Background: Aerobic exercise is known to reduce arterial stiffness; however, high-intensity resistance exercise is associated with increased arterial stiffness. Stretching exercises are another exercise modality, and their effect on arterial stiffness remains unclear. The purpose of this study was to determine whether stretching exercises reduce arterial stiffness in middle-aged and older adults, performing the first meta-analysis of currently available studies. Methods: We searched the literature for randomized controlled trials (RCTs) and non-RCTs published up to January 2020 describing middle-aged and older adults who participated in a stretching intervention vs. controls without exercise training. The primary and secondary outcomes were changes in arterial stiffness and vascular endothelial function and hemodynamic status. Pooled mean differences (MDs) and standard MDs (SMDs) with 95% confidence intervals (CIs) between the intervention and control groups were calculated using a random effects model. Results: We identified 69 trials and, after an assessment of relevance, eight trials, including a combined total of 213 subjects, were analyzed. Muscle stretching exercises were shown to significantly reduce arterial stiffness and improve vascular endothelial function (SMD: −1.00, 95% CI: −1.57 to −0.44, p = 0.0004; SMD: 1.15, 95% CI: 0.26 to 2.03, p = 0.01, respectively). Resting heart rate (HR) and diastolic blood pressure (DBP) decreased significantly after stretching exercise intervention (MD: −0.95 beats/min, 95% CI: −1.67 to −0.23 beats/min, p = 0.009; MD: −2.72 mm Hg, 95% CI: −4.01 to −1.43 mm Hg, p < 0.0001, respectively) Conclusions: Our analyses suggest that stretching exercises reduce arterial stiffness, HR, and DBP, and improve vascular endothelial function in middle-aged and older adults.

[Purpose] Considering that respiratory muscle fatigue is a cause of respiratory failure, we aimed to clarify the characteristics of respiratory muscle fatigue under inhalation load and investigate its impact on individual respiratory muscles. [Participants and Methods] The study included 14 healthy adult male volunteers. Maximal inspiratory and expiratory mouth pressures were measured under inhalation load and while at rest. The statuses of the trapezius, sternocleidomastoid, pectoralis major, diaphragm, rectus abdominis, and external and internal abdominal oblique muscles were also assessed using electromyographic frequency analysis. [Results] The maximal inspiratory and expiratory mouth pressures decreased over time and recovered after rest. The median power frequency decreased significantly in the sternocleidomastoid and rectus abdominis muscles at maximal inspiratory and expiratory mouth pressures, respectively, under inhalation load. [Conclusion] As a characteristic of respiratory muscle fatigue, there is a possibility that decreases in maximal inspiratory and expiratory mouth pressures as a result of the inhalation load affect muscle fatigue in the sternocleidomastoid and rectus abdominis muscles.

This study aimed to evaluate the effects of expiratory muscle training (EMT) on respiratory muscle strength and respiratory distress during inspiratory load. Thirty-one healthy adult males were randomly divided into an EMT group who underwent EMT (n = 15) and a control group who did not undergo EMT (n = 16). The EMT group underwent EMT with a 50% load of maximum expiratory mouth pressure (PEmax) for 15 min, twice a day, every day, for 4 weeks. The parameter of respiratory muscle fatigue was a decrease in maximum inspiratory mouth pressure (PImax) and PEmax during 20 min of inspiratory load; thus, PImax and PEmax during inspiratory load were measured. Respiratory distress during inspiratory load was assessed using the Borg scale. These assessments were performed on the same subjects in each group before and after the 4 week study. In the EMT group, the PEmax values after the study were significantly higher than those before the study (p < 0.01). Furthermore, before the study, the PImax and PEmax values for the EMT group during inspiratory load were significantly lower than those before inspiratory load (p < 0.01). However, after the study, there was no difference in these values between during and before inspiratory load. In the EMT group, the Borg scale value during inspiratory load from 6 to 20 min was significantly lower after the study than before the study (p < 0.05). EMT increases expiratory muscle strength, thereby attenuating decreased respiratory muscle strength (PImax and PEmax) and respiratory distress during inspiratory load in healthy subjects.

[Purpose] This study examined the effects of expiratory muscle training on fatigue in individual respiratory muscles. [Participants and Methods] Healthy adult males (n=31) were randomly assigned to two groups: expiratory muscle training (n=15) and normal controls (n=16). In the expiratory muscle training group, training was performed once for 15 min at 50% load of the maximum expiratory mouth pressure twice daily for 4 weeks. Respiratory muscle fatigue indicators were measured using surface electromyography as the median power frequency of each respiratory muscle at the time of measuring the maximum inspiratory mouth pressure during 20 min of inspiratory muscle loading and maximum expiratory mouth pressure. [Results] In the expiratory muscle training group, the median power frequency values of the sternocleidomastoid, rectus abdominis, and internal oblique/external oblique before expiratory muscle training significantly decreased during inspiratory muscle loading. However, no difference was observed in the median power frequency values measured before and during inspiratory muscle loading after the expiratory muscle training. In the normal controls, the median power frequency values of the sternocleidomastoid and rectus abdominis significantly decreased during inspiratory muscle loading. [Conclusion] Expiratory muscle training increased fatigue tolerance of the sternocleidomastoid, rectus abdominis, and internal and external oblique muscles in healthy individuals.

To clarify the characteristics of respiratory muscle fatigue in breath-loading at 50% maximum expiratory mouth pressure. [Subjects] Eleven healthy males. [Methods] We measured the maximum inspiratory and expiratory mouth pressures, (PImax) and PEmax, during breath-loading and rest, and used electromyography (EMG) frequency analysis to verify the state of the trapezius, sternocleidomastoid, pectoralis major, abdominal rectus, and internal and external oblique muscles. [Results] PImax and PEmax decreased over time and recovered after rest. The median frequency decreased in the rectus abdominis and internal and external oblique muscles at PImax, and in the trapezius, rectus abdominis, and internal and external oblique muscles at PEmax. During the rest period of 30 min, recovery was observed in the external oblique muscle at PImax, and in the abdominal rectus and external oblique muscles at PEmax. [Conclusion] Our results suggest that respiratory muscle fatigue caused by expiratory resistance loading causes decreases in PImax and PEmax.