Wheelchair racing efficiency.

PURPOSE: For individuals with disabilities exercise, such as wheelchair racing, can be an important modality for community reintegration, as well as health promotion. The purpose of this study was to examine selected parameters during racing wheelchair propulsion among a sample of elite wheelchair racers. It was hypothesized that blood lactate accumulation and wheeling economy (i.e. oxygen consumed per minute) would increase with speed and that gross mechanical efficiency would reach an optimum for each athlete. METHOD: Twelve elite wheelchair racers with paraplegia participated in this study. Nine of the subjects were males and three were females. Each subject used his or her personal wheelchair during the experiments. A computer monitored wheelchair dynamometer was used during all testing. The method used was essentially a discontinuous economy protocol. Mixed model analysis of variance (ANOVA) was used to compare blood lactate concentration, economy (minute oxygen consumption), and gross mechanical efficiency across the stages. RESULTS: The results of this study show that both economy and blood lactate concentration increase linearly with speed if resistance is held constant. The subjects in this study had gross mechanical efficiencies (gme) of about 18%, with the range going from 15.222.7%. The results indicate that at the higher speeds of propulsion, for example near race speeds, analysis of respiratory gases may not give a complete energy profile. CONCLUSION: While there is a good understanding of training methods to improve cardiovascular fitness for wheelchair racers, little is known about improving efficiency (e.g. technique, equipment), therefore methods need to be developed to determine efficiency while training or in race situations.

Frequency analysis of kinematics of racing wheelchair propulsion.

The purpose of this study was to describe the frequency content of racing wheelchair propulsion motion data. The selection of the filter corner frequency in previous kinematic analyses of manual wheelchair propulsion was commonly based on gait literature. An estimate of the frequency separating the signal and the noise was determined to make recommendations for low-pass digital filters. The global (noncoordinate specific) cutoff frequency was 6 Hz. The directional cutoff frequencies were 5.1, 3.9, and 5.6 Hz, in the anterior-posterior, superior-inferior and medial-lateral directions, respectively. Recommendations for the corner frequencies of low-pass Butterworth digital filters based on the cutoff frequency are higher than the corner frequencies used in previous studies of manual wheelchair propulsion kinematic data. This study provides a foundation for the data reduction of manual wheelchair propulsion kinematic data that is independent of gait literature.

Kinematic characterization of wheelchair propulsion.

Rehabilitation scientists and biomedical engineers have been investigating wheelchair propulsion biomechanics in order to prevent musculoskeletal injuries. Several studies have investigated wheelchair propulsion biomechanics; however, few have examined wheelchair propulsion stroke patterns. The purpose of this study was to characterize wheelchair propulsion stroke patterns by investigating joint accelerations, joint range of motions, wheelchair propulsion phases, and stroke efficiency. Seven experienced wheelchair users (5 males, 2 females) were filmed using a three-camera motion analysis system. Each subject pushed a standard wheelchair fitted with a force-sensing pushrim (SMARTWheel) at two speeds (1.3 and 2.2 m/s). The elbow angle was analyzed in the sagittal plane, while the shoulder joint was analyzed in the sagittal and frontal planes. Three distinctly different stroke patterns: semi-circular (SC), single looping-over-propulsion (SLOP), and double looping-over-propulsion (DLOP), were identified from the kinematic analysis. Through our analysis of these patterns, we hypothesized that SC was more biomechanically efficient than the other stroke patterns. Future studies using a larger number of subjects and strokes may reveal more significant distinctions in efficiency measures between stroke patterns.

A unified method for calculating the center of pressure during wheelchair propulsion.

The measurement of the center of pressure (COP) has been and continues to be a successful tool for gait analysis. The definition of a similar COP for wheelchair propulsion. however, is not straightforward. Previously, a COP definition similar to that used in force plate analysis had been proposed. Unfortunately, this solution has the disadvantage of requiring a separate COP definition for each plane of analysis. A definition of the generalized center of pressure (GCOP) which is consistent in all planes of analysis is derived here. This definition is based on the placement of a force-moment system, equivalent to the force-moment system at the hub, on a line in space where the moment vector (wrench moment) is parallel to the force vector. The parallel force-moment system is then intersected with three planes defined by anatomical landmarks on the hand. Data were collected using eight subjects at propulsion speeds of 1.34 m/s and 2.24 m/s (1.34 m/s only for subject 1, 0.894 m/s and 1.79 m/s for subject 8). Each subject propelled a wheelchair instrumented with a SMARTwheel. A PEAK 5 video system was used to determine the position of anatomical markers attached to each subject's upper extremity. The GCOP in the transverse plane of the wrist formed clusters for all subject's except subject 2 at 1.34 m/s. The clustering of the GCOP indicates that the line of action for the force applied by the hand is approximately perpendicular to the transverse plane through the wrist. When comparing the magnitude of the moment vector part of the wrench with the moment of the force vector of the wrench about the hub, the wrench moment is approximately an order of magnitude smaller. This indicates that the role of the wrist for wheelchair propulsion is primarily to stabilize the force applied by the arm and shoulder.

Three-dimensional pushrim forces during two speeds of wheelchair propulsion.

Upper limb pain frequently occurs in manual wheelchair users. Analyzing the pushrim forces and hub moments occurring during wheelchair propulsion is a first step in gaining insight into the cause of this pain. The objectives of this study were as follows: to describe the forces and moments occurring during wheelchair propulsion; to obtain variables that characterize pushrim forces and are statistically stable; and to determine how these variables change with speed. Convenience samples (n = 6) of paralympic athletes who use manual wheelchairs for mobility and have unimpaired arm function were tested. Each subject propelled a standard wheelchair on a dynamometer at 1.3 and 2.2 m/s. Biomechanical data were obtained using a force- and moment-sensing pushrim and a motion analysis system. A number of variables that describe the force and moment curves were evaluated for stability using Cronbach's alpha. Those measures found to be stable (alpha > 0.8) at each speed were then examined for differences associated with speed. The tangential, radial, and medial-lateral forces were found to comprise approximately 55, 35, and 10% of the resultant force, respectively. In addition to duration of stroke and propulsion, the following variables were found to be stable and to differ with speed (1.3 m/s +/- SD; 2.2 m/s +/- SD): peak force tangential to the pushrim (45.9 +/- 17.9 N; 62.1 +/- 30 N), peak moment radial to the hub (9.8 +/- 4.5 N x m 13.3 +/- 6 N x m), maximum rate of rise of the tangential force (911.7 +/- 631.7 N/sec; 1262.3 +/- 570.7 N/sec), and maximum rate of rise of the moment about the hub (161.9 +/- 78.3 N x m/s; 255.2 +/- 115.4 N x m/s). This study found stable parameters that characterize pushrim forces during wheelchair propulsion and varied with speed. Almost 50% of the forces exerted at the pushrim are not directed toward forward motion and, therefore, either apply friction to the pushrim or are wasted. Ultimately, this type of investigation may provide insight into the cause and prevention of upper limb injuries in manual wheelchair users.

Uncertainty analysis for wheelchair propulsion dynamics.

Wheelchair propulsion kinetic measurements require the use of custom pushrim force/moment measuring instruments which are not currently commercially available. With the ability to measure pushrim forces and moments has come the development of several dynamic metrics derived for analyzing key aspects of wheelchair propulsion. This paper presents several of the equations used to calculate or derive the primary variables used in the study of wheelchair propulsion biomechanics. The uncertainties for these variables were derived, and then numerically calculated for a current version of the SMARTWheel. The uncertainty results indicate that the SMARTWheel provides data which has better than 5 to 10% uncertainty, depending upon the variable concerned, at the maximum, and during most of the propulsion phase the uncertainty is considerably smaller (i.e., approximately 1%). The uncertainty analysis provides a more complete picture of the attainable accuracy of the SMARTWheel and of the degree of confidence with which the data can be recorded. The derivations and results indicate where improvements in measurement of wheelchair propulsion biomechanical variables are likely to originate. The most efficient approach is to address those variables in the design of the system which make the greatest contribution to the uncertainty. Future research will focus on the point of force application and examination of nonlinear effects.

An analysis of work postures of manual wheelchair users in the office environment.

The goal of this project was to examine the difficulties manual wheelchair users experience in office activities and ascertain whether such problems may be due to poor relationships between the equipment and the users. Sixty adult manual wheelchair users completed a questionnaire about problems encountered in office activities. Filing and writing were the most problematic activities for this group. Phase II of this study consisted of videotaping four subjects performing each activity in their personal office environments, and having them complete a second questionnaire on body-specific locations of discomfort. Videotaped postures and reports of discomfort were matched to determine the existence of poor equipment-user relationships. In filing, low back pain may have been due to bending forward to access lower drawers while seated. For writing, an inappropriate desk-wheelchair relationship that required subjects to bend forward with their arms on a surface that was too high may have caused back, shoulder, and neck discomfort.

Methods for determining three-dimensional wheelchair pushrim forces and moments: a technical note.

This technical note illustrates that some of the differences that have been reported regarding wheelchair propulsion may be due to the methods used to calculate key variables. Wheelchair ambulation is a very important form of locomotion that lacks a standard pushrim force and moment analysis system. We have developed tools for analyzing upper limb biomechanics during manual wheelchair propulsion. Among the tools is a system that allows the direct measurement of global coordinate forces F(x), F(y), F(z) and corresponding moments. The analytical techniques presented here allow calculation of radial (F(r)) and tangential (F(t)) forces, the determination of point of force application (PFA), and the moment applied by the hand (M(hz)). Our results show that the PFA can be calculated from kinetic data. Comparison of the PFA to the second metacarpophalangeal (MP) joint, calculated from kinematic data and used in previous studies, resulted in a 0.2 radian difference on average, with the PFA showing greater variation near the beginning and ending of the propulsion phase. Analysis of methods for calculating the applied tangential force showed that using the PFA provides a more accurate measurement of this force than the previous method of assuming negligible hand-moment contribution. The hand moment was compared using the calculated PFA and assuming the PFA was coincident with the second MP joint. Both methods provided similar results with a mean difference of 0.6 N x m. The methods presented in this paper provide a framework for analyzing wheelchair propulsion forces and moments.

Wrist biomechanics during two speeds of wheelchair propulsion: an analysis using a local coordinate system.

OBJECTIVE: To describe motion, forces, and moments occurring at the wrist in anatomic terms during wheelchair propulsion; to obtain variables that characterize wrist function during propulsion and are statistically stable; and to determine how these variables change with speed. DESIGN: Case series. SETTING: Biomechanics laboratory. PARTICIPANTS: Convenience sample of Paralympic athletes (n = 6) who use manual wheelchairs for mobility and have unimpaired arm function. INTERVENTION: Subjects propelled a standard wheelchair on a dynamometer at 1.3m/sec and 2.2m/sec. Biomechanical data were obtained using a force and moment sensing pushrim and a motion analysis system. MAIN OUTCOME MEASURES: Maximum angles, forces, and moments in a local, wrist coordinate system. Each variable was evaluated for stability using Cronbach's alpha. Measures found to be stable (infinity > .8) at each speed were then compared to look for differences associated with speed. RESULTS: The following measures were stable at both speeds: maximum wrist flexion, ulnar deviation, and radial deviation angles, peak moments acting to cause wrist flexion, extension, and ulnar deviation, peak shear forces acting between the radial and ulnar styloids, and peak axial force acting at the wrist. Of these measures, the following measures differed (p < .05) between speeds (+/-SD): maximum radial deviation (1.3m/sec, 25.1 degrees +/- 9.0; 2.2m/sec, 21.4 degrees +/- 6.9), peak flexion moment (1.3m/ sec, 3.4N.m +/- 3.0; 2.2m/sec, 5.2N.m +/- 3.7), peak extension moment (1.3m/sec, 10.4N.m +/- 4.8; 2.2m/sec, 13.6N.m +/- 5.1), peak shear acting from the ulnar styloid to the radial styloid (1.3m/sec, 2.3N +/- 2.7, 2.2m/sec, 8.3N +/- 7.5) and maximum axial force (1.3m/sec, 50.9N +/- 18.2; 2.2m/sec, 65.9N +/- 27.6). CONCLUSION: This study found stable parameters that characterize wrist biomechanics during wheelchair propulsion and varied with speed. Ultimately these parameters may provide insight into the cause and prevention of wrist injuries in manual wheelchair users.

Pushrim forces and joint kinetics during wheelchair propulsion.

OBJECTIVE: To investigate pushrim forces and joint kinetics during wheelchair propulsion and to discuss the differences between inexperienced and experienced wheelchair users. DESIGN: Cohort study. SETTING: Human engineering laboratory at a state university. SUBJECTS: Four men who use manual wheelchairs for mobility and four nondisabled men who did not have extensive experience pushing a wheelchair; all subjects were asymptomatic for upper extremity pain or injury. METHODS: Subjects pushed a commonly used wheelchair fitted with a force-sensing pushrim on a stationary wheelchair dynamometer. Video and force data were collected for 5 strokes at one speed of propulsion. Pushrim forces and net joint forces and moments were analyzed. MAIN OUTCOME MEASURES: Pushrim forces, radial (Fr) and tangential (Ft), were analyzed and compared for both groups in relation to peak values and time to peak values and as ratios of overall forces generated. Net joint forces and moments were analyzed in a similar fashion. RESULTS: Pushrim forces and joint moments were similar to those previously reported, with radial forces averaging between 34 and 39N and tangential forces ranging on average between 66 and 95N. Tangential forces were higher than radial forces, and mean ratios of tangential forces to the resultant force were approximately 75%, whereas mean radial force ratios were approximately 22%. All subjects showed higher joint moments at the shoulder than at the elbow or wrist. A large component of vertical reaction force was seen at the shoulder. Significant differences (p < .05) were found between groups for peak tangential force and time to peak tangential and peak vertical forces, with wheelchair users having lower values and longer times to reach the peak values. CONCLUSIONS: Discrete variables from the force-time curves can be used to distinguish between wheelchair users and nonusers. The experienced users tended to push longer, used forces with lower peaks, and took longer time to reach peak values. This propulsive pattern may have been developed to reduce the chance of injury by minimizing the forces at the joints, as a means of maximizing efficiency or as a combination of these factors. More work investigating 3-dimensional forces and the influence of seating position and various conditions of propulsion such as speed changes, ramps, and directional changes on injury mechanisms needs to be completed.

Projection of the point of force application onto a palmar plane of the hand during wheelchair propulsion.

The objective of this study was to develop and test a method for projecting the pushrim point of force application (PFA) onto a palmar plane model of the hand. Repetitive wheelchair use often leads to hand and wrist pain or injury. The manner by which the hands grasp the pushrim and how the forces and moments applied to the pushrim are directed may contribute to the high incidence of pain and injury. The projections of the PFA onto the palmar surface model of the hand reside primarily within zone II. These results are in agreement with previous studies which have assumed the PFA to be coincident with one of the metacarpophalangeal (MP) joints. However, the results from three subjects show different PFA patterns within the palmar surface of the hand which can be related to each subject's propulsion pattern, and the PFA is not focused at a single MP joint. Projection of the world coordinates of the four hand marker system onto the palmar plane show the resolution to be within 3 mm, or one half the diameter of the passive reflective markers. The errors in the planar model assumption were greatest for the second and fifth MP markers. This was expected because as the hand grasp changes these markers do not remain coplanar. The results of this study indicate that new knowledge about how forces are applied by the hand onto the pushrim can be obtained using this method. This technical note provides insight into understanding the details within the kinetics of wheelchair propulsion and describes a technique for estimation of the PFA on the palmar surface of the hand. This technical note provides initial results from three different wheelchair users.

Determination of wheelchair dynamic load data for use with finite element analysis.

A methodology is introduced for the experimental determination of the dynamic loads which act on a wheelchair. A box frame wheelchair and a cantilever frame wheelchair were tested on an ANSI/RESNA curb-drop tester [1]. The accelerations of an ANSI/RESNA test dummy [1] were recorded with an array of 12 accelerometers mounted as four three-axis groups. Signal averaging was used to produce a composite dynamic load history. The dynamic loads were calculated from the acceleration data and the inertia of the test dummy using software written by the authors. These loads were imported into a finite element program (ALGOR) [5], [6] as load cases. A prototype carbon fiber design was then optimized through design and analysis iterations. The results of the acceleration data indicate that the curb-drop test produces an asymmetric loading scheme. One of the rear wheels hits the ground before the other, placing most of the dynamic load on one side of the wheelchair. The favored side appears to be fixed at the time of setup. Preliminary results are given for the design of a modular carbon fiber wheelchair using the finite element (FE) method. These results indicate, however, that the use of a static factor of safety is, in most cases, inadequate for the dynamic loads present in the curb-drop test.

Upper limb nerve entrapments in elite wheelchair racers.

The prevalence of upper limb nerve injuries has been reported to be as high as 73% in individuals who rely on manual wheelchairs for mobility. Many authors hypothesize that the repetitive trauma to carpal canal structures caused by propelling a wheelchair is the reason for this high prevalence. The purpose of this study was to determine the prevalence of nerve conduction abnormalities in a group of elite wheelchair racers whose wrists are exposed to additional propulsion-related trauma during training and competition. We performed bilateral upper limb nerve conduction studies on each athlete (n = 12). The racers pushed their chairs an average of 56 miles a week for training purposes. Fifty percent of the athletes (n = 6) had evidence of median mononeuropathy by nerve conduction. Of these 6 racers, 5 had evidence of mononeuropathy bilaterally, making a total of 11 positive hands of the 23 tested. Twenty-five percent of the athletes had evidence of ulnar mononeuropathy at the wrist, and 25% had evidence of ulnar mononeuropathy at the elbow. Seventeen percent of athletes had evidence of radial nerve injury. Years with a disability accounted for a significant amount of the variance in the mean median sensory amplitude (R2 = 0.511; P = 0.020) and the mean ulnar palmar amplitude (R2 = 0.605; P = 0.008). Variables not correlated with nerve conduction studies include age, hours per day in a wheelchair not spent training, years competing, and number of miles pushed in training. Despite the amount of time spent training these wheelchair athletes have a similar or lower prevalence of median mononeuropathy then reported in the general wheelchair-using population.

Life-cycle analysis of depot versus rehabilitation manual wheelchairs.

The proper selection of a wheelchair requires making several critical decisions, not the least of which is what type of wheelchair is appropriate. The International Organization for Standards (ISO) continues to develop and refine wheelchair standards. Standards allow the objective comparison of products from various sources, permitting consumers or clinicians to assess wheelchairs with which they are not familiar by comparing test results. This study consisted of three components: 1) the comparison of fatigue test results with a planar ANSI/RESNA test dummy to a HERL contoured test dummy; 2) the comparison of fatigue test results for common depot versus common rehabilitation manual wheelchairs; and 3) the comparison of fatigue test results for manual rehabilitation wheelchairs with solid 8-inch casters versus those with pneumatic 8-inch casters. Rehabilitation wheelchairs lasted on average 13.2 times longer than the depot wheelchairs. Both types, tested with the standard ISO-ANSI/RESNA dummy, lasted on average 2.1 times longer than those wheelchairs tested using the contoured dummy. The three rehabilitation wheelchairs equipped with 8-inch pneumatic casters lasted on average 3.2 times longer than the 6 rehabilitation wheelchairs equipped with solid 8-inch casters. The depot wheelchairs cost about 3.4 times as much to operate per cycle or per meter than the rehabilitation wheelchairs. The rehabilitation wheelchairs tended to experience component failures, while the depot wheelchairs tended to experience frame failures. Our testing indicates that the tests in the ISO-ANSI/RESNA standards can relate design features to fatigue test results and durability. Rehabilitation wheelchairs tend to use higher quality materials and better manufacturing practices, and they provide greater mobility for wheelchair users. Purchasers and prescribers of wheelchairs should consider the life-cycle cost and not just the purchase price for wheelchairs.

Power wheelchair range testing and energy consumption during fatigue testing.

The range of a power wheelchair depends on many factors including: battery type, battery state, wheelchair/rider weight, terrain, the efficiency of the drive train, and driving behavior. The purpose of this study was to evaluate the feasibility of three methods of estimating power wheelchair range. Another significant purpose was to compare the current draw on pavement to current draw on an International Standards Organization (ISO) Double Drum tester at one m/sec. Tests were performed on seven different power wheelchairs unloaded, and loaded with an ISO 100 kg test dummy. Each chair was configured according to the manufacturer's specifications, and tires were properly inflated. Experienced test technicians were used for the tennis court tests, and treadmill tests. An ISO 100 kg test dummy was used for the ISO Double Drum test. Energy consumption was measured over a distance of 1500 m for each of the three test conditions. The rolling surface was level in all cases. Repeated measure analysis of variance (ANOVA) revealed a significant difference (p = 0.0001) between the predicted range at maximum speed for the three tests. Post hoc analysis demonstrated a significant difference (p < 0.01) in estimated range at maximum speed between the Double Drum test and the treadmill test, as well as between the Double Drum test and the tennis court test. Our results indicate no significant difference (p > 0.05) between the predicted range at maximal speed between the treadmill and tennis court tests. A simple relationship does not exist between the results of range testing with the Double Drum tester and the tennis court. An alternative would be to permit the use of a treadmill for range testing as simple relationships between all pertinent treadmill and tennis court range data were found. For the Double Drum tester used, the current demand is higher than under normal usage. This presents a problem as current is related to load torque in a power wheelchair. Hence, the Double Drum tester friction must be reduced. The predicted range for the tennis court test at maximum speed ranges from a low of 23.6 km to a high of 57.7 km. The range of the power wheelchair can be improved by the use of wet lead acid batteries in place of gel lead acid batteries.

SMARTWheels: development and testing of a system for measuring manual wheelchair propulsion dynamics.

The purpose of this project was to develop a system for dynamically sensing pushrim propulsion forces and torques and to collect kinetic data with the device. A system was developed to detect the forces and torques applied to the wheelchair pushrim, record, store, and process the measured data, and display the kinetic information for analysis. Ten adults, including four male wheelchair users, three ambulatory men, and three ambulatory women, pushed a wheelchair with the SMARTWheel on a dynamometer while their kinematics were videotaped. The kinetic data collected with our wheel were correlated with stick figure representations of digitized kinematic data obtained through video analysis. The close agreement between the kinetic results and the Kinematic results provided a temporal validation of the ability of the wheel to detect forces and torques applied to the wheelchair pushrim. The recorded forces and torques were in agreement with previously reported magnitudes.

Prediction of pulmonary function in wheelchair users.

As a result of the improved medical treatment of infectious diseases, these formerly leading causes of mortality in the United States have been supplanted in rank by chronic events as the major causes of death. The major causes include coronary artery disease, respiratory disease, and cancer. Static and dynamic pulmonary functions in the apparently healthy wheelchair user population were measured and then modelled using stepwise regression. One hundred and nine wheelchair users (97 males, 12 females) with paraplegia (n = 77) or quadriplegia (n = 32) gave informed consent and participated in this study. Subjects ranged from being Olympic caliber wheelchair marathon racers to those who live sedentary life styles. Subjects performed three slow vital capacity (SVC) tests, three forced vital capacity (FVC) tests, and three maximal voluntary ventilation (MVV) tests while seated in their standard wheelchair. The order of the pulmonary function tests was randomized. Subjects also completed two functional residual capacity (FRC) measurements. Analysis of variance revealed significant differences in several pulmonary functions based on gender (FEVC, p = 0.0001, FEV1, p = 0.0001, FEVC 25-75%, p = 0.005, PEF, p = 0.002, FIVC, p = 0.002, RV, p = 0.0001, MVV, p = 0.0001, SVC, p = 0.001). The women's unforced prediction equations using age, height, weight did yield some significant correlations with predictions based upon ambulatory subjects. The men's unforced adapted prediction equations did reveal significant correlations with the validation group for FEVC (r = 0.66, p = 0.007), FEV1 (r = 0.62, p = 0.015), PIF (r = 0.95, p = 0.015), MVV (r = 0.57, p = 0.067), SVC (r = 0.69, p = 0.019), and RV (r = 0.67, p = 0.009). Pulmonary function in male wheelchair users should be predicted using equations which incorporate years with disability and level of impairment. Additional study is required to make any recommendations regarding women wheelchair users. However, study of pulmonary function in women should be made a priority. Pulmonary function is affected by the extent of physical impairment, and tends to decline as years with disability increase.

Effects of prophylactic knee bracing on lower extremity joint position and muscle activation during running.

The primary purpose of a prophylactic knee brace is to decrease injury potential without compromising joint function; however, the extent that these devices can alter knee muscle function is not clear. This study investigated effects of nonprescription prophylactic knee bracing on lower extremity joint position and muscle activation during running. Six healthy male college-aged recreational runners used a motor-driven treadmill under 6 conditions: fast or slow speeds, with and without wearing a prophylactic knee brace, and with and without wearing a weighted vest. Changes in hip, knee, and ankle joint position and electromyographic activity from 9 lower extremity muscles were monitored during the running cycle weightbearing phase. Results revealed significant changes (P < 0.05) in joint position and electromyographic activity for comparisons of slow versus fast, braced versus nonbraced, and weighted versus nonweighted conditions. From 83% to 89% of the braced and nonbraced comparisons generated significant differences in knee joint position while significant hip and ankle joint position changes occurred in 50% to 58% of comparisons. From 67% to 83% of braced and nonbraced comparisons for the 9 muscles produced significant differences in electromyographic activity. Findings suggest that neuromuscular control is altered when external prophylactic devices are applied.

Differential responses to proprioceptive neuromuscular facilitation (PNF) stretch techniques.

The purpose of this study was to investigate the effects of sustained stretch and two common proprioceptive neuromuscular facilitation (PNF) stretch techniques on hamstring muscle activation and knee extension range of motion (ROM) in different athletic populations. Three stretch techniques: stretch-relax (SR), contract-relax (CR), and agonist contract-relax (ACR) were applied to 10 endurance athletes (EN), 10 high intensity athletes (HI), and 10 control subjects (C). The results revealed that ACR produced 89-110% greater hamstring EMG activity (P less than 0.05) and 9-13% more knee joint ROM than CR and SR, respectively. This same pattern was evident for the individual subject groups. Comparisons of mean data among the three subject groups revealed that the EN athletes generated 58-113% more hamstring EMG activity (P less than 0.05) than the HI and C groups, respectively, across all stretch conditions, whereas the EN group attained significantly less ROM than the HI and C groups for CR and ACR conditions. It was postulated that high intensity-short term activity training necessitates less hamstring resistance to knee extension than long term endurance training. The findings suggest that decreases in muscle activity may not be strongly related to increases in joint range of motion and that factors other than muscle relaxation are important in achieving increased ROM. Also, the differential effects of various stretch techniques between dissimilar athletic populations should be considered if stretch-induced injury is to be avoided.

Effects of fatigue on activation profiles and relative torque contribution of elbow flexor synergists.

The purpose of this study was to examine changes in elbow flexion synergies as a result of fatigue. Subjects performed a series of five isometric contractions at 10% maximum voluntary contraction step intervals. Pre- and post-fatigue surface electromyograms for the muscles were rectified, integrated, normalized, a representative equation determined using the least-squares method, and the equations numerically differentiated. The differentiated curves represent the change of excitation (and therefore, change of isometric torque) with respect to the change in resultant torque (dIEMG/dT). Pre-fatigue synergy, as indicated by the dIEMG/dT, was characterized by both co-activation and trade-off patterns. The nature of the synergy was changed as a result of fatigue. This technique, focusing upon synergistic patterns, quantifies differences in excitation profiles in a manner not previously described.