Knee Extension Exercise Research Articles

The blood flow and vascular responses in dynamically exercising skeletal muscles evoked by combination of cold stimulation and voluntary apnea in humans.

We evaluated (1) the combined effects of cold stimulation and voluntary breath holding (apnea) on heart rate, blood pressure, blood flow and vascular responses in dynamically exercising muscles in humans, and (2) if some interactions exist between cold stimulation and apnea on the cardiovascular responses. Nine males and 1 female performed three trials entailing a dynamic two-legged knee extension exercise at a constant workload that elicited heart rates around 100 beats min-1. During the trials the participants performed either: (1) immersed their right hand into ice water maintained at 4°C (cold pressor test; CPT); (2) performed maximal-duration apnea; and (3) performed a combination of CPT and apnea. Leg blood flow (LBF) and cardiac output (CO) were measured simultaneously using two Doppler ultrasound systems. CPT induced a rise in mean arterial pressure (MAP) (P < 0.05) but had no significant effect on CO or exercising leg vascular conductance (LVC). Apnea evoked large pressor responses, bradycardia and decreases in CO, LBF and LVC (all P < 0.05). The increase in MAP induced by combined CPT and apnea was smaller than the sum of those induced separately by CPT or apnea (P < 0.05). Combined CPT and apnea decreased LBF and LVC to a similar extent as apnea alone. Addition of local cold stimulation to apnea does not enhance pressor responses or vasoconstriction within active muscles. This suggests that maximum voluntary apnea evokes massive vasoconstriction, even within exercising muscles, which cannot be enhanced by additional sympathetic stimulation.

The Influence of Mental Fatigue on Physical Performance and Its Relationship with Rating Perceived Effort and Enjoyment in Older Adults

ABSTRACT The study investigated the influence of mental fatigue on older people’s enjoyment during a series of physical exercises. Using a randomized cross-over design, participants (n = 35) completed a 6-minute walking test − 6MWT, a Timed Up and Go—TUG test and three sets of knee extension exercise (first set: KE1, second set: KE2, third set: KE3) under two experimental conditions (control or mental fatigue). The Nonparametric Analysis of Longitudinal Data in Factorial Experiments was used to compare the number of repetitions performed during three sets of resistance exercise between conditions. The same analysis method was applied to compare the perception of effort and enjoyment across five moments (Post-6MWT, Post-TUG, Post-KE1, Post-KE2, Post-KE3) and two conditions and the Visual Analogue Scales (VAS) across four moments (baseline, Pre-6MWT, Pre-TUG, Pre-KE) and two conditions. Mental fatigue did not affect the physical function, perception of effort and enjoyment of exercise in older people. Participants, however, reported higher enjoyment for walking and dynamic balance compared to strength exercise. Mental fatigue had no effect on the physical function, perception of effort and enjoyment of exercise of older people. Participants presented a higher enjoyment for walking and dynamic balance compared to strength exercise. Given the importance of resistance exercises for health, clinicians should prioritize resources to education programs emphasizing the benefits of resistance exercise in both short- and long-term health. Including social interaction opportunities in physical exercise programs and prescribing activities appropriate to participants’ ability levels could enhance engagement and adherence.

Impact of Quadriceps Muscle Fatigue on Ankle Joint Compensation Strategies During Single-Leg Vertical Jump Landing.

This study investigates the impact of quadriceps fatigue on lower limb biomechanics during the landing phase of a single-leg vertical jump (SLJ) in 25 amateur male basketball players from Ningbo University. Fatigue was induced through single-leg knee flexion and extension exercises until task failure. Kinematic and dynamic data were collected pre-fatigue (PRF) and post-fatigue (POF) using the Vicon motion capture system and the AMTI force platform and analyzed using an OpenSim musculoskeletal model. Paired sample t-tests revealed significant changes in knee and hip biomechanics under different fatigue conditions, with knee joint angle (p < 0.001), velocity (p = 0.006), moment (p = 0.006), and power (p = 0.036) showing significant alterations. Hip joint angle (p = 0.002), moment (p = 0.033), and power (p < 0.001) also exhibited significant changes. Muscle activation and joint power were significantly higher in the POF condition, while joint stiffness was lower. These findings suggest that quadriceps fatigue leads to biomechanical adjustments in the knee and hip joints, which may increase the risk of injury despite aiding in landing stability.

Acute Changes in Myocardial Work during Isometric Exercise in Hypertensive Patients with Ischemic Heart Disease: A Case-Control Study.

Background: The acute hemodynamic response to isometric exercise in hypertensive patients' ischemic heart disease (IHD) has been poorly investigated. The aim of this study was to assess acute changes in left ventricular myocardial work (MW) during isometric bilateral knee extension in patients with IHD. Methods: Twenty stable hypertensive patients with IHD and ten healthy, age-matched controls (HC) were enrolled. All subjects performed an isometric knee extension exercise at 30% of their maximal voluntary contraction. The effort was maintained for three minutes or until exhaustion. At baseline, at peak exercise, and after 10 min of recovery, echocardiography evaluation was performed and blood pressure (BP) and heart rate (HR) were measured. Results: The exercise was well tolerated by all subjects. At peak exercise, systolic BP in the IHD was significantly higher than HC (37.6 ± 7.2 vs. 8.4 ± 2.3 mmHg; p 0.002). The HC group had a greater increase in HR than IHD (19.7 ± 6.2 vs. 8.4 ± 2.2 bpm; p 0.009). The E/E' ratio increased in IHD and was unchanged in the control group. The global work index increased significantly in IHD compared to HC (+15% vs. +3%; p 0.026). Global constructive work increased significantly in IHD compared to HC (+29.8% vs. +7.4 respectively, p 0.031). Global wasted work increased by 92.3% in IHD and was unchanged in HC. The global work efficiency decreased in IHD (-18%), but was unchanged in HC (between-groups p 0.019). Stroke volume decreased in IHD and was unchanged in HC. Cardiac output was unchanged in IHD, while it increased in HC. Conclusion: In patients with hypertension and underlying IHD, an acute isometric load causes a great increase in systolic BP and LV filling pressure. It follows a mostly ineffective increase in MW that fails to maintain stroke volume.

Fast Competitive Swimmers Demonstrate a Diminished Diving Reflex.

Competitive swimmers complete 50-m front crawl swimming without breathing or with a limited number of breaths. Breath holding during exercise can trigger diving reflex including bradycardia and diminished active muscle blood flow, whereas oxygen supply to vital organ such as brain is maintained. We hypothesized that swimmers achieving faster time in 50-m front crawl with limited number of breaths demonstrate a blunted diving reflex of cardiac and active muscle blood flow responses with elevated cerebral perfusion to counteract peripheral and central fatigues. Twenty-eight competitive swimmers (12 females) underwent a 50-m front crawl swimming time trial with minimum respiratory interruptions, following which they were categorized into two groups: Fast (n = 13) and Slow (n = 15). Additionally, they performed knee extension exercises with maximal voluntary breath- holding, wherein leg blood flow (Doppler ultrasound), cardiac output (Modelflow), heart rate (electrocardiogram), and middle cerebral artery mean blood velocity (transcranial Doppler ultrasound) were evaluated. The pattern of leg blood flow response differed between the two groups (p = 0.031) with the Fast group experiencing a delayed onset of reductions in leg blood flow (p = 0.035). The onset of bradycardia was also delayed in the Fast group (p = 0.014), with this group demonstrating a higher value of the lowest heart rate (between-trial difference in average: 15.9 [3.73, 28.2] beats/min) and cardiac output (between-trial difference in median: 2.84 L/min) (both, p ≤ 0.013). Middle cerebral artery mean blood velocity was similar between the groups (all p ≥ 0.112). We show that swimmers with superior performance in 50-m front crawl swim with limited breaths display a diminished diving reflex.

Acute Effect Of Knee Extension Exercise Protocol On Muscle Localized Phase Angle Among Young Women

Acute Effect Of Knee Extension Exercise Protocol On Muscle Localized Phase Angle Among Young Women

Differential contribution of elbow flexion and knee extension on vascular and hemodynamic parameters and arterial stiffness indices after acute strength exercise in young adults

BackgroundDifferent types of exercise, performed acutely or chronically, have different repercussions on central hemodynamics, arterial stiffness, and cardiac function. In this study, we aim to compare the effects of acute elbow flexion (EFlex) and knee extension (KExt) exercises on vascular and hemodynamic parameters and arterial stiffness indices in healthy young adults.MethodsYoung adults (20 to 39 years) underwent randomized muscle strength tests to obtain 1 repetition maximum (1RM) for elbow flexion (EFlex) and knee extension (KExt). After a minimum interval of 48 h, cardiovascular parameters were assessed using Mobil-O-Graph® (Mobil-O-Graph, IEM, Germany) at three-time points: at baseline (before exercise), immediately after elbow flexion or knee extension exercises with a load corresponding to 50% of 1RM (T0) and after 15 min of rest (T15).ResultsImmediately after exercise (T0), peripheral systolic blood pressure, peripheral pulse pressure, central systolic blood pressure, and central pulse pressure were significantly higher in KExt than EFlex (Δ 3.13; Δ 3.06; Δ 5.65; Δ 5.61 mmHg, respectively). Systolic volume, cardiac output, and cardiac index were significantly higher immediately after KExt when compared with EFlex (Δ 4.2 ml; Δ 0.27 ml/min and 0.14 l/min*1/m2, respectively). The reflection coefficient and the pulse wave velocity were also significantly higher at T0 in KExt compared to EFlex ( Δ 8.59 and Δ 0.12 m/sec, respectively).ConclusionOur results show differential contribution of muscle mass in vascular and hemodynamic parameters evaluated immediately after EFlex and KExt. In addition, our study showed for the first time that the reflection coefficient, an index that evaluates the magnitude of the reflected waves from the periphery, was only affected by KExt.

Implementation and Clinical Outcomes of Blood Flow Restriction Training on Adults With Cerebral Palsy: A Case Series.

Cerebral palsy (CP) is a congenital neurological disorder that causes musculoskeletal weakness and biomechanical dysfunctions. Strength training guidelines recommend at least 70% of 1-repetition maximum to increase muscle strength and mass. However, individuals with CP may not tolerate such high exercise intensity. Blood flow restriction (BFR) can induce similar gains in strength and muscle mass using loads as low as 20% to 30% 1-repetition maximum. This case series described the safety, feasibility, and acceptability of BFR in adults with CP and examined changes in muscle mass and strength. Three male participants with gross motor function classification system level 3 CP underwent strength training using a periodized 8-week BFR protocol. Outcomes included: Safety via blood pressure during and post-BFR exercises in addition to adverse event tracking; Feasibility via number of support people and time-duration of BFR exercises; Acceptability via rate of perceived discomfort (0-10) and qualitative interviews; Muscle Mass via ultrasonographic cross-sectional area of the quadriceps and hamstring; and Strength via (1) 3-repetition maximum in the leg press and knee extension, (2) isometric knee flexor and extensor muscle force measured with a hand-held dynamometer, and (3) 30-second sit-to-stand test. Participants replaced 2 exercises from their current regimen with seated knee extension and leg press exercises using progressively higher limb occlusion pressure and exercise intensity. Limb occlusion pressure started at 60%, by week 4 progressed to 80%, and then remained constant. The exercise repetition scheme progressed from fixed nonfailure repetition sets to failure-based repetition sets. Blood pressure never exceeded safety threshold, and no adverse events were reported. The BFR training was time-consuming and resource-intensive, but well-tolerated by participants (rate of perceived discomfort with a mean value of 5.8, 100% protocol adherence). Strength, as measured by 3-repetition maximum testing and 30-second sit-to-stand test, increased, but isometric muscle force and muscle mass changes were inconsistent. Blood flow restriction may be an effective means to increase strength in adults with CP who cannot tolerate high-intensity resistance training. Future research should compare BFR to traditional strength training and investigate mediators of strength changes in this population. for more insights from the authors (see the Video, Supplemental Digital Content available at: http://links.lww.com/JNPT/A473 ).

Identifying the Mechanisms of a Peripherally Limited Exercise Phenotype in Patients With Heart Failure With Preserved Ejection Fraction.

We identified peripherally limited patients using cardiopulmonary exercise testing and measured skeletal muscle oxygen transport and utilization during invasive single leg exercise testing to identify the mechanisms of the peripheral limitation. Forty-five patients with heart failure with preserved ejection fraction (70±7 years, 27 females) completed seated upright cardiopulmonary exercise testing and were defined as having a (1) peripheral limitation to exercise if cardiac output/oxygen consumption (VO2) was elevated (≥6) or 5 to 6 with a stroke volume reserve >50% (n=31) or (2) a central limitation to exercise if cardiac output/VO2 slope was ≤5 or 5 to 6 with stroke volume reserve <50% (n=14). Single leg knee extension exercise was used to quantify peak leg blood flow (Doppler ultrasound), arterial-to-venous oxygen content difference (femoral venous catheter), leg VO2, and muscle oxygen diffusive conductance. In a subset of participants (n=36), phosphocreatine recovery time was measured by magnetic resonance spectroscopy to determine skeletal muscle oxidative capacity. Peak VO2 during cardiopulmonary exercise testing was not different between groups (central: 13.9±5.7 versus peripheral: 12.0±3.1 mL/min per kg; P=0.135); however, the peripheral group had a lower peak arterial-to-venous oxygen content difference (central: 13.5±2.0 versus peripheral: 11.1±1.6 mLO2/dL blood; P<0.001). During single leg knee extension, there was no difference in peak leg VO2 (P=0.306), but the peripherally limited group had greater blood flow/VO2 ratio (P=0.024), lower arterial-to-venous oxygen content difference (central: 12.3±2.5 versus peripheral: 10.3±2.2 mLO2/dL blood; P=0.013), and lower muscle oxygen diffusive conductance (P=0.021). A difference in magnetic resonance spectroscopy-derived phosphocreatine recovery time was not detected (P=0.199). Peripherally limited patients with heart failure with preserved ejection fraction identified by cardiopulmonary exercise testing have impairments in oxygen transport and utilization at the level of the skeletal muscle quantified by invasive knee extension exercise testing, which includes an increased blood flow/V̇O2 ratio and poor muscle diffusive capacity. URL: https://www.clinicaltrials.gov; Unique identifier: NCT04068844.

Sixweeks of localized passive heat therapy elicits some exercise-like improvements in resistance artery function.

The purpose of this study was to examine the effects of 6weeks of localized, muscle-focused (quadriceps femoris) passive heat therapy (PHT) on resistance artery function, exercise haemodynamics and exercise performance relative to knee extension (KE) exercise training (EX). We randomized 34healthy adults (ages 18-36; n=17 female, 17male) to receive either PHT or sham heating sessions (120min, 3days/week), or EX (40min, 3days/week) over 6weeks. Blood flow was assessed with Doppler ultrasound of the femoral artery during both passive leg movement (PLM) and a KE graded exercise test. Muscle biopsies were taken from the vastus lateralis at baseline and after 6weeks. Peak blood flow during PLM increased to the same extent in both the EX (∼10.5% increase, P=0.009) and PHT groups (∼8.5% increase, P=0.044). Peak flow during knee extension exercise increased in EX (∼19%, P=0.005), but did not change in PHT (P=0.523) and decreased in SHAM (∼7%, P=0.020). Peak vascular conductance during KE increased by ∼25% in EX (P=0.030) and PHT (P=0.012). KE peak power increased in EX by ∼27% (P=0.001) but did not significantly change in PHT and SHAM groups. Expression of endothelial nitric oxide synthase increased significantly in both EX (P=0.028) and PHT (P=0.0095), but only EX resulted in increased angiogenesis. In conclusion, 6weeks of localized PHT improved resistance artery function at rest and during exercise to the same extent as exercise training but did not yield significant improvements in performance. KEY POINTS: Many for whom exercise would be most beneficial are either unable to exercise or have a very low exercise tolerance. In these cases, an alternative treatment to combat declines in resistance artery function is needed. We tested the hypothesis that passive heat therapy (PHT) would increase resistance artery function, improve exercise haemodynamics and enhance exercise performance compared to a sham treatment, but less than aerobic exercise training. This report shows that 6weeks of localized PHT improved resistance artery function at rest and during exercise to the same extent as exercise training but did not improve exercise performance. Additionally, muscle biopsy analyses revealed that endothelial nitric oxide synthase expression increased in both PHT and exercise training groups, but only exercise resulted in increased angiogenesis. Our data demonstrate the efficacy of applying passive heat as an alternative treatment to improve resistance artery function for those unable to receive the benefits of regular exercise.

A robot-based hybrid lower limb system for Assist-As-Needed rehabilitation of stroke patients: Technical evaluation and clinical feasibility

Background:Although early rehabilitation is important following a stroke, severely affected patients have limited options for intensive rehabilitation as they are often bedridden. To create a system for early rehabilitation of lower extremities in these patients, we combined the robotic manipulator ROBERT® with electromyography (EMG)-triggered functional electrical stimulation (FES) and developed a novel user-driven Assist-As-Needed (AAN) control. The method is based on a state machine able to detect user movement capability, assessed by the presence of an EMG-trigger and the movement velocity, and provide different levels of assistance as required by the patient (no support, FES only, and simultaneous FES and mechanical assistance). Methods:To technically validate the system, we tested 10 able-bodied participants who were instructed to perform specific behaviors to test the system states while conducting knee extension and ankle dorsal flexion exercises. The system was also tested on two stroke patients to establish its clinical feasibility. Results:The technical validation showed that the state machine correctly detected the participants’ behavior and activated the target AAN state in more than 96% of the exercise repetitions. The clinical feasibility test showed that the system successfully recognized the patients’ movement capacity and activated assistive states according to their needs providing the minimal level of support required to exercise successfully. Conclusions:The system was technically validated and preliminarily proved clinically feasible. The present study shows that the novel system can be used to deliver exercises with a high number of repetitions while engaging the participants’ residual capabilities through the AAN strategy.

Improving the neuromuscular fitness of patients with type 2 diabetes by aquatic exercise training - The Diabetes and Aquatic Training Study (DATS 3): a randomized controlled trial.

To compare the effects of aquatic aerobic and combined training on neuromuscular outcomes in patients with type 2 diabetes. Patients with type 2 diabetes were randomized to an aerobic aquatic training (AERO), a combined aquatic training (COMBI) or a procedure control (CON) three weekly for 15 weeks. The sessions were 50 minutes long. Maximal strength and muscle endurance were assessed by the 1RM and maximum repetitions at 60% 1RM tests, respectively, in knee extension and elbow flexion exercises. Timed up and go test, testosterone, cortisol and testosterone:cortisol ratio also were evaluated. Participants had 59.0±8.2 years, 51% women. All groups increased (P<0.001) the maximal knee extension strength (Mean Difference: AERO: 21.1 kg; COMBI: 14.6 kg; CON: 4.4 kg), while only COMBI group increased (P<0.001) the maximal elbow flexion strength (Mean Difference: 2.6 kg). Muscle endurance in both exercises were increased in all groups. The Timed Up and Go test at the usual and maximal speed decreased in all groups. Testosterone were not modified in present study, while cortisol and testosterone:cortisol were improved in COMBI group. Aquatic training, especially combined aquatic training, improve the neuromuscular fitness of patients with type 2 diabetes.

The effect of individualised post-exercise blood flow restriction on recovery following strenuous resistance exercise: A randomised controlled trial

ABSTRACT The purpose was to clarify the effect of individualised post-exercise blood flow restriction (PE-BFR) on measures of recovery following strenuous resistance exercise. Twenty resistance-trained adults were randomised to a PE-BFR or control (CON) group and completed a fatigue protocol of five sets of 10 repetitions of maximal intensity concentric and eccentric seated knee extension exercise. Participants then lied supine with cuffs applied to the upper thigh and intermittently inflated to 80% limb occlusion pressure (PE-BFR) or 20 mmHg (CON) for 30 min (3 × 5 min per leg). Peak torque (PT), time-to-peak torque (TTP), countermovement jump height (CMJ), muscle soreness (DOMS) and perceived recovery (PR) were measured pre-fatigue, immediately post-fatigue and at 1, 24, 48 and 72 h post-fatigue. Using a linear mixed-effect model, PE-BFR was found to have greater recovery of CMJ at 48 h (mean difference [MD]=-2.8, 95% confidence interval [CI] −5.1, 0.5, p = 0.019), lower DOMS at 48 (MD = 3.0, 95% CI 1.2, 4.9, p = 0.001) and 72 h (MD = 1.95, 95% CI −1.2, 1.5, p = 0.038) and higher PR scores at 24 (MD = −1.7, 95% CI −3.4, −0.1, p = 0.038), 48 (MD = −3.1, 95% CI −4.8, −1.5, p < 0.001) and 72 h (MD = −2.2, 95% CI −3.8, −0.5, p = 0.011). These findings suggest that individualised PE-BFR accelerates recovery after strenuous exercise.

α-Adrenergic regulation of skeletal muscle blood flow during exercise in patients with heart failure with preserved ejection fraction.

Heart failure with preserved ejection fraction (HFpEF) has been characterized by lower blood flow to exercising limbs and lower peak oxygen utilization ( ), possibly associated with disease-related changes in sympathetic (α-adrenergic) signaling. Thus, in seven patients with HFpEF (70±6years, 3 female/4 male) and seven controls (CON) (66±3years, 3 female/4 male), we examined changes (%Δ) in leg blood flow (LBF, Doppler ultrasound) and leg to intra-arterial infusion of phentolamine (PHEN, α-adrenergic antagonist) or phenylephrine (PE, α1-adrenergic agonist) at rest and during single-leg knee-extension exercise (0, 5 and 10W). At rest, the PHEN-induced increase in LBF was not different between groups, but PE-induced reductions in LBF were lower in HFpEF (-16%±4% vs. -26%±5%, HFpEF vs. CON; P<0.05). During exercise, the PHEN-induced increase in LBF was greater in HFpEF at 10W (16%±8% vs. 8%±5%; P<0.05). PHEN increased leg in HFpEF (10%±3%, 11%±6%, 15%±7% at 0, 5 and 10W; P<0.05) but not in controls (-1%±9%, -4%±2%, -1%±5%; P=0.24). The 'magnitude of sympatholysis' (PE-induced %Δ LBF at rest-PE-induced %Δ LBF during exercise) was lower in patients with HFpEF (-6%±4%, -6%±6%, -7%±5% vs. -13%±6%, -17%±5%, -20%±5% at 0, 5 and 10W; P<0.05) and was positively related to LBF, leg oxygen delivery, leg , and the PHEN-induced increase in LBF (P<0.05). Together, these data indicate that excessive α-adrenergic vasoconstriction restrains blood flow and limits of the exercising leg in patients with HFpEF, and is related to impaired functional sympatholysis in this patient group. KEY POINTS: Sympathetic (α-adrenergic)-mediated vasoconstriction is exaggerated during exercise in patients with heart failure with preserved ejection fraction (HFpEF), which may contribute to limitations of blood flow, oxygen delivery and oxygen utilization in the exercising muscle. The ability to adequately attenuate α1-adrenergic vasoconstriction (i.e. functional sympatholysis) within the vasculature of the exercising muscle is impaired in patients with HFpEF. These observations extend our current understanding of HFpEF pathophysiology by implicating excessive α-adrenergic restraint and impaired functional sympatholysis as important contributors to disease-related impairments in exercising muscle blood flow and oxygen utilization in these patients.

Pole placement tuning of proportional integral derivative feedback controller for knee extension model

Functional electrical stimulation (FES) has shown potential in rehabilitative exercises for patients recovering from spinal cord injuries. In recent developments, conventional open-loop FES control techniques have evolved into closed-loop systems that employ feedback controllers for automation. However, closed-loop FES systems often face challenges due to muscle non-linear effects, such as fatigue, time delays, stiffness, and spasticity. Therefore, an accurate non-linear knee model is required during the design stage, and precise tuning of the feedback controller parameters is vital. A proportional– integral–derivative (PID) controller is commonly used as a feedback controller due to its simplicity and ease of implementation. However, most PID tuning methods are complex and time consuming. This paper investigates the viability of employing the pole placement technique for tuning a PID controller that regulates the non-linear knee extension model. The pole placement method aims to improve the control and adaptability of the PID controller in closed-loop FES systems, specifically by facilitating knee extension exercises. MATLAB Simulink was used to assess the effectiveness of this tuning approach. Results showed that the PID controller performed satisfactorily without non-linearities, but performance varied with the inclusion of specific non-linearities. The pole placement tuning method facilitated preliminary assessments of PID controller performance, preceding highly advanced optimization.

Single-Joint Type Hybrid Assistive Limb for Knee Training in the Acute Postoperative Phase After Opening Wedge High Tibial Osteotomy: A Feasibility and Safety Trial.

Opening wedge high tibial osteotomy (OWHTO) influences the knee extensor mechanism, the range of passive motion of knee extension and persistent quadriceps, and anterior knee pain and weakness. Rehabilitation should focus on quadriceps strength and improving joint mobility. The single-joint hybrid assistive limb device (HAL-SJ) is a wearable exoskeleton cyborg. In this study, we investigated the feasibility and safety of HAL-SJ training after the early postoperative period following OWHTO and whether the use of this device can improve functional outcomes, including knee muscle extensor strength and knee extension range of motion without knee pain. Patients who had been diagnosed with knee osteoarthritis and had undergone OWHTO were assessed for eligibility in this prospective trial conducted at our institution between June 2015 and November 2020. The participants were split into two groups, i.e., 10 patients in the hybrid assistive limb (HAL) group and eight patients in the control group. We initiated HAL-SJ therapy on postoperative day 8 and continued it until the patient's discharge. During the hospitalization period, patients engaged in HAL-SJ-assisted knee extension exercises. This exercise routine encompassed five sets, each comprising 10 repetitions, and was conducted twice a week. We conducted assessments aimed at detecting any potential adverse events that could be linked to HAL training. Assessment of the knee extension angle via the visual analog scale (VAS) and strength assessments using a hand-held dynamometer (HHD) were conducted. To compare clinical outcomes before and after OWHTO, knee extension angle, the VAS, HHD, Japanese Orthopaedics Association (JOA) score, and the Japanese Knee Osteoarthritis Measure (JKOM) were assessed at four distinct time points. No adverse events were observed during the study. The assessment of clinical outcomes before and after OWHTO demonstrated a gradual improvement in outcomes. The single-joint hybrid assistive limb device in patients who underwent OWHTO appears to be potentially safe. It contributed to enhanced muscle activity efficiency by reducing knee pain and improving knee extension angles in the early postoperative phase.

Differences in knee flexor and extensor force and kinematic variables in rural versus urban area female students in Romania.

The study aimed to identify and explain the typical differences in low-intensity high-volume resistance training (LIHV-RT) performances for major muscle groups between rural versus urban young female students to establish the relevant set of quantitative and qualitative resistance training parameters. The study sample included 46 recreational active female students at the Transilvania University of Brașov, (mean ± SD age, 20 ± 1year; body mass, 60 ± 3kg; height, 160 ± 4cm) grouped urban vs. rural. The study used modified resistance exercise machines for the hamstring- and quadricep-group muscles, equipped with a dynamometer and sensors for identifying developed forces and accelerations. A number of 368 tests were performed, representing two attempts for each subject, for knee flexion and knee extension exercises, with two different loads. For the performance analysis some variables were considered: the maximum number of repetition until failure, maximum force developed, maximum acceleration, the duration of the set and the mean time per repetition. The maximum number of repetition to failure shows a significant higher value for rural than urban in case of knee flexion (d = 0.98 [0.32, 1.54] for load 1(L1) and d = 0.65 [0.03, 1.21] for load 2(L2)) and in case of knee extension (d = 1.89 [1.11, 2.48] for L1 and d = 1.67 [0.92, 2.25] for L2). The total duration of the sets shows a significant higher value for rural than urban in case of knee flexion (d = 0.84 [0.19, 1.39] for L2) and in case of knee extension (d = 1.46 [0.74, 2.03] for L1 and d = 1.56 [0.98, 2.14] for L2). Additionally we found differences in the quality of the relevant repetitions execution and in the impulse developed during the LIHV- MNRF sets. The study's main finding was that there are differences in LIHV-RT performances knee flexion and knee extension antagonistic exercises, between rural and urban female students. We concluded that the obtained results allow teachers to understand the optimal design of RT programs for the different groups of participants, in order to adapt their teaching techniques so that their final objectives are achieved, insisting on particular aspects of the theoretical or practical contents.

Passive Heat Stress, Like Exercise Training, Leads to Improved Vascular Function

Epidemiological data indicate that repeated heat stress improves cardiovascular health, making passive heat therapy (PHT) a potential alternative for those unable to exercise. Few studies to date have examined the potential exercise mimetic effects in humans, and it is unclear how adaptations compare in magnitude to exercise training. OBJECTIVE: To examine the effects of 6 weeks of localized, muscle-focused PHT on resistance artery vascular function, exercise hemodynamics and performance, molecular regulators of vascular tone, and skeletal muscle capillarization relative to the adaptations observed following high-intensity aerobic exercise training focused on the same muscles. HYPOTHESIS: 6 weeks of PHT, applied to the knee extensor muscles through pulsed shortwave diathermy (2 hr, 3 days/week), would improve both resistance artery function and exercise hemodynamics, as well as increase vascular tone regulators more than a sham treatment, but less than single-leg knee extension (KE) exercise training (EX; 40 min, 3 days/week). Methods: We randomized 34 sedentary but otherwise healthy, young adults (ages 18–36; n = 17 female, 17 male) to receive PHT, EX, or sham heating sessions (SHAM; 2 hr, 3 days/week) over 6 weeks. Vascular function was determined through the blood flow response during both a passive leg movement (PLM) assessment and a knee extension graded exercise test (GXTmax). Muscle biopsies were taken from the vastus lateralis at baseline and after 6 weeks of intervention. Results: Peak blood flow during PLM increased to the same extent in both the EX (~10.5% increase, P=0.009) and PHT groups (~8.5% increase, P=0.044). KE peak flow increased in EX (~19%, P=0.005), but did not change in PHT (P=0.523) and decreased in SHAM (~7%, P=0.020). Peak vascular conductance during KE increased by ~25% in EX (P=0.030) and PHT (P=0.012). KE peak power increased in EX by ~27% (P=0.001) but did not significantly change in PHT (P=0.175) and SHAM groups (P=0.111). EX, but not PHT or SHAM, increased muscle capillary-to-fiber ratio (P = 0.0003), capillary density (P = 0.0428), and the Capillary to Fiber Perimeter Exchange Index (P = 0.0089). Protein expression of endothelial nitric oxide synthase (eNOS) increased significantly in both EX (P=0.0028) and PHT (P=0.0095), but only EX resulted in increased angiogenesis. CONCLUSIONS: 6 weeks of localized PHT, when applied to young healthy individuals, improved resistance artery function at rest and during exercise to the same extent as exercise training. Moreover, our data suggest that these PHT-induced improvements can be primarily attributed to increased expression of the regulators of vascular tone and not neo-angiogenesis. In conclusion, passive heat therapy mimics many, but not all the vascular benefits of exercise training. Funding for this study was provided by the Department of Exercise Sciences at Brigham Young University. 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.

Mast cell degranulation is greater when exposed to dialysate collected from exercising skeletal muscle

The effect of histamine is multifaceted and potentially triggers a broad range of cellular adaptations contributing to vascular function, cellular maintenance, metabolism, and inflammation. During exercise, histamine is released from skeletal muscle. This response and the subsequent actions of histamine appear important in obtaining many of the beneficial adaptations to exercise. Increases in exercising skeletal muscle histamine release, in part, occur due to mast cell degranulation. However, the direct effect of exercise on mast cell degranulation has yet to be elucidated. To that end, this preliminary study aimed to quantify in vitro mast cell degranulation when cells are exposed to dialysate taken from exercising and non-exercising skeletal muscle. We hypothesized that greater mast cell degranulation would occur when exposed to dialysate collected from exercising skeletal muscle compared to dialysate collected from non-exercising muscle. Ten subjects (5M/5F, age 26 ± 5 years, weight 76 ± 17 kg, height 168 ± 12 cm) completed 60 minutes of single-leg dynamic knee extension exercise. Prior to exercise, a microdialysis probe was inserted into the vastus lateralis of the exercising and non-exercising legs and perfused with saline at a rate of 5 uL/min. Dialysate was collected before and every 20 minutes during exercise and the subsequent one-hour recovery period. In the exercising skeletal muscle, mast cell degranulation (quantified via b-hexosaminidase release) was greater when exposed to dialysate during exercise versus dialysate collected pre-exercise (P &lt; 0.05). Compared to non-exercising leg dialysate, degranulation was greater for exercising leg dialysate taken between minutes 20 and 40 into exercise (20.6 ± 2.7% vs 15.8 ± 2.0%, P &lt; 0.05) and 40 and 60 into exercise (24.0 ± 2.6 % vs 15.0 ± 2.7 %, P &lt; 0.001) and remained greater for dialysate taken in the first 20 minutes of recovery (21.4 ± 2.8% vs 15.2 ± 3.0%, P &lt; 0.05). These data suggest that there is a soluble factor released from exercising skeletal muscle that causes mast cell degranulation in vitro. These preliminary findings establish a bioassay for further exploration of the identity of the soluble factor released from exercising skeletal muscle, which is responsible for mast cell degranulation in vivo. This research was supported in part by National Institutes of Health Grants AG072805 and HL115027. 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.

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&lt;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&lt;0.001). Controlling for MVC, BMI, peak torque/body weight, and quadricep fat &amp; 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.