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Purpose: To compare deoxygenation of the sternocleidomastoid, scalenes, and diaphragm/intercostals (Dia/IC) during submaximal intermittent neck flexion (INF) versus submaximal inspiratory threshold loading (ITL) in healthy adults., Methods: Fourteen participants performed a randomized, cross-over, repeated measures design. After evaluation of maximal inspiratory pressures (MIP) and maximum voluntary contraction (MVC) for isometric neck flexion, participants were randomly assigned to submaximal ITL or INF until task failure. At least 2 days later, they performed the submaximal exercises in the opposite order. ITL or INF targeted 50 ± 5% of the MIP or MVC, respectively, until task failure. Near-infrared spectroscopy (NIRS) was applied to evaluate changes of deoxy-hemoglobin (ΔHHb), oxy-hemoglobin (ΔO 2 Hb), total hemoglobin (ΔtHb), and tissue saturation of oxygen (StO 2 ) of the sternocleidomastoid, scalenes, and Dia/IC. Breathlessness and perceived exertion were evaluated using Borg scales., Results: Initially during INF, sternocleidomastoid HHb slope was greatest compared to the scalenes and Dia/IC. At isotime (6.5-7 min), ΔtHb (a marker of blood volume) and ΔO 2 Hb of the sternocleidomastoid were higher during INF than ITL. Sternocleidomastoid HHb, O 2 Hb, and tHb during INF also increased at quartile and task failure timepoints. In contrast, scalene ΔO 2 Hb was higher during ITL than INF at isotime. Further, Dia/IC O 2 Hb and tHb increased during ITL at the third quartile and at task failure. Borg scores were lower at task failure during INF compared to ITL., Conclusion: Intermittent INF induces significant metabolic activity of the sternocleidomastoid and a lower perception of effort, which may provide an alternative inspiratory muscle training approach for mechanically ventilated patients., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Purpose: To contrast older and younger adults' prefrontal cortex (PFC) neural activity (through changes in oxygenated hemoglobin) during single and dual tasks, and to compare decrements in task performance., Methods: Changes in oxygenated hemoglobin of dorsolateral PFC were monitored using functional near-infrared spectroscopy during single tasks of spelling backwards (cognitive task) and 30 m preferred paced walk; and a dual task combining both. Gait velocity was measured by a pressure sensitive mat., Results: Twenty sex-matched younger (27.6 ± 3.5 years) and 17 older adults (71.2 ± 4.9 years) were recruited. The left PFC oxygenated hemoglobin decreased from start (1st quintile) to the end (5th quintile) of the walking task in younger adults ( - 0.03 ± 0.03 to - 0.72 ± 0.20 µM; p < .05) unlike the non-significant change in older adults (0.03 ± 0.06 to  -  0.41 ± 0.32 µM, p > .05). Overall, oxygenation increased bilaterally during dual versus single walk task in older adults (Left PFC: 0.22 ± 0.16 vs. - 0.23 ± 0.21 µM, respectively; Right PFC: 0.17 ± 0.18 vs. - 0.33 ± 0.22 µM, respectively), but only in right PFC in younger adults ( - 0.02 ± 0.15 vs.  -  0.47 ± 0.13 µM). Older adults exhibited lower velocity during the dual task compared to younger adults (1.03 ± 0.16 vs. 1.20 ± 0.17 m/s, respectively). Older age was associated with dual task cost on velocity during walking after adjusting for confounding variables., Conclusions: Age-related cognitive decline in older adults may increase neural activity for cognitive tasks and diminish walking automaticity that may lead to decrements during dual tasking; the greater PFC increases in the oxygenated hemoglobin and lower velocity may be due to increased cognitive load and limited attentional resources., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Purpose: To non-invasively examine the effect of acute hypoxia and inspiratory threshold loading (ITL) on inspiratory muscles [sternocleidomastoid (SCM), scalene (SA) and parasternal (PS)] oxygenation in healthy adults using near-infrared spectroscopy (NIRS)., Methods: Twenty healthy adults (12 M/8 F) were randomly assigned to perform two ITL tests while breathing a normoxic or hypoxic (FIO2 = 15 %) gas mixture. NIRS devices were placed over the SCM, PS, SA, and a control muscle, tibialis anterior (TA), to monitor oxygenated (O2Hb), deoxygenated (HHb), total hemoglobin (tHb) and tissue saturation index (TSI). With the nose occluded, subjects breathed normally for 4 min through a mouthpiece that was connected to a weighted threshold loading device. ITL began by adding a 100-g weight to the ITL device. Then, every 2 min 50-g was added until task failure. Vital signs, ECG and ventilatory measures were monitored throughout the protocol., Result: Participants were 31 ± 12 year and had normal spirometry. At task failure, the maximum load and ventilatory parameters did not differ between the hypoxic and normoxic ITL. At hypoxic ITL task failure, SpO2 was significantly lower, and ∆HHb increased more so in SA, SCM and PS than normoxic values. SCM ∆TSI decreased more so during hypoxic compared to normoxic ITL. ∆tHb in the inspiratory muscles (SCM, PS and SA) increased significantly compared to the decrease in TA during both hypoxic and normoxic ITL., Conclusion: The SCM, an accessory inspiratory muscle was the most vulnerable to deoxygenation during incremental loading and this response was accentuated by acute hypoxia.

The purpose of this study was to determine if serum levels of skeletal troponin I (sTnI, fast and slow isoforms) could provide a sensitive marker of respiratory muscle damage in healthy humans subjected to inspiratory loads. To accomplish this, we studied healthy, young (27 ± 2 years, Mean ± SEM, n = 5) and middle-aged (55 ± 5, n = 5) men to (1) determine the magnitude, pattern, and time course of the presence of sTnI in the serum after a single 60 min bout of inspiratory threshold loading [ITL, ~70% of maximal inspiratory pressure (MIP)], (2) determine the distribution and magnitude of DOMS after loading, and (3) compare fast and slow sTnI levels, and their relationship to other markers/indices of muscle injury including delayed onset muscle soreness (DOMS), serum creatine kinase (CK) levels, and force generating capacity of the respiratory muscles [MIP and maximal expiratory pressure (MEP)]. There was a 24 ± 4 and 27 ± 3% increase in fast sTnI 1 hour (p < 0.01) and 3 days (p < 0.01) after ITL. Slow sTnI was elevated by 24 ± 10% (p < 0.05) 4 days postITL. Other indices of respiratory muscle injury such as CK, MIP and MEP did not show a difference in mean data following ITL; DOMS was slightly but significantly increased following ITL. Our results suggest that sTnI has superior sensitivity compared to other biomarkers/indices of skeletal muscle injury. Future studies examining the impact of respiratory muscle injury with ventilator weaning should consider using sTnI as a sensitive marker of skeletal muscle injury.

The purpose of this study was to evaluate the sex differences in delayed onset muscle soreness (DOMS), torque, and accumulation of technetium-99m (Tc-99m) neutrophils in eccentric-exercised muscle. A group of 10 female and 12 male subjects took part in this study. The subjects completed a pre-test using the descriptor differential scale (DDS) to describe DOMS, and tests of concentric and eccentric torque of the right quadriceps. A volume of 100 ml of blood was taken by venipuncture for neutrophil labelling in the early morning of the exercise day. The Tc-99m neutrophils were re-infused intravenously before the eccentric exercise. The exercise stimulus consisted of 300 eccentric repetitions of the right quadriceps muscles. Radionuclide images of both quadriceps muscles (lateral views) were taken at 2 and 4 h. The DDS, and concentric and eccentric torques of the quadriceps were subsequently evaluated at 0 h, 2, 4, 20 and 24 h post-exercise. The presence of Tc-99m neutrophils was greater in the exercised leg than the non-exercised leg at 2 and 4 h post-exercise (P