The effects of inspiratory muscle training on inspiratory muscle strength, lung function and quality of life in adults with spinal cord injuries: a systematic review and Meta-analysis

Figures & data

Figure 1. Flow of studies through the review.

A flow diagram showcasing the amount of studies retrieved for review from 11 databases and 6 registers. At the first stage, 412 studies were identified. After removal of duplicates, initial screening and full-text assessment of eligibility, 6 studies were chosen to include in the review.

Table 1. Summary of included studies (n = 6).

Study	Participants	Intervention	Outcome measures
Soumyashree and Kaur [13]	n = 27 Mean age: 31.7 Injury type: T1-T12, ASIA A and B Diagnosis: 3 months − 1.5 years M:F = 22:5	IMT: Trained at 40% MIP, 15 min sessions, 5x/week for 4 weeks Control: Breathing exercises Performed all sessions supervised at an SCI rehabilitation centre	MIP, MEP
Postma et al. [5]	n = 40 Mean age: 46.85 Injury type: C5-T9, ASIA A, B, C, D Diagnosis: 2–4 months M:F: 35:5	IMT: Received usual care and RIMT. Trained at 60% MIP, 7 sets x 2 min, then 1 min unresisted breathing 5x/week for 8 weeks Control: PROM, muscle strength exercises, and functional training Performed all sessions supervised at 4 different SCI rehabilitation centres	MIP, MEP, FEV1, QOL (SF-36: physical and mental health components)
West et al. [14]	n = 10 Mean age: 29.2 Injury type: C5-C7, ASIA A and B Diagnosis: 4–15 years M:F: 9:1	IMT: Trained at 50–60% MIP, 30 repetitions, 2x/day, 5x/week for 6 weeks Control: placebo inhaler (wet air) Supervised for the first session, then performed the rest of sessions at home	MIP, MEP, FEV1
Mueller et al. [12]	n = 16 Mean age: 38.4 Injury type: C5-C8, ASIA A Diagnosis: 6–8 months M:F: 12:4	IMT: Trained at 80% MIP. Did 90 repetitions for 10 min sessions, 4x/week for 8 weeks Control: Used incentive spirometer Performed all sessions supervised at an SCI rehabilitation centre	MIP, MEP, FEV1, QOL (SF-12: physical and mental components)
Liaw et al. [8]	n = 20 Mean age: 33.7 Injury: C4- C7, ASIA A Diagnosis: 1–4.5 months M:F: 16:4	IMT: Training started at the smallest inspiratory resistance setting (blue, 7 mm). Trained for 15–20min, 2x/day, 7x/week for 6 weeks. Also performed usual care Control: Usual care—PROM, mattress exercise, sitting balance, or upper limb functional training Performed all sessions supervised in inpatient hospital setting	MIP, MEP, FEV1
Derrickson et al. [11]	n = 11 Mean age: 27.8 Injury: C4- C7, ASIA A Diagnosis: 2 days to 2.5 months M:F: 9:2	IMT: Trained with least amount of resistance for 15 min, 2x/day, 5x/week for 7 weeks Control: Abdominal weights Performed all sessions supervised in inpatient hospital setting	MIP

Figure 2. Risk of bias of included studies assessed using the Cochrane Risk of Bias Tool.

A traffic light plot lists the six included studies for the review on the X axis, and six domains of bias on the Y axis. Each study is rated against each domain of bias. The type of bias for each study is rated as low risk (green dot), unclear risk (yellow dot) or high risk (red dot). Incomplete outcome data is the largest source of bias, and selective reporting is the lowest risk of bias.

Figure 3. Mean difference (95% CI) in maximal inspiratory pressure (cmH₂O) due to inspiratory muscle training, estimated by pooling data from six studies (n = 124).

A forest plot comparing the mean difference for maximal inspiratory pressure after inspiratory muscle training (IMT). Data from six studies was pooled. The left side of the graph favours the control group, while the right side favours the experimental group (IMT). The overall mean difference favours IMT, with confidence intervals for five studies favouring the IMT side of the forest plot. However, two confidence intervals cross the line of null effect into the control group side.

Figure 4. Mean difference (95% CI) in maximal expiratory pressure (cmH2O) due to inspiratory muscle training, estimated by pooling data from five studies (n = 113).

A forest plot comparing the mean difference for maximal expiratory pressure after inspiratory muscle training (IMT). Data from five studies was pooled. The left side of the graph favours the control group, while the right side favours the experimental group (IMT). The overall mean difference favours IMT, with one confidence interval completely favouring the IMT side. However, four confidence intervals cross the line of null effect into the control group.

Figure 5. Standardised mean difference (95% CI) in quality of life: physical component due to inspiratory muscle training, estimated by pooling data from two studies (n = 56).

A forest plot comparing the standardised mean difference for quality of life: physical component after inspiratory muscle training (IMT). Data from two studies was pooled. The left side of the graph favours the control group, while the right side favours the experimental group (IMT). The standardised mean difference favours IMT, however both confidence intervals cross the line of null effect into the control group.

Figure 6. Standardised mean difference (95% CI) in quality of life: mental component due to inspiratory muscle training, estimated by pooling data from two studies (n = 56).

A forest plot comparing the standardised mean difference for quality of life: mental component after inspiratory muscle training (IMT). Data from two studies was pooled. The left side of the graph favours the control group, while the right side favours the experimental group (IMT). The standardised mean difference favours the control group, with one confidence interval nearly completely favouring the control group. However, both confidence intervals cross the line of null effect into the experimental group.

Figure 7. Mean difference (95% CI) in Forced expiratory volume in 1 s (L) due to inspiratory muscle training, estimated by pooling data from four studies (n = 86).

A forest plot comparing the mean difference for forced expiratory volume in 1 second after inspiratory muscle training (IMT). Data from four studies was pooled. The left side of the graph favours the control group, while the right side favours the experimental group (IMT). The overall mean difference favours IMT, with one confidence interval completely favouring the IMT side, while the other three confidence intervals cross the line of null effect into the control group.

Figure 8. Mean difference (95% CI) in maximal inspiratory pressure due to inspiratory muscle training, estimated by pooling data from six studies, sub-grouped into studies utilizing non-spring-loaded and spring-loaded threshold devices (n = 124).

A forest plot comparing the mean difference for maximal inspiratory pressure after inspiratory muscle training (IMT). Studies were sub-grouped according to whether they used spring-loaded or non-spring-loaded devices. The right side of the graph favours the IMT group, while the left side favours the control group. The mean difference for both subgroups favours IMT, however one confidence interval from each subgroup crosses the line of null effect to the control group. Overall, the mean difference for maximal inspiratory pressure is higher for spring-loaded devices.

Figure 9. Mean difference (95% CI) in maximal inspiratory pressure due to inspiratory muscle training, estimated by pooling data from four studies, sub-grouped into six and eight week interventions (n = 86).

A forest plot comparing the mean difference for maximal inspiratory pressure after inspiratory muscle training (IMT) interventions lasting six or eight weeks. Data was pooled from four studies. The left side of the graph favours the control group, while the right side favours the experimental group (IMT). The mean difference for six week interventions favours IMT, with one confidence interval favouring the control group. The mean difference for eight week interventions favours IMT, with both confidence intervals of the included studies favouring IMT. Overall, the mean difference for maximal inspiratory pressure is higher after eight compared to six week interventions.

Table 2. Quality of evidence using the GRADE approach (inspiratory muscle training compared to control for adults with spinal cord injuries).

Patient or population: Adults with spinal cord injuries
Setting: Hospital and community
Intervention: Inspiratory muscle training
Comparison: Control
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	№ of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with control	Risk with Inspiratory muscle training
Maximum inspiratory pressure (cmH2O) follow up: range 4 weeks to 8 weeks	The mean maximum inspiratory pressure (cmH2O) ranged from 43 to 78 cmH2O	MD 15.72 cmH2O higher (5.02 higher to 26.41 higher)	–	124 (6 RCTs)	⨁⨁⨁◯ MODERATE ^a	Inspiratory muscle training probably increases maximum inspiratory pressure (cmH2O).
Maximum expiratory pressure (cmH2O) follow up: range 4 weeks to 8 weeks	The mean maximum expiratory pressure (cmH2O) ranged from 41 to 71 cmH2O	MD 5.19 cmH2O higher (4.16 lower to 14.55 higher)	–	113 (5 RCTs)	⨁⨁◯◯ LOW ^a,b	The evidence suggests that inspiratory muscle training results in little to no difference in maximum expiratory pressure (cmH2O).
Forced expiratory volume in 1 s (L) follow up: range 6 weeks to 8 weeks	The mean forced expiratory volume in 1 s (L) ranged from 1.70 to 2.88 L	MD 0.26 L higher (0.19 lower to 0.7 higher)	–	86 (4 RCTs)	⨁⨁◯◯ LOW ^a,b	Inspiratory muscle training may increase/ have little to no effect on forced expiratory volume in 1 s (L) but the evidence is very uncertain.
Quality of life: physical component follow up: 8 weeks	–	SMD 0.12 higher (1.01 lower to 1.25 higher)	–	56 (2 RCTs)	⨁◯◯◯ VERY LOW ^a,b,c	The evidence is very uncertain about the effect of inspiratory muscle training on quality of life: physical component.
Quality of life: mental component follow up: 8 weeks	–	SMD 0.2 lower (1.72 lower to 1.33 higher)	–	56 (2 RCTs)	⨁◯◯◯ VERY LOW ^a,b,c	The evidence is very uncertain about the effect of inspiratory muscle training on quality of life: physical component.

*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).

CI: Confidence interval; MD: Mean difference; SMD: Standardised mean difference.

GRADE Working Group grades of evidence.

High certainty: We are very confident that the true effect lies close to that of the estimate of the effect.

Moderate certainty: We are moderately confident in the effect estimate: The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different.

Low certainty: Our confidence in the effect estimate is limited: The true effect may be substantially different from the estimate of the effect.

Very low certainty: We have very little confidence in the effect estimate: The true effect is likely to be substantially different from the estimate of effect.

Explanations:

^aHigh risk for blinding of participants, outcome assessment and attrition bias (risk of bias).

^bSmall sample size and wide confidence interval includes both no effect and appreciable benefit (imprecision).

^cConsiderable heterogeneity between study results (inconsistency.

Figure 10. Regression coefficients and 95% confidence intervals to determine lesion- specific MIP and MEP values, using constants developed by Mueller et al. [26].

A table displaying the regression coefficients to determine an individual with an SCI’s lesion-specific maximal inspiratory pressure and maximal expiratory pressure values. The table is divided into three columns, with the first column listing person specific characteristics. The second column lists the regression coefficients for maximal inspiratory pressure that correspond to each characteristic in the first column. The third column lists the regression coefficients for maximal expiratory pressure that correspond to the characteristics in the first column. The bottom of the table includes a legend identifying all acronyms used.

Table 3. Example equation to determine lesion-specific MIP value.

Participant characteristics:	Male, ASIA A, C7 lesion, 47 years old, weight 72 kg
Equation:	45.31 (constant) + −11.98 (high tetraplegia group) + 14.95 (male) + (47*-0.60) (age) + (72*0.51) (body weight)
Lesion-specific MIP:	56.8 cmH2O
Improvement needed to avoid developing pneumonia:	56.8 cmH2O (*15%) = 8.52 cmH2O

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