Respiratory muscle training in individuals with spinal cord injury: effect of training intensity and -volume on improvements in respiratory muscle strength

Study design
Retrospective cohort study.
Objectives To investigate the effect of training intensity and -volume on improvements in respiratory muscle strength in
individuals with spinal cord injury (SCI).

Setting
SCI rehabilitation center in Switzerland.

Methods
Inpatients with SCI, lesion level C4-T12, who had at least 10 individualized inspiratory muscle training sessions
with respiratory function measurements before and after the training period. Multiple regression analysis with natural
logarithmic (ln) transformation of the outcome values was used to examine the effect of training intensity and -volume,
lesion level and completeness, and baseline respiratory muscle strength on improvements in respiratory muscle strength.

Results
Overall, 67 individuals were analyzed. Variation in PImax was explained by PImax at baseline and training intensity.
This adjusted effect size suggested a 7% (95% CI 2.8 to 11.6%) increase in PImax per 10 units of increase in training
intensity. Controlling for the variation in baseline PEmax, the effect of training intensity on PEmax was conditional on AIS
(p < 0.021). While individuals with motor complete lesions showed a 6.8% (95% CI 2.1 to 11.7%) increase in PEmax per 10
units of increase in training intensity, the corresponding adjusted effect size in those with motor incomplete lesions was 0.1%
(95% CI −4.3 to 4.5%). The full models explained 57 and 60% of the variance of lnPImax and lnPEmax, respectively.

Conclusion
The intensity of inspiratory muscle training was more relevant than training volume for the improvement of
respiratory muscle strength in individuals with SCI. Thus, training intensity should be chosen as high as possible