High-intensity interval training accelerates oxygen uptake kinetics and improves exercise tolerance for individuals with cystic fibrosis

Abstract

Background: Exercise training provides benefits for individuals with cystic fibrosis; however, the optimal program is unclear. High-intensity interval training is safe and effective for improving 'functional capacity' in these individuals with peak rate of O₂ uptake typically referenced. The ability to adjust submaximal rate of oxygen uptake (V̇O₂ kinetics) might be more important for everyday function because maximal efforts are usually not undertaken. Moreover, the ability of high-intensity training to accelerate V̇O₂ kinetics for individuals with cystic fibrosis could be enhanced with O₂ supplementation during training.

Methods: Nine individuals with cystic fibrosis completed incremental cycling to limit of tolerance followed by 8 weeks of high-intensity interval cycling (2 sessions per week x ~ 45 min per session) either with (n = 5; O2+) or without (AMB) oxygen supplementation (100%). Each session involved work intervals at 70% of peak work rate followed by 60 s of recovery at 35%. For progression, duration of work intervals was increased according to participant tolerance.

Results: Both groups experienced a significant increase in work-interval duration over the course of the intervention (O2+, 1736 ± 141 v. 700 ± 154 s; AMB, 1463 ± 598 v. 953 ± 253 s; P = 0.000); however, the increase experienced by O2+ was greater (P = 0.027). During low-intensity constant-work-rate cycling, the V̇O₂ mean response time was shortened post compared to pre training (O2+, 34 ± 11 v. 44 ± 9 s; AMB, 39 ± 14 v. 45 ± 17 s; P = 0.000) while during high-intensity constant-work-rate cycling, time to exhaustion was increased (O2+, 1628 ± 163 v. 705 ± 133 s; AMB, 1073 ± 633 v. 690 ± 348 s; P = 0.002) and blood [lactate] response was decreased (O2+, 4.5 ± 0.9 v. 6.3 ± 1.4 mmol^. L^{- 1}; AMB, 4.5 ± 0.6 v. 5.2 ± 1.4 mmol^. L^{- 1}; P = 0.003). These positive adaptations were similar regardless of gas inspiration during training.

Conclusion: Eight weeks of high-intensity interval training for patients with cystic fibrosis accelerated V̇O₂ kinetics and increased time to exhaustion. This provides some evidence that these patients may benefit from this type of exercise.

Trial registration: This study was retrospectively registered in the ISRTCN registry on 22/06/2019 (#ISRCTN13864650).

Keywords: Cystic fibrosis high-intensity interval training oxygen supplementation∙V̇O2 kinetics functional capacity exercise tolerance.

Fig. 1

CONSORT diagram outlining the flow of subjects through the stages of the present investigation

Fig. 2

Rate of pulmonary oxygen uptake for a representative subject in the O2+ group before (top panel) and after (bottom panel) an eight-week training intervention comprising HIIT performed twice per week. The data were collected during unloaded cycling (time = − 60 to 0 s) followed by a square-wave increase to 30% of the subject’s peak work rate. Closed circles depict 5-s averages of breath-by-breath V̇O₂ data while solid line depicts modelled fit. Notice the marked reduction in the V̇O₂ MRT (i.e., the time taken for V̇O₂ to reach ~ 63% of the steady-state amplitude) and consequent reduction in the O₂ deficit indicated by the dashed line (O₂ deficit = MRT x Amplitude)

Fig. 3

Group mean ± SD for work-interval duration during week one (gray bars) and week eight (black bars) for the O2+ and AMB groups. * P < 0.05 compared to week one value within group; † P < 0.05 compared to increase for AMB