No abstract

This study tested whether hypercapnic ventilatory response (HCVR) is affected by experience in apnoea and explored the possible underlying mechanisms of this phenomenon, with reference to maximum breath hold time (BHT). Elite apnoea divers (EBH=11) and novice subjects (NBH=10) performed a HCVR test (BM), which was repeated by the latter group on another day (PRE) after subjects executed five repeated maximum apnoeas. Subsequently, after a two week period of daily apnoea training, NBH subjects repeated HCVR test (POST). Diaphragmatic activity was recorded to determine apnoea easy going phase. Baseline HCVR of EBH was not lower than that of NBH. After execution of five apnoeas, HCVR in EBH decreased (P≤0.05) whereas it was not different among BM, PRE, and POST conditions in the NBH. Higher BHT and easy going phase values ensued from apnoea maneuvers in EBH than in NBH (PRE and POST), and in NBH POST compared to PRE condition (P≤0.05). HCVR was highly correlated (P≤0.05) with the cumulative easy going phase in EBH, PRE condition but nothing-similar observed in NBH, neither in PRE nor in POST conditions. These results indicate that at rest HCVR is not lower in experienced, than novice, skin divers; this response becomes dull after five repeated maximum apnoeas only in EBH. In the NBH group, two weeks of apnoea training are not adequate to affect HCVR despite an increase of BHT. It appears that after a repeated maximum apnoeas maneuver experienced skin divers improve BHT by extending easy going phase whereas NBH by other means.

Context: Bridge exercises are extensively used in trunk-strengthening programs. The aim of this study was to investigate the effect of bridging duration on lateral abdominal muscle thickness and gluteus maximus activation. Design: Cross-sectional. Methods: Twenty-five young males participated in this study. Transversus abdominal (TrA), external and internal oblique ultrasound thickness, gluteus maximus electromyographic activation, and sacral tilt angle were simultaneously measured for every second during 30-second bridging exercise. The contraction thickness ratio and root mean squared signal (normalized to maximum isometric contraction signal) during 6 exercise durations (from 0 to 5, 10, 15, 20, 25, and 30 s) were also calculated and compared using analysis of variance designs. Results: TrA and internal oblique contraction thickness ratio and gluteus maximus root mean squared increased during the first 8 to 10 seconds and remained elevated until the end of the 30-second exercise (P < .05). External oblique contraction thickness ratio declined during exercise (P < .05). Five-second bridging showed less TrA thickness and anteroposterior and mediolateral sacral tilt angle and a lower anteroposterior tilt variability compared with bridges, which lasted more than 10 seconds (P < .05). Conclusions: Bridge exercises longer than 10 seconds may be better for promoting TrA recruitment than bridges of shorter duration. Clinicians and exercise specialists could adjust the duration of bridge exercise based on the aims of the exercise program.