Inside a moving vehicle humans are subjected to accelerations. These accelerations may interfere with manual control tasks, reducing manual control performance, in several different ways (McLeod and Griffin, 1989, Journal of Sound and Vibration). For example, accelerations may cause involuntary limb motions, which can lead to involuntary control inputs. This phenomenon is called biodynamic feedthrough (BDFT). BDFT is known to reduce ride comfort, control accuracy and - above all - safety during the operation of large range of vehicles (e.g. air- and rotorcraft, automobiles, hydraulic and electric machinery) and can occur under many different circumstances. Particularly, in closed-loop systems, e.g., a pilot flying a helicopter, BDFT induced inputs can develop into a biodynamic coupling: divergent or weakly damped oscillatory involuntary control inputs. Accelerations may also interfere with manual control performance through other mechanisms, such as visual impairment (‘blurring’ of visual input) or neuro-muscular interference (inducing errors in the percieved state of muscles and limbs). The combined effect of accelerations on manual control performance is labelled as biodynamic interference (see Fig. 1). 

The occurrence of biodynamic interference is influenced by many different factors, which often show complex interactions. Examples of such factors are the control device dynamics and the acceleration frequency characteristics, but also more elusive concepts such as mental workload and fatigue. A particularly challenging aspect in biodynamic interference is the role of the human operator. Our research has shown that the limb dynamics of the human body influence the biodynamic feedthrough dynamics (see Fig. 2). Limb dynamics do not only differ from person to person, but can also vary significantly over time. Limb dynamics depend, amongst other factors,  on the manual control task the human operator is performing. For some tasks a ‘stiffer’ setting of the neuromuscular system may be beneficial where for other tasks a more ‘compliant’ setting is required. In order to mitigate biodynamic interference effects for any setting of the limb dynamics a solution is needed that is capable of adapting to changes in the state of the human operator.