Positional contrastive learning for improved thigh muscle segmentation in MR images.

The accurate segmentation of individual muscles is essential for quantitative MRI analysis of thigh images. Deep learning methods have achieved state-of-the-art results in segmentation, but they require large numbers of labeled data to perform well. However, labeling individual thigh muscles slice by slice for numerous volumes is a laborious and time-consuming task, which limits the availability of annotated datasets. To address this challenge, self-supervised learning (SSL) emerges as a promising technique to enhance model performance by pretraining the model on unlabeled data. A recent approach, called positional contrastive learning, exploits the information given by the axial position of the slices to learn features transferable on the segmentation task. The aim of this work was to propose positional contrastive SSL for the segmentation of individual thigh muscles from MRI acquisitions in a population of elderly healthy subjects and to evaluate it on different levels of limited annotated data. An unlabeled dataset of 72 T1w MRI thigh acquisitions was available for SSL pretraining, while a labeled dataset of 52 volumes was employed for the final segmentation task, split into training and test sets. The effectiveness of SSL pretraining to fine-tune a U-Net architecture for thigh muscle segmentation was compared with that of a randomly initialized model (RND), considering an increasing number of annotated volumes (S = 1, 2, 5, 10, 20, 30, 40). Our results demonstrated that SSL yields substantial improvements in Dice similarity coefficient (DSC) when using a very limited number of labeled volumes (e.g., for S $$ S $$ = 1, DSC 0.631 versus 0.530 for SSL and RND, respectively). Moreover, enhancements are achievable even when utilizing the full number of labeled subjects, with DSC = 0.927 for SSL and 0.924 for RND. In conclusion, positional contrastive SSL was effective in obtaining more accurate thigh muscle segmentation, even with a very low number of labeled data, with a potential impact of speeding up the annotation process in clinics.

Reliability of Mental Workload Index Assessed by EEG with Different Electrode Configurations and Signal Pre-Processing Pipelines.

BACKGROUND AND OBJECTIVE: Mental workload (MWL) is a relevant construct involved in all cognitively demanding activities, and its assessment is an important goal in many research fields. This paper aims at evaluating the reproducibility and sensitivity of MWL assessment from EEG signals considering the effects of different electrode configurations and pre-processing pipelines (PPPs). METHODS: Thirteen young healthy adults were enrolled and were asked to perform 45 min of Simon's task to elicit a cognitive demand. EEG data were collected using a 32-channel system with different electrode configurations (fronto-parietal; Fz and Pz; Cz) and analyzed using different PPPs, from the simplest bandpass filtering to the combination of filtering, Artifact Subspace Reconstruction (ASR) and Independent Component Analysis (ICA). The reproducibility of MWL indexes estimation and the sensitivity of their changes were assessed using Intraclass Correlation Coefficient and statistical analysis. RESULTS: MWL assessed with different PPPs showed reliability ranging from good to very good in most of the electrode configurations (average consistency > 0.87 and average absolute agreement > 0.92). Larger fronto-parietal electrode configurations, albeit being more affected by the choice of PPPs, provide better sensitivity in the detection of MWL changes if compared to a single-electrode configuration (18 vs. 10 statistically significant differences detected, respectively). CONCLUSIONS: The most complex PPPs have been proven to ensure good reliability (>0.90) and sensitivity in all experimental conditions. In conclusion, we propose to use at least a two-electrode configuration (Fz and Pz) and complex PPPs including at least the ICA algorithm (even better including ASR) to mitigate artifacts and obtain reliable and sensitive MWL assessment during cognitive tasks.

The "ON-OFF" Switching Response of Reactive Oxygen Species in Acute Normobaric Hypoxia: Preliminary Outcome.

Exposure to acute normobaric hypoxia (NH) elicits reactive oxygen species (ROS) accumulation, whose production kinetics and oxidative damage were here investigated. Nine subjects were monitored while breathing an NH mixture (0.125 FIO2 in air, about 4100 m) and during recovery with room air. ROS production was assessed by Electron Paramagnetic Resonance in capillary blood. Total antioxidant capacity, lipid peroxidation (TBARS and 8-iso-PFG2α), protein oxidation (PC) and DNA oxidation (8-OH-dG) were measured in plasma and/or urine. The ROS production rate (µmol·min-1) was monitored (5, 15, 30, 60, 120, 240 and 300 min). A production peak (+50%) was reached at 4 h. The on-transient kinetics, exponentially fitted (t1/2 = 30 min r2 = 0.995), were ascribable to the low O2 tension transition and the mirror-like related SpO2 decrease: 15 min: -12%; 60 min: -18%. The exposure did not seem to affect the prooxidant/antioxidant balance. Significant increases in PC (+88%) and 8-OH-dG (+67%) at 4 h in TBARS (+33%) one hour after hypoxia offset were also observed. General malaise was described by most of the subjects. Under acute NH, ROS production and oxidative damage resulted in time and SpO2-dependent reversible phenomena. The experimental model could be suitable for evaluating the acclimatation level, a key element in the context of mountain rescues in relation to technical/medical workers who have not had enough time for acclimatization-as, for example, during helicopter flights.

Near-infrared spectroscopy estimation of combined skeletal muscle oxidative capacity and O2 diffusion capacity in humans.

The final steps of the O2 cascade during exercise depend on the product of the microvascular-to-intramyocyte P O 2 ${P}_{{{\rm{O}}}_{\rm{2}}}$ difference and muscle O2 diffusing capacity ( D m O 2 $D{{\rm{m}}}_{{{\rm{O}}}_2}$ ). Non-invasive methods to determine D m O 2 $D{{\rm{m}}}_{{{\rm{O}}}_2}$ in humans are currently unavailable. Muscle oxygen uptake (m V ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ ) recovery rate constant (k), measured by near-infrared spectroscopy (NIRS) using intermittent arterial occlusions, is associated with muscle oxidative capacity in vivo. We reasoned that k would be limited by D m O 2 $D{{\rm{m}}}_{{{\rm{O}}}_2}$ when muscle oxygenation is low (kLOW ), and hypothesized that: (i) k in well oxygenated muscle (kHIGH ) is associated with maximal O2 flux in fibre bundles; and (ii) ∆k (kHIGH  - kLOW ) is associated with capillary density (CD). Vastus lateralis k was measured in 12 participants using NIRS after moderate exercise. The timing and duration of arterial occlusions were manipulated to maintain tissue saturation index within a 10% range either below (LOW) or above (HIGH) half-maximal desaturation, assessed during sustained arterial occlusion. Maximal O2 flux in phosphorylating state was 37.7 ± 10.6 pmol s-1  mg-1 (∼5.8 ml min-1  100 g-1 ). CD ranged 348 to 586 mm-2 . kHIGH was greater than kLOW (3.15 ± 0.45 vs. 1.56 ± 0.79 min-1 , P < 0.001). Maximal O2 flux was correlated with kHIGH (r = 0.80, P = 0.002) but not kLOW (r = -0.10, P = 0.755). Δk ranged -0.26 to -2.55 min-1 , and correlated with CD (r = -0.68, P = 0.015). m V ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ k reflects muscle oxidative capacity only in well oxygenated muscle. ∆k, the difference in k between well and poorly oxygenated muscle, was associated with CD, a mediator of D m O 2 $D{{\rm{m}}}_{{{\rm{O}}}_2}$ . Assessment of muscle k and ∆k using NIRS provides a non-invasive window on muscle oxidative and O2 diffusing capacity. KEY POINTS: We determined post-exercise recovery kinetics of quadriceps muscle oxygen uptake (m V ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ ) measured by near-infrared spectroscopy (NIRS) in humans under conditions of both non-limiting (HIGH) and limiting (LOW) O2 availability, for comparison with biopsy variables. The m V ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ recovery rate constant in HIGH O2 availability was hypothesized to reflect muscle oxidative capacity (kHIGH ) and the difference in k between HIGH and LOW O2 availability (∆k) was hypothesized to reflect muscle O2 diffusing capacity. kHIGH was correlated with phosphorylating oxidative capacity of permeabilized muscle fibre bundles (r = 0.80). ∆k was negatively correlated with capillary density (r = -0.68) of biopsy samples. NIRS provides non-invasive means of assessing both muscle oxidative and oxygen diffusing capacity in vivo.

Performance fatigability and recovery after dynamic multi-joint maximal exercise in elbow flexors versus knee extensors.

Elbow flexors (EFs) and knee extensors (KEs) have shown differences in performance fatigability and recovery of neuromuscular function after isometric and isotonic single-joint fatiguing contractions. However, dynamic multi-joint movements are more representative of real-world activities. The aim of the study was to assess central and peripheral mechanisms of fatigability after either arm-cranking or cycling. Ten physically active men performed maximal incremental arm-cranking and cycling until task failure. Maximal voluntary isometric contraction (MVIC) and electrically evoked forces of both EF and KE were assessed before (PRE) and 1 (POST) and 20 (POST20) min after exercise. At POST, MVIC decreased similarly to 76 ± 8% and 81 ± 7% (both P < 0.001) of PRE for EF and KE, respectively. MVIC force remained lower than PRE at POST20 for both EF and KE (85 ± 8% vs. 95 ± 3% of PRE, P ≤ 0.033), having recovered less in EF than in KE (P = 0.003). Electrically evoked forces decreased similarly from PRE to POST in EF and KE (all P > 0.05). At POST20, the ratio of low-to-high frequency doublets was lower in EF than in KE (75 ± 13% vs. 85 ± 10% of PRE; P ≤ 0.034). Dynamic maximal incremental exercise acutely induced similar magnitudes of MVIC and evoked force loss in EF and KE. However, at POST20, impaired MVIC recovery and lower ratio of low-to-high frequency doublets in EF than in KE suggest the recovery of neuromuscular function after dynamic maximal exercises is specific to and dependent on changes within the muscles investigated.

Myths and methodologies: The use of equivalence and non-inferiority tests for interventional studies in exercise physiology and sport science.

Exercise physiology and sport science have traditionally made use of the null hypothesis of no difference to make decisions about experimental interventions. In this article, we aim to review current statistical approaches typically used by exercise physiologists and sport scientists for the design and analysis of experimental interventions and to highlight the importance of including equivalence and non-inferiority studies, which address different research questions from deciding whether an effect is present. Initially, we briefly describe the most common approaches, along with their rationale, to investigate the effects of different interventions. We then discuss the main steps involved in the design and analysis of equivalence and non-inferiority studies, commonly performed in other research fields, with worked examples from exercise physiology and sport science scenarios. Finally, we provide recommendations to exercise physiologists and sport scientists who would like to apply the different approaches in future research. We hope this work will promote the correct use of equivalence and non-inferiority designs in exercise physiology and sport science whenever the research context, conditions, applications, researchers' interests or reasonable beliefs justify these approaches.

Role of nitric oxide in convective and diffusive skeletal muscle microvascular oxygen kinetics.

Progress in understanding physiological mechanisms often consists of discrete discoveries made across different models and species. Accordingly, understanding the mechanistic bases for how altering nitric oxide (NO) bioavailability impacts exercise tolerance (or not) depends on integrating information from cellular energetics and contractile regulation through microvascular/vascular control of O2 transport and pulmonary gas exchange. This review adopts state-of-the-art concepts including the intramyocyte power grid, the Wagner conflation of perfusive and diffusive O2 conductances, and the Critical Power/Critical Speed model of exercise tolerance to address how altered NO bioavailability may, or may not, affect physical performance. This question is germane from the elite athlete to the recreational exerciser and particularly the burgeoning heart failure (and other clinical) populations for whom elevating O2 transport and/or exercise capacity translates directly to improved life quality and reduced morbidity and mortality. The dearth of studies in females is also highlighted, and areas of uncertainty and questions for future research are identified.

Skeletal muscle and cerebral oxygenation levels during and after submaximal concentric and eccentric isokinetic exercise.

The aim was to investigate the potential differences in muscle (vastus lateralis) and cerebral (prefrontal cortex) oxygenation levels as well as in the number of repetitions and total work output between isokinetic eccentric and concentric exercise at a moderate relative intensity until exhaustion. Ten recreationally active young men underwent two isokinetic exercise sessions either concentric or eccentric, one on each randomly selected leg. The protocols were performed at 60°/s and an intensity corresponding to 60% of the maximal voluntary contraction (MVC) of each contraction type. Concentric torque was significantly lower compared to eccentric torque in both peak values and at values corresponding to 60% of MVC [230 ± 18 Nm vs. 276 ± 19 Nm (P = .014) and 137 ± 12 Nm vs. 168 ± 11 Nm, respectively (P = .010)]. The participants performed 40% more contractions during eccentric compared to concentric exercise [122 ± 15 vs. 78 ± 7, respectively]. No differences were found in the levels of oxyhaemoglobin, deoxyhemoglobin, total haemoglobin and tissue saturation index when eccentric and eccentric exercise regimes were compared (all P > .05). Our results demonstrate that eccentric exercise of moderate intensity leads to greater resistance to fatigue and more work output compared to concentric exercise, despite the comparable muscle and cerebral oxygenation levels.

Peripheral impairments of oxidative metabolism after a 10-day bed rest are upstream of mitochondrial respiration.

In order to identify peripheral biomarkers of impaired oxidative metabolism during exercise following a 10-day bed rest, 10 males performed an incremental exercise (to determine peak pulmonary V̇O2 (V̇O2 p)) and moderate-intensity exercises, before (PRE) and after (POST) bed rest. Blood flow response was evaluated in the common femoral artery by Eco-Doppler during 1 min of passive leg movements (PLM). The intramuscular matching between O2 delivery and O2 utilization was evaluated by near-infrared spectroscopy (NIRS). Mitochondrial respiration was evaluated ex vivo by high-resolution respirometry in isolated muscle fibres, and in vivo by NIRS by the evaluation of skeletal muscle V̇O2 (V̇O2 m) recovery kinetics. Resting V̇O2 m was estimated by NIRS. Peak V̇O2 p was lower in POST vs. PRE. The area under the blood flow vs. time curve during PLM was smaller (P = 0.03) in POST (274 ± 233 mL) vs. PRE (427 ± 291). An increased (P = 0.03) overshoot of muscle deoxygenation during a metabolic transition was identified in POST. Skeletal muscle citrate synthase activity was not different (P = 0.11) in POST (131 ± 16 nmol min-1  mg-1 ) vs. PRE (138 ± 19). Maximal ADP-stimulated mitochondrial respiration (66 ± 18 pmol s-1  mg-1 (POST) vs. 72 ± 14 (PRE), P = 0.41) was not affected by bed rest. Apparent Km for ADP sensitivity of mitochondrial respiration was reduced in POST vs. PRE (P = 0.04). The V̇O2 m recovery time constant was not different (P = 0.79) in POST (22 ± 6 s) vs. PRE (22 ± 6). Resting V̇O2 m was reduced by 25% in POST vs. PRE (P = 0.006). Microvascular-endothelial function was impaired following a 10-day bed rest, whereas mitochondrial mass and function (both in vivo and ex vivo) were unaffected or slightly enhanced. KEY POINTS: Ten days of horizontal bed rest impaired in vivo oxidative function during exercise. Microvascular impairments were identified by different methods. Mitochondrial mass and mitochondrial function (evaluated both in vivo and ex vivo) were unchanged or even improved (i.e. enhanced mitochondrial sensitivity to submaximal [ADP]). Resting muscle oxygen uptake was significantly lower following bed rest, suggesting that muscle catabolic processes induced by bed rest/inactivity are less energy-consuming than anabolic ones.

Changes in prefrontal cerebral oxygenation and microvascular blood volume in hypoxia and possible association with acute mountain sickness.

NEW FINDINGS: What is the central question of this study? The role of the cerebral haemodynamic response to either normobaric or hypobaric hypoxia in people susceptible to acute mountain sickness (AMS) is still under debate. Prefrontal cortex near-infrared spectroscopy-derived parameters were monitored in normobaric hypoxia at rest and during moderate-intensity exercise in AMS-prone and non-AMS individuals. What is the main finding and its importance? The AMS-prone individuals did not increase microvascular blood volume and showed lower prefrontal cerebral oxygenation in normobaric hypoxia both at rest and during exercise compared with non-AMS subjects, suggesting that these changes might underpin later development of AMS at altitude. ABSTRACT: The aim of this study was to evaluate changes in prefrontal cerebral oxygenation and microvascular blood volume during exercise in normobaric hypoxia and to investigate possible associations with the occurrence of acute mountain sickness (AMS) at altitude. Twenty-two healthy individuals (age, 26 ± 4 years; peak oxygen uptake, 42 ± 4 ml kg-1  min-1 ) were tested in two different conditions: normoxia (NORM) and normobaric hypoxia (fraction of inspired O2  = 0.13; HYPO). Data were collected at rest and during submaximal constant-speed exercise. The peripheral oxyhaemoglobin saturation was measured by finger pulse oximeter. Changes in prefrontal cerebral oxygenation (ΔHbO2 ), deoxygenation (ΔHHb) and microvascular blood volume (ΔHbtot ) were obtained by near-infrared spectroscopy. Within 2 weeks after laboratory testing, subjects rapidly ascended to 3647 m a.s.l., and AMS was evaluated using the Lake Louise scale. Eight subjects were AMS+ , whereas 14 were AMS- . During NORM, near-infrared spectroscopy variables did not change from baseline values both at rest and during exercise, with similar results in AMS+ and AMS- subjects. During HYPO, ΔHHb increased to a similar extent in both groups, both at rest and during exercise. The ΔHbO2 was significantly less in AMS+ compared with AMS- subjects, both at rest [-3.23 ± 5.90 versus 1.44 ± 2.14 µm, P = 0.04, effect size (ES) = 1.1, respectively] and during exercise (-6.56 ± 5.51 versus 0.37 ± 4.36 µm, P < 0.01, ES = 1.2, respectively). Total haemoglobin did not change from baseline, both at rest (-1.67 ± 9.53 µm) and during exercise (-0.96 ± 9.12 µm) in AMS+ subjects, which was significantly different from the AMS- group (5.49 ± 3.99 µm, P = 0.03, ES = 1.0 and 8.17 ± 7.34 µm, P = 0.02, ES = 1.0, respectively). Individuals prone to AMS seem to be unable to increase microvascular blood volume and to maintain oxygenation at the cerebral level during exercise in acute normobaric hypoxia, suggesting that these changes might underpin later development of AMS.

Beet on Alps: Time-course changes of plasma nitrate and nitrite concentrations during acclimatization to high-altitude.

Nitric oxide seems to be involved in the altitude acclimatization process due to its ability to regulate pulmonary, cardiovascular and muscular responses to hypoxia. In this study, we investigated the plasma nitrate (NO3-) and nitrite (NO2-) response to hypobaric hypoxia in two groups of lowlanders exposed at different altitudes. For seven days, fourteen subjects were evaluated at Casati Hut (3269 m a.s.l. M.CEVEDALE) and eleven individuals were studied at Capanna Regina Margherita (4554 m a.s.l. M.ROSA). Before expeditions and at different time points during high-altitude sojourn, plasma NO3- and NO2- concentrations were measured by chemiluminescence. Resting peripheral arterial oxygen saturation (SpO2), heart rate (HR) and mean arterial blood pressure (MAP) were monitored during the experimental period. Possible confounding factors such as dietary NO3- intake, physical activity and altitude changes were controlled. Sea level plasma NO3- and NO2- concentrations significantly increased at altitude in both M.CEVEDALE group (+26.2 µM, p ≤ 0.0001, 95% CI [+17.6, +34.8] and +559.2 nM, p ≤ 0.0001, [+332.8, +785.6]) and M.ROSA group (+18.7 µM, p ≤ 0.0001, [+10.8, +26.5] and +463.7 nM, p ≤ 0.0001, [+314.3, +613.0]). Average peak value in NO metabolites concentration occurred earlier in M.CEVEDALE group vs M.ROSA group (NO3-, day 3 vs day 5, p = 0.007; NO2-, day 3 vs day 5, p = 0.019). In both groups, resting SpO2, HR and MAP values changed according to altitude levels. This study shows that exposure to hypobaric hypoxia affects nitric oxide metabolites, resulting in a significant increase in plasma NO3- and NO2- concentrations from sea level values. Interestingly, the higher the altitude reached, the longer the time taken to reach a peak in plasma concentrations of nitric oxide metabolites.

Effects of NMES pulse width and intensity on muscle mechanical output and oxygen extraction in able-bodied and paraplegic individuals.

PURPOSE: Neuromuscular Electrical Stimulation (NMES) is commonly used in neuromuscular rehabilitation protocols, and its parameters selection substantially affects the characteristics of muscle activation. Here, we investigated the effects of short pulse width (200 µs) and higher intensity (short-high) NMES or long pulse width (1000 µs) and lower intensity (long-low) NMES on muscle mechanical output and fractional oxygen extraction. Muscle contractions were elicited with 100 Hz stimulation frequency, and the initial torque output was matched by adjusting stimulation intensity. METHODS: Fourteen able-bodied and six spinal cord-injured (SCI) individuals participated in the study. The NMES protocol (75 isometric contractions, 1-s on-3-s off) targeting the knee extensors was performed with long-low or short-high NMES applied over the midline between anterior superior iliac spine and patella protrusion in two different days. Muscle work was estimated by torque-time integral, contractile properties by rate of torque development and half-relaxation time, and vastus lateralis fractional oxygen extraction was assessed by Near-Infrared Spectroscopy (NIRS). RESULTS: Torque-time integral elicited by the two NMES paradigms was similar throughout the stimulation protocol, with differences ranging between 1.4% (p = 0.877; able-bodied, mid-part of the protocol) and 9.9% (p = 0.147; SCI, mid-part of the protocol). Contractile properties were also comparable in the two NMES paradigms. However, long-low NMES resulted in higher fractional oxygen extraction in able-bodied (+ 36%; p = 0.006). CONCLUSION: Long-low and short-high NMES recruited quadriceps femoris motor units that demonstrated similar contractile and fatigability properties. However, long-low NMES conceivably resulted in the preferential recruitment of vastus lateralis muscle fibers as detected by NIRS.

Effect of acute nitrite infusion on contractile economy and metabolism in isolated skeletal muscle in situ during hypoxia.

KEY POINTS: Increased plasma nitrite concentrations may have beneficial effects on skeletal muscle function. The physiological basis explaining these observations has not been clearly defined and it may involve positive effects on muscle contraction force, microvascular O2 delivery and skeletal muscle oxidative metabolism. In the isolated canine gastrocnemius model, we evaluated the effects of acute nitrite infusion on muscle force and skeletal muscle oxidative metabolism. Under hypoxic conditions, but in the presence of normal convective O2 delivery, an elevated plasma nitrite concentration affects neither muscle force, nor muscle contractile economy. In accordance with previous results suggesting limited or no effects of nitrate/nitrite administrations in highly oxidative and highly perfused muscle, our data suggest that neither mitochondrial respiration, nor muscle force generation are affected by acute increased concentrations of NO precursors in hypoxia. ABSTRACT: Contrasting findings have been reported concerning the effects of augmented nitric oxide (NO) on skeletal muscle force production and oxygen consumption ( V̇O2 ). The present study examined skeletal muscle mitochondrial respiration and contractile economy in an isolated muscle preparation during hypoxia (but normal convective O2 delivery) with nitrite infusion. Isolated canine gastrocnemius muscles in situ (n = 8) were studied during 3 min of electrically stimulated isometric tetanic contractions corresponding to ∼35% of V̇O2peak . During contractions, sodium nitrite (NITRITE) or sodium chloride (SALINE) was infused into the popliteal artery. V̇O2 was calculated from the Fick principle. Experiments were carried out in hypoxia ( FIO2  = 0.12), whereas convective O2 delivery was maintained at normal levels under both conditions by pump-driven blood flow ( Q̇ ). Muscle biopsies were taken and mitochondrial respiration was evaluated by respirometry. Nitrite infusion significantly increased both nitrite and nitrate concentrations in plasma. No differences in force were observed between conditions. V̇O2 was not significantly different between NITRITE (6.1 ± 1.8 mL 100 g-1  min-1 ) and SALINE (6.2 ± 1.8 mL 100 g-1  min-1 ), even after being 'normalized' per unit of developed force (muscle contractile economy). No differences between conditions were found for maximal ADP-stimulated mitochondrial respiration (both for complex I and complex II), leak respiration and oxidative phosphorylation coupling. In conclusion, in the absence of changes in convective O2 delivery, muscle force, muscle contractile economy and mitochondrial respiration were not affected by acute infusion of nitrite. The previously reported positive effects of elevated plasma nitrite concentrations are presumably mediated by the increased microvascular O2 availability.

Effects of Different Training Interventions on the Recovery of Physical and Neuromuscular Performance After a Soccer Match.

Trecroci, A, Porcelli, S, Perri, E, Pedrali, M, Rasica, L, Alberti, G, Longo, S, and Iaia, FM. Effects of different training interventions on the recovery of physical and neuromuscular performance after a soccer match. J Strength Cond Res 34(8): 2189-2196, 2020-In competitive soccer, players are frequently required to play in periods with congested fixtures in which they have limited time to recover between matches (3-4 days). Thus, finding the most appropriate intervention strategy to limit players' neuromuscular (muscle function of lower limbs) and physical (running performance) impairments in this short period becomes crucial. The aim of the study was to examine how muscle function of knee extensors and flexors and sprint performance recovered +72 hours after match in relation to different field-based training sessions. Using a crossover design, 9 subelite players (age 17.6 ± 0.5 years, height 1.77 ± 0.02 m, body mass 66.4 ± 5.8 kg) underwent a soccer-specific training (SST) session or an active recovery regime (AR) on the second day after a match. Immediately after (0 hour) and +72 hours after match, 30-m sprint and repeated sprint ability (RSA) were assessed. Maximum isometric voluntary force (MVF) of knee extensors and flexors was determined at 120° and 90° (with 180° being full extension), respectively. SST and AR promoted similar effects on the recovery kinetics of sprint, RSA, and MVF of knee extensors (p > 0.05). However, compared with SST, AR promoted a significantly better restoration of MVF of knee flexors (p < 0.05) after +72 hours from the match. Because muscle fatigue has been related with increased hamstring injury risk, a training based on AR can be a valid intervention to promote the recovery of muscle force production of knee flexors and reduce hamstring injury risk in the postmatch period.

Ergogenic effects of beetroot juice supplementation during severe-intensity exercise in obese adolescents.

Previous studies showed a higher O2 cost of exercise, and therefore, a reduced exercise tolerance in patients with obesity during constant work rate (CWR) exercise compared with healthy subjects. Among the ergogenic effects of dietary nitrate ([Formula: see text]) supplementation in sedentary healthy subjects, a reduced O2 cost and enhanced exercise tolerance have often been demonstrated. The aim of this study was to evaluate the effects of beetroot juice (BR) supplementation, rich in [Formula: see text], on physiological variables associated with exercise tolerance in adolescents with obesity. In a double-blind, randomized crossover study, 10 adolescents with obesity (8 girls, 2 boys; age = 16 ± 1 yr; body mass index = 35.2 ± 5.0 kg/m2) were tested after 6 days of supplementation with BR (5 mmol [Formula: see text] per day) or placebo (PLA). Following each supplementation period, patients carried out two repetitions of 6-min moderate-intensity CWR exercise and one severe-intensity CWR exercise until exhaustion. Plasma [Formula: see text] concentration was significantly higher in BR versus PLA (108 ± 37 vs. 15 ± 5 µM, P < 0.0001). The O2 cost of moderate-intensity exercise was not different in BR versus PLA (13.3 ± 1.7 vs. 12.9 ± 1.1 ml·min-1·W-1, P = 0.517). During severe-intensity exercise, signs of a reduced amplitude of the O2 uptake slow component were observed in BR, in association with a significantly longer time to exhaustion (561 ± 198 s in BR vs. 457 ± 101 s in PLA, P = 0.0143). In obese adolescents, short-term dietary [Formula: see text] supplementation is effective in improving exercise tolerance during severe-intensity exercise. This may prove to be useful in counteracting early fatigue and reduced physical activity in this at-risk population.

Triggered intravoxel incoherent motion MRI for the assessment of calf muscle perfusion during isometric intermittent exercise.

The main aim of this paper was to propose triggered intravoxel incoherent motion (IVIM) imaging sequences for the evaluation of perfusion changes in calf muscles before, during and after isometric intermittent exercise. Twelve healthy volunteers were involved in the study. The subjects were asked to perform intermittent isometric plantar flexions inside the MRI bore. MRI of the calf muscles was performed on a 3.0 T scanner and diffusion-weighted (DW) images were obtained using eight different b values (0 to 500 s/mm2 ). Acquisitions were performed at rest, during exercise and in the subsequent recovery phase. A motion-triggered echo-planar imaging DW sequence was implemented to avoid movement artifacts. Image quality was evaluated using the average edge strength (AES) as a quantitative metric to assess the motion artifact effect. IVIM parameters (diffusion D, perfusion fraction f and pseudo-diffusion D*) were estimated using a segmented fitting approach and evaluated in gastrocnemius and soleus muscles. No differences were observed in quality of IVIM images between resting state and triggered exercise, whereas the non-triggered images acquired during exercise had a significantly lower value of AES (reduction of more than 20%). The isometric intermittent plantar-flexion exercise induced an increase of all IVIM parameters (D by 10%; f by 90%; D* by 124%; fD* by 260%), in agreement with the increased muscle perfusion occurring during exercise. Finally, IVIM parameters reverted to the resting values within 3 min during the recovery phase. In conclusion, the IVIM approach, if properly adapted using motion-triggered sequences, seems to be a promising method to investigate muscle perfusion during isometric exercise.

Carbon monoxide Supplementation: Evaluating its Potential to Enhance Altitude Training Effects and Cycling Performance in Elite Athletes.

Altitude training is a cornerstone for endurance athletes for improving blood variables and performance with optimal effects observed at ⁓2300-2500 meters above sea level (m.a.s.l.). However, elite cyclists face challenges such as limited access to such altitudes, inadequate training facilities, and high expenses. To address these issues, a novel method involving daily exposure to carbon monoxide (CO) has been proposed to amplify altitude training adaptations at suboptimal altitudes. Thirty-one male cyclists were assigned to three groups: Live-High and Train-High with CO inhalation (LHTHCO), Live-High Train-High (LHTH), and Live-Low Train-Low (LLTL). The LHTHCO group underwent CO inhalation twice daily in the afternoon/evening to elevate carboxyhemoglobin concentration to ⁓10%. Hematological variables, in-vivo muscle oxidative capacity, and physiological indicators of cycling performance were assessed before and after a 3-week altitude training camp at 2100 m.a.s.l. LHTHCO demonstrated a larger increase in hemoglobin mass (Hbmass) compared to both LHTH and LLTL. While there were no statistical differences between LHTHCO and LHTH in submaximal and maximal performance measures, LHTHCO displayed greater improvements in 1-min maximal power output during incremental testing (Wmax), power output at lactate threshold, and maximal oxygen consumption (VO2max) compared to LLTL. LHTH demonstrated a larger improvement than LLTL in Wmax andVO2maxwith no group differences in Hbmass or submaximal measures. Muscle oxidative capacity did not differ between groups. These findings suggest that combining moderate altitude training with daily CO inhalation promotes hematological adaptations more effectively than moderate altitude alone and enhances cycling performance metrics in cyclists more than sea-level training.

Accelerometer-based measures in Friedreich ataxia: a longitudinal study on real-life activity.

Quantitative measurement of physical activity may complement neurological evaluation and provide valuable information on patients' daily life. We evaluated longitudinal changes of physical activity in patients with Friedreich ataxia (FRDA) using remote monitoring with wearable sensors. We performed an observational study in 26 adult patients with FRDA and 13 age-sex matched healthy controls (CTR). Participants were asked to wear two wearable sensors, at non-dominant wrist and at waist, for 7 days during waking hours. Evaluations were performed at baseline and at 1-year follow-up. We analysed the percentage of time spent in sedentary or physical activities, the Vector Magnitude on the 3 axes (VM3), and average number of steps/min. Study participants were also evaluated with ataxia clinical scales and functional tests for upper limbs dexterity and walking capability. Baseline data showed that patients had an overall reduced level of physical activity as compared to CTR. Accelerometer-based measures were highly correlated with clinical scales and disease duration in FRDA. Significantly changes from baseline to l-year follow-up were observed in patients for the following measures: (i) VM3; (ii) percentage of sedentary and light activity, and (iii) percentage of Moderate-Vigorous Physical Activity (MVPA). Reduction in physical activity corresponded to worsening in gait score of the Scale for Assessment and Rating of Ataxia. Real-life activity monitoring is feasible and well tolerated by patients. Accelerometer-based measures can quantify disease progression in FRDA over 1 year, providing objective information about patient's motor activities and supporting the usefulness of these data as complementary outcome measure in interventional trials.