensity higher than men). 341 Palpation symptoms among women were strongly related to knee extensor strength and 342 weight. The most likely explanation is that weak knee extensors cause increased demand on the 343 arms during tasks such as getting up from a chair or using an assistive device for ambulation. 344 Increased weight will also result in an increased demand on the arms during similar tasks. Footline: Leg Weakness and Shoulder Overuse 15 345 Unfortunately, we did not have sufficient power to allow us to distinguish a threshold model 346 from the predicted curvilinear model. From the graph of the proportion of females with 347 palpation-provoked symptoms versus quintiles of knee extensor strength, it did appear that the 348 proportion of symptomatic females was highest in the mid-range for strength. However, it was 349 not possible to determine whether females with moderate weakness were truly at higher risk for 350 shoulder symptoms than profoundly weak subjects or whether this peak was simply due to 351 random error. 352 In terms of predicting resistance symptoms, we were not able to draw any definitive 353 conclusions. While it does appear that some aspect of lower extremity strength is a significant 354 predictor for resistance symptoms for both genders, the results were variable between KNEES, 355 HIPS and ALL, depending on which genders were included in the model. The results for males 356 suggested that knee extensor strength is more important. However, for females the results were 357 not as clear and there remains some doubt as to whether hip extensor, knee extensor strength, or 358 some combination of both is the best predictor for females. Because of the high correlations 359 between strength variables, a larger study is needed to determine which aspect of lower extremity 360 strength is most important when predicting resistance symptoms and whether there are actually 361 any gender-related differences. 362 Shoulder abduction strength was not found to be a significant predictor of shoulder 363 symptoms in this population. Shoulder flexion strength met the cutoff criterion in the univariate 364 analysis for palpation symptoms among females (p-value = 0.150), but was not selected in the 365 stepwise multivariate analysis. Previous research on other populations has shown a relationship 366 between weak shoulder muscles and shoulder symptoms in able-bodied adults (abductors and 367 external rotators)18 and in wheelchair athletes (adductors and internal rotators).19,20 It is possible Footline: Leg Weakness and Shoulder Overuse 16 368 that other shoulder strength measures such as adductor or internal rotator strength, which were 369 not measured in this study, are related to shoulder symptoms in this population. However, 370 despite this, the fact that knee extensor strength was a good predictor of shoulder symptoms 371 provides support for our hypothesis that lower extremity weakness plays an important role in the 372 production of shoulder symptoms in this population. 373 Age was an important factor for predicting resistance symptoms. We had predicted that 374 duration of time since polio would be more important than chronological age in this population, 375 but duration was not significant even at the univariate level. We had also predicted that 376 symptoms would increase as age increased. However, the results showed that the proportion 377 symptomatic subjects was highest among the younger females and the middle-age males in our 378 study population. We speculate that these age levels may be most closely associated with the 379 activity levels that provoke the symptoms. 380 In able-bodied populations, repetitive manual work is a known risk factor for shoulder 381 symptoms.21'22 A previous study involving 32 polio survivors reported that the experience of 382 pain was related to level of physical activity.5 383 activity level or transfer activity level would be an important factor in predicting the presence of 384 shoulder symptoms. However, none of the activity levels were significant at the univariate level 385 for resistance symptoms and only upper limb activity level was significant at the univariate level 386 for palpation symptoms (p-value = 0.033). One possible explanation is that our activity 387 questionnaire provided us with only a gross measure of upper and lower limb activity. In order 388 to cover individuals with a wide range of strengths and activity levels, we were forced to make 389 our questions as broad as possible. If we had limited our study to individuals with significant 390 lower extremity weakness and concentrated more closely on activities performed by people at Footline: Leg Weakness and Shoulder Overuse In this study, we expected that lower limb 17 391 this strength level, we expect that we would have found a stronger association between activity 392 level and shoulder symptoms. 393 Another limitation of this study was that we did not have the power to test interactions 394 between independent variables due to the relatively low percentage of subjects with each 395 symptom cluster. More data are needed in order to capture the complicated synergisms that may 396 exist between variables. For example, we would expect that there would be an interaction 397 between strength and weight. Previous studies have documented that the amount of muscle 398 strength required to perform daily activities increases as weight increases.23'24'25 Weight was an 399 important predictor for palpation symptoms along with overall knee extensor strength. We 400 attempted to capture the interaction between knee strength and weight by calculating the ratio 401 between the two variables (knee extensor strength divided by weight). However, our analysis 402 showed that this ratio did not predict the presence of palpation-provoked symptoms as well as the 403 model with weight and KNEES. 404 Future studies are needed in this area involving larger samples to better characterize the 405 shapes of the distributions of symptom risk. Research involving other populations with varying 406 levels of lower extremity weakness is also needed to determine if these results are generalizable 407 to other groups. For example, the elderly are at high risk for lower extremity weakness due to a 408 reduction in activity level and the decline in muscle strength associated with normal aging. In a 409 sample of 58 subjects with no history of any neuromuscular disorders, aged 60 to 88 years, we 410 found that 39% had bilateral knee extensor strength that was less than 79 lb. (unpublished data). 411 According to our model, these people may be at high risk for development of shoulder overuse 412 symptoms. Footline: Leg Weakness and Shoulder Overuse 413 Biomechanical studies of the compensation patterns used by people with lower extremity 414 weakness are also needed, both to identify the specific activity patterns and to determine whether 415 there are actual gender differences. Finally, there is a need for studies which examine the 416 effectiveness of therapies designed to either reduce the stress on the shoulders or increase the 417 strength of the lower extremities as a way of preventing or reducing overuse symptoms in the 418 shoulder. 419 420 421 CONCLUSIONS The results of the present study indicate that there is a relationship between lower 422 extremity weakness and shoulder symptoms. In this sample of polio survivors, knee extensor 423 strength was identified as an important predictor of shoulder symptoms, with individuals with 424 moderate weakness at highest risk. Body weight and age were also relevant factors. These 425 results have important implications for people with significant levels of lower extremity 426 weakness, who tend to increase their reliance on the upper extremities for mobility and activities 427 of daily living. For these people, shoulder overuse problems can have a significant effect on 428 quality of life. Additional research is needed to increase the awareness of the prevalence and 429 impact of upper extremity overuse disorders in people with lower extremity weakness. 430 431 Acknowledgments: The authors would like to thank Roberta Costello, RN, Jeannine Jacobs, 432 RN, Julie Nagorsky, PT, Christina Palmer, PTA, and Steve Sepel, PT for their assistance with 433 data collection. We would also like to thank Yvonne Randolph for her help with recruiting and 434 scheduling subjects. Finally, we gratefully acknowledge the time and effort of our research 435 subjects without whom this research would not have been completed. Footline: Leg Weakness and Shoulder Overuse 19 436 REFERENCES 437 1. Kibler WB, Chandler TJ, Stracener ES. Musculoskeletal adaptations and injuries due to 438 439 440 441 442 443 overtraining. Exerc Sports Sei Rev 1992; 20: 99-126. 2. Salazar-Grueso EF, Siegel I, Roos RP. The post-polio syndrome: evaluation and treatment. Comprehensive Therapy 1990; 16(2): 24-30. 3. 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Upper-extremity tendinitis and overuse syndromes in the athlete. Clin Sports Med 1998; 17(3): 433-448. Footline: Leg Weakness and Shoulder Overuse 21 481 482 483 484 485 486 23. Hyatt RH, Whitelaw MN, Bhat A, Scott S, Maxwell JD. Association of muscle strength with functional status of elderly people. Age Ageing 1990; 19: 330-336. 24. Konczak J, Meeuwsen HJ, Cress ME. Changing affordances in stair climbing: the perception of maximal climbability in young and older adults. J Exp Psych 1992; 18: 691-697. 25. Büchner DM, DeLateur BJ. The importance of skeletal muscle strength to physical function in older adults. Ann Behav Med 1991; 13: 91-98. 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 Footline: Leg Weakness and Shoulder Overuse 22 504 LEGENDS 505 Figure 1 illustrates the relationship between knee extensor strength and the proportion of females 506 with Cluster 1 (palpation) symptoms. Quintiles of strength among females are shown along the 507 X axis, arrayed from weakest to strongest. The proportion of women with palpation-provoked 508 symptoms in each quintile is shown on the Y axis. 509 510 Figure 2 depicts the relationship between the proportion of females with Cluster 1 (palpation) 511 symptoms and weight. Quintiles of weight, from lightest to heaviest, are shown on the X axis. 512 The bars represent the proportion of women with Cluster 1 (palpation) symptoms in each 513 quintile. 514 515 Figure 3 illustrates the relationship between overall leg extensor strength (ALL) and Cluster 2 516 (resistance) symptoms. The quintiles of strength are arrayed from weakest to strongest along the 517 X axis, and the proportion of subjects with resistance-induced symptoms in each quintile is 518 shown on the Y axis. 519 520 Figure 4 illustrates the relationship between age and Cluster 2 (resistance) symptoms. The 521 quintiles of age are ordered from youngest to oldest along the X axis. The bars represent the 522 proportion of subjects in each quintile with resistance-induced symptoms. Footline: Leg Weakness and Shoulder Overuse 23 #» ~0' K\' ^J n0' #-J **>' ^ ^ (r,' Bilateral Knee Extensor Strength (lb) Weight (kg) a. 0.0 &' &' N#' Bilateral Leg Extensor Strength (lb) &' Age (yr) Table 1. Symptom Evaluation Protocol Procedure Test Arm Position Biceps Shoulder in neutral rotation; Pressure applied in bicipital palpation elbow flexed 90°; forearm groove on anterior shoulder supinated Supraspinatus Arm relaxing at side; Pressure applied on tendon insertion site just proximal palpation to greater tuberosity of humerus Supraspinatus Arm straight out at side Examiner pushes on arm above (impingement) and internally rotated with elbow while subject resists test thumb pointing towards floor Biceps test Shoulder in neutral; elbow Examiner attempts to supinate flexed 90°; palm down forearm while subject resists Footline: Leg Weakness and Shoulder Overuse Table 2. Prediction of Shoulder Symptoms Provoked by Palpation Confidence Interval Odds Ratio Upper Lower 0.000 2.346 3.668 1.500 Knees -1 0.014 13.454 107.589 1.683 Knees - 2 0.020 11.412 88.756 1.467 Knees - 3 0.006 18.526 146.600 2.341 Knees - 4 0.055 6.885 49.428 0.959 Variable* p-value Constant 0.000 Weight *.variables are in quintiles Footline: Leg Weakness and Shoulder Overuse Table 3. Prediction of Shoulder Symptoms Provoked by Resistance Tests Confidence Interval Odds Ratio Upper Lower 0.052 5.833 34.436 0.988 All-2 0.376 2.308 14.717 0.362 All-3 0.044 5.250 30.621 0.900 All-4 0.065 6.000 34.317 1.049 Age-1 0.442 1.634 5.709 0.467 Age-2 0.036 3.916 13.988 1.096 Age-3 0.985 1.012 3.787 0.271 Age-4 0.185 2.337 8.215 0.665 Variable* p-value Constant 0.001 All- 1 * variables are in quintiles Footline: Leg Weakness and Shoulder Overuse Table 4. Comparison of Regression Models Model: KNEES and AGE Males Variable* Model: HIPS and AGE Males Females Odds ratio Odds ratio Females Variable* Odds ratio Odds ratio KNEES-1 7.269 5.549 fflPS-1 3.995 10.032* KNEES-2 3.952 2.235 HIPS-2 2.798 2.860 KNEES-3 22.218* 4.838 HIPS-3 3.819 5.793 KNEES-4 2.095 4.870 fflPS-4 1.446 6.406* AGE-1 2.154 1.567 AGE-1 0.855 2.845 AGE-2 16.396* 3.399 AGE-2 3.979 3.641 AGE-3 11.759* 0.310 AGE-3 4.050* 0.395 AGE-4 3.732 1.215 AGE-4 1.245 1.863 Sensitivity 0.758 0.449 Sensitivity 0.435 0.441 Specificity 0.507 0.693 Specificity 0.702 0.725 Note: The models which resulted from the stepwise multivariate analysis are in bold. * - variables are in quintiles t-p<0.05 *-p<0.01 Footline: Leg Weakness and Shoulder Overuse TABLE 1. SUMMARY OF POST-POLIO RESEARCH Authors Length of Study Population Muscle(s) Results Dalakas et al.(1986)' 27 polio survivors* (symptomatic) ave. of8.2yr. (range 4.5 - 20 yr.) overall body score annual decline of 1% in mean score Munsat, Andres, and Thibideau (1987)5 6 polio survivors (symptomatic) 400 to 2100 days unknown no significant change in strength Agre and Rodriquez(1990)6 23 polio survivors* 12 controls 2yr. biceps, hamstring quadriceps no significant change in any variables for either group Agre and Rodriquez (1991)7 44 polio survivors* 38 controls lyr. quadriceps (affected side only11) no significant change in any measures for either group Muninetal. (1991)9 7 polio survivors* (symptomatic) 3yr. quadriceps 29% increase on affected side, 14% increase on the nonaffected side Grimby, Hedberg, and Henning (1994)2 20 polio survivors* (12 unstable and 8 stable) 4-5 yr. quadriceps and hamstring (affected side only11) significant decrease in all measures for unstable group; only for knee flexion in stable group Agreetal(1995)3 78 polio survivors* 4yr. quadriceps and hamstring (affected side only^) significant decrease in quadriceps strength only Grimby, Kvist, and Grangard(1996)4 18 polio survivors* 4yr. quadriceps, hamstrings in 26 legs total thigh muscle strength decreased 7.8%+ 2.9% ave. of 2.1 yr. (range 199 to 1070 days) Shld. abductors and adductors; Elbow flexors and extensors; Wrist flexors and extensors; Hip abductors, adductors, and flexors; Knee flexors and extensors; Ankle dorsiflexors and plantarflexors significant increase in strength in 10 out of 22 muscles for symptomatic group; significant decrease in 1 out of 22 muscles for asymptomatic group 7 years quadriceps (affected side only11) no significant difference in rate of strength loss between groups Ivanyietal. (1996)' Rodriquez, Agre, and Franke (1997)8 56 polio survivors* (43 symptomatic and 13 asymptomatic) 23 polio survivors* (11 unstable and 12 stable) 14 controls* * - all subjects were less than 65 years old at initial visit - if both legs affected, stronger one was tested 11 22 Footline: Strength in Polio Survivors Table 2. Strength Testing Protocol Muscle Group Body Position Position of Limb HHD Placement Stabilization Point Just proximal to ulnar styloid Contralateral shoulder Shld. Ext. Rotation Sitting Shoulder at neutral; elbow flexed 90° Shld. Abduction Supine Shoulder abducted 90° Midshaft of humerus Anterior aspect of shoulder Shld. Flexion Sidelying Shoulder flexed 90 elbow extended Midshaft of humerus Anterior aspect of shoulder Shld Extension Sidelying Shoulder at neutral; elbow flexed 90° Proximal to olecranon Anterior aspect of shoulder Elbow Extension Sidelying Shoulder at neutral; elbow flexed 90° Proximal to ulnar styloid; Shoulder dorsal surface of forearm Elbow Flexion Sidelying Shoulder at neutral; elbow flexed 90° Palmar surface of forearm; Shoulder proximal to wrist Wrist Flexion Sitting Shoulder at neutral; elbow flexed 90° Dorsal aspect of hand Forearm Wrist Extension Sitting Shoulder at neutral; elbow flexed 90° Palmar aspect of hand Forearm Hip Abduction Supine Hip abducted to 45°; with contralateral hip neutral Proximal to superior pole Hip of patella on lateral aspect of thigh Hip Flexion Sidelying* Hip flexed to 30°; knee flexed 60° Proximal to superior side of patella Pelvis Hip Extension Sidelying* Hip neutral; knee extended Proximal to popliteal crease Pelvis Knee Flexion Sidelying* Hip flexed 10°; knee flexed 30° Proximal to maleoli on posterior aspect of calf Anterior aspect of femur Knee Extension Sidelying* Knee flexed 45° Proximal to malleoli on anterior aspect of tibia Femur Metatarsals Tibia Ankle D. Flexion Supine Hip, knee, ankle at 0° Ankle P. Flexion Supine Hip, knee, ankle at 0° Metatarsal heads Tibia * Leg positioned on raised powder board Footline: Strength in Polio Survivors 23 Table 3. Characteristics of Subjects in Upper Extremity Group* Variable Present age (years) Age (at onset of acute polio, years) Height (cm) Male Subjects N = 32 Mean (SD) Female Subjects N = 39 Mean (SD) 57.84(11.7) 56.31(8.6) 7.15(6.3) 6.41(6.5) 175.40(7.9) 162.19(6.4) 86.77 (18.4) 70.07 (16.8) Left Shoulder External Rotator 20.23 (9.4) 15-70 (4.6) Right Shoulder External Rotator 20.96(7.8) 16.14(4.8) Left Wrist Flexor 23.06 (7.8) 16-50 (4.7) Right Wrist Flexor 26.67(6.4) 19.10(5.0) Left Wrist Extensor 26.69(7.0) 17.92(5.2) Right Wrist Extensor 26.11(6.7) 18.19(5.8) Left Shoulder Abductor 30.37(13.1) 19.26(6.2) Right Shoulder Abductor 29.39(13.3) 18.83(6.6) Left Shoulder Flexor 34.27(14.3) 21.89(5.5) Right Shoulder Flexor 34.13(12.0) 21.66(6.8) Left Shoulder Extensor 36.38(13.3) 23.24(6.0) Right Shoulder Extensor 34.36(12.2) 21.75(6.7) Left Elbow Extensor 31.50(15.4) 23.67(6.3) Right Elbow Extensor 33.95 (8.6) 23.09 (6.8) Left Elbow Flexor 44.19(14.5) 28.53(7.5) Right Elbow Flexor 44.55(12.4) 29.70(9.3) Weight (kg) Strength (at initial visit lb) * Reasons for excluding subjects from upper extremity group: 26 subjects had pain during testing, 17^cts were Sria for one one or or more muscle groups groups,: and 6 subjects had initial strength equal to zero m one or more muscle missing data for more muscle groups 24 Footline: Strength in Polio Survivors Table 4. Effect Sizes for Upper Extremity Muscles Muscle Group Effect Size Right Wrist Flexor 1.109 Left Shoulder External Rotator 0.794 Left Elbow Extensor 0.758 Left Shoulder Extensor 0.719 Right Elbow Extensor 0.694 Right Shoulder External Rotator 0.670 Right Shoulder Extensor 0.525 Left Wrist Flexor 0.496 Left Shoulder Abductor 0.455 Right Shoulder Flexor 0.455 Left Wrist Extensor 0.448 Right Elbow Flexor 0.444 Left Elbow Flexor 0.421 Right Shoulder Abduction 0.391 Left Shoulder Flexor 0.310 Right Wrist Extensor 0.222 Footline: Strength in Polio Survivors 25 Table 5. Characteristics of Subjects in Lower Extremity Group* Male Subjects N = 30 Mean (SD) Female Subjects N = 35 Mean (SD) 57.93 (10.6) 54.80 (7.3) 7.55 (6.2) 5.91 (6.2) Height (cm) 177.10(1.8) 163.14(6.6) Weight (kg) 84.17(17.8) 71.10(13.8) Left Hip Flexor 43.21 (13.8) 29.60(10.3) Right Hip Flexor 45.07(13.1) 30.82 (10.2) Left Hip Extensor 36.40(11.7) 26.75 (8.9) Right Hip Extensor 35.79(11.6) 25.56 (8.4) Left Hip Abductor 42.00 (13.0) 28.22 (8.6) Right Hip Abductor 38.57(12.4) 25.13(7.7) Left Knee Flexor 38.80(16.1) 27.97(11.5) Right Knee Flexor 36.67 (13.2) 22.51(9.7) Left Knee Extensor 43.20 (20.7) 29.47(13.1) Right Knee Extensor 45.09 18.8) 32.01 (15.5) Left Ankle Dorsiflexor 32.45(15.1) 25.40(10.8) Right Ankle Dorsiflexor 25.72 (13.6) 21.77(10.6) Left Ankle Plantarflexor 42.25 (16.8) 35.17(14.7) Right Ankle Plantarflexor 39.10(19.2) 29.56 (14.2) Variable Present age (years) Age (at onset of acute polio, years) Strength (at initial visit lb) * Reasons for excluding subjects from lower extremity group: 12 subjects had pain during testing, 13 subjects were missing data for one or more muscle groups, and 30 subjects had initial strength equal to zero in one or more muscle groups. Footline: Strength in Polio Survivors 26 Table 6. Effect Sizes for Lower Extremity Muscles Muscle Group Effect Size Left Ankle Dorsiflexor 1.050 Right Ankle Dorsiflexor 0.856 Left Knee Flexor 0.682 Left Hip Flexor 0.419 Right Hip Flexor 0.383 Right Knee Flexor 0.218 Right Knee Extensor 0.128 Right Hip Extensor -0.024 Left Hip Abductor -0.037 Left Hip Extensor -0.083 Left Knee Extensor -0.110 Right Hip Abductor -0.130 Right Ankle Plantarflexor -0.296 Left Ankle Plantarflexor -0.368 Footline: Strength in Polio Survivors 27 £. Table 7. Comparison of Rate of Deterioration of Strength* in Young and Old Polio Survivors Mean (SD) Muscle Group Young Group (40-50 yr.) N=18 Old Group (60-70 yr.) N=17 Mann-Whitney U p-value Lower Extremity** -0.031 (2.9) -0.999(3.1) 0.317 Left Hip Flexor -2.314(4.4) -1.858(3.1) 0.621 Right Hip Flexor -1.055(5.3) -2.785 (3.9) 0.249 Left Knee Flexor -2.507 (2.3) -1.590(2.4) 0.248 Right Knee Flexor -0.520 (2.6) -1.460(4.5) 0.756 Left Ankle Dorsiflexor -4.337 (3.7) -4.820 (4.2) 0.644 Right Ankle Dorsiflexor -2.446 (2.0) -3.592 (3.2) 0.310 * represented by robust slope calculated based on strength data from three visits ** average slope across all lower extremity muscles