Methodological considerations on near-infrared spectroscopy derived muscle oxidative capacity.

PURPOSE: Different strategies for near-infrared spectroscopy (NIRS)-derived muscle oxidative capacity assessment have been reported. This study compared and evaluated (I) approaches for averaging trials; (II) NIRS signals and blood volume correction equations; (III) the assessment of vastus lateralis (VL) and tibialis anterior (TA) muscles in two fitness levels groups. METHODS: Thirty-six participants [18 chronically trained (CT: 14 males, 4 females) and 18 untrained (UT: 10 males, 8 females)] participated in this study. Two trials of twenty transient arterial occlusions were performed for NIRS-derived muscle oxidative capacity assessment. Muscle oxygen consumption ([Formula: see text]O2m) was estimated from deoxygenated hemoglobin (HHb), corrected for blood volume changes following Ryan (HHbR) and Beever (HHbB) equations, and from oxygen saturation (StO2) in VL and TA. RESULTS: Superimposing or averaging [Formula: see text]O2m or averaging the rate constants (k) from the two trials resulted in equivalent k values [two one-sided tests (TOST) procedure with 5% equivalence margin-P < 0.001]. Whereas HHbR (2.35 ± 0.61 min-1) and HHbB (2.34 ± 0.58 min-1) derived k were equivalent (P < 0.001), StO2 derived k (2.81 ± 0.92 min-1) was greater (P < 0.001) than both. k values were greater in CT vs UT in both muscles (VL: + 0.68 min-1, P = 0.002; TA: + 0.43 min-1, P = 0.01). CONCLUSION: Different approaches for averaging trials lead to similar k. HHb and StO2 signals provided different k, although different blood volume corrections did not impact k. Group differences in k were detected in both muscles.

Heart Rate Variability Thresholds: Agreement with Established Approaches and Reproducibility in Trained Females and Males.

PURPOSE: To determine in trained females and males: i) the agreement between the gas exchange threshold (GET), lactate threshold 1 (LT1) and heart rate variability threshold 1 (HRVT1), as well as between the respiratory compensation point (RCP), lactate threshold 2 (LT2) and heart rate variability threshold 2 (HRVT2) and ii) the reproducibility of HRVT1 and HRVT2 during two-min incremental step protocols. METHODS: Fifty-seven trained participants (24 females) completed a 2 min step incremental test to task failure. Nineteen participants (8 females) completed a second test to evaluate reproducibility. Gas exchange and ventilatory responses, blood lactate concentration, and RR time series were recorded to assess the oxygen consumption (V̇O2) and heart rate (HR) associated with the GET, RCP, LT1, LT2, HRVT1 and HRVT2. RESULTS: V̇O2-GET vs V̇O2-HRVT1 and HR-GET vs HR-HRVT1 were statistically different for females (29.5 ± 4.0 vs 34.6 ± 6.1 mL·kg-1·min-1; 154 ± 11 vs 166 ± 12 bpm) and for males (33.9 ± 4.2 vs 42.7 ± 4.6 mL·kg-1·min-1; 145 ± 11 vs 165 ± 9 bpm) (p < 0.001). V̇O2 and HR at HRVT1 were greater than at LT1 (p < 0.05). V̇O2-RCP vs V̇O2-HRVT2 and HR-RCP vs HR-HRVT2 were not statistically different for females (40.1 ± 4.7 vs 39.5 ± 6.7 mL·kg-1·min-1; 177 ± 9 vs 176 ± 9 bpm) and males (48.4 ± 5.4 vs 47.8 ± 4.8 mL·kg-1·min-1; 176 ± 8 vs 175 ± 9 bpm) (p > 0.05). V̇O2 and HR responses at LT2 were similar to HRVT2 (p > 0.05). Intraclass correlation (ICC) for V̇O2-HRVT1, HR-HRVT1, V̇O2-HRVT2, and HR-HRVT2 indicated good reproducibility when comparing the two different timepoints to standard methods. CONCLUSIONS: Whereas HRVT2 is a valid and reproducible estimate of the RCP/LT2, current approaches for HRVT1 estimation did not show good agreement with outcomes at GET and LT1.

Heavy-, Severe-, and Extreme-, but not Moderate-Intensity Exercise Increase V̇o2max and Thresholds after 6 Weeks of Training.

INTRODUCTION: This study assessed the effect of individualized, domain-based exercise intensity prescription on changes in maximal oxygen uptake (V̇O2max) and submaximal thresholds. METHODS: Eighty-four young healthy participants (42 Females, 42 Males) were randomly assigned to six age, sex, and V̇O2max-matched groups (14 participants each). Groups performed continuous cycling in the 1) moderate (MOD)-, 2) lower heavy (HVY1)-, and 3) upper heavy-intensity (HVY2)- domain; interval cycling, in the form of 4) high-intensity interval training (HIIT) in the severe-intensity domain, or 5) sprint-interval training (SIT) in the extreme-intensity domain; or no exercise for, 6) control (CON). All training groups except SIT, were work-matched. Training participants completed three sessions per week for six weeks with physiological evaluations performed at PRE, MID and POST intervention. RESULTS: Compared to the change in V̇O2max (∆V̇O2max) in CON (0.1 ± 1.2 mL·kg-1·min-1), all training groups except MOD (1.8 ± 2.7 mL·kg-1·min-1), demonstrated a significant increase (p < 0.05). HIIT produced the highest increase (6.2 ± 2.8 mL·kg-1·min-1) followed by HVY2 (5.4 ± 2.3 mL·kg-1·min-1), SIT (4.7 ± 2.3 mL·kg-1·min-1), and HVY1 (3.3 ± 2.4 mL·kg-1·min-1), respectively. The Δ PO at the estimated lactate threshold (θLT) was similar across HVY1, HVY2, HIIT and SIT which were all greater than CON (p < 0.05). The Δ V̇O2 and Δ PO at θLT for MOD was not different from CON (p > 0.05). HIIT produced the highest Δ PO at maximal metabolic steady state, which was greater than CON, MOD, and SIT (p < 0.05). CONCLUSIONS: This study demonstrated that i) exercise intensity is a key component determining changes in V̇O2max and submaximal thresholds and ii) exercise intensity domain-based prescription allows for a homogenous metabolic stimulus across individuals.

Women at Altitude: Sex-Related Physiological Responses to Exercise in Hypoxia.

Sex differences in physiological responses to various stressors, including exercise, have been well documented. However, the specific impact of these differences on exposure to hypoxia, both at rest and during exercise, has remained underexplored. Many studies on the physiological responses to hypoxia have either excluded women or included only a limited number without analyzing sex-related differences. To address this gap, this comprehensive review conducted an extensive literature search to examine changes in physiological functions related to oxygen transport and consumption in hypoxic conditions. The review encompasses various aspects, including ventilatory responses, cardiovascular adjustments, hematological alterations, muscle metabolism shifts, and autonomic function modifications. Furthermore, it delves into the influence of sex hormones, which evolve throughout life, encompassing considerations related to the menstrual cycle and menopause. Among these physiological functions, the ventilatory response to exercise emerges as one of the most sex-sensitive factors that may modify reactions to hypoxia. While no significant sex-based differences were observed in cardiac hemodynamic changes during hypoxia, there is evidence of greater vascular reactivity in women, particularly at rest or when combined with exercise. Consequently, a diffusive mechanism appears to be implicated in sex-related variations in responses to hypoxia. Despite well-established sex disparities in hematological parameters, both acute and chronic hematological responses to hypoxia do not seem to differ significantly between sexes. However, it is important to note that these responses are sensitive to fluctuations in sex hormones, and further investigation is needed to elucidate the impact of the menstrual cycle and menopause on physiological responses to hypoxia.

Recommendations for Women in Mountain Sports and Hypoxia Training/Conditioning.

The (patho-)physiological responses to hypoxia are highly heterogeneous between individuals. In this review, we focused on the roles of sex differences, which emerge as important factors in the regulation of the body's reaction to hypoxia. Several aspects should be considered for future research on hypoxia-related sex differences, particularly altitude training and clinical applications of hypoxia, as these will affect the selection of the optimal dose regarding safety and efficiency. There are several implications, but there are no practical recommendations if/how women should behave differently from men to optimise the benefits or minimise the risks of these hypoxia-related practices. Here, we evaluate the scarce scientific evidence of distinct (patho)physiological responses and adaptations to high altitude/hypoxia, biomechanical/anatomical differences in uphill/downhill locomotion, which is highly relevant for exercising in mountainous environments, and potentially differential effects of altitude training in women. Based on these factors, we derive sex-specific recommendations for mountain sports and intermittent hypoxia conditioning: (1) Although higher vulnerabilities of women to acute mountain sickness have not been unambiguously shown, sex-dependent physiological reactions to hypoxia may contribute to an increased acute mountain sickness vulnerability in some women. Adequate acclimatisation, slow ascent speed and/or preventive medication (e.g. acetazolamide) are solutions. (2) Targeted training of the respiratory musculature could be a valuable preparation for altitude training in women. (3) Sex hormones influence hypoxia responses and hormonal-cycle and/or menstrual-cycle phases therefore may be factors in acclimatisation to altitude and efficiency of altitude training. As many of the recommendations or observations of the present work remain partly speculative, we join previous calls for further quality research on female athletes in sports to be extended to the field of altitude and hypoxia.

Sodium bicarbonate induces alkalosis, but improves high-intensity cycling performance only when participants expect a beneficial effect: a placebo and nocebo study.

The study aimed to investigate the effects of sodium bicarbonate (NaHCO3) intake with divergent verbal and visual information on constant load cycling time-to-task failure, conducted within the severe intensity domain. Fifteen recreational cyclists participated in a randomized double-blind, crossover study, ingesting NaHCO3 or placebo (i.e., dextrose), but with divergent information about its likely influence (i.e., likely to induce ergogenic, inert, or harmful effects). Performance was evaluated using constant load cycling time to task failure trial at 115% of peak power output estimated during a ramp incremental exercise test. Data on blood lactate, blood acid-base balance, muscle electrical activity (EMG) through electromyography signal, and the twitch interpolation technique to assess neuromuscular indices were collected. Despite reduced peak force in the isometric maximal voluntary contraction and post-effort peripheral fatigue in all conditions (P < 0.001), neither time to task failure, EMG nor, blood acid-base balance differed between conditions (P > 0.05). Evaluation of effect sizes of all conditions suggested that informing participants that the supplement would be likely to have a positive effect (NaHCO3/Ergogenic: 0.46; 0.15-0.74; Dextrose/Ergogenic: 0.45; 0.04-0.88) resulted in improved performance compared to control. Thus, NaHCO3 ingestion consistently induced alkalosis, indicating that the physiological conditions to improve performance were present. Despite this, NaHCO3 ingestion did not influence performance or indicators of neuromuscular fatigue. In contrast, effect size estimates indicate that participants performed better when informed that they were ingesting an ergogenic supplement. These findings suggest that the apparently ergogenic effect of NaHCO3 may be due, at least in part, to a placebo effect.

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.

Decrease in work rate in order to keep a constant heart rate: biomarker of exercise intolerance following a 10-day bed rest.

Aerobic exercise prescription is often set at specific heart rate (HR) values. Previous studies demonstrated that during exercise carried out at a HR slightly above that corresponding to the gas exchange threshold (GET), work rate (WR) has to decrease in order to maintain HR constant. We hypothesized a greater WR decrease at a fixed HR after simulated microgravity/inactivity (bed rest, BR). Ten male volunteers (23 ± 5 yr) were tested before (PRE) and after (POST) a 10-day horizontal BR and performed on a cycle ergometer 1) incremental exercise; b) 15-min HRCLAMPED exercise, in which WR was continuously adjusted to maintain a constant HR, corresponding to that at 120% of GET determined in PRE; 3) two moderate-intensity constant WR (MOD) exercises. Breath-by-breath O2 uptake (V̇o2), HR, and other variables were determined. After BR, peak V̇o2 (V̇o2peak) and GET significantly decreased, by ∼10%. During HRCLAMPED (145 ± 11 beats·min-1), the decrease in WR needed to maintain a constant HR was greater in POST versus PRE (-39 ± 10% vs. -29 ± 14%, P < 0.01). In six subjects the decreased WR switched from the heavy- to the moderate-intensity domain. The decrease in WR during HRCLAMPED, in PRE versus POST, was significantly correlated with the V̇o2peak decrease (R2 = 0.52; P = 0.02). A greater amplitude of the slow component of the HR kinetics was observed during MOD following BR. Exercise at a fixed HR is not associated with a specific WR or WR domain; the problem, affecting exercise evaluation and prescription, is greater after BR. The WR decrease during HRCLAMPED is a biomarker of exercise intolerance after BR.NEW & NOTEWORTHY During a 15-min exercise carried out at a heart rate (HR) slightly above that corresponding to the gas exchange threshold, to keep HR constant work rate significantly decreased; the decrease was more pronounced after a 10-day horizontal bed rest. The work rate decrease at a fixed HR can be considered a systemic biomarker of exercise intolerance during microgravity/inactivity and could also be easily and reliably determined during spaceflights or in patients.

Fitness Level- and Sex-Related Differences in Macrovascular and Microvascular Responses during Reactive Hyperemia.

PURPOSE: Reactive hyperemia (RH) is widely used for the investigation of macrovascular (flow-mediated dilation, or FMD) and microvascular (near-infrared spectroscopy-vascular occlusion test, or NIRS-VOT) function. Mixed results have been reported on fitness level- and sex-related differences in FMD outcomes, and little is known about microvascular differences in untrained and chronically trained males and females. METHODS: Fifteen chronically trained (CT: 8 males, 7 females) and 16 untrained (UT: 8 males, 8 females) individuals participated in this study. Aerobic fitness (V˙O2max) was assessed during a cycling incremental exercise test to volitional exhaustion. FMD and NIRS-VOT were performed simultaneously on the lower limb investigating superficial femoral artery and vastus lateralis muscle, respectively. RESULTS: %FMD was not different between groups (CT males, 4.62 ± 1.42; CT females, 4.15 ± 2.23; UT males, 5.10 ± 2.53; CT females, 3.20 ± 1.67). Peak blood flow showed greater values in CT versus UT (P ≤ 0.0001) and males versus females (P = 0.032). RH blood flow area under the curve was greater in CT versus UT (P = 0.001). At the microvascular level, desaturation and reperfusion rates were faster in CT versus UT (P = 0.018 and P = 0.013) and males versus females (P = 0.011 and P = 0.005). V˙O2max was significantly correlated with reperfusion rate (P = 0.0005) but not with %FMD. CONCLUSIONS: Whereas NIRS-VOT outcomes identified fitness- and sex-related differences in vascular responses, %FMD did not. However, when RH-related outcomes from the FMD analysis were considered, fitness- and/or sex-related differences were detected. These data highlight the importance of integrating FMD and NIRS-VOT outcomes for a more comprehensive evaluation of vascular function.

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.

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.

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.

New On-Water Test for the Assessment of Blood Lactate Response to Exercise in Elite Kayakers.

PURPOSE: Lactate thresholds are physiological parameters used to train athletes and monitor performance or training. Currently, the assessment of lactate thresholds in kayakers is performed in a laboratory setting utilizing specific ergometers; however, laboratory tests differ from on-water evaluation for several reasons. The aim of this study was to assess reliability and validity of a new on-water incremental test for the assessment of blood lactate response to exercise in flat-water kayakers. Maximal lactate steady state test (MLSS) was used as criterion measurement. METHODS: Eleven junior (16.5 ± 1.9 yr) élite flat-water kayakers performed: i) an incremental cardiopulmonary test up to voluntary exhaustion on a stationary kayak ergometer to determine peak oxygen uptake; ii) an on-water 1000-m distance trial (T1000) to record best performance time and average speed (S1000); iii) two repetitions of on-water incremental kayaking test (WIK test); iv) several repetitions of on-water constant speed tests to determine MLSS. Speed, HR, and blood lactate concentrations were determined during on-water tests. RESULTS: The best performance time in T1000 was 262 ± 13 s, corresponding to an S1000 of 3.82 ± 0.19 m·s. Lactate threshold determined by modified Dmax method (LTDmod) during WIK test was 2.78 ± 1.02 mmol·L and the corresponding speed (SLT) was 3.34 ± 0.16 m·s. Test-retest reliability, calculated on SLT, was strong (ICC = 0.95 and r = 0.93). MLSS test corresponded to 3.06 ± 0.68 mmol·L and was reached at a speed (SMLSS) of 3.36 ± 0.14 m·s. Correlation coefficient between SLT and SMLSS was 0.90 (P = 0.0001). Interestingly, a significant correlation (r = 0.96, P < 0.0001) was observed between SLT and S1000. CONCLUSIONS: The WIK test showed good reliability and validity for the assessment of speed corresponding to LTDmod in flat-water kayakers and it could be a useful tool to monitor athletic performance. The speed value at LTDmod nicely predicted performance on 1000 m.

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.

Comparison between Slow Components of HR and V˙O2 Kinetics: Functional Significance.

PURPOSE: Aerobic exercise prescription is often based on a linear relationship between pulmonary oxygen consumption (V˙O2) and heart rate (HR). The aim of the present study was to test the hypothesis that during constant work rate (CWR) exercises at different intensities, the slow component of HR kinetics occurs at lower work rate and is more pronounced that the slow component of V˙O2 kinetics. METHODS: Seventeen male (age, 27 ± 4 yr) subjects performed on a cycle ergometer an incremental exercise to voluntary exhaustion and several CWR exercises: 1) moderate CWR exercises, below gas exchange threshold (GET); 2) heavy CWR exercise, at 45% of the difference between GET and V˙O2 peak (Δ); 3) severe CWR exercise, at 95% of Δ; 4) "HRCLAMPED" exercise in which work rate was continuously adjusted to maintain a constant HR, slightly higher than that determined at GET. Breath-by-breath V˙O2, HR, and other variables were determined. RESULTS: In moderate CWR exercises, no slow component of V˙O2 kinetics was observed, whereas a slow component with a relative amplitude (with respect to the total response) of 24.8 ± 11.0% was observed for HR kinetics. During heavy CWR exercise, the relative amplitude of the HR slow component was more pronounced than that for V˙O2 (31.6 ± 11.2% and 23.3 ± 9.0%, respectively). During HRCLAMPED, the decrease in work rate (~14%) needed to maintain a constant HR was associated with a decreased V˙O2 (~10%). CONCLUSIONS: The HR slow component occurred at a lower work rate and was more pronounced than the V˙O2 slow component. Exercise prescriptions at specific HR values, when carried out for periods longer than a few minutes, could lead to premature fatigue.

Effects of a Short-Term High-Nitrate Diet on Exercise Performance.

It has been reported that nitrate supplementation can improve exercise performance. Most of the studies have used either beetroot juice or sodium nitrate as a supplement; there is lack of data on the potential ergogenic benefits of an increased dietary nitrate intake from a diet based on fruits and vegetables. Our aim was to assess whether a high-nitrate diet increases nitric oxide bioavailability and to evaluate the effects of this nutritional intervention on exercise performance. Seven healthy male subjects participated in a randomized cross-over study. They were tested before and after 6 days of a high (HND) or control (CD) nitrate diet (~8.2 mmol∙day(-1) or ~2.9 mmol∙day(-1), respectively). Plasma nitrate and nitrite concentrations were significantly higher in HND (127 ± 64 µM and 350 ± 120 nM, respectively) compared to CD (23 ± 10 µM and 240 ± 100 nM, respectively). In HND (vs. CD) were observed: (a) a significant reduction of oxygen consumption during moderate-intensity constant work-rate cycling exercise (1.178 ± 0.141 vs. 1.269 ± 0.136 L·min(-1)); (b) a significantly higher total muscle work during fatiguing, intermittent sub-maximal isometric knee extension (357.3 ± 176.1 vs. 253.6 ± 149.0 Nm·s·kg(-1)); (c) an improved performance in Repeated Sprint Ability test. These findings suggest that a high-nitrate diet could be a feasible and effective strategy to improve exercise performance.