Rosie Twomey

AltitudeOmics: on the consequences of high-altitude acclimatization for the development of fatigue during locomotor exercise in humans

The development of muscle fatigue is oxygen (O2)-delivery sensitive [arterial O2 content (CaO2) × limb blood flow (QL)]. Locomotor exercise in acute hypoxia (AH) is, compared with sea level (SL), associated with reduced CaO2 and exaggerated inspiratory muscle work (Winsp), which impairs QL, both of which exacerbate fatigue individually by compromising O2 delivery. Since chronic hypoxia (CH) normalizes CaO2 but exacerbates Winsp, we investigated the consequences of a 14-day exposure to high altitude on exercise-induced locomotor muscle fatigue. Eight subjects performed the identical constant-load cycling exercise (138 ± 14 W; 11 ± 1 min) at SL (partial pressure of inspired O2, 147.1 ± 0.5 Torr), in AH (73.8 ± 0.2 Torr), and in CH (75.7 ± 0.1 Torr). Peripheral fatigue was expressed as pre- to postexercise percent reduction in electrically evoked potentiated quadriceps twitch force (ΔQtw,pot). Central fatigue was expressed as the exercise-induced percent decrease in voluntary muscle activation (ΔVA). Resting CaO2 at SL and CH was similar, but CaO2 in AH was lower compared with SL and CH (17.3 ± 0.5, 19.3 ± 0.7, 20.3 ± 1.3 ml O2/dl, respectively). Winsp during exercise increased with acclimatization (SL: 387 ± 36, AH: 503 ± 53, CH: 608 ± 67 cmH2O·s(-1)·min(-1); P < 0.01). Exercise at SL did not induce central or peripheral fatigue. ΔQtw,pot was significant but similar in AH and CH (21 ± 2% and 19 ± 3%; P = 0.24). ΔVA was significant in both hypoxic conditions but smaller in CH vs. AH (4 ± 1% vs. 8 ± 2%; P < 0.05). In conclusion, acclimatization to severe altitude does not attenuate the substantial impact of hypoxia on the development of peripheral fatigue. In contrast, acclimatization attenuates, but does not eliminate, the exacerbation of central fatigue associated with exercise in severe AH.

AltitudeOmics: exercise-induced supraspinal fatigue is attenuated in healthy humans after acclimatization to high altitude.

We asked whether acclimatization to chronic hypoxia (CH) attenuates the level of supraspinal fatigue that is observed after locomotor exercise in acute hypoxia (AH).

Acute and chronic hypoxia: implications for cerebral function and exercise tolerance.

Purpose: To outline how hypoxia profoundly affects neuronal functionality and thus compromises exercise performance. Methods: Investigations were reviewed and evaluated that used electroencephalography (EEG) and transcranial magnetic stimulation (TMS) to detect neuronal changes at rest and those studying fatiguing effects on whole-body exercise performance in acute (AH) and chronic hypoxia (CH). Results: At rest during very early hypoxia (<1-h), slowing of cerebral neuronal activity is evident despite no change in corticospinal excitability. As time in hypoxia progresses (3-h), increased corticospinal excitability becomes evident; however, changes in neuronal activity are unknown. Prolonged exposure (3–5 d) causes a respiratory alkalosis which modulates Na+ channels, potentially explaining reduced neuronal excitability. Locomotor exercise in AH exacerbates the development of peripheral fatigue; as the severity of hypoxia increases, mechanisms of peripheral fatigue become less dominant and CNS hypoxia becomes the predominant factor. The greatest central fatigue in AH occurs when SaO2 is ≤75%, a level that coincides with increasing impairments in neuronal activity. CH does not improve the level of peripheral fatigue observed in AH; however, it attenuates the development of central fatigue paralleling increases in cerebral O2 availability and corticospinal excitability. Conclusions: The attenuated development of central fatigue in CH might explain the improvements in locomotor exercise performance commonly observed after acclimatisation to high altitude.

Exercise Performance and Corticospinal Excitability during Action Observation

Purpose: Observation of a model performing fast exercise improves simultaneous exercise performance; however, the precise mechanism underpinning this effect is unknown. The aim of the present study was to investigate whether the speed of the observed exercise influenced both upper body exercise performance and the activation of a cortical action observation network (AON). Method: In Experiment 1, 10 participants completed a 5 km time trial on an arm-crank ergometer whilst observing a blank screen (no-video) and a model performing exercise at both a typical (i.e., individual mean cadence during baseline time trial) and 15% faster than typical speed. In Experiment 2, 11 participants performed arm crank exercise whilst observing exercise at typical speed, 15% slower and 15% faster than typical speed. In Experiment 3, 11 participants observed the typical, slow and fast exercise, and a no-video, whilst corticospinal excitability was assessed using transcranial magnetic stimulation. Results: In Experiment 1, performance time decreased and mean power increased, during observation of the fast exercise compared to the no-video condition. In Experiment 2, cadence and power increased during observation of the fast exercise compared to the typical speed exercise but there was no effect of observation of slow exercise on exercise behavior. In Experiment 3, observation of exercise increased corticospinal excitability; however, there was no difference between the exercise speeds. Conclusion: Observation of fast exercise improves simultaneous upper-body exercise performance. However, because there was no effect of exercise speed on corticospinal excitability, these results suggest that these improvements are not solely due to changes in the activity of the AON.

Physiological Responses to Graded Acute Normobaric Hypoxia Using an Intermittent Walking Protocol

Abstract Objective.—The study aimed to examine the physiological responses to acute normobaric hypoxia during an intermittent walking protocol. Methods.—Twelve active healthy male participants completed a 125-minute test that involved rest and walking (50% V̇o2max) during normoxic (20.93%O2) and 2 hypoxic conditions (14%O2 and 12%O2). A range of physiological markers were measured throughout the test. Lake Louise Questionnaire scores and Environmental Symptoms Questionnaire cerebral scores were used as a measurement of acute mountain sickness symptoms. Results.—Oxygen saturation, thermal sensation scale, heart rate, perceived thirst, core temperature, rating of perceived exertion, feeling state, and Δbody mass all positively correlated with the highest Lake Louise Questionnaire and Environmental Symptoms Questionnaire cerebral scores (P < .05) and were significantly different between the 3 conditions during the exercise phases. Conclusion.—A range of physiological markers are associated with symptoms of acute mountain sickness following brief periods of hypoxic exposure.