In the context of rhythmic coordination it is essential to understand not only the neural factors that delineate coordination, but also the mechanical context under which coordination is performed. This is specifically notable in the context of intra-limb coordination, where mechanical links between segments and joints have profound and significant influence on coordination. In other words, the central nervous system might be exposed to a novel set of constraints associated with the complexity of the mechanical connections which exist between the joints and segments within limbs, and muscles that spread over two or more joints (bi- or multi-functional muscles). Intra-limb coordination recognizes two main constraints: interaction torque and bi-functional muscles. In order to reveal constraints that arise due rhythmic multi-joint coordination and how the CNS adapts to them, a custom designed robot motor arm was used to explore these mechanical factors in the elbow joint complex during rhythmic coordination. The custom designed robot arm was used to interact with a part of a body (i.e. elbow joint complex) where interaction torque is negligible; therefore, the focus of the research was on the constraints that are not under the influence of interaction torque. The main finding of the project was that force synchrony is a significant constraint that influences rhythmic intra-limb coordination. In relation to mechanical constraint of bi-functional muscles, only one out of two bi-functional muscles was found to be involved in coordination pattern where better stability was achieved. Moreover, it was concluded that bi-functional muscles may be incorporated in force synchrony constraint. The origin of the force synchrony constraint was analysed from three different perspectives (cognitive, neural and mechanical) and the suggestion was made that force synchrony may also constrain inter-limb coordination, generalizing therefore the importance of this constraint to the broad spectrum of rhythmic coordination. Further discussion focussed on possible future research directions that could explore additional constraints of intra-limb coordination, such as interaction torque.