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% O2 (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.
Highlights
Military, commercial, and technical divers are exposed to elevated hydrostatic pressures for extended periods, typically up to 6 h (Florian et al, 2016)
Our study found similar decreases in neuromuscular activation in large muscles, but not in small muscles
The present study demonstrates that the effects of resting, consecutive, long-duration hyperoxic immersions have on neuromuscular performance
Summary
Commercial, and technical divers are exposed to elevated hydrostatic pressures for extended periods, typically up to 6 h (Florian et al, 2016). Exposures to increased partial pressure of oxygen (hyperoxia) in addition to WI exacerbate changes to human performance. Maximal isokinetic (IK) knee extension torque increased by 11 and 5% post-WI on WI 3 and WI 5 with greater neuromuscular activation post-WI than pre-WI. Maximum IK elbow flexion torque did not change; biceps brachii neuromuscular activation was greater post-WI than pre-WI (Myers et al, 2018). The exposure to the microgravity environment caused noticeable increases in neuromuscular activation and decrements to maximal strength performance of load bearing muscles on WI 3 with full recovery occurring 3 days after the last WI. The load-bearing and non-load-bearing muscle groups worked harder to maintain performance (Myers et al, 2018)
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