**1. Introduction**

Many studies [1–3] assert that wheelchair users su ffer from upper limb injuries more frequently than the rest of the population. Since the handrim is the world's most used manual propulsion system [4], the main causes of upper limb pain depend on the motion of the handrim system that is a pushing movement. Outdoor and indoor motor activities are extremely important for the well-being of everyone. For disabled people, motor activities [5] are also an important tool in rehabilitation from a physical and psychological point of view. Even though motor activities for disabled people are extremely important, they are not easy to practice. First of all, specific sports require specific wheelchairs [6–12]; secondly, the areas where the disabled can practice sport have to be properly equipped; finally, the disabled are not independent for the transportation of the wheelchair for a specific sport.

The above reasons motivated us to develop a wheelchair with an innovative system of propulsion, which not only allows for the practice of outdoor activities autonomously, but also eliminates the need of a specific wheelchair for sport.

As shown in [13], during a propulsion cycle with the handrim system, the glenohumeral contact force has high peaks. This is one of the factors that can increase the risk of injuries to the shoulders. In addition, in the Conclusions section of [14] "The latter makes tangential force propulsion not only less e fficient, but also more straining for the shoulder". Di fferent articles compare the handrim system with alternative systems of propulsion, such as a lever system [15] and a handcycle [13].

Another approach considers the use of a rowing gesture in order to obtain the propulsion. Furthermore, the rowing stroke [16] is divided into four phases and di fferent articles have studied the efficiency of the rowing gesture [17]. The rowing stroke is a complex movement; the muscles of the legs, trunk, back, shoulders and arms are involved. The rowing stroke can be performed by disabled athletes with di fferent levels of spinal injuries [18]. Disabled people can perform this movement depending on the height of the spinal injuries.

In the last two years, the first prototype, named Handwheelchiar.q01 [19], was released. The first prototype tested the functioning of the innovative system of propulsion and highlighted some critical issues.

In addition to the Handwheelchair.q01, the authors of this paper have wide experience with means of mobility for disabled people [20,21].

#### **2. Rowing Gesture: General Features**

The innovative system of propulsion is inspired by the rowing gesture. One of the more important characteristics of the rowing gesture is that the drive phase is obtained using a pulling movement of the arm, instead of a pushing one, typical of handrim and lever systems. The pulling movement could be a good alternative compared to the pushing movement. In this work, a cable solution was introduced in order to realise the rowing motion as a system of propulsion. The cable solution allows users to optimise their motion based on their own individual physical characteristics.

The rowing gesture is composed of two phases. During the traction phase, the user provides power, while in the recovery phase the user goes back to the initial position.

During the traction phase shown in Figure 1, the user pulls two cables by two handles wrapped around two pulleys. Each pulley transmits the torque and rotation to the wheel by a unidirectional mechanism, named a ratchet system. A power spring, which connects the pulley to the chassis of the wheelchair, is loaded. In this phase, the angular speed of the pulley and the wheel are equal.

**Figure 1.** Rowing gesture during the traction phase.

During the recovery phase shown in Figure 2, the user stops pulling and the power spring, previously loaded, rotates the pulleys in the opposite direction ( ω w > 0, ωP < 0). The cables are wrapped around each pulley and the user can start another traction phase.

**Figure 2.** Rowing gesture during the recovery phase.

In Figure 3, the angular position, the angular speed of the pulley and the wheel are shown with the three assumptions:


**Figure 3.** Angular speed and angular position of the pulley and the wheel.

In Section 4, the mechanism of transmission of motion will be accurately described.

#### **3. Application of the Innovative System in Sport**

The innovative system of propulsion can be employed by different means of manual mobility for sport: Handbike and Wheelchair racing.

The innovative system can be installed on the Handwheelchair.q racing wheelchair, as shown in Figure 4, with a few modifications of standard racing wheelchairs. The push-rims have been removed, while a pair of traction pulleys and a pair of return pulleys have been placed. The Handwheelchair.q racing wheelchair with the innovative system of propulsion keeps the same characteristics of a racing wheelchair: two rear traction wheels and a front steering wheel.

**Figure 4.** Innovative system applied to the racing wheelchair.

The innovative system can be employed on the Handbike. Figure 5a shows the functional design of Handbike.q for categories H1, H2, H3 and H4, namely disabled with spinal cord injuries and Figure 5b for categories H5, namely disabled with amputated limbs. A pair of pulleys has been seated, one on each side, in order to balance the fork transversely. A return pulley has been located in order to optimise the athlete's motion. The Handbike.q with the innovative system of propulsion retains the same characteristics of the Handbike: a traction steering front wheel.

**Figure 5.** (**a**) Innovative system applied to the recumbent Handbike; (**b**) Innovative system applied to the Handbike.
