Motor Control (2010-present)
For animals that use flapping flight, wing velocity is the product of wing stroke amplitude and wingbeat frequency. In hummingbirds, variation in stroke amplitude is particularly important for regulating force output, whereas wingbeat frequency is more tightly constrained. We demonstrated that hummingbirds control wing stroke amplitude using an elegant motor control strategy of spatial recruitment. The motor units of the pectoralis major muscle show synchronized activation and the height of the motor unit spike correlates with the angular extent of the wing stroke amplitude. During brief bursts of high wingbeat frequency, the birds will also use temporal recruitment of motor units (Altshuler et al, 2010). In other studies, we demonstrated specializations for high wingbeat frequency that include homogenous fibre type composition (Welch and Altshuler, 2009), very high temperature dependency (Reiser et al, 2013), and the mechanisms of motor unit synchronization (Donovan et al., 2013).
Our current research in motor control focuses on dynamic shape change, also called wing morphing. We are examining how the intrinsic muscles of the wings are activated, and the resulting muscle force dynamics that lead to changes in wing shape configurations.