Three-dimensional kinematics of the shoulder complex during wheelchair propulsion: a technical report.

Methods for the three-dimensional (3-D) kinematic analysis of the shoulder complex (humerus relative to trunk) are presented and their use demonstrated in this analysis of shoulder motion during wheelchair propulsion. Ten subjects propelled two different wheelchairs (adjustable and conventional chairs) while the motions of the left arm and trunk were measured using a video tracking system. Eulerian angles described the sequence-dependent rotations of the humerus relative to the trunk. Wheel angular velocity and acceleration, hand position on the handrim, and duration of cycle subphases were also measured. Selected temporal and kinematic parameters were derived from the time-normalized average cycle of each subject on each wheelchair. Within-subject variation of these parameters according to wheelchair type were compared using a two-tailed t-test for paired observations. The adjustable chair made available a larger propulsion are compared with the conventional chair. Only the minimum amount of elevation demonstrated a significant difference between chairs (the conventional chair had a smaller minimum than the adjustable chair) at the corrected significance level of p < 0.001. Other differences, though not statistically significant, were still informative. Less shoulder internal rotation but more overall shoulder motion was observed during recovery phase in the adjustable chair as compared with the conventional chair. The methods presented for measuring the 3-D kinematics of the shoulder complex during wheelchair propulsion proved feasible for future use in studies that will address shoulder kinetics, energy requirements, wheelchair design, and chronic use disorders.

Kinematics of the elbow during wheelchair propulsion: a comparison of two wheelchairs and two stroking techniques.

OBJECTIVE: The kinematics of the elbow joint were studied for two types of wheelchairs and during two types of propulsive strokes. PARTICIPANTS: Ten serially selected healthy volunteers propelled a standard and a lightweight wheelchair on a roller system with both circular and pumping strokes. DESIGN: Kinematic data for the wheelchair and the upper extremity were collected by an optical tracking system. These kinematic descriptors were subsequently time-normalized with a spline algorithm to provide a graphic description of the wheelchair strokes. MAIN OUTCOME MEASURES: Thirteen discrete variables were compared for the two chairs and the two propulsive strokes. RESULTS: Total elbow motion ranged from 60.9 degrees of flexion to 5.2 degrees of extension. Maximal elbow flexion velocity ranged from 515.4 degrees to 572.8 degrees per second. Kinematic differences between the two wheelchairs were minimal, with a trend for 8.3 degrees to 5.2 degrees more elbow flexion in the lightweight wheelchair (p < .05), depending on the stroke used. With the use of any one chair, the style of the stroke had no significant effect on elbow kinematics, but the use of a pumping stroke did decrease propulsion arc by 12 degrees to 14 degrees (p < .05). CONCLUSION: No major differences regarding elbow kinematics were seen between the two types of wheelchairs. The pumping-stroke technique resulted in a shortened handrim contact arc.

Valgus-varus motion of the knee in normal level walking and stair climbing.

OBJECTIVE: The knee valgus-varus moment and the knee angles were compared between normal level walking and stair climbing. DESIGN: Ten healthy subjects were tested for ascent, descent, and level walking. BACKGROUND: An understanding of the normal valgus-varus motion of the knee during stair climbing is needed to apply biomechanical analysis of stair climbing as a evaluation tool for knee osteoarthritis patients. METHODS: A motion analysis system, three force plates, and a flight of stairs were used to collect kinematic and kinetic data. The knee angles and moments were calculated from the collected kinematic and kinetic data. RESULTS: The knee varus angle for the maximum knee valgus moments in stair climbing was significantly greater than that in level walking. The knee valgus moment was significantly correlated to ground reaction forces and knee valgus-varus angle during stair climbing and level walking. CONCLUSIONS: There is a coupling between the knee valgus-varus motion and flexion-extension motion. Ground reaction forces are the major contributors to the within-subject variation in the knee valgus-varus moment during stair climbing and level walking. The knee valgus-varus angle is a major contributor to the between-subject variation in the knee valgus moment during stair climbing and level walking.

Reproducibility of the kinematics and kinetics of the lower extremity during normal stair-climbing.

The purpose of this study was to examine the intrasubject reproducibility of the kinematic and kinetic measures of the lower extremity during normal stair-climbing. Three-dimensional video and force-plate data were collected for three trials per subject during each of three conditions: ascending, descending, and level walking. Three-dimensional angles and moments of the ankle, knee, and hip joints were calculated. The coefficient of multiple correlation was used to determine the intrasubject reproducibility of joint angles and resultant moments. Analysis of variance with repeated measures was conducted to compare the magnitudes of the coefficients between different steps, different joints, and different joint functions. The results showed that (a) generally, the kinematic and kinetic measures of normal subjects climbing stairs were reproducible; (b) the kinetic measures during the transition steps from level walking to ascending and from descending to level walking were significantly less reproducible than those during the other steps; (c) the data from the sagittal plane were more reproducible than those from the other two planes; and (d) the kinetic measures were more reproducible than the kinematic measures, especially for abduction-adduction and internal-external rotation.

Calibration of measured center of pressure of a new stairway design for kinetic analysis of stair climbing.

A stairway that allows the collection of kinetic data is essential for biomechanical studies on stair climbing. There is a need to validate the measured center of pressure (COP) on the surface of a stair in order to verify the accuracy of the calculation of joint kinetics. The purpose of this study was to validate a new stairway design for kinetic analysis of stair climbing through a calibration and error analysis of the COP obtained from this system. The new stairway design allows the collection of kinetic data for multiple steps without any constraint to foot placement. Known vertical forces were applied to known locations on the surface of each stair and each force plate. Multiple regression analyses were conducted to determine the distribution pattern of the error in the measured COP. It was found that the error in the COP was a function of location on the stair or force plate. The magnitude of the vertical force had no significant effect on the error in the measured COP. The distribution pattern of the error in the measured COP on the force plates used in this study matched the results in the literature. A healthy female subject was used as a subject in a stair climbing test. The error in the measured COP had a significant effect on the calculated joint resultant moments, especially the abduction-adduction and internal-external rotation moment. The correction of these errors should make the kinetic calculation in stair climbing more accurate.

Comparison of intersegmental tibiofemoral joint forces and muscle activity during various closed kinetic chain exercises.

The purpose of this study was to analyze intersegmental forces at the tibiofemoral joint and muscle activity during three commonly prescribed closed kinetic chain exercises: the power squat, the front squat, and the lunge. Subjects with anterior cruciate ligament-intact knees performed repetitions of each of the three exercises using a 223-N (50-pound) barbell. The results showed that the mean tibiofemoral shear force was posterior (tibial force on femur) throughout the cycle of all three exercises. The magnitude of the posterior shear forces increased with knee flexion during the descent phase of each exercise. Joint compression forces remained constant throughout the descent and ascent phases of the power squat and the front squat. A net offset in extension for the moment about the knee was present for all three exercises. Increased quadriceps muscle activity and the decreased hamstring muscle activity are required to perform the lunge as compared with the power squat and the front squat. A posterior tibiofemoral shear force throughout the entire cycle of all three exercises in these subjects with anterior cruciate ligament-intact knees indicates that the potential loading on the injured or reconstructed anterior cruciate ligament is not significant. The magnitude of the posterior tibiofemoral shear force is not likely to be detrimental to the injured or reconstructed posterior cruciate ligament. These conclusions assume that the resultant anteroposterior shear force corresponds to the anterior and posterior cruciate ligament forces.

Activation of the rotator cuff in generating isometric shoulder rotation torque.

This study compared and quantified electromyographic muscle activation of the rotator cuff with the isometric torque generated by performing shoulder rotation in various positions. Twenty healthy volunteers were tested in 29 shoulder positions. Using a Cybex II dynamometer synchronously with electromyography, surface electrodes were placed over the pectoralis major muscle and three parts of the deltoid muscle. Intramuscular wire electrodes were inserted into the four rotator cuff muscles. We found that the greatest external rotation isometric force is generated in the frontal and scapular planes in the neutral or full internal rotation positions. The sagittal, dependent, and the scapular plane with 45 degrees of elevation in rotational positions of either full or half external rotation generated the greatest torques for internal rotation isometric force. The rotator cuff muscles generated greatest electromyographic activity in neutral to midrotational positions. The scapular plane with 90 degrees of shoulder elevation in neutral rotation best isolated the subscapularis muscle. The infraspinatus-teres minor muscles were isolated in the sagittal plane with 90 degrees of shoulder elevation in a half externally rotated position. We were unable to isolate the supraspinatus muscle in any of these tested positions. These positions are recommended for manual muscle testing and for strengthening these muscles.

EMG analysis of shoulder positioning in testing and strengthening the supraspinatus.

We examined the electromyographic (EMG) activity of the supraspinatus and other rotator cuff muscles, the three portions of the deltoid muscle, and the pectoralis major muscle in two previously suggested positions for isolating the supraspinatus. The position suggested by Jobe and colleagues is with the elbow extended, the shoulder in full internal rotation, and the arm in the scapular plane. Blackburn and colleagues recommended the prone position, with the elbow extended and the arm abducted to 100 degrees and externally rotated. Fine-wire EMG activity was obtained from the rotator cuff muscles and surface EMG from the other muscles in 17 subjects tested in these two positions. Both positions resulted in significant activity of the supraspinatus, but the difference between these two positions was not statistically significant. The Jobe position produced greater activation of the anterior deltoid and pectoralis major, whereas the Blackburn position caused greater activation of the posterior deltoid. Both positions produced significant activation of the middle deltoid. We conclude that either position can be used to strengthen the supraspinatus; however, neither position selectively isolates the supraspinatus during manual muscle testing.

Accuracy of a video strain measurement system.

The purpose of this study was to determine the accuracy of a video system which our laboratory has been using to measure soft tissue strain. Both static and dynamic error analyses were performed to assess the accuracy of our video system. Static error was defined as the amount of movement reported by the video system for markers that were stationary. Dynamic error was defined as the difference between the motion of the markers as reported by the video system and their actual motion. Two sets of fluorescent markers were attached to a servo-hydraulic materials test machine. One marker set was attached to the hydraulic actuator (moving markers) and the other set was attached to the base of the machine (stationary markers). Five different marker sizes, five camera distances, and seven different loading rates were studied. Results indicated that the static error was independent of marker size, and that the dynamic error was independent of the loading rate and marker size for loading rates of 50% of the camera field of view (CFV) per second or slower. For loading rates greater than 50 percent of CFV per second, the marker size did have an affect on the dynamic error. The mean static error was found to be 0.026 percent of CFV and the mean dynamic error was found to be 0.062 percent of CFV.

Tensile properties of the supraspinatus tendon.

The tensile properties of the supraspinatus tendon were investigated in 11 shoulders from fresh cadavers. The tendon was divided into three longitudinal strips: anterior, middle, and posterior. Each specimen was mounted on a materials testing machine, with four fluorescent markers placed on both surfaces of the tendon strip. The positions of these markers were recorded during the test by two synchronized video cameras. Load-deformation and strain curves were determined, and the stress-strain curve, strength, and modulus of elasticity were calculated. The posterior strip was thinner in cross section than the others (p = 0.0355). The ultimate load and ultimate stress were significantly greater in the anterior strip (16.5 +/- 7.1 MPa) than in the middle (6.0 +/- 2.6 MPa) and posterior (4.1 +/- 1.3 MPa) strips (p < 0.0001). The modulus of elasticity also was significantly greater in the anterior strip (p < 0.0001), but there was no significant difference between the superficial and deep surfaces. It is concluded that the anterior portion of the supraspinatus tendon is mechanically stronger than the other portions, and it seems to perform the main functional role of the tendon.

Material properties of the plantar aponeurosis.

Material properties of the plantar aponeurosis were determined by a two-dimensional video tracking method to simultaneously measure the aponeurosis deformation. Failure loads averaged 1189 +/- 244 N and were higher in men. Average stiffness of the intact fascia was 203.7 +/- 50.5 N/mm at a loading rate of 11.12 N/sec and it did not vary significantly for the loading rates of 11.12 to 1112 N/sec. The high tensile loads required for failure were consistent with clinical and biomechanical studies and indicated the importance of the aponeurosis in foot function and arch stability.

Measurement of joint kinematics using ExpertVision system.

Three-dimensional kinematic calculations based on the output from a video-based passive marker detection system was developed. Three-dimensional position data of the markers placed on the limb were obtained with the system and then run through a program that calculated absolute and relative joint kinematics based on Eulerian angle and screw axis description. In this study, the accuracy and limitation of the system for kinematic analysis were examined.