Pneumatic muscle actuators based on McKibben muscles have performance characteristics that may be of considerable significance in robotics due to their power/weight ratio and use as user friendly soft drives. However, the dynamic response (bandwidth) has been inferior to electric systems, with a secondary concern over system stiffness. In this paper, the bandwidth limit is addressed from two perspectives; air flow effects and the physical structure of the actuator. It is shown that by reducing the dead volume within the muscle structure (by the addition of a variety of filler materials) the bandwidth can be increased by up to 400%, with similar increases in system stiffness. At the same time the air volume used to power the actuator can be reduced by up to 80-90%. The methods of achieving these improvements are fully assessed. Also, by ensuring effective air flow rates, it is shown that bandwidth limits can be increased by several 100% and potentially increases of 1000s% are possible.