Brain-muscle interplay during endurance self-paced exercise in normobaric and hypobaric hypoxia

Time-continuous analysis of muscle and cerebral oxygenation during repeated treadmill sprints under heat stress: a statistical parametric mapping study

PURPOSE

We examined how heat exposure affects muscle and cerebral oxygenation kinetics using statistical parametric mapping (SPM) during repeated treadmill sprints.

METHODS

Eleven recreationally active males performed three sets of five 5-s sprints with 25 s of recovery and 3 min between sets in hot (38 °C) and temperate (25 °C) conditions. Continuous measurements of muscle (vastus lateralis) and cerebral (prefrontal cortex) tissue oxygenation were obtained using near-infrared spectroscopy. One-way ANOVA SPM{F} statistics were applied to pooled sprint data, with each condition including 15 time-series (three sets of five sprints) combined. Each time-series included the sprint and subsequent recovery phases.

RESULTS

Muscle tissue saturation index further decreased in hot compared to temperate condition, from the middle of the 5-s sprint phase (~ 2.9 s) until the end of the recovery period (p < 0.001), while total hemoglobin concentration was significantly higher in the early phase of recovery (from 5.1 to 11.8 s, p = 0.003). Cerebral tissue saturation index decreased from 0.7 s to 13.0 s (p < 0.001) in the heat. Total hemoglobin concentration was lower in hot condition during both the sprint phase and the initial third of the recovery (from 0 to 11.7 s, p < 0.001), as well as during the recovery (from 20.5 to 24.8 s, p = 0.007).

CONCLUSION

Adding heat stress to repeating treadmill sprints further lowered muscle oxygenation levels during both the sprint and recovery phases, and limited cerebral tissue perfusion during the sprint and the initial recovery phases. The use of SPM for continuous analysis of near-infrared spectroscopy data provides new insights beyond summary statistics.

Neuromuscular Fatigue Induced by Cycling at a Fixed Level of Perceived Effort: Effects of Different Purported Hypoxic Methods

We compared neuromuscular fatigue induced by cycling at a fixed perceived effort in normoxic condition (NOR) and three purported hypoxia modalities: systemic hypoxia (SyH, FiO2 = 0.13), blood flow restriction (BFR, 50% arterial occlusion pressure) and airflow restriction mask (ARM, calibrated to ~3500 m). Seventeen healthy young participants cycled for 20 min at a self-selected power output corresponding to a hard effort (15/20, Borg scale) on an innovative cycle ergometer allowing immediate neuromuscular evaluation. Isometric maximum voluntary contraction of the knee extensors (IMVC), central (voluntary activation, VA) and peripheral fatigue were measured before and every 5 min during cycling. Power output, peripheral oxygen saturation (SpO2), quadriceps oxygenation (near-infrared spectroscopy, TSI) and pain were assessed throughout cycling. Power output was lower in BFR and SyH compared to NOR and ARM and was lower in BFR compared to SyH. SpO2 was reduced only in SyH (mean 77% ± 4%). In all conditions, IMVC decreased from minute 5 and subsequently plateaued (~-10% to -20%), except in BFR, wherein it further declined to -40% ± 14% at minute 20 in the presence of lowered VA and exacerbated muscle pain compared to other conditions. Muscle TSI was further decreased in SyH compared to other conditions. Our results confirm the inability of ARM to induce hypoxia. Compared to other conditions, BFR showed a greater reduction in IMVC and VA, in the presence of a higher quadriceps pain and no greater muscle deoxygenation. These results underline the psychophysiological impact of quadriceps pain on both maximal and submaximal motor output.

Muscle Oximetry in Sports Science: An Updated Systematic Review

BACKGROUND

In the last 5 years since our last systematic review, a significant number of articles have been published on the technical aspects of muscle near-infrared spectroscopy (NIRS), the interpretation of the signals and the benefits of using the NIRS technique to measure the physiological status of muscles and to determine the workload of working muscles.

OBJECTIVES

Considering the consistent number of studies on the application of muscle oximetry in sports science published over the last 5 years, the objectives of this updated systematic review were to highlight the applications of muscle oximetry in the assessment of skeletal muscle oxidative performance in sports activities and to emphasize how this technology has been applied to exercise and training over the last 5 years. In addition, some recent instrumental developments will be briefly summarized.

METHODS

Preferred Reporting Items for Systematic Reviews guidelines were followed in a systematic fashion to search, appraise and synthesize existing literature on this topic. Electronic databases such as Scopus, MEDLINE/PubMed and SPORTDiscus were searched from March 2017 up to March 2023. Potential inclusions were screened against eligibility criteria relating to recreationally trained to elite athletes, with or without training programmes, who must have assessed physiological variables monitored by commercial oximeters or NIRS instrumentation.

RESULTS

Of the identified records, 191 studies regrouping 3435 participants, met the eligibility criteria. This systematic review highlighted a number of key findings in 37 domains of sport activities. Overall, NIRS information can be used as a meaningful marker of skeletal muscle oxidative capacity and can become one of the primary monitoring tools in practice in conjunction with, or in comparison with, heart rate or mechanical power indices in diverse exercise contexts and across different types of training and interventions.

CONCLUSIONS

Although the feasibility and success of the use of muscle oximetry in sports science is well documented, there is still a need for further instrumental development to overcome current instrumental limitations. Longitudinal studies are urgently needed to strengthen the benefits of using muscle oximetry in sports science.

The impact of cold, hypoxia, and physical exertion on pistol accuracy and tactical performance

The purpose of this study was to examine the impact of independent cold and combined cold and hypoxic exposures on operational-specific task performance including pistol marksmanship, pistol magazine reload ability, and subjective and objective thermal indices before and after a whole-body physical exertional task. Twelve participants were exposed to Thermoneutral Normoxic (24 °C; FiO2 21%), Cold Normoxic (10 °C; FiO2 21%), and Cold Hypoxic (10 °C; FiO2 14%) conditions for 30min before performing pistol marksmanship at distances of 6.40 and 13.72m and a pistol magazine reload task before and after 3 sets of sandbag deadlifts at 50% body mass. Thermal perception and hand temperatures were collected before and after the physical exertion task. There were no significant differences in Pistol Accuracy performance at distances of 6.40 and 13.72m due to physical exertion, cold, or hypoxia. Following physical exertion, Pistol Accuracy was similar between Thermoneutral and Cold Normoxic conditions but lead to 17% and a 10% reduction in performance during the Cold Hypoxic condition, compared to Thermoneutral and Cold Normoxic conditions. There was no change in Pistol Accuracy for the Thermoneutral Normoxic condition. The pistol magazine reload task was not impacted by physical exertion, but there was a reduction in performance in Cold Normoxic 21% (4.04s) and Cold Hypoxic 16% (3.08s) conditions. Physical exertion did not impact hand temperature but did increase thermal perception scores for all conditions. These findings indicate that cold exposure reduced both tactical dexterity and pistol marksmanship, however, physical exertion may offset these deficits via an increase in thermal perception. Additionally, hypoxemia was the primary mediator of marksmanship performance in cold hypoxic environments following an acute bout of physical exertion. Thus, in cold mountainous environments, marksmen should be aware of their elevation and utilize brief episodes of physical activity to enhance their thermal state when marksmanship is a priority for operational success.