1. Introduction
Two main modes of manual wheelchair (MWC) propulsion are described in the literature, namely the synchronous mode (Syn) in which the arms work together, and the asynchronous mode (Asy) in which the arms work alternately (Goosey-Tolfrey and Kirk Citation2003). Faupin et al. (Citation2013) showed that the Asy mode allows greater continuity of application of forces on the wheelchair ergometer, thereby reducing the risk of developing injury. However, these results were obtained during sprints in laboratory conditions, where the lateral movements of the MWC under Asy condition are neutralized. Thus, the consequences of this “steering” movement, due in particular to the rotation of the trunk during propulsion, have never been studied.
MWC propulsion is generally described as a symmetrical task due to the difficulties of bilateral measurements. Nevertheless, some authors have shown that a low asymmetry exists in the MWC propulsion, and it is even more important in difficult conditions, when rolling resistance or speed increases (Hurd et al. Citation2008; Soltau et al. Citation2015). However, all studies were carried out in Syn propulsion and we do not know of any study that analysed the symmetry during the Asy propulsion.
Few studies have been conducted on trunk control in propulsion. Gagnon et al. (Citation2016) have shown that an increase in upper limb and trunk strength, as well as improved stability, can optimize propulsion and certainly reduce peripheral muscle fatigue and the risk of injuries. Sauret et al. (Citation2013) have shown that forward/backward stability depends on the propulsion technique of the subject. However, in these studies, only the Syn propulsion was analysed.
The main objective of this work is to analyse the influence of the Syn and Asy modes during start-up and propulsion on biomechanical parameters determining the symmetry and on the stability of the trunk; and this, on the field.
2. Methods
2.1. Participant
One subject participated in this case study. He is a sporty man, practicing wheelchair tennis. He is a femoral amputee. He is 33 years old, measures 1.69 m for 80 kg.
2.2. Materials
An instrumented Wheelchair Ergometer (FRET) was used (Vaslin et al. Citation2011). It measures the forces applied to the hand rim, the forces at the seat and backrest, as well as acceleration and movement.
The vicon system is a tool for measuring motion in 3D. It allows to collect kinematic data.
2.3. Testing procedure
The subject made 4 trials: two starts and two propulsions. Each of these trials was made in Syn and Asy propulsion. The subject was asked to propel his wheelchair at a moderate speed and maintain that speed for all tests.
2.4. Measurements
The variations of the pressure centre (PC, expressed in cm), along the anteroposterior axis (PCx) and the medio-lateral axis (PCy) were collected, as well as the propulsive moment on the right wheel (Mz-R, expressed in N.m−1) and on the left wheel (Mz-L, expressed in N.m−1). The temporal parameters of the propulsion cycle were recorded, namely the push time (PT, expressed in % of the total cycle time), the rest time (RT, expressed in% of the total cycle time), and the cycle time (CT, expressed in seconds).
Finally, the trunk amplitudes (expressed in degree) and the symmetry index (ISI) (Chenier et al. Citation2017) were calculated.
3. Results and discussion
The parameters collected are presented in for start-up and in for propulsion.
Table 1. Mean ± standard deviation of the results obtained during start-up.
Table 2. Mean ± standard deviation of the results obtained during propulsion.
4. Conclusions
In Asy mode, the propulsion symmetry appears to be lower than the Syn propulsion by 22% for start-up and 20% for propulsion. The subject seems more unstable, with significant PC amplitudes, with greater trunk movements
The subject seems more unstable in Asy mode, with notably a displacement of the PCy more important compared to Syn mode, and this difference is accentuated during startup. This instability is associated with greater trunk movements in Asy vs Syn, especially a more pronounced trunk rotation due to the alternating propulsion of each arm.
In Asy, the subject has a lower PT and a higher RT: the subject pushes shorter with a longer rest time. In addition, the propulsive moment is higher for the Syn mode, and it is even more important for propulsion vs start-up. This can be explained by the fact that only one arm at a time exerts a force on the hand rim.
These preliminary results could explain the privileged use of Syn propulsion in sports activities by spinal cord injured people with instability of the trunk. It seems interesting to continue this study with a larger sample and subjects with different pathologies to fully validate the trends that can be observed.
References
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