Kinematic Data Collection Research Articles

A curve fitting methodology to determine impact location, timing, and instantaneous post-impact ball velocity in cricket batting

This study aimed to develop a methodology for accurate determination of the impact location of a cricket ball on the bat face, as well as the identification of bat–ball contact timing and post-impact instantaneous ball velocity in a whole-body kinematic data collection environment. Three-dimensional kinematic data of bat and ball were recorded during 14 batting strokes: 8 hitting a static ball and 6 against a bowling machine. Curves were fitted separately to the pre- and post-impact phases of the ball position data against time in three axes according to logarithmic equations determined from mechanical principles. Separate Fourier series models were similarly fitted to the four corners of the bat face against time during the downswing prior to ball impact. Time of impact for the dynamic ball trials was determined based on the intersection of pre- and post-impact curves, with impact location calculated from ball and bat face curves at this time. R2 values for the goodness of fit of the ball and bat curves averaged 0.99 ± 0.04 and 1.00 ± 0.00 with root mean square errors of 7.5 ± 2.6 and 0.8 ± 0.2 mm, respectively. Calculated impact locations were assessed against measured impact locations derived from the impression imparted to a fine powder coating on the bat face, finding absolute differences of 6.4 ± 4.2 and 7.1 ± 4.4 mm in the transverse and longitudinal axes of the bat, respectively. Thus, an automated curve fitting methodology enables the accurate determination of cricket bat–ball impact characteristics for use in experimental investigations.

A model to calculate the progression of the centre of pressure under the foot during gait analysis

Pedobarography and the centre of pressure (COP) progression is useful to understand foot function. Pedobarography is often unavailable in gait laboratories or completed asynchronously to kinematic and kinetic data collection. This paper presents a model that allows calculation of COP progression synchronously using force plate data. The model is an adjunct to Plug-In-Gait and was applied to 49 typically developing children to create reference COP data. COP progressions were noted to spend 8% of stance behind the ankle joint centre, traverse lateral of the longitudinal axis of the foot through the midfoot for 76% of stance and finishing past the second metatarsal head on the medial side for 16% of stance. It is hoped the model will bridge the information gap for gait laboratories lacking pedobarography during foot assessments and will open up the possibility of retrospective research into COP progression based indices on kinematic data.

Computerized spiral analysis using the iPad

BackgroundDigital analysis of writing and drawing has become a valuable research and clinical tool for the study of upper limb motor dysfunction in patients with essential tremor, Parkinson’s disease, dystonia, and related disorders. We developed a validated method of computerized spiral analysis of hand-drawn Archimedean spirals that provides insight into movement dynamics beyond subjective visual assessment using a Wacom graphics tablet. While the Wacom tablet method provides robust data, more widely available mobile technology platforms exist. New methodWe introduce a novel adaptation of the Wacom-based method for the collection of hand-drawn kinematic data using an Apple iPad. This iPad-based system is stand-alone, easy-to-use, can capture drawing data with either a finger or capacitive stylus, is precise, and potentially ubiquitous. ResultsThe iPad-based system acquires position and time data that is fully compatible with our original spiral analysis program. All of the important indices including degree of severity, speed, presence of tremor, tremor amplitude, tremor frequency, variability of pressure, and tightness are calculated from the digital spiral data, which the application is able to transmit. Comparison with existing methodWhile the iPad method is limited by current touch screen technology, it does collect data with acceptable congruence compared to the current Wacom-based method while providing the advantages of accessibility and ease of use. ConclusionsThe iPad is capable of capturing precise digital spiral data for analysis of motor dysfunction while also providing a convenient, easy-to-use modality in clinics and potentially at home.

Effects of Locomotor Exercise Intensity on Gait Performance in Individuals With Incomplete Spinal Cord Injury.

High-intensity stepping practice may be a critical component to improve gait following motor incomplete spinal cord injury (iSCI). However, such practice is discouraged by traditional theories of rehabilitation that suggest high-intensity locomotor exercise degrades gait performance. Accordingly, such training is thought to reinforce abnormal movement patterns, although evidence to support this notion is limited. The purposes of this study were: (1) to evaluate the effects of short-term manipulations in locomotor intensity on gait performance in people with iSCI and (2) to evaluate potential detrimental effects of high-intensity locomotor training on walking performance. A single-day, repeated-measures, pretraining-posttraining study design was used. Nineteen individuals with chronic iSCI performed a graded-intensity locomotor exercise task with simultaneous collection of lower extremity kinematic and electromyographic data. Measures of interest were compared across intensity levels of 33%, 67%, and 100% of peak gait speed. A subset of 9 individuals participated in 12 weeks of high-intensity locomotor training. Similar measurements were collected and compared between pretraining and posttraining evaluations. The results indicate that short-term increases in intensity led to significant improvements in muscle activity, spatiotemporal metrics, and joint excursions, with selected improvements in measures of locomotor coordination. High-intensity locomotor training led to significant increases in peak gait speed (0.64-0.80 m/s), and spatiotemporal and kinematic metrics indicate a trend for improved coordination. Measures of gait performance were assessed during treadmill ambulation and not compared with a control group. Generalizability of these results to overground ambulation is unknown. High-intensity locomotor exercise and training does not degrade, but rather improves, locomotor function and quality in individuals with iSCI, which contrasts with traditional theories of motor dysfunction following neurologic injury.

Different coordination and flexibility of the spine and pelvis during lateral bending between young and older adults

This study examined coordination of the spine and pelvis during lateral bending of the trunk in older adults. Thirty-four healthy subjects (17 young and 17 older adults) demonstrated lateral bending at a controlled speed while holding a bar at approximately 180 degrees of shoulder flexion. Kinematic data collection was completed on the thoracic spine, lumbar spine, and pelvis. The coupling angle was calculated to examine the thorax–lumbar, lumbar–pelvis, and thorax–pelvis coordination patterns. The older adults demonstrated a reduced range of motion (ROM) of the lumbar spine, while both groups revealed similar ROM in the thorax and in the pelvis. The coupling angle between the straightening and bending phases was different only for the older adults in the thorax–lumbar (23.4±8.0 vs. −1.6±4.4, p=0.004) and the lumbar–pelvis (65.4±7.2 vs. 86.1±7.8, p=0.001) coordination. However, there was no group difference in the thorax–pelvis coordination. These findings indicate that age-related changes in the lumbar region affect coordination patterns only during the bending phase. The older adults preserved a similar pattern of movement to the young adults during the straightening phase, but the coordination variability of the coupling angles was greater for the older adults than for the young adults. This movement pattern suggests that the older adults lacked consistent trunk control in an attempt to optimize lateral bending coordination.

A Prospective Comparison of Pulmonary Function Using Traditional and Kinematic Measures in Children With and Without Adolescent Idiopathic Scoliosis

PurposeTraditional pulmonary function testing can be difficult for both the subject and the test administrator and are dependent on the subject's effort and ability to follow directions. An alternative to traditional pulmonary function testing is the kinematic analysis of the chest wall. Kinematic analysis is a reliable and accurate method to evaluate pulmonary function testing that does not have the restrictions of traditional methods. It is the purpose of this study to present a new model for measuring chest motion during pulmonary function testing of children with adolescent idiopathic scoliosis (AIS) and able-bodied children. ProceduresTraditional pulmonary function testing and kinematic assessment of the chest wall was measured simultaneously during a flow volume loop and maximum voluntary ventilation test. Fifteen children with AIS and 15 able-bodied children were measured. Differences between the two groups (AIS and able-bodied) and the two testing methods (traditional and kinematic testing) were analyzed. Correlations for the two testing methods and interclass coefficients for the kinematic analysis were measured. FindingsThere were no significant differences between the control group and the scoliosis group when comparing data from traditional and kinematic assessments. When comparing the differences between the traditional and kinematic data collection methods, there were significant differences for the flow volume loop and maximum voluntary ventilation. For all significant parameters, the kinematic analysis demonstrated higher values. Moderate to high Pearson correlations were found between collection methods, and high to moderate interclass correlation coefficient values were found for the kinematic analysis of the chest wall. Principal ConclusionsKinematics of the chest wall can be used as a valuable resource in the future when measuring pulmonary function when a traditional method is not a viable option.

Collecting shoulder kinematics with electromagnetic tracking systems and digital inclinometers: A review

The shoulder complex presents unique challenges for measuring motion as the scapula, unlike any other bony segment in the body, glides and rotates underneath layers of soft tissue and skin. The ability for clinicians and researchers to collect meaningful kinematic data is dependent on the reliability and validity of the instrumentation utilized. The aim of this study was to review the relevant literature pertaining to the reliability and validity of electromagnetic tracking systems (ETS) and digital inclinometers for assessing shoulder complex motion. Advances in technology have led to the development of biomechanical instrumentation, like ETS, that allow for the collection of three-dimensional kinematic data. The existing evidence has demonstrated that ETS are reliable and valid instruments for collecting static and dynamic kinematic data of the shoulder complex. Similarly, digital inclinometers have become increasingly popular among clinicians due to their cost effectiveness and practical use in the clinical setting. The existing evidence supports the use of digital inclinometers for the collection of shoulder complex kinematics as these instruments have been demonstrated to yield acceptable reliability and validity. While digital inclinometers pose a disadvantage to ETS regarding accuracy, precision, and are limited to two-dimensional and static measurements, this instrument provides clinically meaningful data that allow clinicians and researchers the ability to measure, monitor, and compare shoulder complex kinematics.

Effects of an Obesity-Specific Marker Set on Estimated Muscle and Joint Forces in Walking

The accuracy of muscle and joint contact forces (JCF) estimated from dynamic musculoskeletal simulations is dependent upon the experimental kinematic data used as inputs. Subcutaneous adipose tissue makes the measurement of representative kinematics from motion analysis particularly challenging in overweight and obese individuals. The purpose of this study was to develop an obesity-specific kinematic marker set/methodology that accounted for subcutaneous adiposity and to determine the effect of using such a methodology to estimate muscle and JCF in moderately obese adults. Experimental kinematic data from both the obesity-specific methodology, which utilized digitized markers and marker clusters, and a modified Helen Hayes marker methodology were used to generate musculoskeletal simulations of walking in obese and nonobese adults. Good agreement was found in lower-extremity kinematics, muscle forces, and hip and knee JCF between the two marker set methodologies in the nonobese participants, demonstrating the ability for the obesity-specific marker set/methodology to replicate lower-extremity kinematics. In the obese group, marker set methodology had a significant effect on lower-extremity kinematics, muscle forces, and hip and knee JCF, with the Helen Hayes marker set methodology yielding larger muscle and first peak hip and knee contact forces compared with the estimates derived when using the obesity-specific marker set/methodology. This study demonstrates the need for biomechanists to account for subcutaneous adiposity during kinematic data collection and proposes a feasible solution that may improve the accuracy of musculoskeletal simulations in overweight and obese people.

Shoe traction and surface compliance affect performance of soccer-related movements

Purpose: To determine how shoe-surface interaction, specifically traction and compliance, affects performance and biomechanics of soccer-related movements.Methods: Third generation artificial turf was installed in the laboratory to allow for kinetic and kinematic data collection both on the turf and on a laboratory surface (Pulastic sports surface). Twelve male athletes performed five 5 m sprint accelerations and five 180° sprint turns in three different shoe-surface conditions (indoor soccer shoe on the laboratory surface, indoor soccer shoe on the turf surface, soccer cleat on turf surface). Comparisons between the indoor shoe across surfaces indicated compliance effects and comparisons between the cleat and indoor shoe on turf indicated traction effects.Results: Performance increased for the sprint acceleration in the indoor shoe on the turf compared to the laboratory (1.04 s vs. 1.08 s); however, no further increase in acceleration performance occurred with the soccer cleat. For the turn movement, no change in performance occurred comparing the indoor shoe across surfaces however an increase in turn performance was seen when using the soccer cleat on turf compared to the indoor shoe (2.67 s vs. 2.56 s). The cleat had both increased utilised translational and rotational traction compared to the indoor shoe on turf for the turn movement. The cleat also resulted in increased ankle eversion moments as well as increased knee abduction and external rotation moments compared to the indoor shoe on the turf surface for the turn movement.Conclusion: Both compliance and traction shoe-surface characteristics affect performance; however, the effects of the different characteristics are different depending on the movement type.

Biomechanical loading of the shoulder complex and lumbosacral joints during dynamic cart pushing task

The primary objective of this study was to quantify the effect of dynamic cart pushing exertions on the biomechanical loading of shoulder and low back. Ten participants performed cart pushing tasks on flat (0°), 5°, and 10° ramped walkways at 20 kg, 30 kg, and 40 kg weight conditions. An optoelectronic motion capturing system configured with two force plates was used for the kinematic and ground reaction force data collection. The experimental data was modeled using AnyBody modeling system to compute three-dimensional peak reaction forces at the shoulder complex (sternoclavicular, acromioclavicular, and glenohumeral) and low back (lumbosacral) joints. The main effect of walkway gradient and cart weight, and gradient by weight interaction on the biomechanical loading of shoulder complex and low back joints was statistically significant (all p < 0.001). At the lumbosacral joint, negligible loading in the mediolateral direction was observed compared to the anterioposterior and compression directions. Among the shoulder complex joints, the peak reaction forces at the acromioclavicular and glenohumeral joints were comparable and much higher than the sternoclavicular joint. Increased shear loading of the lumbosacral joint, distraction loading of glenohumeral joint and inferosuperior loading of the acromioclavicular joint may contribute to the risk of work-related low back and shoulder musculoskeletal disorder with prolonged and repetitive use of carts.

Modeling and In Vitro Experimental Validation for Kinetics of the Colonoscope in Colonoscopy

Colonoscopy is the most sensitive and specific means for detection of colon cancers and polyps. To make colonoscopy more effective several problems must be overcome including: pain associated with the procedure, the risk of perforation, and incomplete intubation colonoscopy. Technically, these problems are the result of loop formation during colonoscopy. Although, several solutions such as modifying the stiffness of the colonoscope, using an overtube and developing image-guided instruments have been introduced to resolve the looping problem, the results of these systems are not completely satisfactory. A new paradigm to overcome loop formation is proposed that is doctor-assistive colonoscopy. In this approach, the endoscopists performance is enhanced by providing using a kinetic model that provides information such as the shape of the scope, direction of the colon and forces exerted within certain sections. It is expected that with the help of this model, the endoscopist would be able to adjust the manipulation to avoid loop formation. In the present studies, the kinetic model is developed and validated using an ex vivo colonoscopy test-bed with a comprehensive kinematic and kinetic data collection. The model utilizes an established colon model based on animal tissue with position tracking sensors, contact force sensors for the intraluminal portion of the scope and a Colonoscopy Force Monitor for the external insertion tube.

Functional anatomy and biomechanics of the equine thoracolumbar spine: a review

Growing interest in the underlying mechanisms of an equine spine in motion has yielded very informative data. In the beginning most of the knowledge on functional anatomy of the back was provided by dissections on cadavers. With time, the approach to the subject changed and new techniques like the use of high speed cameras for collection of kinematic and kinetic data and electromyography techniques were employed. Gaits such as walk, trot, and canter are studied in more detail for the magnitude of movements of different segments of the spine during a stride, and for the temporal pattern of the muscular activity. Use of these modern techniques has added tremendously to our understanding of the functional peculiarities of the equine spine, but still there are many unanswered questions. This article reviews not only the current information on this topic, but also hints at the required future developments that can help us better understand structural peculiarities of the equine spine and their functional implications.

Biomechanical Analysis Of Sit-To-Stand Motion Towards Design Of A Mobility Assist Device For People With Disabilities

A typical sit-to-stand movement analysis is analyzed in designing a mobility assist device for people with disabilities. An in-house motion-capture system was utilized for collecting the kinematic data, in which the motion of markers affixed to a moving subject is recorded, followed by image processing to obtain the coordinates of the markers. These coordinates are then processed to obtain the kinematic variables that describe joint angular movements. Hence, using the kinematic data collection, static force and required power analyses are performed. Results of this study indicate the feasibility of the assist device and form a basis for its design specifications.

Motion-analysis studies of transtibial prosthesis users

Three-dimensional motion analysis has been used since the beginning of the 1980s to evaluate many aspects of physical function of transtibial amputees. Despite its common use for clinical research, there is large variability in methods of capturing three-dimensional data, description of these methods, reporting of joint kinematics and interpretation of research findings. The aim of the following review is to critically examine the specific methodologies used by researchers when collecting three-dimensional kinematic data on transtibial amputees and to provide an overview of the methods used. Systematic review. A systematic review of the literature between January 1984 and June 2009 was conducted. A total of 68 papers were identified for review based on the following criteria: experimental research design, collection of three-dimensional kinematic data of lower-extremity joints, and inclusion of transtibial amputees as experimental subjects. A number of methodological shortcomings were identified in the papers reviewed. The authors recommend that future studies more appropriately address the product name and number of prosthetic components used; how the position of reflective markers on the prosthesis is defined; presentation of data from both sound and affected sides; and definition of the neutral position of the ankle when reporting kinematic data. Where possible, the authors recommend use of a control group. This paper has identified numerous sources of discrepancy and potential error in kinematic data collected on trans-tibial amputees. Clinicians and researchers should make themselves aware of these issues when collecting and interpreting gait data.

Investigation to predict patellar tendon reflex using motion analysis technique

The investigation of patellar tendon reflex involves development of a reflex hammer holder, kinematic data collection and analysis of patellar reflex responses using motion analysis techniques. The main aim of this research is to explore alternative means of assessing reflexes as a part of routine clinical diagnosis. The motion analysis system was applied to provide quantitative data which is a more objective measure of the patellar tendon reflex. Kinematic data was collected from 28 males and 22 females whilst subjected to a knee jerk test. Further analysis of kinematic data was performed to predict relationships which might affect the patellar tendon reflex. All subjects were seated on a high stool with their legs hanging freely within the capture volume of the motion analysis system. Knee jerk tests were applied to all subjects, on both sides of the leg, by eliciting hypo, hyper, and normal reflexes. An additional reinforcement technique called the Jendrassik manoeuvre was also performed under the same conditions to elicit a normal patellar tendon reflex. The comparison of reflex response between genders showed that female subjects generally had a greater response compared to males. However, the difference in reflex response between the left leg and the right leg was not significant. Tapping strength to elicit a hyper-reflex produced greater knee-jerk compared to the normal clinical tapping strength. All results were in agreement with clinical findings and results found by some early researchers.

Collecting kinematic data on a ski/snowboard track with panning, tilting, and zooming cameras: Is there sufficient accuracy for a biomechanical analysis?

For biomechanical research in several sports (e.g. skiing and snowboarding), field experiments are essential because these activities are performed over a great distance and in conditions that could not be reproduced in a controlled laboratory environment. High technical standards in kinematic set-up are necessary to achieve the required accuracy for biomechanical analysis. The purpose of this study was to determine the accuracy of the kinematic data collected in a ski and snowboard field experiment. Eight tests generally used in laboratory settings were adapted to field conditions on a skiing slope to determine the error related to motion capture. The calculated photogrammetric errors in the x-, y-, and z-direction were 11 mm, 9 mm, and 13 mm, respectively. The maximum error caused by soft tissue artifacts was 39 mm. These results indicate that accuracy of kinematic data in the described field experiment was comparable to that found in literature for laboratory experiments. It may be concluded that accurate kinematic data collection for skiing and snowboarding can be performed in a field setting and that these results are accurate enough to serve as input data for further analyses.

Computernavigierter Gelenkersatz am Knie mit dem Orthopilot®

Reproducible, precise implantation of a bicondylar knee prosthesis considering size of implant, axial conditions in coronal and sagittal planes, rotation, and ligament tension in extension and flexion. Progressive painful gonarthrosis, when conservative treatment is no longer an option. Revision of unicondylar prosthesis. General contraindications to bicondylar knee replacement. Revision after bicondylar replacement. Severe limitation of hip joint mobility, e.g., after arthrodesis of the hip joint or ipsilateral hip joint ankylosis. Morbid obesity. Approach to the knee joint for alloarthroplasty. Placement of the screws and fixation of the infrared reflectors at femur and tibia. After adjustment of the double camera, collection of kinematic data via standardized motion patterns and identification of predetermined anatomic landmarks at the knee and ankle joint. By means of this data, controlled resection of the tibia, determination of the ligament tension in extension and flexion, planning of the femoral osteotomies, controlled distal resection of the femur. Following intraoperative verification of the distal femur resection, navigation of the position of the femur to complete femoral resection. Placement of the trial components, determination of the tibial onlay thickness, adjustment of the rotation of the tibial component, and final preparation of the tibial shaft. Preparation of the patella by resection of osteophytes, denervation, and possibly onlay patellar resection using a saw. Finally, implantation of the tibial component (cemented or noncemented), the tibial onlay, the femoral component (cemented or noncemented), and possibly cementation of the patellar onlay. After hardening, control of knee movement in straight position and wound closure in layers. Early functional treatment using continuous passive motion device. Pain-adapted increase of weight bearing. Low-molecular-weight heparin for 5-6 weeks. Meanwhile, several studies have demonstrated that computer navigation helps to provide more accuracy in implant positioning, compared with conventional techniques in total knee replacement. Long-term survival of the implants promises to be superior after physiological leg axis restoration. Own results: 100 consecutive implantations: average duration of surgery 80 min, blood loss 360 ml, one deep infection (healed after early revision), one arthrofibrosis requiring revision surgery, average range of motion on the day of discharge 110 degrees in flexion (90-120 degrees) and full extension, after 3 months average 125 degrees in flexion (90-140 degrees). No clinical signs of instability. Postoperative radiologic evaluation with standard radiographs of the knee joint in coronal and sagittal planes took place right after surgery and again after 3 months.

Characterization of motor control in handwriting difficulties in children with or without developmental coordination disorder

The purpose of this study was to characterize handwriting deficits in children with developmental coordination disorder (DCD) using computerized movement analyses. Seventy-two children (40 females, 32 males; mean age 7 y, SD 7 mo; range 6 y 2 mo to 7 y 11 mo) with handwriting deficits (33 with DCD, 39 without DCD); and 22 age- and sex-matched children without handwriting deficits were asked to perform handwriting tasks on a digital tablet for the collection of kinematic and kinetic data. Practice times required to achieve automation of movement when writing an unfamiliar character were used to assess the motor learning of handwriting. The children were asked to copy three simple and three complex characters, and the velocity and axial pen force used for corresponding strokes were compared. The attainment of automated handwriting was markedly slower in children with handwriting deficits and DCD, who used a faster stroke velocity to write simple characters (1.22 times those without handwriting deficits), but when writing complex characters, their stroke velocity and pen force were lower (0.85 and 0.89 times those without handwriting deficits, respectively). By linking the results with neuromotor control theories, it was determined that children with DCD have difficulties performing the open-loop and closed-loop movements required for fluent handwriting.

Three-dimensional, automated, real-time video system for tracking limb motion in brain–machine interface studies

Collection and analysis of limb kinematic data are essential components of the study of biological motion, including research into biomechanics, kinesiology, neurophysiology and brain–machine interfaces (BMIs). In particular, BMI research requires advanced, real-time systems capable of sampling limb kinematics with minimal contact to the subject's body. To answer this demand, we have developed an automated video tracking system for real-time tracking of multiple body parts in freely behaving primates. The system employs high-contrast markers painted on the animal's joints to continuously track the three-dimensional positions of their limbs during activity. Two-dimensional coordinates captured by each video camera are combined and converted to three-dimensional coordinates using a quadratic fitting algorithm. Real-time operation of the system is accomplished using direct memory access (DMA). The system tracks the markers at a rate of 52 frames per second (fps) in real-time and up to 100 fps if video recordings are captured to be later analyzed off-line. The system has been tested in several BMI primate experiments, in which limb position was sampled simultaneously with chronic recordings of the extracellular activity of hundreds of cortical cells. During these recordings, multiple computational models were employed to extract a series of kinematic parameters from neuronal ensemble activity in real-time. The system operated reliably under these experimental conditions and was able to compensate for marker occlusions that occurred during natural movements. We propose that this system could also be extended to applications that include other classes of biological motion.

Comparison of Kinematics, Kinetics, and EMG Throughout Wheelchair Propulsion in Able-Bodied and Persons With Paraplegia: An Integrative Approach

A systematic integrated data collection and analysis of kinematic, kinetic, and electromyography (EMG) data allow for the comparison of differences in wheelchair propulsion between able-bodied individuals and persons with paraplegia. Kinematic data from a motion analysis system, kinetic data from force-sensing push rims, and electromyography data from four upper-limb muscles were collected for ten push strokes. Results are as follows: Individuals with paraplegia use a greater percentage of their posterior deltoids, biceps, and triceps in relation to maximal voluntary contraction. These persons also reached peak anterior deltoid firing nearly 10 deg earlier on the push rim, while reaching peak posterior deltoid nearly 10 deg later on the push rim. Able-bodied individuals had no triceps activity in the initial stages of propulsion while their paraplegic groups had activity throughout. Able-bodied participants also had, on average, peak resultant, tangential, and radial forces occurring later on the push rim (in degrees). There are two main conclusions that can be drawn from this integrative investigation: (1) A greater "muscle energy," as measured by the area under the curve of the percentage of EMG throughout propulsion, results in a greater resultant joint force in the shoulder and elbow, thus potentially resulting in shoulder pathology. (2) Similarly, a greater muscle energy may result in fatigue and play a factor in the development of shoulder pain and pathology over time; fatigue may compromise an effective propulsive stroke placing undue stresses on the joint capsule. Muscle activity differences may be responsible for the observed kinematic and kinetic differences between the two groups. The high incidence of shoulder pain in manual wheelchair users as compared to the general population may be the result of such differences, although the results from this biomedical investigation should be examined with caution. Future research into joint forces may shed light on this. Further investigation needs to focus on whether the pattern of kinematics, kinetics, and muscle activity during wheelchair propulsion is compensatory or evolutionary by tracking individuals longitudinally.