Consecutive, Resting, Long-Duration Hyperoxic Exposures Alter Neuromuscular Responses During Maximal Strength Exercises in Trained Men

Abstract

Purpose : The main objective of this study was to investigate the physiological effects of repetitive diving-induced hyperoxic conditions at 1.35 atmospheres absolute (ATA) on neuromuscular strength performance. We hypothesized that following five days of consecutive, resting, long-duration (6 h or more) hyperoxic water immersions (WIs) neuromuscular strength performance would be reduced with a longer recovery time in comparison to previously reported normoxic WIs. Methods: Thirteen ( n = 13) active male divers [31.3 ± 1.7 (24–43) years, mean ± years] completed five consecutive days of 6-h resting WIs with 18-h surface intervals while breathing 100% O 2 ( n = 13) at 1.35 ATA. Skeletal muscle performance assessments occurred immediately before and after each WI and 24 and 72 h after the final WI. Performance assessments included maximum voluntary isometric contraction (MVIC) and maximal isokinetic (IK) knee extensions and elbow flexions, and isometric maximum handgrip (MHG) strength. Neuromuscular activation was also measured on the quadriceps, biceps brachii, and brachioradialis via surface electromyography (sEMG). Results: MHG declined by 7.8% ( p < 0.001) by WI 5 with performance returning to baseline by 24-h post-WI. Brachioradialis neuromuscular activation increased by 42% on WI 5. MVIC knee extension performance dropped by 4% ( p = 0.001) on WI 3 with a 11% overall decrease in quadriceps neuromuscular activation. Maximal IK knee extension dropped by 3.3% on WI 5 with 9% drop in overall quadriceps activation during the same period. MVIC elbow flexion declined by 5.1% on WI 5 but returned to baseline by 72-h post-WI. Maximal IK elbow flexion performance dropped by 8.6% on WI 5 with a continual decline in biceps brachii neuromuscular activation of 24% on WI 5. Conclusion: Consecutive, resting, long-duration hyperoxic WIs reduce muscular performance in multiple muscle groups and alter neuromuscular activation after 3 days of WI with performance adaptations recovering toward baseline by the end of the WI 5. However, neuromuscular activation remains decreased and appears to last beyond the 72-h post-WI recovery period.

Endurance Exercise Performance Is Reduced after 6-h Dives at 1.35 ATA When Breathing 100% Oxygen Compared with Air

“…Neither breathing gas nor repeated diving had an effect on maximal handgrip strength. Although maximal handgrip force does not seem to change after a single 6-h water immersion to 4.5 m (9), previous data have demonstrated fluctuations during five consecutive resting dives at shallow depths, particularly on days 2 and 3, but ultimately return to baseline after the fifth dive (3). Furthermore, maximum handgrip strength was not affected in divers after a dry chamber dive to 1.6 ATA while breathing 100% O 2 for 3 h (20).…”

“…However, previous data have shown that long-duration resting dives on five consecutive days reduce some aspects of muscular performance (1). Additionally, depending on the operational objectives, repetitive long-duration diving may involve various forms of physical activity and breathing gases different from the composition of normobaric air, such as 100% oxygen (O 2 ), which has been postulated to further exacerbate muscular decrements (2,3). Previous investigations on long-duration dives over consecutive days have focused primarily on muscular strength measures, whereas the effects on aerobic endurance performance are not well understood.…”

“…Breathing 100% O 2 for extended periods may also adversely affect physical performance, although data are scarce. Previous work from our laboratory found that during five 6-h resting dives to 4.6 m on consecutive days while breathing 100% O 2 (1.35 atmospheres absolute [ATA] O 2 ), there were reductions in maximum isometric handgrip, knee extension, and elbow flexion strength; decreases in isokinetic knee extension and elbow flexion strength, along with diminished hand grip endurance; and increased rate of fatigue in the knee extensors when measured at approximately 1-h postdiving (2,3). Further, some of the muscular decrements lasted for at least 24 h postdiving, suggesting a prolonged negative effect of consecutive, long-duration hyperoxic diving.…”

“…Further, consecutive day long-duration diving, particularly with 100% O 2 , causes pulmonary oxygen toxicity symptoms like inspiratory burning, coughing, chest tightness, and dyspnea, and reduced lung function (10). Moreover, some diving-induced changes may not return to predive values for up to 24 h after diving (1)(2)(3)8).…”