Unilateral Knee Extension Exercise Research Articles

Blunted Exercise Pressor Reflex in Individuals with Down Syndrome

INTRODUCTION: Individuals with Down syndrome (DS) exhibit autonomic dysfunction, which contributes to reduced work capacity. The chemically sensitive component of the exercise pressor reflex, the metaboreflex, is responsible for exercise-induced sympathoexcitation and can be assessed via post-exercise muscle ischemia (PEMI). Blunted sympathoexcitation is common in individuals with DS and contributes to the physiological basis for reduced work capacity observed this population, but the influence of the metaboreflex is unknown. Using unilateral isometric knee extension exercise with PEMI, we hypothesized that individuals with DS would demonstrate a reduced metaboreflex compared to individuals without DS. METHODS: Twenty-four individuals with DS (M/F: 13/11; 24±5yrs; 30.3±6.2kg/m2) and without DS (M/F: 13/11; 25±4yrs; 26.5±4.5kg/m2) performed a unilateral isometric knee extension at 30% of their maximal voluntary contraction using their dominant leg on a leg dynamometer. Following 2-min of contraction, a thigh-cuff was rapidly inflated to 220 mmHg on the exercised leg for 3-min to isolate the activation of the muscle metaboreflex via PEMI. Beat-to-beat systolic blood pressure (SBP), stroke volume (SV), mean arterial pressure (MAP), and cardiac output (CO) were assessed using finger photoplethysmography coupled with Modelflow. Heart rate (HR) was collected via three-lead electrocardiogram. RESULTS: Despite similar baseline values of all variables in both groups, individuals with DS demonstrated a blunted pressor response to the isometric knee extension compared to individuals without DS (SBP; DS: 133±17 vs. Non-DS: 167±28 mmHg), and the blunted SBP response was maintained with PEMI (SBP; DS: 124±19 vs. Non-DS: 150±21 mmHg; time × group interaction, p<0.001). Individuals with DS also exhibited a reduced HR 2-min into the contraction compared to those without DS (HR; DS: 90±16 vs. Non-DS: 114±22 bpm; timexgroup interaction, p<0.001). Controlling for MVC, BMI, peak torque/body weight, and quadricep fat & lean mass did not impact our results. Further, individuals with DS had a lower SV during the PEMI compared to individuals without DS (SV; DS: 93±24 vs. Non-DS: 113±23 mL/min; timexgroup interaction, p=0.003). CONCLUSION: Individuals with DS demonstrated a diminished metaboreflex response compared to their peers without DS, during a task known to induce sympathoexcitation, even when controlling for MVC. Our novel findings suggest that reduced influence of the metaboreflex contributes to the reduced exercise pressor response in persons with DS. Such exercise-specific peripheral autonomic perturbations contribute beyond our previous cardiac autonomic findings demonstrating blunted sympathoexcitatory perturbations in persons with DS, which likely contribute to reduced work capacity for this population. This research was funded in part by the American College of Sports Medicine Doctoral Research Award (#21-01558). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Influence of unilateral and bilateral knee extension fatigue protocols on inter-limb asymmetries assessed through countermovement jumps

ABSTRACT This study explores the sensitivity of jump type (unilateral and bilateral) and output variable (mean force, propulsive impulse, and jump height) to detect the changes in inter-limb asymmetries induced by unilateral and bilateral fatigue protocols. Thirty-eight individuals performed two testing sessions that consisted of (I) nine “pre-fatigued” countermovement jumps (CMJs; three bilateral and six unilateral [three with each leg]), (II) fatigue protocol and (III) nine “post-fatigued” CMJs. The testing sessions only differed in the fatigue protocol (five sets to failure against the 15-repetition maximum load using either the unilateral or bilateral knee extension exercise). The magnitude of all CMJ-derived variables (mean force, impulse, and jump height) decreased following both unilateral (p ≤ 0.002) and bilateral fatigue protocols (p ≤ 0.018). However, only unilateral protocol accentuated inter-limb asymmetries, which was detected for all variables during the unilateral CMJ (from −4.33% to −2.04%; all p < 0.05) but not during the bilateral CMJ (from −0.64% to 0.54%; all p > 0.05). The changes in inter-limb asymmetries following the unilateral and bilateral fatigue protocols were not significantly correlated between the unilateral and bilateral CMJs (r s ≤ 0.172). The unilateral CMJ should be recommended for the testing purposes over the bilateral CMJ due to its greater sensitivity to detect the selective effects of fatigue.

Different time course recovery of muscle edema within the quadriceps femoris and functional performance after single- vs multi-joint exercises.

This study aimed to verify the time course recovery of muscle edema within the quadriceps femoris and functional performance after lower-body single- and multi-joint exercises. For this within-participant unilateral and contralateral experimental design, fourteen untrained young males performed a unilateral knee extension exercise (KE), and a unilateral leg press (LP) exercise in a counterbalanced order. At pre-, post-, 24 h, 48 h, 72 h, and 96 h after exercise, the peak torque (PT), unilateral countermovement jump (uCMJ) performance, and rectus femoris (RF) and vastus lateralis (VL) muscle thicknesses were recorded in both legs. The PT decreased immediately after (p = 0.01) both exercises (KE and LP) and was fully recovered 24 h after KE (p = 0.38) and 48 h after LP (p = 0.68). Jump height and power, in the uCMJ, followed the same PT recovery pattern after both exercises. However, vertical stiffness (Kvert) was not affected at any time point after both protocols. The RF thickness increased after both exercises (p = 0.01) and was fully restored 48 h after KE (p = 0.86) and 96 h after LP (p = 1.00). The VL thickness increased after both exercises (p = 0.01) and was fully restored 24 h after LP (p = 1.00) and 48 h after KE (p = 1.00). The LP exercise, compared to KE, induced more prolonged impairment of functional performance and delayed recovery of RF muscle edema. However, the VL edema-induced muscle swelling recovery was delayed after the KE exercise. The different recovery kinetics between functional performance and muscle damage should be taken into consideration depending on the objectives of the next training sessions.

The Hypoalgesic Effect of Low-Load Exercise to Failure Is Not Augmented by Blood Flow Restriction

ABSTRACTPurpose: To 1) examine whether blood flow restriction would provide an additional exercise-induced hypoalgesic response at an upper and lower limb when it is incorporated with low-load resistance exercise until failure, and 2) examine if increases in blood pressure and discomfort, with blood flow restricted exercise, would mediate the exercise-induced hypoalgesia over exercise without blood flow restriction. Methods: Forty healthy young participants completed two trials: four sets of unilateral knee extension exercise to failure at 30% of one-repetition maximum, with and without blood flow restriction. Pressure pain thresholds were assessed before (twice) and 5-min post exercise at an upper and lower limb. Blood pressure and discomfort ratings were recorded to examine mediating effects on exercise-induced hypoalgesia with blood flow restricted exercise. Results: Pressure pain threshold increased following both exercise conditions compared to a control, without any differences between exercise conditions at the upper (exercise conditions vs. control: ~0.37 kg/cm2) and lower (exercise conditions vs. control: ~0.60 kg/cm2) limb. The total number of repetitions was lower for exercise with blood flow restriction compared to exercise alone [median difference (95% credible interval) of −27.0 (−29.8, −24.4) repetitions]. There were no mediating effects of changes in blood pressure, nor changes in discomfort, for the changes in pressure pain threshold at either the upper or lower limb. Conclusion: The addition of blood flow restriction to low-load exercise induces a similar hypoalgesic response to that of non-blood flow restricted exercise, with a fewer number of repetitions.

Effects of low load exercise with and without blood-flow restriction on microvascular oxygenation, muscle excitability and perceived pain

ABSTRACT This paper aimed to examine the acute effect of low-load (LL) exercise with blood-flow restriction (LL-BFR) on microvascular oxygenation and muscle excitability of the vastus medialis (VM) and vastus lateralis (VL) muscles during a single bout of unilateral knee extension exercise performed to task failure. Seventeen healthy recreationally resistance-trained males were enrolled in a within-group randomized cross-over study design. Participants performed one set of unilateral knee extensions at 20% of one-repetition maximum (1RM) to task failure, using a LL-BFR or LL free-flow (LL-FF) protocol in a randomized order on separate days. Changes in microvascular oxygenation and muscle excitability in VL and VM were assessed using near-infrared spectroscopy (NIRS) and surface electromyography (sEMG), respectively. Pain measures were collected using the visual analog scale (VAS) before and following set completion. Within- and between- protocol comparisons were performed at multiple time points of set completion for each muscle. During LL-BFR, participants performed 43% fewer repetitions and reported feeling more pain compared to LL-FF (p<0.05). Normalized to time to task failure, LL-BFR and LL-FF generally demonstrated similar progression in microvascular oxygenation and muscle excitability during exercise to task failure. The present results demonstrate that LL-BFR accelerates time to task failure, compared with LL-FF, resulting in a lower dose of mechanical work to elicit similar levels of oxygenation, blood-pooling, and muscle excitability. LL-BFR may be preferable to LL-FF in clinical settings where high workloads are contraindicated, although increased pain experienced during BFR may limit its application. Highlights Compared to free flow (FF), neuromuscular fatigue mechanisms are accelerated during blood flow restricted (BFR) training. This can be observed as changes in microvascular oxygenation and muscle excitability occurring at a ∼43% faster mean rate during BFR compared to FF. BFR exercise seems to elicit the same level of neuromuscular fatigue as FF training within a shorter timeframe. This reduces total joint load and may be especially helpful in cases where high training volumes may be contraindicated (e.g. recovering from a sports injury or orthopedic surgery).

Central and Peripheral Thermal Signatures of Brain-Derived Fatigue during Unilateral Resistance Exercise: A Preliminary Study.

Simple SummaryFatigue is considered a brain-derived emotion that could impact performance during the execution of physical exercises. Infrared thermography is a valuable technique able to measure the psychophysiological state associated with emotions in a contactless manner. The aim of the study is to test the capability of infrared thermography to evaluate the central and peripheral physiological effect of fatigue through facial skin and muscle temperature modulations collected during the execution of a unilateral resistance exercise of the lower limb. Both time- and frequency-domain analyses were performed on the temperature time course of the face and limbs. Particularly, significant correlations between features extracted from the thermal signals and the perceived exertion were found. These findings confirmed the ability of thermal imaging to detect both peripheral and central effects of fatigue in response to physical exercises. These results could foster the employment of infrared thermography to monitor the psychophysiological state of the athletes during training. The possibility to calibrate the training load in accordance with the psychophysiological conditions could improve the performance of the athletes during the training process and competitions.Infrared thermography (IRT) allows to evaluate the psychophysiological state associated with emotions from facial temperature modulations. As fatigue is a brain-derived emotion, it is possible to hypothesize that facial temperature could provide information regarding the fatigue related to exercise. The aim of this study was to investigate the capability of IRT to assess the central and peripheral physiological effect of fatigue by measuring facial skin and muscle temperature modulations in response to a unilateral knee extension exercise until exhaustion. Rate of perceived exertion (RPE) was recorded at the end of the exercise. Both time- (∆TROI: pre–post exercise temperature variation) and frequency-domain (∆PSD: pre–post exercise power spectral density variation of specific frequency bands) analyses were performed to extract features from regions of interest (ROIs) positioned on the exercised and nonexercised leg, nose tip, and corrugator. The ANOVA-RM revealed a significant difference between ∆TROI (F(1.41,9.81) = 15.14; p = 0.0018), and between ∆PSD of myogenic (F(1.34,9.39) = 15.20; p = 0.0021) and neurogenic bands (F(1.75,12.26) = 9.96; p = 0.0034) of different ROIs. Moreover, significant correlations between thermal features and RPE were found. These findings suggest that IRT could assess both peripheral and central responses to physical exercise. Its applicability in monitoring the psychophysiological responses to exercise should be further explored

Effect of different eccentric tempos on hypertrophy and strength of the lower limbs.

The purpose of this study was to evaluate the effects of altering the duration of the eccentric phase in isotonic contractions on muscle hypertrophy and strength of the quadriceps femoris. Ten healthy young adults (8 men and 2 women: Height: 173.3 ± 9.6 cm: Body mass: 69.84 ± 10.88 kg; Body fat: 19.47 ± 8.42%; Age: 25.3 ± 4.8 years) performed unilateral isotonic knee extension exercise, whereby each leg was randomly allocated to perform the eccentric phase of movement with a duration of either 2 seconds (G2S) or 4 seconds (G4S). Both conditions carried out the concentric phase of each repetition at a 1 second duration with no rest in the transition phases. Each condition performed 5 sets using 70% of 1 repetition maximum until muscle failure with 3 minutes of rest between sets for 8 weeks. The change in muscle strength was assessed by 1RM knee extension and muscle thickness was assessed by A-mode ultrasound. For each outcome variable, linear mixed-effects models were fit using restricted maximum likelihood. Hedges’ g effect sizes were calculated to provide insights into the magnitude of effects. Results showed all muscles increased in size over time; mean effects were similar in all muscles except for the vastus medialis, which favored the G4S condition. Conversely, only a trivial and highly variable effect was observed between interventions for strength gain. Our results suggest different eccentric durations produce similar increases in hypertrophy of the vastus lateralis and rectus femoris; however, the vastus medialis showed greater growth from the slower eccentric duration. Eccentric duration did not differentially affect strength-related adaptations.

Resistance training with different repetition duration to failure: effect on hypertrophy, strength and muscle activation.

BackgroundThis study investigated the effects of two 14-week resistance training protocols with different repetition duration (RD) performed to muscle failure (MF) on gains in strength and muscle hypertrophy as well as on normalized electromyographic (EMG) amplitude and force-angle relationships.MethodsThe left and right legs of ten untrained males were assigned to either one of the two protocols (2-s or 6-s RD) incorporating unilateral knee extension exercise. Both protocols were performed with 3–4 sets, 50–60% of the one-repetition maximum (1RM), and 3 min rest. Rectus femoris and vastus lateralis cross-sectional areas (CSA), maximal voluntary isometric contraction (MVIC) at 30o and 90o of knee flexion and 1RM performance were assessed before and after the training period. In addition, normalized EMG amplitude-angle and force-angle relationships were assessed in the 6th and 39th experimental sessions.ResultsThe 6-s RD protocol induced larger gains in MVIC at 30o of knee angle measurement than the 2-s RD protocol. Increases in MVIC at 90o of knee angle, 1RM, rectus femoris and vastus lateralis CSA were not significant between the 2-s and 6-s RD protocols. Moreover, different normalized EMG amplitude-angle and force-angle values were detected between protocols over most of the angles analyzed.ConclusionPerforming longer RD could be a more appropriate strategy to provide greater gains in isometric maximal muscle strength at shortened knee positions. However, similar maximum dynamic strength and muscle hypertrophy gains would be provided by protocols with different RD.

Effects Of Lactate Infusion On Resistance Exericse Induced MTORC1-signaling And Protein Synthesis In Human Muscle

Lactate has recently been highlighted as a potential signaling molecule. In myotubes, lactate incubation increase mTORC1-signaling, reduce myostatin expression and induce myotube growth. This indicates that lactate could be a potential mediator of muscle adaptations to resistance exercise. PURPOSE: Here we wanted to study the acute molecular response in human skeletal muscle to resistance exercise performed with our without a venous infusion of lactate. The primary outcomes of the study was intracellular signaling, rate of protein synthesis (FSR) and blood/muscle levels of lactate and pH. METHODS: 16 healthy females and males participated in the study which consisted of two resistance exercise sessions performed under venous infusion of sodium lactate or saline, in a randomized, blinded and counterbalanced fashion. In the overnight fasted state infusion was employed during ~60 min of rest and unilateral knee-extension exercise. Blood was sampled repeatedly during trials and muscle biopsies were collected at rest and at 0, 90, 180 min and 24 h after exercise. Oral D2O ingestion was used to determine FSR during 24 h of recovery. RESULTS: With saline, blood lactate levels reached 3.0 mmol/l post exercise, while lactate infusion resulted in 130% greater lactate levels post exercise that also remained higher than at rest and saline up to 90 min of recovery. Post exercise muscle levels of lactate were 20% higher with lactate compared to saline infusion (32 vs 27 mmol/kg d.w). Lactate infusion had an alkalizing effect in blood with pH being 7.44 after exercise with lactate and 7.34 with saline. This effect was not noted in muscle were pH was reduced by 0.06 units after exercise in both trials. Exercise increased the phosphorylation of mTORS2448 (~40%), S6K1T389 (~3-fold) and S6S240/244 (~9-fold) during recovery, without any differences between trials. Effects of exercise without any influence of lactate infusion was also noted for eEF2T56, AMPKT172, PRAS40T246 and p44T202/T204. FSR over 24h of recovery did not differ between saline (0.067 %/h) and lactate infusion (0.060 %/h). CONCLUSIONS: In this model blood lactate levels did not modulate resistance exercise induced mTORC1-signaling or FSR. As only small differences were noted for muscle levels of lactate, its potential role as signaling molecule should not be discarded.

Discomfort And Ratings Of Perceived Exertion To Practical Vs. Traditional Blood Flow Restriction Resistance Exercise

Elastic knee wraps are used to produce blood flow restriction (BFR) but it is unclear how discomfort and perceived exertion may compare to more traditional ways of producing BFR such as nylon cuffs where the pressure is known. PURPOSE: To investigate how elastic knee wraps (practical) compare in ratings of perceived exertion (RPE) and discomfort after exercising to failure when compared to nylon cuffs (traditional) or low and high loads without BFR. METHODS: Nine participants (male=7, female=2) completed this study. The average age and body mass index were 22 (4) years and 25.4 (1.5) kg/m2. Each participant completed six conditions, in a randomized order, of unilateral knee extension exercise to failure for four sets. Two conditions (30% one-repetition maximum, 1-RM) included elastic knee wraps that were either stretched by two inches from resting length (Practical-Low) or they were stretched to a new length that was 85% of the thigh circumference (Practical-High). Two more conditions (30%-1RM) used nylon cuffs that were inflated to either 80% (BFR-High) or 40% (BFR-Low) of arterial occlusion pressure. The last two conditions had no restriction stimulus and were 30% 1-RM (LL) or 70% 1-RM (HL). Discomfort (0-10) and RPE (6-20) were measured before exercise and at the end of the four sets. The change scores from before exercise to the end of set 4 were used for analysis. Friedman’s test and Conover’s post hoc test were used to determine if there was a difference in discomfort and RPE between conditions. Statistical significance was set at p<0.05. RESULTS: Practical-High had larger changes in discomfort compared to HL (8 vs 6, p=0.007) and LL (8 vs 6, p=0.018). Practical-Low had a smaller change in discomfort compared to BFR-High (7 vs. 9, p=0.028) but it was not different from BFR-Low (7 vs. 7, p=0.450). No differences were found between Practical-High vs. BFR-High (8 vs. 9, p=0.211) or Practical-High vs. BFR-Low (8 vs 7, p=0.316). Practical-Low had smaller changes in RPE compared to BFR-High (12 vs 11, p=0.024) but there was no difference in RPE between Practical-High and the other conditions (p>0.05). CONCLUSIONS: When exercising to failure, both discomfort and RPE are impacted by the pressure used and elastic knee wraps can produce changes in discomfort and RPE levels that are comparable to high pressure BFR.

Muscle Swelling Following Low Load Blood Flow Restriction Exercise Does Not Differ Between Cuff Widths In The Lower Body

Acute muscle swelling is a purported mechanism for muscle hypertrophy following blood flow restriction (BFR) training. Currently there are numerous cuff widths used within the lower body BFR literature. However, studies suggest that growth may be attenuated with a wider cuff. Whether this is related to a differential acute swelling response has not been previously shown. PURPOSE: To examine the acute changes in muscle swelling following low load BFR exercise in the lower body, in response to different cuff widths inflated to the same relative pressure. METHODS: Ninety-six (43 men, 53 women) participants completed two conditions (one each leg). Participants completed four sets of unilateral knee extension exercise to failure using 30% of their one repetition maximum (1RM) with BFR applied with either a narrow (5 cm) or a wide (12 cm) cuff inflated to 40% of their arterial occlusion pressure. Muscle thickness and echo intensity were measured at two sites (proximal and distal) before and after each exercise bout as surrogate markers of swelling. A repeated measures analysis with a between subject factor of sex was used to assess changes. Bayes Factors (BF10) were used to quantify evidence. RESULTS: The difference in acute changes in muscle thickness (BF10: 0.43) and echo intensity (BF10: 0.87) between cuff widths was not different between the proximal (i.e. wide cuff covered this site) and distal (no cuff was over this site) location. Further, changes in muscle thickness at the proximal [5cm: 0.58 cm vs. 12 cm: 0.57 cm; median difference (95% credible interval) of 0.009 (-0.04, 0.06) cm] and distal [5 cm: 0.63 cm vs. 12 cm: 0.63 cm; median difference (95% credible interval) of 0.00002 (-0.03, 0.04) cm] site did not differ based on cuff width or sex (Men: 0.58 cm vs. Women: 0.57 cm and Men: 0.64 cm vs. Women: 0.63 cm for proximal and distal sites, respectively). Echo intensity appeared to decrease at the proximal and distal sites with no differences between cuff widths. However, there was some evidence that this change at the distal site may be different between sexes [BF10: 49.8; Men: -1.9 vs. Women: -4.2 AU). CONCLUSIONS: Acute muscle swelling occurs in men and women, even when using a wider cuff. Thus, if there is to be attenuation in growth with a wider cuff, it is unlikely to be due to differences in acute swelling.

Lighter-Load Exercise Produces Greater Acute- and Prolonged-Fatigue in Exercised and Non-Exercised Limbs

ABSTRACT Purpose: The present study compared the fatigue and perceptual responses to volume-load matched heavier- and lighter- load resistance exercise to momentary failure in both a local/exercised, and non-local/non-exercised limb. Methods: Eleven resistance-trained men undertook unilateral maximal voluntary contraction (MVC) testing for knee extension prior to and immediately, 24 hr- and 48 hr- post heavier (80% MVC) and lighter (40% MVC) load dynamic unilateral knee extension exercise. Only the dominant leg of each participant was exercised to momentary failure using heavier and lighter loads, and perceptions of discomfort were measured immediately upon exercise cessation. Results: Point estimates and confidence intervals suggested that immediately post-exercise there was greater fatigue in both the exercised and non-exercised legs for the lighter- load condition. At 24 hr the exercised leg under the heavier-load condition had recovered to pre-exercise strength; however, the exercised leg under lighter- load condition had still not fully recovered by 48 hr. For the non-exercised leg, only the lighter-load condition induced fatigue; however, recovery had occurred by 48 hr. Median discomfort ratings were statistically significantly different (Z = −2.232, p = .026) between lighter and heavier loads (10 [IQR = 0] and 8 [IQR = 3], respectively). Conclusions: This study suggests that lighter-load resistance exercise induces greater fatigue in both the exercised- and non-exercised limbs, compared to heavier-load resistance exercise. These findings may have implications for exercise frequency as it may be possible to engage in heavier-load resistance exercise more frequently than a volume-load matched protocol using lighter loads.Abbreviations CI: Confidence intervals: ES: Effect size: MVC: Maximum voluntary contraction; Nm:Newton meters; RM: Repetition maximum; SD: Standard deviation; SI: Strength index

Acute responses of comprehensive gonadosteroids and corticosteroids to resistance exercise before and after 10weeks of supervised strength training.

What is the central question of this study? Although acute responses of the principal gonadosteroid and corticosteroid hormones to resistance exercise are well documented, there is no information regarding how the key lower-concentration intermediary hormones respond and potentially influence these hormonal pathways. What is the main finding and its importance? This study provides evidence for cascading conversions of some gonadosteroids, and the data suggest that the testosterone concentration increases independently of these hormones. These findings challenge future studies to determine the exact physiological roles of the lower-concentration gonadosteroids and corticosteroids during and immediately after resistance exercise. Resistance training is a potent stimulus for muscle growth, and steroid hormones are known to play a role in this adaptation. However, very little is known about the acute exercise-induced gonadosteroid and corticosteroid hormone responses, including those of key lower-concentration intermediate hormones. The present study determined the acute responses of these steroid hormone families using quantitative ultra-high performance liquid chromatography tandem mass spectrometry after resistance exercise in strength-trained men. Venous and fingertip blood samples were obtained pre-, mid-, 5min post- and 15min post-resistance exercise, both before and after 10weeks of supervised resistance training. The experimental resistance exercise sessions consisted of three sets of 10 repetitions of bilateral leg-press exercise and three sets of 10 repetitions of unilateral knee-extension exercise, with 2 and 1min recovery between sets, respectively. Statistically significant (P<0.05) increases in the concentration of hormones in the gonadosteroid [including dehydroepiandrosterone (DHEA), androstenedione, testosterone and estrone] and the corticosteroid (including cortisol, corticosterone and cortisone) families were demonstrated after both experimental resistance exercise sessions, irrespective of training status. Correlation analyses revealed relationships between the following hormones: (i) DHEA and androstenedione; (ii) DHEA and cortisol; (iii) androstenedione and estrone; and (iv) 11-deoxycortisol and cortisol. Testosterone appears to increase acutely and independently of other intermediary hormones after resistance exercise. In conclusion, lower-concentration intermediary gonadosteroids (e.g. estrone) and corticosteroids (e.g. corticosterone) respond robustly to resistance exercise in strength-trained men, although it seems that testosterone concentrations are regulated by factors other than the availability of precursor hormones and changes in plasma volume.

Does the duration of static stretching acutely interferes on the strength endurance performance?

Background: Stretching may promote detrimental effects on power output and maximal strength, but its direct effect on strength endurance remains unclear, as well as the influence of stretching duration. Objective: We aimed to evaluate the direct effect of static stretching of the quadriceps muscle, as well as the stretching duration, on the strength endurance during a unilateral knee extension exercise. Methods: Fifteen strength-trained men (age 28 ± 3 years, height 1.70 ± 0.09 m, body mass 70 ± 5 kg, training experience 5 ± 1 years) took part in a randomized counterbalanced cross-over study. Participants' total number of repetitions was assessed during strength endurance tests (four sets until failure at 70% of one-repetition maximum) performed under three different conditions in separate days: control - no stretching (CON), short-duration stretching (SDS) and long-duration stretching (LDS). Three stretching exercises, with 3 sets lasting 30 seconds each, were performed during SDS, while the number of sets during LDS was doubled. Data were analyzed using mixed models and magnitude-based inferences (MBI). Results: Despite of a significant decrease in the number of repetitions during the strength endurance test performed across the exercise sets (main Set effect p < .001), neither the number of repetitions in each set (main Condition effect p = .95) nor the total number of repetitions (main Condition effect p = .86) were significantly different between the conditions. MBI analysis revealed that changes in the total number of repetitions after SDS and LDS were mainly trivial compared to CON. Conclusions: Regardless of its duration, an acute session of static stretching did not influence strength endurance.

Intramuscular inflammatory and resolving lipid profile responses to an acute bout of resistance exercise in men.

Lipid mediators including classical arachidonic acid‐derived eicosanoids (e.g. prostaglandins and leukotrienes) and more recently identified specialized pro‐resolving‐mediator metabolites of the omega‐3 fatty acids play essential roles in initiation, self‐limitation, and active resolution of acute inflammatory responses. In this study, we examined the bioactive lipid mediator profile of human skeletal muscle at rest and following acute resistance exercise. Twelve male subjects completed a single bout of maximal isokinetic unilateral knee extension exercise and muscle biopsies were taken from the m.vastus lateralis before and at 2, 4, and 24 h of recovery. Muscle tissue lipid mediator profile was analyzed via liquid chromatography–mass spectrometry (LC‐MS)‐based targeted lipidomics. At 2 h postexercise, there was an increased intramuscular abundance of cyclooxygenase (COX)‐derived thromboxanes (TXB 2: 3.33 fold) and prostaglandins (PGE 2: 2.52 fold and PGF 2α: 1.77 fold). Resistance exercise also transiently increased muscle concentrations of lipoxygenase (LOX) pathway‐derived leukotrienes (12‐Oxo LTB 4: 1.49 fold and 20‐COOH LTB 4: 2.91 fold), monohydroxy‐eicosatetraenoic acids (5‐HETE: 2.66 fold, 12‐HETE: 2.83 fold, and 15‐HETE: 1.69 fold) and monohydroxy‐docosahexaenoic acids (4‐HDoHE: 1.69 fold, 7‐HDoHE: 1.58 fold and 14‐HDoHE: 2.35 fold). Furthermore, the abundance of CYP pathway‐derived epoxy‐ and dihydroxy‐eicosatrienoic acids was increased in 2 h postexercise biopsies (5,6‐EpETrE: 2.48 fold, 11,12‐DiHETrE: 1.66 fold and 14,15‐DiHETrE: 2.23 fold). These data reveal a range of bioactive lipid mediators as present within human skeletal muscle tissue and demonstrate that acute resistance exercise transiently stimulates the local production of both proinflammatory eicosanoids and pathway markers in specialized proresolving mediator biosynthesis circuits.

Acute Muscular Responses to Practical vs. Traditional Blood Flow Restriction Resistance Exercise

PURPOSE: To compare the impact of blood flow restriction (BFR) resistance exercise on changes in muscular force output (MVC), muscle thickness (MTH) and total exercise volume (TEV) when using elastic knee wraps (practical) or nylon cuffs (traditional) inflated to 40 and 80% of arterial occlusion pressure (AOP). METHODS: Participants (male=7, female=2) were 22 (4) years and had a body mass index of 25.4 (1.5) kg/m2. A randomized cross-over study design used unilateral knee extension exercise (4 sets to failure) with six different conditions at three separate visits. Low-load (LL, 30% 1-RM) exercise was performed with four conditions: elastic knee wraps (Valeo ®) stretched two inches from resting length (K2) and to a value that was 85% of thigh circumference (K85), and nylon cuffs inflated to 40% (BFR40) and 80% (BFR80) of AOP. LL (30% of 1-RM) and high-load (HL, 70% of 1-RM) exercise without restriction were also performed. MVC and MTH were measured pre and post exercise. TEV was also calculated for each condition. Two-way [Condition x Time] repeated measures ANOVA and one-way repeated measures ANOVA were used to analyze the data. Data reported as mean (standard deviation). Statistical significance was set at p<0.05. RESULTS: MVC decreased from pre to post-exercise for all conditions [∆HL: -90 (81) N, ∆LL: -126 (57) N, ∆BFR40: -168 (89) N, ∆BFR80: -240 (134) N, ∆K2: -178 (91) N, ∆K85: -197 (57) N, p<0.05]. The changes in MVC were significantly different in K85 vs. HL (p<0.001) and K85 vs. LL (p=0.013). HL and BFR80 MVC at 15 minutes post-exercise were not different from pre-values (∆HL: -53 (68) N, p=0.095; ∆BFR80: -67 (77) N, p=0.138) but LL, BFR40, K2 and K85 were still significantly below pre-values (p<0.05). MTH changes were similar from pre to post-exercise [∆HL: 0.22 (0.22) cm, ∆LL: 0.26 (0.1) cm, ∆BFR40: 0.26 (0.14) cm, ∆BFR80: 0.28 (0.19) cm, ∆K2: 0.26 (0.21) cm, ∆K85: 0.25 (0.13) cm, p=0.892]. HL TEV was higher [889.6 (227.7) kg] compared to all the other conditions (p<0.05) while the LL [686.1 (173.1) kg] was higher than the BFR40 [576.8 (160.7) p=0.026], BFR80 [434.9 (142.3) kg, p<0.001] and K85 [520.2 (139.2) kg, p=0.023] conditions. CONCLUSIONS: Exercising to fatigue with elastic knee wraps could be used to produce similar acute changes in MVC, MTH and TEV compared to known BFR pressures.

Does the Expectancy on the Static Stretching Effect Interfere With Strength-Endurance Performance?

Bertolaccini, AL, da Silva, AA, Teixeira, EL, Schoenfeld, BJ, and de Salles Painelli, V. Does the expectancy on the static stretching effect interfere with strength-endurance performance? J Strength Cond Res 35(9): 2439-2443, 2021-Static stretching (SS) may interfere with strength performance. Such interference, however, may be partially attributed to the subjects' or researcher's expectancy about the SS effects. We aimed to examine whether the manipulation of subjects' expectancy of SS on force production could influence strength-endurance during unilateral knee extension exercise. Eighteen strength-trained men were randomly divided into positively biased (PB; N = 9) or negatively biased (N = 9) groups on the possible effects of SS on performance. Subjects' total number of repetitions and total volume of exercise were assessed during strength-endurance tests (4 sets performed to failure at 70% of 1 repetition maximum) performed under 2 different conditions on separate days: Control-no stretching (CON); or SS. Static stretching consisted of 3 sets of 3 stretching exercises, lasting 30 seconds each. Data were analyzed using mixed models. Neither the total number of repetitions nor the total volume was significantly different between the CON and SS conditions, nor for type of bias (all p > 0.05). However, the number of repetitions in the last set of exercise was greater during SS compared with CON for the PB group (p = 0.01). Although previous negative or positive information about SS did not interfere with the total number of repetitions and total volume of exercise, previous positive information about SS improved performance in the last set of exercise. Expectancy therefore may have played a partial role influencing strength-endurance in previous studies.

Tissue Oxygenation in Response to Different Relative Levels of Blood-Flow Restricted Exercise.

Blood flow restrictive (BFR) exercise elicits a localized hypoxic environment compatible with greater metabolic stress. We intended to compare the acute changes in muscle microvascular oxygenation following low-intensity knee extension exercise, combined with different levels of BFR. Thirteen active young men (age: 23.8 ± 5.4 years) were tested for unilateral knee extension exercise (30 + 15 + 15 + 15 reps at 20% one repetition maximum) on four different conditions: no-BFR (NOBFR), 40, 60, and 80% of arterial occlusion pressure (AOP). Deoxyhemoglobin+myoglobin concentration Deoxy[Hb+Mb], total hemoglobin [T(H+Mb)] and tissue oxygen saturation [TOI] were measured on the vastus lateralis muscle using near-infrared spectroscopy (NIMO, Nirox srl, Brescia, Italy). The magnitude of change in Deoxy[Hb+Mb]during exercise was similar between 60 and 80% AOP. Overall, compared to that seen during 60 and 80% AOP, NOBFR as well as 40% AOP resulted in a lower magnitude of change in Deoxy[Hb+Mb] (p < 0.05). While the oxygen extraction decreased during each inter-set resting interval in NOBFR and 40% AOP, this was not the case for 60 or 80% AOP. Additionally, TOI values obtained during recovery from each set of exercise were similarly affected by all conditions. Finally, our data also show that, when performed at higher restrictive values (60 and 80%), BFR exercise increases total Deoxy[Hb+Mb] extraction (p < 0.05). Taken together, we provide evidence that BFR is effective for increasing deoxygenation and reducing tissue oxygenation during low-intensity exercise. We also showed that when using low loads, a relative pressure above 40% of the AOP at rest is required to elicit changes in microvascular oxygenation compared with the same exercise with unrestricted conditions.

PL - 035 Effects of lactate infusion on the molecular response to resistance exercise in men and women

PL - 035 Effects of lactate infusion on the molecular response to resistance exercise in men and women

Improvement of Lower-Body Resistance-Exercise Performance With Blood-Flow RestrictionFollowing Acute Caffeine Intake.

To examine the effects of acute caffeine (CAF) intake on physical performance in 3 sets of unilateral knee extensions with blood-flow restriction. In a double-blind crossover design, 22 trained men ingested 6mg·kg-1 of CAF or a placebo (PLA), 1 h prior to performing unilateral knee-extension exercise with blood-flow restriction until exhaustion (30% of 1 maximal repetition). There was a significant difference in the number of repetitions between the CAF and PLA conditions in the first set (28.3 [5.3] vs 23.7 [3.2]; P = .005), second set (11.6 [3.1] vs 8.9 [2.9]; P = .03), and total repetitions performed across the 3 sets (44.5 [9.4] vs 35.0 [6.6]; P = .001). Blood lactate was also significantly different (P = .03) after exercise between the CAF (7.8 [1.1]mmol·L-1) and PLA (6.0 [0.9]mmol·L-1). In regard to pain perception, there was a difference between the CAF and PLA in the second (6.9 [1.5] vs 8.4 [1.4]; P = .04) and third sets (8.7 [0.4] vs 9.5 [0.6]; P = .01). No differences were found for perceived effort. Acute caffeine intake increases performance and blood lactate concentration and reduces perception of pain in unilateral knee-extension exercise with blood-flow restriction.