Intercostal Muscles Oxygenation and Breathing Pattern during Exercise in Competitive Marathon Runners

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.

Exploring the physiological benefits of carrying a suspended backpack versus a traditional backpack

This study investigates the differences in metabolic energy cost and physiological adaptations between carrying a suspended backpack and a traditional backpack during exercise. For that, 30 males completed the Bruce test while carrying a loaded backpack. Researchers used a metabolic system to obtain variables, analysed muscle oxygen saturation, and used a 2-way RM ANOVA. As results, a significant fatigue interaction was found, but the interaction between fatigue and backpack was non-significant. Using a suspended backpack resulted in energetic advantages in oxygen consumption, muscle oxygen saturation, and performance compared to a traditional backpack. In conclusion, this study offers insights into the physiological implications of using a suspended backpack, suggesting it may reduce the risk of musculoskeletal issues and improve performance for those carrying heavy loads.Practitioner summary: The suspended-load backpacks have been proposed as an alternative to traditional backpacks. This study highlighted that the use of a suspended backpack provided some energetical advantages adaptation compared to the traditional backpack in terms of oxygen consumption, muscle oxygen saturation and performance during a multistage treadmill test walking-running test.

Determination of the Respiratory Compensation Point by Detecting Changes in Intercostal Muscles Oxygenation by Using Near-Infrared Spectroscopy

This study aimed to evaluate if the changes in oxygen saturation levels at intercostal muscles (SmO2-m.intercostales) assessed by near-infrared spectroscopy (NIRS) using a wearable device could determine the respiratory compensation point (RCP) during exercise. Fifteen healthy competitive triathletes (eight males; 29 ± 6 years; height 167.6 ± 25.6 cm; weight 69.2 ± 9.4 kg; V˙O2-máx 58.4 ± 8.1 mL·kg−1·min−1) were evaluated in a cycle ergometer during the maximal oxygen-uptake test (V˙O2-máx), while lung ventilation (V˙E), power output (watts, W) and SmO2-m.intercostales were measured. RCP was determined by visual method (RCPvisual: changes at ventilatory equivalents (V˙E·V˙CO2−1, V˙E·V˙O2−1) and end-tidal respiratory pressure (PetO2, PetCO2) and NIRS method (RCPNIRS: breakpoint of fall in SmO2-m.intercostales). During exercise, SmO2-m.intercostales decreased continuously showing a higher decrease when V˙E increased abruptly. A good agreement between methods used to determine RCP was found (visual vs NIRS) at %V˙O2-máx, V˙O2, V˙E, and W (Bland-Altman test). Correlations were found to each parameters analyzed (r = 0.854; r = 0.865; r = 0.981; and r = 0,968; respectively. p < 0.001 in all variables, Pearson test), with no differences (p < 0.001 in all variables, Student’s t-test) between methods used (RCPvisual and RCPNIRS). We concluded that changes at SmO2-m.intercostales measured by NIRS could adequately determine RCP in triathletes.

Sex-Differences in the Oxygenation Levels of Intercostal and Vastus Lateralis Muscles During Incremental Exercise

This study aimed to examine sex differences in oxygen saturation in respiratory (SmO₂-m.intercostales) and locomotor muscles (SmO₂-m.vastus lateralis) while performing physical exercise. Twenty-five (12 women) healthy and physically active participants were evaluated during an incremental test with a cycle ergometer, while ventilatory variables [lung ventilation ( V . E), tidal volume (Vt), and respiratory rate (RR)] were acquired through the breath-by-breath method. SmO₂ was acquired using the MOXY^® devices on the m.intercostales and m.vastus lateralis. A two-way ANOVA (sex × time) indicated that women showed a greater significant decrease of SmO₂-m.intercostales, and men showed a greater significant decrease of SmO₂-m.vastus lateralis. Additionally, women reached a higher level of ΔSmO₂-m.intercostales normalized to V . E (L⋅min^-1) (p < 0.001), whereas men had a higher level of ΔSmO₂-m.vastus lateralis normalized to peak workload-to-weight (watts⋅kg^-1, PtW) (p = 0.049), as confirmed by Student's t-test. During an incremental physical exercise, women experienced a greater cost of breathing, reflected by greater deoxygenation of the respiratory muscles, whereas men had a higher peripheral load, indicated by greater deoxygenation of the locomotor muscles.