Proceedings of The Physiological Society
University of Cambridge (2004) J Physiol 555P, PC12
The influence of breathing 40 % oxygen on the response to maximal voluntary contraction of the forearm in human subjects
G. Fordy and Janice M. Marshall
Department of Physiology, Division of Medical Sciences, The Medical School, Birmingham B15 2TT, UK
It is widely accepted that breathing supplementary O2 during whole body dynamic exercise, enhances performance (Linossier et al. 2000). The aim of the present study was to test the effect of supplementary O2 on muscle haemodynamics and time to exhaustion in a protocol involving repetitive maximal handgrip exercise.
10 healthy male subjects with age, mass and height of 23.7 ± 0.3 years, 77.8 ± 1.91 kg and 1.79 ± 0.19 m respectively (mean ± S.E.M.) were used with local ethics committee approval. Two different protocols were conducted in a single-blind crossover design. Each protocol consisted of 2 periods of maximal handgrip exercise to exhaustion separated by a 5-minute recovery period with subjects breathing 40 % O2 during exercise or recovery. Forearm blood flow (FBF) was measured by venous occlusion plethysmography. Arterial blood pressure (ABP) was measured continuously by Finapres.
In protocol 1, post-contraction FBF was lower when subjects breathed 40 % O2 during contraction than when they breathed air throughout: at 15 s after contraction 1, FBF was 24.11 ± 2.13 vs 18.64 ± 1.95 and at 15 s after contraction 2 FBF was 25.89 ± 2.13 vs 18.40 ± 1.52 ml 100 ml-1 min-1*; air vs 40 % O2: * P < 0.05 Factorial ANOVA. Time to exhaustion was longer for contraction 1 than contraction 2 in both air-and 40 % O2-breathing trials: 254 ± 24.52 vs 170.5 ± 20.82 and 268 ± 21.04 vs 170.66 ± 25.29 s respectively: P < 0.05 Student's paired t test.
In protocol 2, post-contraction FBF was not different when subjects breathed 40 % O2 during recovery than when they breathed air throughout for contraction 1 or 2. However, time to exhaustion was lengthened for contraction 2 when subjects breathed 40 % O2 during recovery: 172.6 ± 32.6 vs 119 ± 19.44 s , contraction 1 vs 2, air breathing and 169 ± 28.87 vs 158.2 ± 32.27 s, contraction 1 vs 2, 40 % O2 breathing.
These results indicate that breathing 40 % O2 can have two effects on the response to maximal forearm contraction. When supplementary O2 was given, even during maximum contraction, forearm post-contraction hyperaemia was reduced indicating additional O2 delivered during contraction reduced the accumulation of vasodilator metabolites. When supplementary O2 was given during recovery, time to exhaustion of subsequent contraction was lengthened: this may reflect a greater rephosphorylation of ATP from creatine phosphate.
Where applicable, experiments conform with Society ethical requirements