Acute Effects of a Respiratory Sprint-Interval Session on Muscle Contractility

Respiratory muscle training has been shown to improve physical performance in healthy individuals and patients. One training modality for both inspiratory and expiratory muscles is respiratory muscle endurance training (RMET), which consists of normocapnic hyperpnea at constant ventilation for 30 min. Here, a new training regimen, respiratory muscle sprint-interval training (RMSIT), is introduced and tested for its potential to fatigue respiratory muscles. In addition, effects of both modalities on airway properties are investigated.

In 12 healthy subjects (six men and six women; 24 ± 3 yr; forced expiratory volume in 1 s, 115% ± 10%), changes in inspiratory transdiaphragmatic twitch pressure (Pdi,tw) and expiratory gastric twitch pressure (Pga,tw) were assessed during cervical magnetic stimulation or thoracic magnetic stimulation before and after a single bout of RMET and RMSIT. At similar time points, mechanical airway properties were assessed by impulse oscillometry. RMET was performed for 30 min at 60% of maximal voluntary ventilation, with constant tidal volume and breathing frequency. RMSIT consisted of six 30-s respiratory sprints (with 2-min breaks in between) at constant tidal volume, with the greatest possible breathing frequency and added resistance.

Pdi,tw and Pga,tw decreased significantly after RMET (-17.7% ± 9.0% and -22.4% ± 18.5%; P < 0.01) and RMSIT (-18.1% ± 12.8% and -21.2% ± 13.1%; P < 0.01), and changes did not differ between training modalities (P = 0.50 and P = 0.12), suggesting similar levels of fatigue. Work of breathing per minute was 2.4 ± 0.8-fold greater in RMSIT than in RMET, whereas total work of breathing was substantially smaller in RMSIT (3.4 ± 0.8 kJ) than in RMET (15.0 ± 0.42 kJ). No subject showed clinically relevant changes in mechanical airway properties.

Despite different work history, RMSIT appears to place a metabolic load on respiratory muscles similarly to RMET and could therefore be considered a time-saving and safe training alternative.