Inspiratory muscle adaptations following pressure or flow training in humans

Skeletal muscle adapts differently to training with high forces or with high velocities. The effects of these disparate training protocols on the inspiratory muscles were investigated in ten healthy volunteers. Five subjects trained using high force (pressure) loads (pressure trainers) and five trained using high velocity (flow) loads (flow trainers). Pressure training entailed performing 30 maximal static inspiratory efforts against a closed airway. Flow training entailed performing 30 sets of three maximal dynamic inspiratory efforts against a minimal resistance. Training was supervised and carried out 5 days a week for 6 weeks. Inspiratory flow rates and oesophageal pressure-time curves were measured before and after training. Peak inspiratory pressures during maximal static and dynamic efforts and peak flows during the maximal dynamic efforts were calculated. The time-to-peak pressure and rate of rise in peak pressure during maximal static and dynamic manoeuvres were also calculated before and following training. Maximal static pressure increased in the pressure training group and maximal dynamic pressure increased in the flow training group. Both groups increased the rate of pressure production (dP/dt) during their respective maximal efforts. The post-training decrease in time-to-peak pressure was proportionately greater in the flow trainers than in the pressure trainers. The differences in time-to-peak pressure between the two groups were consistent with the different effects of force and velocity training on the time-to-peak tension of skeletal muscle.