Discussion
PD, muscle fatigue
RECRUITMENT
The present study aimed to compare the effectiveness of IS versus TIMT, when used for IMT, on lung functions in patients with PD. The results of the present study showed that MIP and 6-MWD improved with both IS and TIMT. No significant differences were observed with any of the techniques for PFT (FVC, FEV1, and PEFR). When both groups were compared, a greater improvement was observed in the TIMT group than in the IS group. When both groups were compared, large effects were observed for the mean difference of MIP (Partial Eta Squared = 0.719) and 6-MWD (Partial Eta Squared = 0.655). Therefore, TIMT has more beneficial effects on MIP and 6-MWD than IS in PD patients.In the literature, it is already reported that in PD, patients have decreased respiratory muscle strength and enduranceIn the present study, baseline values of MIP for Hoehn & Yahr stages 1–3 were 53.33 cmHNo study in our knowledge has used IS and TIMT for IMT and compared their effects in patients with PD; therefore, comparing the present study's findings with other studies is difficult. However, several previous studies have reported the beneficial effects of IMT on respiratory functions. Inzelberg et al. reported improved endurance and strength of the inspiratory muscle in patients with PD after specific IMTIn the present study, no significant improvements were observed in PFTs (FVC, FEV1, and PEFR) in both groups (IS and TIMT). The possible reason for this could be exercise-type specificity. There is evidence that when the same exercise type is used for testing and training, the greatest training effects will occur, called exercise-type specificityGosselink et al. reported other effects of IMT, including decreased perception of discomfort in the respiratory muscles, redistribution of blood flow to the locomotor and respiratory muscles, and delay in respiratory muscle fatigueIn the present study, TIMT has produced better results than IS in improving MIP and 6-MWD. Therefore, the TIMT device is a better choice for IMT than IS in patients with PD. However, if TIMT is challenging to understand and use for these patients, then the physical therapist should start with a simple device that also provides feedback to the patients, which is IS. The mechanism of TIMT is pressure-based loading, and the principle of usage is inspiration against a fixed resistance pressure, which may explain the observed differences between TIMT and IS. This process is comparable to the resistance/weight exercises used to strengthen the extremities' muscles. With the TIMT device, resistance training occurs for the inspiratory muscles, which produces several benefits, including increased muscle strength and endurance, increased oxygen intake by working muscles, and reduced muscle fatigue. All of which will increase functional fitnessIn the present study, the use of IS also, for six weeks, increased MIP and 6-MWD. Some previous studies showed that inspiratory muscle strength increases after IS use due to increased recruitment of motor unitsIn the present study, the average values of 6-MWD were 264.33 and 262.11 m in IS and TIMT groups, respectively. One of the previous studies by Falvo and EarhartNo improvements were observed in the present study in FVC, FEV1, and PEFR in both groups. This means both IS and TIMT failed to improve pulmonary function tests in patients with PD. According to Shei et al.