Exercise reduces circulating biomarkers of cellular senescence in humans.

Cellular senescence has emerged as a significant and potentially tractable mechanism of aging and multiple aging-related conditions. Biomarkers of senescent cell burden, including molecular signals in circulating immune cells and the abundance of circulating senescence-related proteins, have been associated with chronological age and clinical parameters of biological age in humans. The extent to which senescence biomarkers are affected by interventions that enhance health and function has not yet been examined. Here, we report that a 12-week structured exercise program drives significant improvements in several performance-based and self-reported measures of physical function in older adults. Impressively, the expression of key markers of the senescence program, including p16, p21, cGAS, and TNFα, were significantly lowered in CD3+ T cells in response to the intervention, as were the circulating concentrations of multiple senescence-related proteins. Moreover, partial least squares discriminant analysis showed levels of senescence-related proteins at baseline were predictive of changes in physical function in response to the exercise intervention. Our study provides first-in-human evidence that biomarkers of senescent cell burden are significantly lowered by a structured exercise program and predictive of the adaptive response to exercise.

The senescence-associated secretome as an indicator of age and medical risk.

Produced by senescent cells, the senescence-associated secretory phenotype (SASP) is a potential driver of age-related dysfunction. We tested whether circulating concentrations of SASP proteins reflect age and medical risk in humans. We first screened senescent endothelial cells, fibroblasts, preadipocytes, epithelial cells, and myoblasts to identify candidates for human profiling. We then tested associations between circulating SASP proteins and clinical data from individuals throughout the life span and older adults undergoing surgery for prevalent but distinct age-related diseases. A community-based sample of people aged 20-90 years (retrospective cross-sectional) was studied to test associations between circulating SASP factors and chronological age. A subset of this cohort aged 60-90 years and separate cohorts of older adults undergoing surgery for severe aortic stenosis (prospective longitudinal) or ovarian cancer (prospective case-control) were studied to assess relationships between circulating concentrations of SASP proteins and biological age (determined by the accumulation of age-related health deficits) and/or postsurgical outcomes. We showed that SASP proteins were positively associated with age, frailty, and adverse postsurgery outcomes. A panel of 7 SASP factors composed of growth differentiation factor 15 (GDF15), TNF receptor superfamily member 6 (FAS), osteopontin (OPN), TNF receptor 1 (TNFR1), ACTIVIN A, chemokine (C-C motif) ligand 3 (CCL3), and IL-15 predicted adverse events markedly better than a single SASP protein or age. Our findings suggest that the circulating SASP may serve as a clinically useful candidate biomarker of age-related health and a powerful tool for interventional human studies.

The Impact of Frailty on Patient-Centered Outcomes Following Aortic Valve Replacement.

BACKGROUND: Frailty confers risk for surgical morbidity and mortality. Whether patient-reported measures of health, well-being, or quality of life respond differently to surgery in non-frail and frail individuals is unknown. METHODS: Older adults with severe aortic stenosis presenting for surgery were assessed for frailty using Cardiovascular Health Study Criteria. Patient-reported measures of functional capacity (Duke Activity Status Index [DASI]), physical and mental health (Medical Outcomes Study Short Form-Physical and Mental Component Scales [SF-12 PCS and SF-12 MCS, respectively]), well-being (linear analogue self-assessment [LASA]), and quality of life (LASA) were administered before and 3 months after surgery. RESULTS: Of 103 participants (mean age of 80.6 years), 54 were frail. Frail participants had lower baseline DASI, SF-12 PCS, SF-12 MCS, physical well-being, and quality of life scores than non-frail participants. At follow-up, frail participants showed significant improvement in physical function, with DASI and SF-12 PCS scores improving by 50% and 14%, respectively. Non-frail subjects did not significantly improve in these measures. SF-12 MCS scores also improved to a greater extent in frail compared to non-frail participants (3.6 vs < 1 point). Furthermore, the frail participants improved to a greater extent than non-frail participants in physical well-being (21.6 vs 7.1 points) and quality of life measures (25.1 vs 8.7 points). CONCLUSIONS: Frailty is prevalent in older adults with severe aortic stenosis and is associated with poor physical and mental function, physical well-being, and quality of life. In response to surgery, frail participants exhibited greater improvement in these patient-centered outcomes than non-frail peers.

Relationship between pre-transplant physical function and outcomes after kidney transplant.

BACKGROUND: Performance-based measures of physical function predict morbidity following non-transplant surgery. Study objectives were to determine whether physical function predicts outcomes after kidney transplant and assess how physical function changes post-transplant. METHODS: We conducted a prospective study involving living donor kidney transplants recipients at our center from May 2012 to February 2014. Physical function was measured using the Short Physical Performance Battery (SPPB [balance, chair stands, gait speed]) and grip strength testing. Initial length of stay (LOS), 30- day rehospitalizations, allograft function, and quality of life (QOL) were assessed. RESULTS: The majority of the 140 patients in our cohort had excellent pre-transplant physical function. In general, balance scores were more predictive of post-transplant outcomes than the SPPB. Decreased pre-transplant balance was independently associated with longer LOS and increased rehospitalizations but not with post-transplant QOL; 35% of patients experienced a clinically meaningful (≥ 1.0 m/s) improvement in gait speed 4 months post-transplant. CONCLUSIONS: Decreased physical function may be associated with longer LOS and rehospitalizations following kidney transplant. Further studies are needed to confirm this association. The lack of relationship between pre-transplant gait speed and outcomes in our cohort may represent a ceiling effect. More comprehensive measures, including balance testing, may be required for risk stratification.

Quantification of GDF11 and Myostatin in Human Aging and Cardiovascular Disease.

Growth and differentiation factor 11 (GDF11) is a transforming growth factor ß superfamily member with a controversial role in aging processes. We have developed a highly specific LC-MS/MS assay to quantify GDF11, resolved from its homolog, myostatin (MSTN), based on unique amino acid sequence features. Here, we demonstrate that MSTN, but not GDF11, declines in healthy men throughout aging. Neither GDF11 nor MSTN levels differ as a function of age in healthy women. In an independent cohort of older adults with severe aortic stenosis, we show that individuals with higher GDF11 were more likely to be frail and have diabetes or prior cardiac conditions. Following valve replacement surgery, higher GDF11 at surgical baseline was associated with rehospitalization and multiple adverse events. Cumulatively, our results show that GDF11 levels do not decline throughout aging but are associated with comorbidity, frailty, and greater operative risk in older adults with cardiovascular disease.

Functional outcome measures of patients following hemipelvectomy.

BACKGROUND: Major amputations are indicated for curative treatment of some tumors of the pelvis. Previous literature suggests that patients with a hemipelvectomy amputation are more efficient walking with crutches than using a prosthesis. OBJECTIVES: The purpose of this study was to evaluate whether modern prosthetic use after hemipelvectomy may be a viable option for patients than in the past. STUDY DESIGN: Case control trial. METHODS: We identified five patients who underwent hemipelvectomy amputation and fit with high-level prosthetic components. Patients were evaluated using a timed up and go, 5-m walk, 400-m walk, and stair climb tests to evaluate functional performance with a prosthesis and without. Short Form-36 scores were collected as well. These results were compared to matched controls. RESULTS: There was a trend for faster locomotion using crutches over wearing a prosthesis in the timed up and go, and 5-m and 400-m walk; no difference was seen in stair climbing. Short Form-36 scores showed decreased physical component score, but equal mental component score compared to the general population. CONCLUSION: Our results show that in addition to advances in surgical techniques, prosthetic rehabilitation and management are beginning to optimize functional mobility with the prosthesis. CLINICAL RELEVANCE: Patients who use a modern prosthesis following hemipelvectomy demonstrated good clinical function with and without their prosthesis. Although health status scores were decreased in the physical component, mental component scores were equal to healthy controls.

Analysis of ankle-hindfoot stability in patients with ankle instability and normals.

PURPOSE: We devised a testing apparatus for in vivo analysis of ankle stability. The purpose of the study was to test the reliability of this apparatus and to determine the stability pattern of the ankle-hindfoot complex in healthy, asymptomatic volunteers and in patients with ankle instability. METHODS: Ten healthy individuals were studied, and testing was repeated on the same day and different days. Three patients with symptomatic, unstable ankles were also tested on both involved and uninvolved sides. Constant inversion torque was applied, then internal rotation torque, while moving the ankle throughout the range of sagittal motion. Three-dimensional kinematics of the ankle-hindfoot complex were measured by an electromagnetic tracking system. RESULTS: Measurements were repeatable, with intraclass correlation coefficients 0.9 or better. Variability was observed among controls, but motion curve patterns were consistent. Motion curve slopes were sensitive in differentiating between unstable and stable ankles. CONCLUSIONS: Most previous reports are in vitro studies conducted with the ankle in one position, manual stress applied, or joint positions estimated with planar radiographs. Our study indicated that more accurate diagnosis of severity of ankle ligament injuries may be possible.

Electromyographic activity in the immobilized shoulder girdle musculature during ipsilateral kinetic chain exercises.

OBJECTIVE: To quantify the electromyographic activity in the shoulder girdle musculature during ipsilateral kinetic chain exercises performed in a shoulder immobilizer in asymptomatic men. DESIGN: Descriptive. SETTING: Motion analysis laboratory at a tertiary care center. PARTICIPANTS: Five asymptomatic male volunteers, ages 24 to 32 years. INTERVENTION: Fine-wire (supraspinatus, infraspinatus, upper subscapularis) and surface (deltoids, trapezii, biceps, serratus anterior) electrodes recorded electromyographic activity from each muscle during a split-stance cross-body rotation (twisting to the opposite side at high, mid, and low levels), split stance attempted ipsilateral floor touch, and attempted overhead reach. All movements were initiated from the immobilized scapula and were tested with and without a combined step. MAIN OUTCOME MEASURE: Mean peak normalized (percentage of maximum voluntary contraction [%MVC]) electromyographic activity of each muscle during each exercise. RESULTS: For all exercises, biceps and infraspinatus activity remained low (<10% MVC), whereas upper subscapularis activity was moderate to very high (29%-68% MVC). Supraspinatus activity was low (<20% MVC) for all motions except the attempted overhead reach (23% MVC). Serratus electromyographic activity was less than 20% of MVC for all motions and was most responsive to added stepping (23%-136% MVC without stepping vs 24%-199% MVC with stepping). Cross-body rotation at lower heights progressively increased serratus activity while decreasing supraspinatus, upper trapezius, and anterior deltoid activity. CONCLUSIONS: Based on these electromyographic data, selected kinetic chain exercises could potentially be implemented during periods of shoulder immobilization. All exercises examined could potentially be safe after superior labral anteroposterior repair, but not after subscapularis repair. All exercises, with the exception of the attempted overhead reach, could potentially be safe after supraspinatus repair, with or without concomitant infraspinatus repair. Early activation of the serratus anterior could potentially be achieved by performing cross-body rotations, particularly at lower heights.

Effects of ankle-foot orthoses on ankle and foot kinematics in patients with subtalar osteoarthritis.

OBJECTIVE: To determine whether different foot orthoses have a similar effect on foot kinematics in subjects with subtalar osteoarthritis (OA) when walking on various ground conditions. DESIGN: Within-subject comparison study. SETTING: Biomechanics research laboratory. PARTICIPANTS: Ten subjects with unilateral subtalar OA. INTERVENTIONS: Custom-made ankle foot orthosis (AFO), rigid hindfoot orthosis (HFO-R), and articulated hindfoot orthosis (HFO-A) were used by subjects walking on level, ascending, and descending ramp, and side slope conditions. MAIN OUTCOME MEASURES: The triplanar range of motion of the calcaneus relative to tibia (hindfoot) and metatarsal relative to calcaneus (forefoot) was measured using an 8-camera motion analysis system when subjects with subtalar OA wore different foot orthoses. RESULTS: Braces tended to perform similarly in reducing motion of the forefoot and hindfoot for all ground conditions when compared with unbraced but wearing shoes. The AFO significantly restricted frontal plane hindfoot motion during ramp descent (P<.01) and on a side slope when the arthritic subtalar joint was higher than the unaffected side (P=.02). The HFO-A provided significant frontal plane hindfoot motion restriction during ramp descent (P<.01) and on a side slope when the arthritic subtalar joint was lower than the unaffected side (P=.03). The HFO-R significantly restricted frontal plane hindfoot motion in all ground conditions except ramp ascent (P<.05). CONCLUSIONS: The HFO-R provides significant subtalar joint motion restriction while walking. The HFO-R may be considered an optimal orthosis for patients with subtalar OA pain arising from subtalar motion.

Electromyographic activity in the immobilized shoulder girdle musculature during scapulothoracic exercises.

OBJECTIVE: To quantify the electromyographic activity in the shoulder girdle musculature during scapulothoracic exercises performed in a shoulder immobilizer in asymptomatic men. DESIGN: Descriptive. SETTING: Motion analysis laboratory at a tertiary care center. PARTICIPANTS: Five asymptomatic male volunteers ages 24 to 32 years. INTERVENTION: Fine-wire (supraspinatus, infraspinatus, upper subscapularis) and surface (deltoids, trapezii, biceps, serratus anterior) electrodes recorded electromyographic activity from each muscle during scapular clock, elevation, depression, protraction, and retraction exercises completed during a single testing session in random order. MAIN OUTCOME MEASURE: Mean peak normalized (percentage of maximal voluntary contraction [MVC]) electromyographic activity of each muscle during each exercise. RESULTS: Biceps activity was uniformly low (<20% MVC), whereas upper subscapularis activity was uniformly high (40%-63% MVC). Both scapular depression and protraction elicited low activity (<20% MVC) in the supraspinatus, infraspinatus, anterior deltoid, and biceps brachii muscles, while generally producing greater than 20% MVC activity in the trapezii and serratus. Scapular depression produced the largest serratus anterior activity (47% MVC). CONCLUSIONS: These data are the first to describe the electromyographic activity during scapulothoracic exercises while in a shoulder immobilizer. Based on electrophysiologic data in normal volunteers, our findings suggest that during periods of shoulder immobilization: (1) scapular depression and protraction exercises could potentially be safely performed after rotator cuff repair to facilitate scapulothoracic rehabilitation, (2) all exercises studied could potentially be safe after superior labral anteroposterior shoulder repair, and (3) all exercises studied should be avoided after subscapularis repair. Further investigation in symptomatic individuals may facilitate refinement of these recommendations.

The effect of scapular protraction on isometric shoulder rotation strength in normal subjects.

To measure the effect of scapular protraction on isometric shoulder rotation strength, 20 normal subjects completed 2 maximal isometric internal and external rotation contractions in 2 scapular positions (scapula neutral [SN] and scapula protracted [SP]) from 3 arm positions (90 degrees internal rotation [IR], 45 degrees internal rotation [MR], and 90 degrees external rotation [ER]). Scapular protraction reduced shoulder rotation strength in 5 of 6 test positions (P < .0004), with significant interactions between scapular position and arm position (P < .001) and between scapular position and contraction type (P < .0001). Protraction significantly reduced IR strength by 13% to 24% relative to SN. The effect of SP on ER strength was more position-dependent, increasing strength by 6% in the IR position and decreasing it by 7% in the MR position and 20% in the ER position. In conclusion, acute changes in scapular position affect shoulder isometric IR and ER strength. The potential adverse effects of scapular protraction on shoulder rotation strength should be considered during the evaluation and treatment of shoulder pain.

Effects of ankle-foot orthoses on ankle and foot kinematics in patient with ankle osteoarthritis.

OBJECTIVE: To determine if different foot orthoses have a similar effect on foot kinematics in subjects with ankle osteoarthritis (OA) when walking on various ground conditions. DESIGN: Within-subject comparisons study. SETTING: Biomechanics research laboratory. PARTICIPANTS: Thirteen subjects with unilateral ankle OA. INTERVENTIONS: Custom-made ankle-foot orthosis (AFO), rigid hindfoot orthosis (HFO-R), and articulated hindfoot orthosis (HFO-A) were used by subjects when walking on level, ascending and descending ramp, and side-slope conditions. MAIN OUTCOME MEASURES: The range of motion of the hindfoot (calcaneus relative to tibia) and forefoot (metatarsal relative to calcaneus) was measured using an 8-camera motion analysis system. RESULTS: The AFO and HFO-R provided the best sagittal plane hindfoot motion restriction over all ground conditions (P<.001). The HFO-R allowed the greatest sagittal plane forefoot motion when walking over level (P=.01) and side-slope (P<.02) conditions, the greatest frontal plane forefoot motion walking down the ramp (P=.003), and the greatest transverse plane forefoot motion when walking over level (P=.011) and ramp-ascending conditions (P=.005). The HFO-A restricted motion of the unaffected joint and did not effectively restrict hindfoot motion. CONCLUSIONS: The HFO-R not only provides selective restriction to the ankle-hindfoot motion, but also allows sufficient forefoot motion compared with the AFO. We consider the HFO-R to be the best option of all tested orthoses for treating patients with ankle OA pain arising from ankle motion.

The effect of visual biofeedback on the propulsion effectiveness of experienced wheelchair users.

OBJECTIVE: To determine the effect of visual feedback on the propulsion effectiveness of experienced manual wheelchair users. DESIGN: Controlled trial. SETTING: A motion analysis laboratory. PARTICIPANTS: A convenience sample of 16 healthy men and 2 healthy women with T4-L2 traumatic paraplegia, a mean age of 38+/-9 years, and a mean duration of manual wheelchair-based mobility of 14+/-8 years. INTERVENTION: Propulsion was assessed as the subjects propelled an instrumented wheelchair (with and without visual biofeedback) on a custom-built dynamometer at propulsion intensities of .15 and .25W/kg for 10 minutes. MAIN OUTCOME MEASURES: The primary outcome variable was the fraction of effective force (FEF) (ie, the ratio of effective to total force) applied by the subject to the wheelchair's pushrim. Secondary variables included velocity, stroke frequency, and stroke angle. RESULTS: A 2-factor analysis of variance with repeated measurements was used to detect significant differences between the outcome variables. The FEF ratio was 73.9% without feedback and 72.5% with feedback at the lower-intensity level. Propulsion during the higher intensity condition both with and without feedback resulted in a statistically significant improvement in the FEF (73.9%-78.7% with no feedback, 72.5%-80.2% with feedback), compared with the lower-intensity level. Stroke angle increased from 84.3 degrees to 98.7 degrees and frequency decreased from 66 to 57.8 strokes/min with feedback. CONCLUSIONS: Visual biofeedback may have little utility in improving the force effectiveness of manual wheelchair propulsion in experienced wheelchair users. Experienced wheelchair users may have already optimized their stroke in a manner that balances energy expenditure with stroke efficiency. Other variables such as stroke length and frequency may be more amenable to visual biofeedback.

The effect of custom-made braces for the ankle and hindfoot on ankle and foot kinematics and ground reaction forces.

OBJECTIVE: To assess the effects on gait of custom-made polypropylene orthoses: ankle-foot orthosis (AFO), rigid hindfoot orthosis (HFO-R), and articulated hindfoot orthosis (HFO-A). DESIGN: Experimental assessment. SETTING: Institutional practice, motion analysis laboratory. PARTICIPANTS: Twenty asymptomatic normative subjects. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Three-dimensional kinematics, ground reaction force, and time-related factors in 4 conditions: shoe only, and shod with the AFO, HFO-R, and HFO-A. RESULTS: The AFO and HFO-R limited sagittal and coronal plane ankle-hindfoot motion. The HFO-A limited hindfoot coronal motion while allowing normal sagittal motion. At the midfoot, the AFO and HFO-A limited transverse motion, but the HFO-A also limited sagittal and coronal motion. Use of the HFO-R resulted in exaggerated midfoot sagittal and coronal motion. Braces that limited motion to a greater degree were associated with more atypical kinetic variables, indicative of less dynamic gait. The HFO-A resulted in ground reaction forces most similar to unbraced conditions. CONCLUSIONS: Alteration in gait was affected by orthosis design. Orthoses with a rigid component crossing a joint restricted motion at that joint, but potentially compromised typical gait kinetic factors. For immobilizing the hindfoot, the HFO-A may be more comfortable and still provide more stability than the HFO-R or AFO.

Partial weight-bearing gait using conventional assistive devices.

OBJECTIVE: To determine if subjects can offload the right lower extremity to a targeted amount of weight bearing using assistive devices. DESIGN: Case series. SETTING: Motion analysis laboratory. PARTICIPANTS: Ten healthy subjects (5 men, 5 women) without lower-extremity injury and minimal experience using ambulatory aids. INTERVENTIONS: Before data collection subjects were trained by a physical therapist to offload the right lower extremity by 50% by using an assistive device and a bathroom scale for feedback on weight reduction. MAIN OUTCOME MEASURES: Vertical ground reaction force was measured by using forceplates while subjects walked at a self-selected speed by using a 3-point partial weight-bearing (PWB) gait pattern with axillary crutches, forearm crutches, and wheeled walker. We also measured vertical ground reaction force by using a single-point cane. RESULTS: Each gait aid significantly reduced the right lower-extremity peak vertical ground reaction force. Participants were able to achieve the target of approximately 50% weight reduction with the axillary (50% reduction) and forearm (56% reduction) crutches. The wheeled walker resulted in a peak vertical load of 64% of body weight, which was in excess of the target load. A single-point cane produced a peak vertical load of 76% of body weight. CONCLUSIONS: By using a bathroom scale, healthy subjects could be trained to achieve a target goal of 50% PWB with axillary and forearm crutches. A wheeled walker resulted in weight bearing greater than the target of 50% of body weight. Subjects were able to offload the right lower extremity by about 25% of body weight by using a single-point cane.

The effect of seat position on wheelchair propulsion biomechanics.

This study examined the effect of seat position on handrim biomechanics. Thirteen experienced users propelled a wheelchair over a smooth level floor at a self-selected speed. Kinetic and temporal-distance data were collected with the use of an instrumented rim and a motion analysis system. A custom-designed axle was used to change the seat position. We used repeated measures analysis of variance to evaluate if differences existed in the temporal-distance and kinetic data with change in seat position. Results showed that a shorter distance between the axle and shoulder (low seat height) improved the push time and push angle temporal variables (p < 0.0001). Tangential force output did not change with seat position. Axial and radial forces were highest in the lowest seat position (p < 0.001). Propulsion efficiency as measured by the fraction of effective force did not significantly change with seat position.

A new method to quantify demand on the upper extremity during manual wheelchair propulsion.

OBJECTIVE: To use an ergonomics-based rating that characterizes both demand on, and capacity of, upper-extremity muscle groups during wheelchair propulsion to help identify the muscle groups most at risk for pain or overuse injury in a relatively demanding wheelchair propulsion task. DESIGN: Case series. SETTING: Biomechanics research laboratory. PARTICIPANTS: Sixteen manual wheelchair users with complete (American Spinal Injury Association grade A) T6-L2 paraplegia. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Internal peak joint moments required by each of the major upper-extremity muscle groups for propelling a wheelchair up a ramp; isometric strength of each of the muscle groups in positions simulating wheelchair propulsion; and wheelchair propulsion strength rating (WPSR) for each muscle group, calculated by normalizing the joint demands to their capacity. RESULTS: The largest joint moment was for shoulder flexion, at 39.7+/-13.9Nm. Shoulder flexion also accounted for the peak WPSR value of 66.5%+/-20.3%. Supination and pronation movements had low peak moment requirements (3.4Nm, 5.0Nm, respectively) but high WPSR values (41%, 53%, respectively). CONCLUSIONS: Even a relatively benign ramp (2.9 degrees ) places a large demand on the musculature of the upper extremity, as assessed by using the WPSR to indicate muscular demand.

Functional outcome of patients with rotationplasty about the knee.

Rotationplasty is a surgical procedure designed to achieve a durable reconstruction after the resection of tumors about the knee. However, because of the recent advances with expandable prostheses, rotationplasty has been less popular in the skeletally immature patient, particularly in the United States. We assessed the functional outcome of patients who had rotationplasty to allow better comparison with other operative techniques in this patient population. Seven patients, who were operated on at our institution at an average age of 9.4 years (range, 5-14 years), had a followup of at least 4 years and were evaluated in the Motion Analysis Laboratory. The gait analysis included kinetic, kinematic and temporal-distance parameters to evaluate the patient's functional performance. The data also were compared with measurements of a population of 25 able-bodied subjects and with four subjects with distal above-knee amputation. All patients had the ability to weightbear fully. All patients ambulated without assistive devices. Gait analysis of patients with rotationplasty revealed only slight asymmetry regarding stride duration, stride length, cadence, velocity and stance-swing ratio compared with healthy subjects. Although the gait was similar to subjects with distal above-knee amputation, knee motion was superior in patients who had rotationplasty. Rotationplasty offers a durable reconstruction. Rotationplasty allows the patient to actively control the knee, which results in a coordinated gait pattern, which is similar to the gait of the able-bodied population, and better than in subjects with distal-knee amputation.

Upper-extremity torque production in men with paraplegia who use wheelchairs.

OBJECTIVES: To study maximal upper-extremity torque values and agonist/antagonist torque ratios in a sample of individuals with paraplegia and to compare these values with a sample of age-, gender-, and weight-matched able-bodied individuals. DESIGN: Cross-sectional, case-control study. SETTING: A biomechanics laboratory. PARTICIPANTS: A convenience sample of 15 men with complete (American Spinal Injury Association class A) T5-L2 paraplegia and 15 able-bodied control subjects. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Maximal isometric torques of 12 upper-extremity muscle groups (shoulder, elbow, and wrist flexion and extension; shoulder abduction and adduction; shoulder internal and external rotation; elbow pronation and supination) were measured with custom dynamometers. RESULTS: Maximal torque values and agonist/antagonist torque ratios for the shoulder, elbow, and wrist functions did not differ between the control subjects and those with complete paraplegia, with the exception of the supination/pronation torque ratio, which was significantly higher in the able-bodied control group. CONCLUSION: Wheelchair propulsion and other functional activities, such as transfers, do not significantly affect maximum torque production of the upper extremities in individuals with paraplegia. On the basis of these findings, arguments that upper-extremity muscle imbalances are important contributory factors to upper-extremity pain and dysfunction in this group may be too simplistic.

Effect of scapular protraction and retraction on isometric shoulder elevation strength.

OBJECTIVES: To examine the effect of scapular protraction (SP) and scapular retraction (SR) on isometric shoulder elevation strength measured in the sagittal plane and to test the hypothesis that strength would be significantly reduced when tested in the SP position relative to the neutral resting scapular position (SN). DESIGN: Prospective before-after trial. SETTING: Multidisciplinary sports medicine center. PARTICIPANTS: Ten healthy volunteers (5 men, 5 women) ages 26 to 43 years recruited from the Mayo Clinic, Rochester, MN. INTERVENTIONS: Subjects completed 3 maximal isometric shoulder elevation contractions at 90 degrees of sagittal plane elevation in the SN, SP, and SR positions. The order of scapular positions was varied to minimize fatigue effects. Mean isometric strength values were compared by using Student t tests. MAIN OUTCOME MEASURES: Isometric shoulder elevation strength for the 3 scapular positions. RESULTS: Isometric strength was significantly lower for the SP position compared with the SN position (8.5 +/- 3.4 kg vs 11.1 +/- 4.0 kg, P <.0005) and for the SR position relative to the SN position (7.8 +/- 3.3 kg vs 11.1 +/- 4.0 kg, P <.00003). Strength values did not differ between the SP and SR positions (P =.38). CONCLUSIONS: Movement of the scapula into a protracted or retracted position results in a statistically significant reduction in isometric shoulder elevation strength as measured in this study. Further research is warranted to examine the relationship between scapular position and shoulder muscle function.