The effect of resultant force at the pushrim on shoulder kinetics during manual wheelchair propulsion: a simulation study

Effect of Haptic Training During Manual Wheelchair Propulsion on Shoulder Joint Reaction Moments

Background

Manual wheelchair propulsion remains a very ineffective means of locomotion in terms of energy cost and mechanical efficiency, as more than half of the forces applied to the pushrim do not contribute to move the wheelchair forward. Manual wheelchair propulsion training using the haptic biofeedback has shown an increase in mechanical efficiency at the handrim level. However, no information is available about the impact of this training on the load at the shoulders. We hypothesized that increasing propulsion mechanical efficiency by 10% during propulsion would not yield clinically significant augmentation of the load sustained at the shoulders.

Methods

Eighteen long-term manual wheelchair users with a spinal cord injury propelled a manual wheelchair over a wheelchair simulator offering the haptic biofeedback. Participants were asked to propel without the Haptic Biofeedback (HB) and, thereafter, they were subjected to five training blocks BL1–BL5 of 3 min in a random order with the haptic biofeedback targeting a 10% increase in force effectiveness. The training blocs such as BL1, BL2 BL3, BL4, and BL5 correspond, respectively, to a resistant moment of 5, 10, 15, 20, and 25%. Pushrim kinetics, shoulder joint moments, and forces during the propulsive cycle of wheelchair propulsion were assessed for each condition.

Results

The tangential force component increases significantly by 74 and 87%, whereas value for the mechanical effective force increases by 9% between the pretraining and training blocks BL3. The haptic biofeedback resulted in a significant increase of the shoulder moments with 1–7 Nm.

Conclusion

Increases in shoulder loads were found for the corresponding training blocks but even though the percentage of the increase seems high, the amplitude of the joint moment remains under the values of wheelchair propulsion found in the literature. The use of the HB simulator is considered here as a safe approach to increase mechanical effectiveness. However, the longitudinal impact of this enhancement remains unknown for the impact on the shoulder joint. Future studies will be focused on this impact in terms of shoulder risk injury during manual wheelchair propulsion.

Fast Forward-Dynamics Tracking Simulation: Application to Upper Limb and Shoulder Modeling

OBJECTIVE

Musculoskeletal simulation can be used to estimate muscle forces in clinical movement studies. However, such simulations typically only target movement measurements and are not applicable to force exertion tasks which are commonly used in rehabilitation therapy. Simulations can also produce nonphysiological joint forces or be too slow for real-time clinical applications, such as rehabilitation with real-time feedback. The objective of this study is to propose and evaluate a new formulation of forward-dynamics assisted tracking simulation that incorporates measured reaction forces as targets or constraints without any additional computational cost.

METHODS

We illustrate our method with idealized proof-of-concept models and evaluate it with two upper limb cases: Tracking of hand reaction forces during an isometric force-generation task and constraining glenohumeral joint reaction forces for stability during arm elevation.

RESULTS

We show that the addition of reaction force optimization terms within our simulations generates plausible muscle force predictions for these tasks, which are strongly related to reaction forces in addition to movement. Execution times for all models tested were not different when run with or without the reaction force optimization term, ensuring that the simulations are fast enough for real-time clinical applications.

CONCLUSION

Our novel reaction force optimization term leads to more realistic shoulder reaction forces, without any additional computational costs.

SIGNIFICANCE

Our formulation is not only valuable for shoulder simulations, but could be used in various clinical situations (e.g., for different joints and rehabilitation therapy tasks) where the direction and/or magnitude of reaction forces are of interest.

A systematic review: the influence of real time feedback on wheelchair propulsion biomechanics

BACKGROUND

Clinical guidelines recommend that, in order to minimize upper limb injury risk, wheelchair users adopt a semi-circular pattern with a slow cadence and a large push arc.

OBJECTIVES

To examine whether real time feedback can be used to influence manual wheelchair propulsion biomechanics.

REVIEW METHODS

Clinical trials and case series comparing the use of real time feedback against no feedback were included. A general review was performed and methodological quality assessed by two independent practitioners using the Downs and Black checklist. The review was completed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta Analyses (PRISMA) guidelines.

RESULTS

Six papers met the inclusion criteria. Selected studies involved 123 participants and analysed the effect of visual and, in one case, haptic feedback. Across the studies it was shown that participants were able to achieve significant changes in propulsion biomechanics, when provided with real time feedback. However, the effect of targeting a single propulsion variable might lead to unwanted alterations in other parameters. Methodological assessment identified weaknesses in external validity.

CONCLUSIONS

Visual feedback could be used to consistently increase push arc and decrease push rate, and may be the best focus for feedback training. Further investigation is required to assess such intervention during outdoor propulsion. Implications for Rehabilitation Upper limb pain and injuries are common secondary disorders that negatively affect wheelchair users' physical activity and quality of life. Clinical guidelines suggest that manual wheelchair users should aim to propel with a semi-circular pattern with low a push rate and large push arc in the range in order to minimise upper limbs' loading. Real time visual and haptic feedback are effective tools for improving propulsion biomechanics in both complete novices and experienced manual wheelchair users.

Reconfiguration of the upper extremity relative to the pushrim affects load distribution during wheelchair propulsion

OBJECTIVE

Repetitive loading during manual wheelchair propulsion (WCP) is associated with overuse injury to the upper extremity (UE). The aim of this study was to determine how RF redirection and load distribution are affected by changes upper extremity kinematic modifications associated with modifications in seat positions during a WCP task. The aim of this study was to determine how RF redirection and load distribution are affected by upper extremity kinematic changes associated with seat position adjustment during a WCP task.

DESIGN

Dynamic simulations using an experiment-based multi-link inverse dynamics model were used to generate solutions for redistributing UE mechanical load in different seating positions without decrements in WCP task performance.

METHODS

Experimental RF and kinematic data were collected for one subject propelling at a self-selected speed and used as input into the model. Shoulder/axle distance, wrist angular position, and RF direction were systematically modified to simulate how the mechanical demand imposed on the upper extremity (elbow and shoulder net joint moments (NJMs) and net joint forces) may vary.

RESULTS

Load distribution depended on UE orientation relative to the wheel. At peak force, lower shoulder/axle distances and more anterior wrist positions on the pushrim allowed for more extended elbow positions and reduced total NJM load.

INTERPRETATION

Simulation results incorporating subject-specific data may provide mechanically based information to guide clinical interventions that aim to maintain WCP performance and redistribute load by modifying RF direction, seat configuration and hand/rim interaction.

Simulated effect of reaction force redirection on the upper extremity mechanical demand imposed during manual wheelchair propulsion

BACKGROUND

Manual wheelchair propulsion is associated with overuse injuries of the shoulder. Reaction force redirection relative to upper extremity segments was hypothesized as a means to redistribute mechanical load imposed on the upper extremity without decrements in wheelchair propulsion performance.

METHODS

Two individuals performed wheelchair propulsion under simulated inclined (graded) conditions using self-selected control strategies. Upper extremity kinematics and reaction forces applied to the wheel were quantified and used as input into an experiment-based multi-link inverse dynamics model that incorporates participant-specific experimental results. Reaction force direction was systematically modified to determine the mechanical demand imposed on the upper extremity (elbow and shoulder net joint moments and net joint forces) during wheelchair propulsion. Results were presented as solution spaces to examine the upper extremity load distribution characteristics within and between participants across a range of reaction force directions.

FINDINGS

Redirection of the reaction force relative to the upper extremity segments provides multiple solutions for redistributing mechanical demand across the elbow and shoulder without decrements in manual wheelchair propulsion performance. The distribution of load across RF directions was participant specific and was found to vary with time during the push phase.

INTERPRETATION

Solution spaces provide a mechanical basis for individualized interventions that aim to maintain function and redistribute load away from structures at risk for injury (e.g. reduce demand imposed on shoulder flexors (reduce shoulder net joint moment) or reduce potential for impingement (reduce shoulder net joint force).

BIOMECHANICS OF WHEELCHAIR PROPULSION

With progress of modern technology, manually-propelled wheelchairs are still of importance for individuals with mobility impairments. The repeated wheelchair propulsion and strenuous daily activities cause high loads and thus injuries on the upper extremity joints. Over the past few years, a considerable number of studies have been made on biomechanical analysis of wheelchair propulsion and wheelchair-related activities. Thorough investigation of biomechanics during wheelchair propulsion enhances comprehension of mechanism of injuries and provides information to improve wheelchair design and fitting. Numerous investigations have been made to demonstrate factors which cause low effectiveness of force application and inefficiency of movements. Emphasis was also placed on developing analytical models to simulate wheelchair propulsion.

The influence of altering push force effectiveness on upper extremity demand during wheelchair propulsion

Manual wheelchair propulsion has been linked to a high incidence of overuse injury and pain in the upper extremity, which may be caused by the high load requirements and low mechanical efficiency of the task. Previous studies have suggested that poor mechanical efficiency may be due to a low effective handrim force (i.e. applied force that is not directed tangential to the handrim). As a result, studies attempting to reduce upper extremity demand have used various measures of force effectiveness (e.g., fraction effective force, FEF) as a guide for modifying propulsion technique, developing rehabilitation programs and configuring wheelchairs. However, the relationship between FEF and upper extremity demand is not well understood. The purpose of this study was to use forward dynamics simulations of wheelchair propulsion to determine the influence of FEF on upper extremity demand by quantifying individual muscle stress, work and handrim force contributions at different values of FEF. Simulations maximizing and minimizing FEF resulted in higher average muscle stresses (23% and 112%) and total muscle work (28% and 71%) compared to a nominal FEF simulation. The maximal FEF simulation also shifted muscle use from muscles crossing the elbow to those at the shoulder (e.g., rotator cuff muscles), placing greater demand on shoulder muscles during propulsion. The optimal FEF value appears to represent a balance between increasing push force effectiveness to increase mechanical efficiency and minimize upper extremity demand. Thus, care should be taken in using force effectiveness as a metric to reduce upper extremity demand.