Respiratory muscle performance with stretch‐shortening cycle manoeuvres: maximal inspiratory pressure–flow curves

Aim: To test the hypothesis that the maximal inspiratory muscle (IM) performance, as assessed by the maximal IM pressure–flow relationship, is enhanced with the stretch‐shortening cycle (SSC). Methods: Maximal inspiratory flow–pressure curves were measured in 12 healthy volunteers (35 ± 6 years) during maximal single efforts through a range of graded resistors (4‐, 6‐, and 8‐mm diameter orifices), against an occluded airway, and with a minimal load (wide‐open resistor). Maximal inspiratory efforts were initiated at a volume near residual lung volume (RV). The subjects exhaled to RV using slow (S) or fast (F) manoeuvres. With the S manoeuvre, they exhaled slowly to RV and held the breath at RV for about 4 s prior to maximal inspiration. With the F manoeuvre, they exhaled rapidly to RV and immediately inhaled maximally without a post‐expiratory hold; a strategy designed to enhance inspiratory pressure via the SSC. Results: The maximal inspiratory pressure–flow relationship was linear with the S and F manoeuvres (r² = 0.88 for S and r² = 0.88 for F manoeuvre, P < 0.0005 in all subjects). With the F manoeuvre, the pressure–flow relationship shifted to the right in a parallel fashion and the calculated maximal power increased by approximately 10% (P < 0.05) over that calculated with the S manoeuvre. Conclusion: The maximal inspiratory pressure–flow capacity can be enhanced with SSC manoeuvres in a manner analogous to increases in the force–velocity relationship with SSC reported for skeletal muscles.