Author(s): DODD, E., BROWNSTEIN, C., Institution: NEWCASTLE UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 240

INTRODUCTION:
While oxygen delivery during submaximal exercise is considered adequate to support oxidative metabolism (1), evidence from small muscle mass exercise suggests it may be suboptimal for preserving contractile function (2). Augmenting oxygen delivery via non-local ischemic contractions that heighten the muscle metaboreflex has been shown to attenuate contractile impairments of non-ischemic muscles during small muscle mass exercise (2, 3). These findings suggest that normal vasoregulation may meet metabolic demand but may not be optimised for muscle function (2, 4). Whether metaboreflex-mediated augmentation of oxygen delivery influences muscle oxygenation and neuromuscular fatigability during large muscle mass exercise, and whether such effects are intensity dependent, remains unknown. Therefore, this study examined whether this method could enhance muscle oxygenation and attenuate neuromuscular fatigability of the knee extensors during cycling at different intensities.
METHODS:
Fifteen participants (9 men, 6 women; 25 ± 4 yr) completed six visits. Visit one included a VO2peak test to determine moderate (MOD), heavy (HVY), and severe (SVR) intensities. In a randomised crossover design, participants completed 8-min cycling bouts at each intensity under control conditions and with metaboreflex augmentation induced by ischemic arm contractions from min 3. Arm contractions were performed for 3 min, with cuffs remaining inflated (200 mmHg) until post-exercise measures were taken (MTR protocol). Vastus lateralis oxygenation was recorded using near-infrared spectroscopy. Knee extensor neuromuscular function was assessed pre- and post-exercise using maximal voluntary contractions and electrically evoked twitch and doublet responses via femoral nerve stimulation, as was blood pressure. A specialised cycle ergometer enabled neuromuscular assessments to be performed within 15 s post-exercise.
RESULTS:
The MTR protocol increased mean arterial pressure at all intensities (p = .001). Oxygenated haemoglobin (O2Hb) was higher during MOD (p = .007) and HVY (p = .039) with MTR compared with control. Reductions in potentiated twitch force (Qtw.pot) and high-frequency doublet force (Db100) were attenuated following MTR compared with control at MOD (Qtw.pot p = .017; Db100 p = .022) and HVY (Qtw.pot p = .006; Db100 p = .047). No differences in neuromuscular fatigability or O2Hb were observed during SVR.
CONCLUSION:
During cycling below the respiratory compensation point, the MTR protocol increased muscle oxygenation and attenuated contractile impairments. The finding that reductions in contractile function were attenuated even at MOD suggests that contractile impairments are oxygen-delivery dependent across the exercise-intensity spectrum.

References
(1) Poole et al., Med Sci Sports Exerc, 2008 (2) Drouin et al., J Physiol, 2023 (3) Perrey et al., J Appl Physiol, 2001 (4) Tschakovsky & Hughson, Am J Physiol, 1999