R H Rozendal

Inertia and muscle contraction parameters for musculoskeletal modelling of the shoulder mechanism

To develop a musculoskeletal model of the shoulder mechanism, both shoulders of seven cadavers were measured to obtain a complete set of parameters. Using antropometric measurements, the mass and rotational inertia of segments were estimated, followed by three-dimensional measurements of all morphological structures relevant for modelling, i.e. muscle origins and insertions, muscle bundle directions, ligament attachments and articular surfaces; all in relation to selected bony landmarks. Subsequently, muscle contraction parameters as muscle mass and physiological cross-sectional area were measured. The method of data collection and the results for inertia and muscle contraction parameters as prerequisities for modelling are described.

Geometry parameters for musculoskeletal modelling of the shoulder system

A dynamical finite-element model of the shoulder mechanism consisting of thorax, clavicula, scapula and humerus is outlined. The parameters needed for the model are obtained in a cadaver experiment consisting of both shoulders of seven cadavers. In this paper, in particular, the derivation of geometry parameters from the measurement data is described. The results for one cadaver are presented as a typical example. Morphological structures are modelled as geometrical forms. Parameters describing this form are estimated from 3-D position coordinates of a large number of datapoints on the morphological structure, using a least-squares criterion. Muscle and ligament attachments are represented as a plane or as a (curved) line. Muscle paths are determined by a geometrical form of the bony contour around which the muscle is wrapped. Muscle architecture is determined by the distribution of muscle bundles over the attachment area, mapping the distribution of the origin to the insertion. Joint rotation centers are derived from articular surfaces. Hence, muscle moment arms can be calculated. The result of this study is a set of parameters for each cadaver, describing very precisely the geometry of the shoulder mechanism. This set allows positioning of muscle force vectors a posteriori, and recalculation of position coordinates and moment arms for any position of the shoulder.

Wheelchair ergonomics and physiological testing of prototypes

Abstract Two hand rim propelled wheelchairs, a daily-use (active) wheelchair (R) and a marathon sports wheelchair (S), were compared to a three-wheeled crank (C) and a (synchronic) lever (L) propelled wheelchair. All wheelchairs were analysed with respect to cardio-respiratory parameters ([Vdot] E, [Vdot] O2 , HR, RER), power output and gross mechanical efficiency during a continuous exercise test (speed of the treadmill V = 0·96 ms-1; every third minute a one degree increase of the slope). Non-wheelchair users (NW: N = 10) were compared to wheelchair sportsmen (WS: N = 3). The cardio-respiratory strain of hand rim propulsion increases more swiftly for both R and S wheelchairs than for the C and L systems. Mechanical efficiency is significantly lower for the hand rim wheelchairs with a remarkably low efficiency for the S wheelchair. The S wheelchair however showed the lowest energy losses and a lower [Vdot]O 2 compared to the R wheelchair, these being important modalities for high speed and long distance ...

Effect of handrim velocity on mechanical efficiency in wheelchair propulsion

To study the effect of tangential speed of the handrims independent of external power output on gross mechanical efficiency (ME), nine able-bodied subjects performed wheelchair exercise tests on a stationary ergometer. The ergometer allowed for measurement of torque and three-dimensional forces on the rims and tangential velocity of the rear wheels. The experiment comprised two series of submaximal tests against constant external power outputs (0.25 and 0.50 W.kg-1) and four wheelchair speeds (0.83, 1.11, 1.39, and 1.67 m.s-1), which simulated a wheelchair speed of 1.67 m.s-1 and mechanical advantages of 0.43-0.87. ME stayed below 10.5% and changed inversely with speed of movement of the handrims. Peak torques on the right handrim stayed even with speed, leading to a significant increase in peak power output. Energy losses owing to braking torques at the beginning and end of the push phase increased with handrim speed but hardly exceeded 5 W. The effective force component applied to the handrims was below 71% of the magnitude of the total force vector and dropped up to 13% with increasing handrim speed. It is suggested that an ineffective direction of forces on the rims might (partly) be responsible for the low ME and for a decrease in ME in relation to tangential handrim velocity. This suggestion is discussed from a number of theoretical perspectives. It is concluded that the use of handrims with a lower mechanical advantage will increase wheelchair propulsion efficiency.

Relationship between physical strain during standardised ADL tasks and physical capacity in men with spinal cord injuries

To describe physical strain during activities of daily living (ADL), 44 men with spinal cord injuries (C4-L5) performed a set of standardised tasks. The physical strain was defined as the highest heart rate response expressed as a percentage of the individual heart rate reserve (%HRR). The physical strain averaged over the subjects who performed all tasks (n = 24) was (mean ± SD): 20.2 ± 7.2 %HRR (washing hands), 20.4 ± 7.3 %HRR (passing a side-hung door), 28.8 ± 10.8 %HRR (transfer to a toilet), 31.2 ± 13.1 %HRR (ascending an 8 cm curb), 33.9 ± 12.0 %HRR (transfer to a shower seat), 35.1 ± 10.5 %HRR (transfer to bed), 36.4 ± 13.3 %HRR (preparing lunch), 37.1 ± 12.0 %HRR (washing up), 38.7 ± 14.9 %HRR (ascending a ramp), 39.8 ± 15.6 %HRR (transfer to a shower wheelchair), 41.4 ± 12.1 %HRR (changing sheets), and 45.9 ± 10.4 %HRR (entering a car). Physical strain could be notably high, but large variations among subjects were present. During all tasks, subjects with tetraplegia had significantly higher levels of strain than subjects with low (T6-L5) lesions. Physical strain was inversely related to parameters of physical capacity: isometric strength (r: -0.34 to -0.72), sprint power (r: —0.34 to -0.69), peak oxygen uptake (r: -0.41 to -0.81) and maximal power output (r: -0.52 to -0.82). Parameters of physical capacity were better predictors of physical strain than was the lesion level, and explained 37-71% of the variance in strain during ADL. It was also concluded that the method used in this study provides a quantitative and objective estimation of physical strain and may therefore be a useful tool to identify task difficulty during rehabilitation and to evaluate the results of task and physical training on the physical strain during ADL.

Optimum cycle frequencies in hand-rim wheelchair propulsion

SummaryTo study the effect of different cycle frequencies on cardio-respiratory responses and propulsion technique in hand-rim wheelchair propulsion, experienced wheelchair sportsmen (WS group; n=6) and non-wheel chair users (NW group; n=6) performed wheelchair exercise tests on a motor-driven treadmill. The WS group wheeled at velocities of 0.55, 0.83, 1.11 and 1.39 m · s−1 and a slope of 2°. The NW group wheeled at 0.83, 1.11 and 1.39 m · s−1 and a 1° slope. In each test, a 3-min period at a freely chosen cycle frequency (FCF: 100%) was followed by four 3-min blocks of paced cycle frequencies at 60%, 80%, 120% and 140% FCF. Effects of both cycle frequency and velocity on physiological and propulsion technique parameters were studied.Analysis of variance showed a significant effect (p<0.05) of cycle frequency on oxygen cost and gross mechanical efficiency in both the WS and NW group. This indicated the existence of an optimum cycle frequency which is close to the FCF at any given velocity. The optimum cycle frequency increased with velocity from 0.67 to 1.03 cps over the range studied (p< 0.05). Oxygen cost was ∼10% less at 100% FCF than at 60% or 140% FCF. Gross mechanical efficiency for the WS group at 100% FCF was 8.5%, 9.7%, 10.4% and 10.1%, respectively, at the four velocities. The similarity in the trend of oxygen cost and gross mechanical efficiency data in both the WS and NW groups suggests that an optimum cycle frequency is not merely a consequence of practice alone, but also reflects a physiologically determined optimum, dependent on muscle mechanics, e.g. velocity of contraction and power output of the muscles used.

Mechanical properties of passive rat muscle during sinusoidal stretching

The dynamic passive response of the left gastrocnemius medialis muscle of thirty male Wistar rats was studied as a function of muscle dimensions and absolute and relative amount of connective tissue. Values of the absolute active and passive length-force curves (active force, passive force, active working range) correlated well (coefficients of correlation in a range of 0.62–0.92) with morphological variables (such as muscle optimum length, mean muscle fibre optimum length, physiological cross section, muscle weight and amount of intramuscular connective tissue). To eliminate dimensional effects the active and passive length-force curves were normalized taking maximal active twitch force and muscle optimum length as reference values (100%). The width of the normalized active length-force curve (relative active working range) was correlated negatively with muscle weight, muscle optimum length and physiological cross section. Relative amount of connective tissue and passive tension at optimum length (both independent of muscle dimensions) were positively correlated, indicating that passive muscles are stiffer when relative amount of intramuscular connective tissue is higher. Sinusoidal movements with several amplitudes and frequencies of movement were imposed on the passive gastrocnemius medialis muscle over a range of muscle lengths. In accordance with the approximately exponential increase of static passive muscle force with length, muscle length has a large influence on the shape and magnitude of the hysteresis diagrams resulting from sinusoidal movements: the value of all variables selected increases approximately exponentially with muscle length with the exception of the value of loss tangent, a factor indicating the amount of energy dissipated during each cycle relative to the amount of energy stored and released elastically. Velocity of movement has only minor influence on variables of the hysteresis diagrams as is shown by changing the frequency of movement. As loss tangent and relative amount of connective tissue did not vary with muscle dimensions in the muscles studied, it is likely that material properties of the components causing passive resistance were similar in these muscles.

Passive resistance of the human knee : the effect of remobilization

Changes of circumferential dimensions and passive resistance of the human knee caused by immobilization, were studied during remobilization. Patients immobilized with a long leg cast after tibial fractures or ligamentous injuries were studied immediately after removal of the cast and after mean periods of 18, 36 and 81 days of remobilization. Immobilization resulted in a decrease of circumferential dimensions. The difference in mid-thigh circumference between the immobilized and the unaffected leg was still present after 81 days of remobilization both for the patients with tibial fractures and for the remobilization both for the patients with tibial fractures and for the patients with ligamentous lesions. An increase of midpatellar circumference was present exclusively in the patients with ligamentous lesions at all four testing dates, indicating that this is an effect of the ligamentous lesion and not of immobilization per se. Variables of the hysteresis diagrams, resulting from sinusoidal movement of the knee at a range of knee angles, were used to quantify passive resistance of the knee in the flexion-extension plane (the muscles crossing the knee are inactive). Variables related to the elastic storage and release of energy, and variables related to energy dissipation were discerned. During remobilization the increased resistance to flexion (shown by the variables related to the elastic storage of energy), as found immediately after removal of the cast, disappears and the resistance becomes identical to the resistance of the unaffected leg. This may indicate a rapid readaptation of the length of ventral structures (shortened due to immobilization in a shortened position) to almost normal values.(ABSTRACT TRUNCATED AT 250 WORDS)

Inter-individual differences in the passive resistance of the human knee

Abstract The passive resistance of the knee to angular motion in the flexion-extension plane was investigated in groups of healthy males (n = 29) and females (n = 20). ‘Least square’ fitting procedures proved to be reliable for approximating the equilibrium angle of the knee and variables of the moment/angle diagrams. To assess the influence of the dimensions of the lower limb on the resistance of the knee, a multiple regression analysis was performed, using seven dimensional parameters of the lower limb. The results indicate that for males 35–77% (mean 58%) of the total variance is accounted for by the dimensional parameters. For females this range is 9–74% (mean 44%). Differences between males and females exist in all selected resistance variables. To decrease the influence of dimensional parameters, the slopes of the exponential curves relating moment and knee angle are expressed as percentages of the absolute moment values. When the values of these ‘relative slopes’ are used, differences between males and females become less in flexion and are absent when the knee is extended. These results indicate that male-female differences can partly be ascribed to differences in dimensions.

Passive Resistance of the Knee after Anterior Cruciate Ligament Reconstruction

In this study the data of dynamic mechanical tests were used as objective criteria to evaluate the results of a combined extra- and intra-articular reconstruction of the anterior cruciate ligament (ACL). With these tests the passive response of the knee and its surrounding tissues to sinusoidal strain in the flexion-extension plane was quantified.