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| Citation | Study Design | Population | Intervention | Outcomes | Limitations |
|
| Wells et al. 2005 [24] | RCT | National-level competitive swimmers, 15.6 ± 1.3 years n = 34 (20 females, 14 males) | Duration: 12 weeks | At 6 weeks, no change in MIP and MEP in IMRT or sham groups; at 12 weeks, ∆MIP = 14.4 cmH20 and ∆MEP = 20 cmH20 in females (combining IMRT and sham subjects) with no changes in males | No statistical between-group comparisons reported |
| Frequency: 10 sessions/week | MVV15, FEV1, and FVC increased in both IMRT and sham groups after 12 weeks; no difference between IMRT and sham at 6 weeks |
| Intensity: 50% weeks 1–3 and 60% weeks 3–6 for MIP and MEP; 70% weeks 7–9 and 80% weeks 10–12 for MIP and MEP | No differences in performance (swim velocity) or dyspnea |
| Volume: 10 breaths per session |
| Type: inspiratory and expiratory flow-resistive loading |
| Equipment: PowerLung |
| Control: sham IMRT (10% MIP and MEP) for 6 weeks followed by moderate IMRT (50% weeks 7–9 and 60% weeks 10–12 for MIP and MEP) |
| (Both groups continued regular swim training; only first 6 weeks represent differences between IMRT and sham) |
|
| Kilding et al. 2010 [25] | RCT | Club-level competitive swimmers n = 16 (6 females, 10 males) | Duration: 6 weeks | ∆MIP = 10.5 cmH20 in IMRT group vs. 0.3 cmH20 in sham group | |
| Frequency: 7 days/week | Swim time improved for 100 m and 200 m time trials, but not for 400 m time trial |
| Intensity: 50% MIP. Instructed to increased load periodically so that 30 breaths could only just be completed | Rating of perceived exertion decreased across a range of intensities |
| Volume: 30 breaths, twice a day | FVC, FEV1, PEF: No change |
| Type: pressure threshold loading | MEP not reported |
| Equipment: POWER-breathe |
| Control: sham IMRT, 60 slow protracted breaths once daily at 15% MIP |
|
| Lemaitre et al. 2013 [26] | Controlled before and after study | Swimmers, 13–18 yr, avg. training 45–48 wk/yr, 20 h/wk n = 20 (7 females, 13 males) | Duration: 8 weeks | ∆MIP = ≈25 cmH20 in RMET group vs. no change in control group | MIP and MEP reported in figures (absolute values not reported) |
| Frequency: 5 days per week | ∆MEP = ≈25 cmH20 in RMET group vs. no change in control group |
| Intensity: 60% of MVV12 | Competition swim time on 50 m and 200 m improved |
| Volume: 30 min | Respiratory endurance test breathing duration increased from 16 to 24.6 min |
| Type: voluntary isocapnic hyperpnea (respiratory muscle endurance training or RMET) | VEmax and maximum breathing frequency increased |
| Equipment: SpiroTiger | Rating of perceived exertion and rating of perceived dyspnea reduced |
| Control: usual training only | during the 50 m and 200 m race |
| FVC (% pred) and MVV increased |
|
| Lomax et al. 2019 [27] | RCT | Swimmers, two groups based on training distance (low and high) n = 33 (15 females, 18 males) | Duration: 6 weeks | ∆MIP = ≈55 cmH20 (high-training IMRT group), ≈35 cmH20 (low-training IMRT group) and ≈20 cmH20 (high-training control group) | MIP reported in figures (pre and post absolute values not reported). 36% improvement in MIP (combined for high and low-training IMRT groups) reported in text of article |
| Frequency: 7 days/wk | No change in MEP |
| Intensity: 50% MIP. Instructed to increased load periodically so that 30 breaths could only just be completed | 100 m and 200 m swimming times improved in the low-training IMRT group only |
| Volume: 30 breaths, twice a day |
| Type: pressure threshold loading |
| Equipment: POWER-breathe |
| Control: usual swim training only |
|
| Okrzymowska et al. 2019 [29] | RCT | Disabled swimming division athletes, 16–20 yr n = 16 (8 females, 8 males) | Duration: 8 weeks | ∆MIP = 33 cmH20 (IMRT group) and 16 cmH20 (control group) | |
| Frequency: 5 days/week | FVC, FEV1, and PEF increased in IMRT group |
| Intensity: 30% MIP in week 1, increased to 40% in weeks 2 and 3, 50% in weeks 4 and 5, and 60% in weeks 6–8 | MEP increased in both groups |
| Volume: 30 breaths, 5 min in week 1 increased to 15 min in week 8, twice a day |
| Type: pressure threshold loading |
| Equipment: philips respironics |
| Control: usual swim training only |
|
| Vašíčková et al. 2017 [28] | Randomized controlled trial (parallel arm with control group receiving the IMRT intervention after a 1-month washout) | Club-level fin-swimmers n = 20 (did not report sample size by sex) | Duration: 4 weeks | MIP increased by 20.8% in the IMRT group vs. 1.5% in the control group (post 4 weeks) | Results reported as median values; absolute values not reported for MIP and MEP |
| Frequency: 7 days/week | MEP increased by 10.6% in the IMRT group vs. 5.1% decrease in the control group (post 4 weeks) |
| Intensity: 30% MIP and MEP and increased by 2 cm H20 every week until maximum possible resistance on the threshold devices | Length able to swim for one inspiration increased by 27.4% (IMRT in first phase), 20.7% (IMRT in second phase) |
| Volume: 10 maximal inspirations and 10 maximal expirations (strength) + 15 min of continuous breathing against resistance (endurance) | FVC, FEV1, PEF: no change |
| Type: pressure threshold loading (inspiratory and expiratory) |
| Equipment: philips respironics |
| Control: usual swim training (with IMRT completed in second phase after washout) |
|
| Mackala et al. 2019 [30] | RCT | Club-level competitive junior soccer players n = 16 males | Duration: 8 weeks | ∆MIP = 44 cmH20 (IMRT group) vs. 11 cmH20 (control group) | |
| Frequency: 5 days/week | ∆MEP = 41 cmH20 (IMRT group) vs. 4 cmH20 (control group) |
| Intensity: 40% MIP in week 1, increased by 5% every week to 80% in week 8 | Running test distance increased by 5% in IMRT group vs. 2.1% in the control group (both changes were statistically significant) |
| Volume: 5 repetitions in week 1 to 15 repetitions in week 8, each repetition was 45 s of IMRT followed by a 15 s break, twice a day | FVC improved in IMRT group |
| Type: pressure threshold loading | FEV1 improved in both groups |
| Equipment: philips respironics |
| Control: usual training only |
|
