ECSS Paris 2023: OP-PN15
INTRODUCTION: Near-infrared spectroscopy (NIRS) is used to indicate the balance of local oxygen (O2) delivery and O2 uptake in exercising muscle. Muscle oxygen saturation (SmO2) generally decreases proportionally to exercise intensity and duration, and increases during recovery. Reoxygenation represents a relative excess in O2 delivery during recovery while O2 uptake declines as the local metabolic milieu is restored. Reoxygenation is typically evaluated in a single working muscle, where SmO2 will reach peak values above resting baseline (hyperaemia) within 1-3 minutes after maximal exercise. We sought to compare reoxygenation kinetics between working and accessory muscles during an incremental cycling exercise step test (IET) as a function of increasing intensity. We hypothesised that reoxygenation would be faster in working muscle, slower in accessory muscle, and slower overall with increasing intensity. METHODS: Twenty-one trained cyclists (10 F, 11 M) performed two IET trials at 1.0+0.5 W·kg-1 per 5-min stage, with 1 min rest between stages, to maximal tolerance. Moxy NIRS sensors (Fortiori Design LLC, Hutchinson, MN, USA) were placed on vastus lateralis (VL), rectus femoris (RF), erector spinae (ES), and deltoid (DL) muscles. Reoxygenation kinetics were evaluated during rest intervals as the time to recover half the SmO2 amplitude from the end of work to the peak SmO2 value (half recovery time, HRT in seconds). A linear mixed effects model was used to analyse HRT with fixed effects for trial, relative intensity (% peak workload), and muscle site, with random effects of slope and intercept by participant. Post hoc estimated marginal means were contrasted across intensity at 50%, 75%, and 100%, and between muscle sites. RESULTS: Reoxygenation kinetics were generally slower (HRT was greater) with increasing exercise intensity beyond 50% in the VL, RF, and ES muscles (each p<0.01), but not DL (p>0.05). VL had the lowest between- and within-participant variation and recovered faster than other sites (HRT model estimates [95% CI]: VL=9 [6, 11], 12 [9, 14], 17 [13, 21] sec at 50, 75, 100% intensity, respectively). RF, ES, and DL were progressively slower at all intensities (p<0.001), except for ES and DL at 100% (ES=38 [34, 42] vs DL=40 [36, 45] sec; contrast=3 [-3, 9] sec, p=0.68). CONCLUSION: In a cycling IET, reoxygenation kinetics are faster in working muscle than accessory muscle, and generally slower overall as systemic metabolic demands increase with intensity. The VL is the primary working muscle in cycling and is consistently prioritised for recovery, as might be expected where motor recruitment and metabolic demand are highest. Slower recovery and higher variability in other muscle sites hint at heterogeneities in accessory muscle recruitment strategies and systemic competition for cardiac output. Integrating NIRS responses across working and accessory muscles may help to reveal more about local contributions and limitations to performance.
Read CV Jem ArnoldECSS Paris 2023: OP-PN15
INTRODUCTION: Repeated sprint training in hypoxia (RSH) was shown as an effective method for enhancing repeated sprint ability. Since the required hypoxic device is not always available throughout a season or for each athlete, an alternative method called repeated sprint training with hypoventilation at low lung volume (RSH-VHL) was developed to induce a hypoxic stress. However, it also generates acidosis and hypercapnia. Recently, the concept of exercising with bouts of end-expiratory breath-hold until the voluntary breaking point (UBP) has been proposed, offering an even more hypoxemic and hypercapnic stimulus during high-intensity interval training, although this has not been applied specifically to repeated-sprints training. Therefore, the objective of this study was to compare the physiological responses of repeated sprint training in normoxia (RSN), RSH-VHL, and repeated sprint training during end-expiratory breath-hold until the breaking point (RSH-UBP). Due to putative higher hypoxic and hypercapnic stress, we hypothesized a greater amplitude in stroke volume changes and muscle deoxygenation/reoxygenation (i.e., Tissue Saturation Index, TSI) during RSH-UBP compared to RSH. METHODS: Ten healthy active men performed 3 sessions of sprint training (2 sets of 8 sprints with 5 min of rest between sets; exercise:rest ratio of 1:2) in a randomized order. Sprint duration was 10 s for RSN and RSH-VHL conditions, while it depended on the apnea duration for RSH-UBP. Pulse oxygen saturation (SpO2), gas exchange, cardiac hemodynamics, muscle oxygenation, and total work were continuously recorded during the sessions. RESULTS: The time spent <96% of SpO2 (all p<0.010) and mean end tidal carbon dioxide pressure (all p<0.001) during the exercise bouts were higher in both RSH-VHL (81±65 s and 33.6±4.2 mmHg) and RSH-UBP (74±57 s and 32.9±3.5 mmHg) than in RSN (11±14 s and 27.8±4.2 mmHg). The pH similarly decreased from pre- to post-session between sprint modalities (p=0.137). Total work was lower (p<0.001) during RSH-UBP (33.1±5.8 kJ) compared to RSH-VHL (46.5±5.7 kJ) or RSN (47.4±6.0 kJ). Stroke volume and cardiac output did not differ between sprint modalities (all p>0.4). Amplitude in TSI changes was smaller (p<0.050) during RSH-UBP (7.0±4.3%) compared to RSH-VHL (10.3±6.0%) but not compared to RSN (10.3±7.1%). CONCLUSION: While RSH-UBP induced a greater hypoxic and hypercapnic stress than RSN, no difference was observed when compared to RSH-VHL. The reduction in total work during RSH-UBP was attributed to participants inability to maintain long-enough apnea, leading to a decrease in sprint duration. Consequently, the muscle deoxygenation level during RSH-UBP appeared blunted. In conclusion, acutely, RSH-VHL appeared as a more effective condition than RSH-UBP. Further interventional training studies comparing the two strategies are required to assess if RSH-VLH can better preserve training load and elicit consistent physiological adaptations.
Read CV Antoine RaberinECSS Paris 2023: OP-PN15
INTRODUCTION: Specific responses to hypoxia at rest and during exercise have been observed in healthy adults born pre-term [1]. Nocturnal pulse oxygen saturation (SpO2) recordings, together with acute mountain sickness (AMS) assessment, could offer insights into the aetiology of prematurity-related altitude (in)tolerance. METHODS: In this study, 12 pre-term (Mean±SD; age: 21±3 yr, BMI: 23±3 kg/m^2, gestational age: 29±2 wk) and 12 term-born (22±3 yr, 23±2 kg/m^2, 40±1 wk) male adults underwent an overnight normobaric hypoxic exposure equivalent to 4200 m. AMS was assessed using the Lake Louise scale 6 h after hypoxic room entry (9pm), and the following morning 1 h after waking (7am). Participants were classified as AMS+ if their total symptom score was ≥3, with a headache score ≥1 [2]. SpO2 was recorded continuously at 3 Hz at the fingertip. Data from 11pm to 5am were extracted, and mean SpO2 and proportion of the 6 h with SpO2<80% (TST80) were calculated. Desaturations were defined by rate (>0.1%/s), magnitude (≥2%), and total duration until re-saturation (≥10 s & ≤60 s) [2]. The cumulative desaturation areas above the curve, relative to each respective onset value, indicated the hypoxic burden (%min/h). Groups were compared using independent t-tests and Mann-Whitney U tests, and are reported as Mean±SD and Median[IQR], respectively. Receiver operating characteristic (ROC) analysis was used to indicate the predictive potential of SpO2 metrics for morning AMS incidence. The area under the ROC curve (AUC) is reported, representing the balance between true- and false-positive AMS classifications. RESULTS: Before sleep, 9 term-born and 7 pre-term participants were AMS+. Upon waking, 5 term-born and 6 pre-term participants were AMS+. Nocturnal mean SpO2 was similar between the pre-term and term-born groups (77±3 vs 77±4%; p=0.661), as was TST80 (72±29 vs 70±27%; p=0.879). However, mean SpO2 and TST80 predicted morning AMS considerably better in the pre-term (AUC=0.889 and 0.944, respectively) than in term-born (AUC=0.457 and 0.571, respectively) participants. Pre-term adults experienced more desaturations (413[291] vs 122[209]; p=0.008), albeit shorter in average duration (17±2 vs 21±2 s; p<0.001). Pre-term participants also experienced a significantly greater hypoxic burden (32[26] vs. 7[25] %min/h; p=0.039). However, desaturation-related metrics did not predict morning AMS incidence accurately in the two groups separately or combined (all AUC<0.743). CONCLUSION: These data indicate high predictive potential of composite nocturnal SpO2 metrics for AMS incidence in healthy adults born pre-term. However, while desaturations were more frequent in pre-term adults, inducing a greater hypoxic burden, they were neither predictive of AMS-related outcomes in pre-term participants, nor in their term-born counterparts. References [1] Narang et al (2022) Eur J Appl Physiol. 122(9), 1991-2003. [2] Roach et al (2018) High Alt Med Biol. 19(1), 4-6. [3] Taha et al (1997) Sleep. 20(11), 991-1001.
Read CV Benjamin NarangECSS Paris 2023: OP-PN15