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Wheeled Mobility and Seating Equipment

Axle Position of Wheelchair

Most lightweight and ultralight weight wheelchairs offer adjustable axle position. This allows the center of gravity to be adjusted appropriately for each individual, improving biomechanical efficiency and effectiveness of propulsion.

Author Year

Country
Research Design Score
Total Sample Size

Methods Outcome
Freixes et al. 2010

Argentina

Post-test

N=8

Population: Mean age: 32.4 yr; Gender: males=8, females=0; Level of injury: C6=8; Level of severity: AIS A=8; Mean time since injury: 37.4 mo.

Intervention: Propulsion during four wheelchair axle positions (P1 -up and forward, P2-down and forward, P3-down and backward, P4-up and backward).

Outcome Measures: Speed, Acceleration, Stroke frequency, Shoulder range of motion.

1.      P1 demonstrated the highest propulsion speed and P3 the slowest (p<0.05).

2.      Stroke frequency was significantly higher in P1 than P2 and P3 (p=0.05).

3.      A lower range of motion was observed in P1 compared to P2 and P3 (p<0.05); the range of motion in P4 was less than P3 in the transversal plane (p<0.05).

4.      No significant shoulder range of motion differences in the coronal and sagittal planes.

Mulroy et al. 2005

USA

Post-test

N=13

Population: Mean age:37.2yr; Gender: males=13, females=0; Level of injury: paraplegia=13; Time post injury: 3-37yr; Chronicity=chronic.

Intervention: Propulsion of a test wheelchair with two different seat positions [posterior (SP) or anterior (SA)] during free, fast and 8% graded condition.

Outcome Measures: Hand force and torque on pushrim; 3D motion of upper extremities and trunk during propulsion; Peak force (posterior and superior).

1.     During free propulsion, peak superior force was low, but increased during fast and 8% graded propulsion. The superior force was lower in the SP position than in the SA position for all conditions. During free propulsion, the superior force was a negative distraction force in SP (-4.2N) and a positive distraction force in SA (3.2N).

2.     During free and fast propulsion, peak posterior force was unaltered, but increased in the SP position during 8% graded propulsion. Posterior force was higher during fast and graded propulsion, as compared to free propulsion.

3.     The SA position had a significantly lower internal rotation effect than the SP position.

4.     A significantly greater transverse plane power was generated in the SA condition, as compared to the SP condition.

Samuelsson et al. 2004

Sweden

Post-test

NInitial=13; NFinal=12

Population: Mean age: 48.0 yr; Gender: males=10, females=2; Level of injury: paraplegia; Level of severity: Frankel A=7, D=5; Mean time in w/c/day: 11.6 hr.

Intervention: Two different rear-wheel position wheelchairs [5° seat incline (P1) and 12° seat incline (P2)], while on a treadmill or a computer for 30 min/activity.
Outcome Measures: Oxygen consumption, Respiratory exchange, Power output, Heart rate, Pulmonary ventilation, Freely chosen push frequency, Stoke angle, Pelvic lateral tilt, Pelvic sagittal rotation, Estimated seating comfort, Estimated activity performance.

1.     Changing the rear wheel position from P1 to P2 produced a change in the weight distribution (p<0.001).

2.     Changing from P1 to P2 also influenced stroke angle and push frequency during propulsion (p<0.05).

3.     Trends were not found for the remaining parameters studied.

Boninger et al. 2000

USA

Post-test

N=40

Population: Age range: 20.6-64.6 yr; Gender: males=28, females=12; Weight range: 43.2-106.0 kg. Height range: 154.9-20.3 cm; Level of injury: paraplegia=40; Range of time since injury: 1.3-25.2 yr; Chronicity=chronic.

Intervention: Propulsion of personal wheelchair on a dynamometer at two different stable speeds (0.9 m/sec-SP1; 1.8 m/sec-SP2) and starting from a still stop to the fastest possible speed (PTU). Outcome Measures: Axle position relative to the shoulder at rest (horizontal and vertical), Pushrim mechanical variables: Frequency of propulsion, Peak and rate of rise of resultant force, Planar movement and push angle.

1.     Frequency of propulsion was positively correlated with axle position at SP1 (p<0.05) and SP2 (p<0.01).

2.     The push angle was decreased in all conditions when the axle position was behind the position of the shoulder (SP1, p=0.05; SP2, p<0.05; PTU, p<0.05).

3.     A larger distance between the axle and shoulder also reduced the push angle in SP1 and SP2 (p<0.05).

4.     The largest distance between the axle and the shoulder correlated with faster loading of the pushrim at SP2 (p<0.05).

Discussion

There were four studies addressing the effect of rear axle position on wheelchair propulsion with individuals with a spinal cord injury.

Boninger et al. (2000) completed a study that showed axle position relative to the shoulder was associated with significant differences in pushrim biomechanics. They found that with the axle further back relative to the shoulder there is more rapid loading of the pushrim, and increased stroke frequency was required. Additionally, individuals attained a slower speed when starting from a dead stop and there was a decrease in the push angle. An increase in the vertical distance between the axle and the shoulder resulted in a decrease in push angle. With a decrease in push angle, force was applied to the pushrim for a shorter period and thus the frequency of propulsion had to increase to maintain speed. They suggested that providing users with a wheelchair with adjustable axle position and setting up the chair to meet the user’s needs could improve propulsion biomechanics and reduce the risk of secondary injuries because of wheelchair propulsion.

Mulroy et al. (2005) studied the effect of changing the fore-aft seat position on shoulder joint forces, moments and powers during three levels of effort of wheelchair propulsion. They found that the seat posterior position resulted in a statistically significant reduction in peak superior shoulder joint forces during free, fast and graded propulsion. They concluded that the posterior seat position may reduce the risk of rotator cuff tendinopathy.

Samuelsson et al. (2004) also studied the effect of rear wheel position on wheelchair propulsion and seating aspects. A more forward position of the rear wheel had a significant effect on stroke frequency and push angle. They also reported an increase in the weight distribution with the more forward position of the wheel. However, in their study they did not find any difference between the two-wheel positions with respect to mechanical efficiency, estimated exertion, and breathlessness, seating comfort, estimated propulsion qualities, pelvic position or activity performance.

Freixes et al. (2010) also assessed the changes in speed, acceleration, stroke frequency and shoulder ROM in relation to four different axle positions. The study showed that the up and forward axle position resulted in an increase in speed and acceleration with a higher stroke frequency and a decreased shoulder ROM. The axle position of down and backward axle position resulted in a lower speed and acceleration with a lower stroke frequency and an increased shoulder ROM. The authors indicated that these were clinically important findings for wheelchair propulsion in their homes.

Conclusion

There is level 4 evidence (from four post-test studies: Mulroy et al. 2005; Samuelsson et al. 2004; Boninger et al. 2000; Freixes et al. 2010) that the more forward the rear wheel is positioned, the greater the improvement in pushrim biomechanics, shoulder joint forces, push frequency, speed, acceleration and stroke angle.

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