Most tracheoles extend parallel to the muscle fibres. The high tracheolar densities and penetration of flight muscle cells by tracheoles allow flying insects to achieve high oxygen consumption rates.The maximum partial pressure gradient available to drive the diffusion of oxygen to the cells is fixed by the atmospheric partial pressure of oxygen.However flushing air through the tracheae by active muscular movements of the body, coordinated with the opening and closing of the spiracles can increase the pressure in the tracheoles.The contraction of muscles squeezes the trachea enabling mass flow of air in and out of the trachea.