Knee Extensor Research Articles

Neuromuscular Adaptations in Response to Disuse and Weight-Training Rehabilitation are Enhanced in Resistance Trained Individuals

INTRODUCTION: Lower-limb disuse from immobilization results in a decrease in muscle strength, volume, and function. However, muscle atrophy from disuse does not entirely account for the observed strength and functional declines. Additionally, prior engagement in resistance training (RT) has been linked to the preservation of muscular strength and neuromuscular function. Therefore, the purpose of this study was to assess the influence of a single-leg immobilization protocol, followed by structured RT rehabilitation protocol, on muscle strength, volume, and neural activation in healthy young adults with and without previous strength training experience. Methods: Participants (10 Trained (T): 8 men, 2 women; 11 Untrained (UT): 8 men, 3 women) underwent 2-weeks of left-knee immobilization at 90° knee-flexion with a hinged immobilizer knee-brace. Participants were given a pair of axillary crutches for ambulation during this time. Following immobilization, all participants underwent an 8-week structured RT rehabilitation protocol. Participants visited the laboratory for three testing sessions (baseline test on Day 0; post-immobilization at the end of week 2; and post-RT rehab at the end of week 10). Maximal knee extensor isometric strength at 45°was quantified using an isokinetic dynamometer (Biodex). Voluntary muscle activation was quantified as the root mean square (RMS) of the interference electromyography (EMG) signals derived from two indwelling fine-wire electrodes in the vastus-lateralis muscle. Additionally, a continuous wavelet transform (CWT) was performed on the EMG to determine amplitude versus frequency characteristics of the signals and how this amplitude varied with time in the 13-30 (beta) and 30-60 (piper) Hz bands. Mid-thigh muscle cross-sectional area (mCSA) and density were also quantified using peripheral quantitative computed tomography (pQCT) during all testing sessions. Results: The T group was significantly stronger (p=0.019), had greater muscle density (p=0.005) and mid-thigh mCSA (p<0.001) across all sessions when compared with the UT group. However, there were no significant time or interaction effects for strength or muscle density losses (p>0.05). While both groups demonstrated increased muscle activation across sessions (RMS: p=0.04; CWT: p=0.021), the T group demonstrated a greater increase in the neural drive from baseline to week 10 when compared with the UT group (RMS: p= 0.002; CWT: p=0.027). CONCLUSION: In younger adults with or without prior strength training experience, we find that losses in knee extensor isometric strength, muscle density, and mid-thigh mCSA are minimal following a 2-week immobilization protocol. However, certain neuromuscular adaptations during immobilization and following weight-training rehabilitation are enhanced to a greater degree in those with prior training, which is seemingly indicative of greater synchrony in descending cortical drive and motor unit recruitment. These latter findings warrant continued investigation using additional innovative methodologies (e.g., fMRI, TMS, etc.) for assessing the mechanisms underlying the effects of prehab protocols on neuromuscular adaptations. PGRF and Nix family foundation scholarship to Marina Meyer. 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.

Motor unit loss and neuromuscular junction degeneration precede clinically diagnosed sarcopenia

Background: Degeneration of motoneuron and neuromuscular junctions (NMJ) and loss of motor units (MUs) contribute to age-related muscle wasting and weakness, leading to sarcopenia. However, these features have not been adequately investigated in humans. This study aimed to compare neuromuscular system integrity and function across different stages of sarcopenia, with a particular focus on NMJ stability and MU properties. We hypothesized that progressive impairment of the neuromuscular system would be a hallmark of the progression of sarcopenia. Methods: We recruited 42 healthy young individuals (Y) (aged 25.98±4.6 yr; 57% females) and 88 older individuals (aged 75.9±4.7 yr; 55% females). The older group underwent a sarcopenia screening according to the revised guidelines of the European Working Group on Sarcopenia in Older People (EWGSOP2). In all groups, knee extensor muscle force was evaluated by isometric dynamometry, muscle size by ultrasound and MUP properties by intramuscular electromyography (iEMG). MU number estimate (iMUNE) was also obtained. Blood samples and muscle biopsies were collected to assess biomarkers of neuromuscular degeneration. Results: 39 older individuals were non-sarcopenic (NS), 31 pre-sarcopenic (PS) and 18 sarcopenic (S). A progressive decline in quadriceps force, cross-sectional area and appendicular lean mass was detected with the different stages of sarcopenia. Handgrip force and short physical performance battery (SPPB) scores were also progressively reduced. iEMG recordings showed increased near fiber segment jitter in NS, PS and S compared to the Y group, highlighting a decreased NMJ transmission stability. Elevated concentration of serum C-terminal agrin fragment and altered Cav3 protein expression further supported the finding of age-related NMJ instability in all the older groups. The iMUNE was lower in all older groups, confirming age-related loss of MUs. Motoneuron firing rate was decreased in S vs Y. Age-related increases in MU potential complexity were also observed. These observations were accompanied by increased muscle denervation and axonal damage, respectively, indicated by the increase in NCAM-positive fibres and the increase in serum concentration of neurofilament light chain. Notably, most of these MU and NMJ parameters did not differ in older individuals with or without sarcopenia. Conclusion: Alterations in MU properties, axonal damage, altered innervation profile and NMJ instability are signatures of neuromuscular system ageing. These neuromuscular impairments are accompanied by muscle atrophy and weakness, however, they appear to precede clinically diagnosed sarcopenia, as they are already detectable in older NS individuals. These are important parameters to monitor in order to counteract these impairments and slow down the onset and progression of sarcopenia. The present work was funded by the PRIN project ‘NeuAge’ (2017CBF8NJ_001) to MVN and MAP and the Milky Way Foundation, the Baxter Foundation and the Li Ka Shing Foundation to HMB. EM was supported by the Stanford Wu Tsai Human Performance Institute fellowship and Marie Skłodowska-Curie Actions postdoctoral fellowship. We also acknowledge co-funding from Next Generation EU to MVN, in the context of the National Recovery and Resilience Plan, Investment PE8 — Project Age-It: “Ageing Well in an Ageing Society”. This resource was co-financed by the Next Generation EU [DM 1557 11.10.2022]. The views and opinions expressed are only those of the authors and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. 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.

Targeted activation of Nrf2 prevents losses in leg muscle mass and strength during 2 weeks of immobilization in young adults

Introduction: Leg immobilization results in substantial losses in muscle mass and strength. Strategies aimed at minimizing these losses have proven largely ineffective. Elevated oxidative stress has been identified as a potential mechanism contributing to these losses. Therefore, we tested the hypothesis that PB125, an activator of Nrf2 (the master regulator of the endogenous antioxidant system), and MitoQ, a mitochondrial-targeted antioxidant, would decrease the deleterious effects of limb immobilization on muscle mass and strength. Methods: A double-blind, placebo-controlled trial was performed in a cohort of twenty young healthy adults (6M/14F, Age: 28±7 y; Height: 169±7 cm; Mass: 70±14 kg). Participants were randomized into either placebo (n=7), PB125 (n=6), or MitoQ (n=7). Supplementation and measures of physical activity using an accelerometer began 2 weeks prior to single leg immobilization and continued through 2 weeks of immobilization. Knee extensor muscle strength was tested before and after immobilization using isometric maximal voluntary contractions (MVC) and isokinetic contractions (120 and 60 degrees/s). Muscle mass was determined by MRI, and thigh lean muscle volume from image slices between the patellar tendon and gluteal muscle were assessed. Results: Physical activity, measured by steps per day, decreased by 55-65% during limb immobilization for all groups (p <0.05). Isometric muscle strength was significantly decreased following placebo (145±40 to 119±27 kg; p <0.05) and MitoQ (148±36 to 118±36 kg; p <0.05), but not PB125 (140±55 to 144±71 kg, p=0.7). Similarly, isokinetic muscle strength measured at 120 and 60 degrees/s was significantly decreased in placebo and MitoQ but preserved with PB125. Lean muscle volume in the immobilized limb significantly decreased by ~4% in placebo (p<0.05) and MitoQ (p<0.05) but was preserved with PB125 (p =0.55). Conclusions: Targeted activation of Nrf2 with PB125 preserved muscle mass and strength following 2 weeks of leg immobilization. In contrast, both placebo and MitoQ had no impact on immobilization-induced losses in muscle mass and strength. These findings provide novel evidence that targeting Nrf2 offsets the detrimental skeletal muscle effects of limb immobilization in young, healthy individuals. NIH-R01HL142603 and VA Merit-I01CX001999. 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.

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.

Anthropometric, neuromuscular, physiologic and training variables as determinants to laboratory cycling performance.

The goal of this study was to verify whether anthropometric, physiological and neuromuscular factors, as well as training characteristics, could predict cycling performance during maximal incremental and time-to-exhaustion tests. Twenty cyclists were evaluated: Anthropometric variables, knee extensor muscle activation and architecture, training history, and training volume were assessed. Second ventilatory threshold (VT<inf>2</inf>), maximal oxygen uptake (VO<inf>2MAX</inf>), and maximal power output (PO<inf>MAX</inf>) were assessed during the incremental test. Muscle architecture of the vastus lateralis (VL) and rectus femoris (RF) muscles was evaluated bilaterally to calculate the mean thighs' muscle thickness, pennation angle and fascicle length, at rest condition. After that, time-to-exhaustion test at PO<inf>MAX</inf> was performed. Muscle activation of the VL, RF and vastus medialis (VM) was evaluated of both legs. Cyclists' height (r2=0.37), experience time and training volume (r2=0.46) were predictors of PO<inf>MAX</inf> (P<0.02), while cadence (r2=0.30) was the only predictive variable for the time-to-exhaustion performance (P<0.01). These results suggest that training characteristics and experience are important when training for incremental cycling conditions, whereas cadence (and its determinant variables) should be looked at during maximal and exhaustive conditions.

AN INVESTIGATION OF SEX-BASED DIFFERENCES IN PHYSICAL AND PSYCHOLOGICAL RECOVERY, AND RETURN TO SPORT, FOLLOWING ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION

INTRODUCTION &amp; AIMS Despite the increasing rate of anterior cruciate ligament (ACL) tears and surgical reconstruction (ACLR), little is known about the post-operative recovery in males versus females. Understanding differences in the recovery between sexes will assist in better tailoring rehabilitation, return to sport (RTS) and counselling pathways. This study investigated sex-based differences in the physical and psychological recovery of both females and males after ACLR. METHODS This study recruited 104 patients (49 females, 55 males) undergoing ACLR. Patients were assessed pre-operatively and at 6, 12 and 24 months post-surgery, via patient-reported outcome measures (PROMs) including the International Knee Documentation Committee (IKDC) form, the Tegner Activity Scale (TAS) and the Anterior Cruciate Ligament Return to Sport after Injury (ACL-RSI) score. Patients embarked on an assessment of peak isokinetic knee extensor (PKET) and flexor (PKFT) torque and a 4-hop performance battery. Limb Symmetry Indices (LSIs) were calculated. The incidence of RTS was investigated. RESULTS All PROMs significantly improved (p&amp;lt;0.05), though females reported significantly lower ACL-RSI (p=0.002) and IKDC (p=0.007) scores. While no sex-based differences were observed in hop test LSIs, males demonstrated significantly higher mean LSIs for PKET at 6 (p=0.037) and 24 (0.047) months, and PKFT at 6 (p=0.007) and 12 (p=0.002) months. At 24-months post-surgery, a significantly greater (p=0.030) percentage of male patients had returned to pivoting sports. CONCLUSION This study demonstrates the disparity between sexes in physical and psychological recovery, as well as RTS status, in community-level patients undergoing ACLR. The development and implementation of enhanced post-operative patient-centered care may be warranted tailored to sex, encompassing rehabilitation, education, and counseling after ACLR to promote increased engagement in rehabilitation.

A RANDOMIZED CONTROLLED TRIAL EVALUATING AN ACCELERATED WEIGHT-BEARING REHABILITATION PATHWAY AFTER MATRIX-INDUCED AUTOLOGOUS CHONDROCYTE IMPLANTATION FOR SYMPTOMATIC KNEE CARTILAGE DEFECTS

INTRODUCTION &amp; AIMS Matrix-induced autologous chondrocyte implantation (MACI) has demonstrated encouraging outcomes in treating symptomatic knee cartilage lesions which, if untreated, can progress toward early osteoarthritis. Rehabilitation is imperative to optimize outcome, though has been traditionally conservative. This study investigated the long-term outcomes of an accelerated return to full weight bearing (WB) after MACI. METHODS This prospective randomized controlled trial (RCT) allocated 35 patients (37 knees) to a 6-week (n=18) or 8-week (n=19) return to full WB after MACI. Patients were evaluated pre-operatively and at 1, 2, 5 and ≥10 years, via patient-reported outcome measures (PROMs) including the Knee Osteoarthritis Outcome Score (KOOS). Single limb hop capacity and peak knee extensor and flexor torque were assessed, with limb symmetry indices (LSIs) calculated. Magnetic resonance imaging (MRI) evaluated repair tissue, while a validated MRI composite graft score was calculated. RESULTS While the 6-week WB group reported significantly better 1-year KOOS Quality of Life scores, no other differences (p&amp;gt;0.05) in PROMs existed. The peak knee extensor torque LSI significantly improved (p&amp;lt;0.0001) over time, with mean LSIs of 100.8 (6-week) and 99.1 (8-week) at ≥10 years. No group differences (p&amp;gt;0.05) were observed in hop LSIs. A non-significant decline (p&amp;gt;0.05) was observed for the MRI composite score from 1-year to final ≥10-year review and, apart from a significant group effect (p=0.028) for graft tissue intensity in favor of the 6-week group suggesting repair tissue more reflective of native cartilage, no other MRI-based differences (p&amp;gt;0.05) existed. At ≥10-years, no grafts on MRI had failed, though 3 patients (6-week n=1, 8-week n=2) had progressed toward knee arthroplasty. CONCLUSION The 6-week accelerated rehabilitation program provided comparable clinical and MRI-based outcomes beyond 10 years post-surgery, without jeopardizing the graft.

Relationships between nitric oxide biomarkers and physiological outcomes following dietary nitrate supplementation

Dietary nitrate (NO3−) supplementation can increase nitric oxide (NO) bioavailability, reduce blood pressure (BP) and improve muscle contractile function in humans. Plasma nitrite concentration (plasma [NO2−]) is the most oft-used biomarker of NO bioavailability. However, it is unclear which of several NO biomarkers (NO3−, NO2−, S-nitrosothiols (RSNOs)) in plasma, whole blood (WB), red blood cells (RBC) and skeletal muscle correlate with the physiological effects of acute and chronic dietary NO3− supplementation. Using a randomized, double-blind, crossover design, 12 participants (9 males) consumed NO3−-rich beetroot juice (BR) (∼12.8 mmol NO3−) and NO3−-depleted placebo beetroot juice (PL) acutely and then chronically (for two weeks). Biological samples were collected, resting BP was assessed, and 10 maximal voluntary isometric contractions of the knee extensors were performed at 2.5–3.5 h following supplement ingestion on day 1 and day 14. Diastolic BP was significantly lower in BR (−2 ± 3 mmHg, P = 0.03) compared to PL following acute supplementation, while the absolute rate of torque development (RTD) was significantly greater in BR at 0–30 ms (39 ± 57 N m s−1, P = 0.03) and 0–50 ms (79 ± 99 N m s−1, P = 0.02) compared to PL following two weeks supplementation. Greater WB [RSNOs] rather than plasma [NO2−] was correlated with lower diastolic BP (r = −0.68, P = 0.02) in BR compared to PL following acute supplementation, while greater skeletal muscle [NO3−] was correlated with greater RTD at 0–30 ms (r = 0.64, P=0.03) in BR compared to PL following chronic supplementation. We conclude that [RSNOs] in blood, and [NO3−] in skeletal muscle, are relevant biomarkers of NO bioavailability which are related to the reduction of BP and the enhanced muscle contractile function following dietary NO3− ingestion in humans.

Ischemic Conditioning Reduces Neuromuscular Fatigability During Dynamic Exercise Post Stroke

INTRODUCTION: In addition to baseline muscle weakness, stroke survivors often demonstrate increased neuromuscular fatigability (an acute exercise-induced reduction in power, hereafter referred to as fatigability), which limits endurance during functional tasks. Ischemic conditioning (IC) is a non-invasive and easy-to-administer intervention that can reduce fatigability in stroke survivors during a sustained isometric contraction of their paretic knee extensors. However, IC’s effects on fatigability during dynamic contractions are unknown, despite the greater relevance to everyday activities. Additionally, fatigability is known to be task specific. Thus, the purpose of this study was to quantify the effects of IC on fatigability (percent reduction in power) during dynamic contractions of the paretic knee extensors in stroke survivors. We hypothesized that fatigability would be less after a single session of IC versus IC-sham treatment in stroke survivors. Methods: Eight stroke survivors (66 ± 6 years of age, 6 male) performed 60 maximal voluntary concentric contractions (1 every 4 seconds) with their paretic knee extensors against a resistance of 30% of their maximal voluntary isometric contraction torque through a 60-degree range of motion after receiving a single session of IC and IC-sham treatment on two separate days. IC consisted of 5 sets of 5-minute upper thigh blood flow occlusion at 225 mmHg (25 mmHg for IC-sham) with 5 minutes of no occlusion between each set. The order of the 2 sessions was randomized. All participants visited the laboratory on a different day for functional measurements (Fugl-Meyer Assessment, 10-meter walk test, and 6-minute walk test). Reduction in power was calculated as the difference between the highest average power output from 5 consecutive contractions within the first 15 contractions and the average power output from the last 5 contractions. A paired t-test was used to compare if fatigability during dynamic exercise would differ between the 2 sessions after IC and IC-sham treatment. Pearson correlation was performed to determine the relationship between the difference in fatigability (after IC versus IC-sham treatment) and functional measurements. Results: After a single session of IC treatment, stroke survivors were less fatigable compared to IC-sham treatment (21.9 ± 19.2% power reduction vs. 29.4 ± 19.0%, p = 0.016). Improvement in fatigability after IC versus IC-sham treatment was positively correlated with Fugl-Meyer Assessment lower extremity motor score ( r = 0.82, p = 0.013). CONCLUSION: These preliminary results indicate that IC could serve as a potential intervention to reduce fatigability during dynamic exercise in stroke survivors, especially those who are mildly affected by stroke. Funding Source: American Heart Association Predoctoral Fellowship (903373, ZZ) and Eunice Kennedy Shriver National Institute of Child Health and Human Development R01 Grant (HD099340, AH &amp; MD). 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.

A RANDOMIZED CONTROLLED TRIAL INVESTIGATING PATIENT RECOVERY AFTER ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION UNDERTAKEN WITH A QUADRICEPS VERSUS HAMSTRINGS TENDON AUTOGRAFT

INTRODUCTION &amp; AIMS Anterior cruciate ligament (ACL) tears are common. However, a lack of high-quality evidence exists comparing different graft options in patients undergoing surgical reconstruction (ACLR). This randomized controlled trial (RCT) investigated the course of recovery in patients undergoing ACLR with either a quadriceps (QT) or hamstrings (HT) tendon autograft. METHODS This study randomized 112 patients to one of the two graft reconstruction cohorts (HT=55, QT=57), subsequently undergoing ACLR and a structured rehabilitation program. Patients were assessed pre-surgery and at 6 weeks and 3, 6, 12 and 24 months, with a range of patient-reported outcome measures (PROMs) including the International Knee Documentation Committee form (IKDC) and the Anterior Cruciate Ligament Return to Sport after Injury (ACL-RSI) score. Graft laxity, peak isokinetic knee extensor and flexor strength and a 6-hop performance battery were assessed. Limb Symmetry Indices (LSIs) were calculated. RESULTS All PROMs significantly improved (p&amp;lt;0.0001). Apart from the ACL-RSI score which was significantly better (p&amp;lt;0.05) in the HT group at 3, 6 and 12 months, no other group differences (p&amp;gt;0.05) were observed. No group differences (p=0.407) were observed for knee laxity. While the HT group demonstrated significantly greater (p&amp;lt;0.05) quadriceps strength LSIs at 6 and 12 months, the QT group demonstrated significantly greater (p&amp;lt;0.05) hamstrings strength LSIs at 6, 12 and 24 months. The HT group demonstrated significantly greater (p&amp;lt;0.05) LSIs for the single horizontal (6 months), lateral (6 and 12 months) and medial (6 months) hop tests. CONCLUSION The HT group reported a higher level of psychological readiness to return to sport, while demonstrating greater quadriceps strength (and hop test) LSIs. Greater hamstring strength LSIs were observed for the QT cohort. Longer-term review will continue to evaluate RTS and later-stage re-injury between the two graft constructs.

Repeated bout effect and muscle damage at variable eccentric exercise intensities in active young men: a longitudinal repeated measures investigation

Abstract Exercise-induced muscle damage (EIMD) and repeated bout effect (RBE) are widely researched across various populations and at various intensities. Despite the existence of vast literature, there is lack of comparison of low versus submaximal versus maximal intensity required for preconditioning. The aim of the study was to compare the muscle damage and RBE at various intensities of eccentric exercise in active young men. Thirty-six healthy, physically active men were recruited and randomly assigned to three different groups low-high (L-H, n = 12), submaximal-high (M-H, n = 12) and maximal-high (H-H, n = 12). All participants performed 2 exercise bouts separated by 14 days. L-H, M-H and H-H groups performed low (10% of 1RM), moderate (50% of 1RM) and high (90% of 1RM) intensity eccentric exercise for knee extensors, respectively, in the 1st bout followed by high (100% of 1RM) intensity in the second bout. Muscle soreness (SOR), thigh circumference (CIR), maximal voluntary isometric contraction (MVIC), range of motion (ROM) and blood lactate (Bl Lac) were measured before, immediately, at 24 h, at 48 h and at 72 h after exercise. A significant effect of time appeared for MVIC (), CIR (), ROM () and Bl Lac (). The bout × time interaction, as well as bout × time × group interaction was also found significant indicating changes in muscle strength and ROM. Circumference changed significantly with a significant bout × group interaction effect . SOR () was significant between the bouts. Therefore, exhibiting attenuation of muscle damage markers after the second bout. Findings of the present study showed that muscle damage was evident at all three intensities. Moreover, it was greater after moderate and high intensity as compared to low intensity eccentric exercise. RBE was elicited after three intensities indicating their role in preconditioning the muscles of active men.

A RANDOMIZED CONTROLLED TRIAL ASSESSING A BRACE-FREE AND ACCELERATED WEIGHT-BEARING PROTOCOL AFTER SURGICAL REPAIR OF ACUTE PROXIMAL HAMSTRING TENDON AVULSIONS

INTRODUCTION &amp; AIMS Proximal hamstring tendon avulsion from the ischial tuberosity is a significant injury, with surgical repair advocated. After surgery, limited data exists regarding the optimal rehabilitation regime with extensive variation in published protocols. This study investigated patient outcomes following a traditionally conservative (CR) versus accelerated (AR) rehabilitation regimen after proximal hamstring tendon repair. METHODS This prospective randomized controlled trial (RCT) allocated 50 patients undergoing proximal hamstring tendon repair to either a braced, partial weight-bearing rehabilitation regime (CR=25) or an accelerated, unbraced regime, that permitted full weight-bearing as tolerated (AR=25). Patients were evaluated pre-operatively and at 3, 6 and 12 months post-surgery, via patient-reported outcome measures (PROMs) including the Lower Extremity Functional Scale (LEFS), Perth Hamstring Assessment Tool (PHAT) and 12-item Short Form Health Survey (SF-12). The single (SHD), triple (THD) and triple crossover (TCHD) hop tests were assessed at 6 and 12 months, as was peak isometric hamstring strength and peak isokinetic knee extensor and flexor torque. RESULTS All PROMs improved (p&amp;gt;0.05) and, while the AR group reported a significantly better Physical Component Score for the SF-12 at 3 months (p=0.022), as well as a lower severity of hamstring pain at 12 months (p=0.032), there were no other group differences. Peak isometric hamstrings strength and peak isokinetic quadriceps and hamstrings torque symmetry were all comparable between groups (p&amp;gt;0.05). While the AR group demonstrated significantly better (p=0.009) limb symmetry for the THD at 6 months, no other hop test differences were seen between groups. Three re-injuries have been observed (CR=2, AR=1). CONCLUSION After proximal hamstring repair surgery, post-operative outcomes following an accelerated rehabilitation regimen were largely comparable to a traditionally conservative

THE EFFECTS OF DOWNHILL WALKING ON INSULIN SENSITIVITY, ARTERIAL HEALTH, MUSCLE STRENGTH AND FUNCTIONAL PHYSICAL FITNESS IN PEOPLE WITH TYPE 2 DIABETES MELLITUS

INTRODUCTION &amp; AIMS Exercise is effective in preventing and managing Type 2 Diabetes Mellitus (T2DM). However, a significant number of people do not exercise as they perceive exercise to be physically challenging. Eccentric exercise, a novel aerobic exercise modality is less metabolically demanding and has been shown to have positive effects on blood glucose levels, cardiovascular fitness, and muscle strength in healthy populations. This research was conducted to explore the impact of eccentric exercise, specifically downhill walking, on insulin sensitivity, arterial health, muscle strength, and physical functional fitness in individuals with T2DM. METHODS A 12-week randomised controlled trial was conducted to investigate the effects of downhill, level, and uphill walking on people with T2DM. Sedentary adult participants with T2DM were randomised to perform downhill walking (DW), level walking (LW), or uphill walking (UW) for 30 minutes twice a week for twelve weeks at a standard speed of 2.5km/hr. The primary outcome measure was glycosylated haemoglobin (HbA1c), while secondary measures included arterial stiffness, strength, and physical fitness. RESULTS A significant reduction in HbA1c between baseline and 12 weeks was observed in the UW group However, per-protocol analysis showed a significant decrease in HbA1c in the DW group post-intervention as well. Central Systolic blood pressure significantly decreased between baseline and post-intervention in the DW group. Participants in DW group and UW group showed significant improvements in distance walked in 6MWT post-intervention. A significant increase in knee extensors isometric strength between baseline and 12 weeks was observed for the DW group only. CONCLUSION DW was as effective as UW for improving insulin sensitivity and more effective than LW and UW for improving central systolic blood pressure, muscle strength and functional physical fitness. DW is a viable option for those seeking a less demanding form of exercise.

Anterior-Posterior Center of Pressure Is Associated With Knee Extensor Moment During Landing After Anterior Cruciate Ligament Reconstruction.

A reduced knee extensor moment (KEM) in the involved limb and asymmetry in the KEM during landing tasks are observed after anterior cruciate ligament reconstruction (ACLR). There is limited information about the association of kinetic and kinematic parameters with the KEM during landing after ACLR. This study investigated the association of the anterior-posterior center of pressure (AP-COP) position, vertical ground reaction force (VGRF), and lower limb joint angles with the KEM during landing in female athletes following ACLR. Cross-sectional study. Twenty-two female athletes who underwent ACLR performed a drop vertical jump at 7.9 (1.7)months after surgery. We evaluated the KEM, AP-COP position, VGRF, and sagittal plane hip, knee, and ankle angles using a 3-dimensional motion analysis system with force plates. The peak KEM in the involved limb was significantly smaller than that in the uninvolved limb during landing (1.43 [0.33]N·m/kg/m vs 1.84 [0.41]Nm/kg/m, P = .001). The VGRF in the involved limb was significantly smaller than that in the uninvolved limb (11.9 [2.3]N/kg vs 14.6 [3.5]N/kg, P = .005). The limb symmetry index of the KEM was predicted by that of the VGRF (P < .001, R2 = .621, β = 0.800). The KEM was predicted by the AP-COP position in the involved limb (P = .015, R2 = .227, β = 0.513) and by the VGRF in the uninvolved limb (P = .018, R2 = .213, β = 0.500). No significant correlation was noted between the KEM and the lower limb joint angles. The AP-COP position and VGRF were associated with the KEM during landing. Evaluating the VGRF and AP-COP position, not the lower limb joint angles, may contribute to understanding the KEM during double-leg landing after ACLR in the clinical setting.

Resistance exercise following short term muscle disuse leads to enhanced mitochondrial activity and dynamics

Introduction: Short-term muscle unloading (~7-10 days) can be usually experienced following injury or hospitalisation, leading to muscle disuse atrophy, muscle weakness and changes in motor control. In such contexts, exercise countermeasures can be employed to overcome these neuromuscular impairments. Surprisingly, the effects of exercise countermeasures following the exposure to muscle unloading has been scarcely investigated. Hence, this study aimed to investigate the functional and molecular adaptations to a 21-day resistance training (RT) program following short term muscle disuse. We hypothesised that a period of resistance exercise following short-term unloading would speed up the recovery on muscle mass and function mostly by an effcient counteraction of the molecular regulators of muscle disuse atrophy consistent with the exercise modality employed. Methods: A 10-day unilateral lower limb suspension (ULLS) model was applied to eleven healthy young males (22.09 ± 2.91 y), followed by a 21-day RT program for the knee extensors performed at 70% of the 1RM (3 times/wk, 9 sessions in total). Data acquisition was performed before the ULLS period, after 10 days of unloading and after 21 days of resistance exercise. Quadriceps femoris isometric maximum voluntary contraction (MVC) was evaluated by dynamometry and quadriceps CSA was assessed by ultrasonography. Succinate dehydrogenase (SDH, a key component of the citric acid cycle and of the respiratory electron transfer chain) staining was performed on frozen cryosections obtained from VL biopsies, whereas western blot analyses were carried out for several mitochondrial-related proteins and transcriptomics data were obtained by RNA-seq. Results: Following ULLS, QF MVC and CSA decreased (-29.3%, p&lt;0.001, and -4.5%, p&lt;0.05, respectively). After the 21-d of RT, MVC was fully brought back (+42% compared to post-ULLS) whereas QF CSA showed a very marked hypertrophy (+18.6%, p&lt;0.001, compared to post-ULLS). SDH immunoreactivity was not affected by unloading but revealed a significant increase after exercise compared to post ULLS values (~+20%, p&lt;0.001). In addition, mitochondrial dynamics were highly influenced by resistance exercise, as mitochondrial pro-fusion (MFN1, MFN2, OPA1) and fission (DRP1, pDRP1616) proteins were markedly increased in response to RT compared to post-ULLS values (p&lt;0.05). Further, PGC-1a levels showed a trend to decrease after ULLS but even a stronger trend to increase after resistance exercise compared to post-ULLS (p=0.056). Transcriptomics analyses showed that the most differentially expressed genes were identified in the pathways related to oxidative phosphorylation, in which the top regulated genes after resistance training were mitochondrial related genes (CKMT2, UQCRH, ACSS1, MDH1, COX7A2, CYCS, SLC16A1), presenting a marked reduction after ULLS and being significantly enhanced after RT. When compared to baseline, the genes which showed a positive “rebound effect” after resistance exercise were mostly related to mitochondrial function (MT-ATP6, MT-CO2, MT-ND3). Noteworthy, among these latter genes, the top upregulated one was APLNR, coding for apelin receptor protein, a positive regulator of inter-myofibrillar mitochondrial content in sarcopenia and ageing. Conclusions: Resistance exercise was effective in recovering muscle mass and function after 10 days of disuse, but it enhanced mitochondrial activity, biogenesis, and dynamics far beyond the expected effects for such exercise modality. In fact, mitochondrial-related genes expression was the most affected by exercise. This suggests that mitochondrial dynamics could play an essential role in the recovery of neuromuscular alterations induced by short term disuse. We put forward the hypothesis that the prior level of physical activity and a prior exposure to short-term muscle disuse could be driving the nature of adaptations to subsequent resistance training. Funding: The present work was funded by the Italian Space Agency (ASI), MARS-PRE, Project, n. DC-VUM-2017-006. 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.

Association Between Knee Flexor Strength and Preservation of the Tibial Attachment of the Sartorial Fascia During Hamstring Tendon Harvest.

During anterior cruciate ligament (ACL) reconstruction, there are various autograft options. Donor-site morbidity is an important consideration while deciding the type of the autograft. Gracilis and semitendinosus autografts are commonly used in ACL reconstruction, resulting in weakness of the hamstring muscle. We hypothesized that if we preserved the tibial insertion site of the sartorial fascia (SF) during hamstring tendon harvest, there would be better recovery of knee flexor strength. Case-control study; Level of evidence, 3. In this retrospective study, 34 patients (aged 20-59 years) underwent ACL reconstruction using hamstring tendon autograft with 2 different incision techniques on the SF. The tibial attachment site of the SF was preserved in 17 patients. The insertion site of the muscle was incised transversely in 17 patients. The follow-up duration was ≥2 years. Patients were recalled to the institute for examination and muscle strength assessment. The results were compared between the groups in terms of flexor and extensor knee isokinetic muscle strength at 60 and 180 deg/s. There was no statistical difference between the groups in terms of age, sex, or body mass index. When compared with patients whose SF attachment site was incised, patients with a preserved SF tibial insertion were found to have a higher flexion peak torque at the angular speed of 180 deg/s (P < 002). No statistically significant difference was noted at 60 deg/s. During collection of gracilis and semitendinosus autografts, preserving the SF tibial attachment site was associated with better knee flexion peak torque.

Task-specific resistance training adaptations in older adults: comparing traditional and functional exercise interventions.

Muscle strength declines ∼3% per year after the age of 70. Resistance training guidelines for older adults are often based on free-weight and machine exercises, which may be inaccessible and lack carryover to activities of daily living. We tested the hypothesis that resistance training adaptations in older adults are task-specific. Thirty adults (8 males, 22 females; mean age = 71 years) were randomly assigned to participate in 6weeks of supervised, high-intensity resistance training (twice per week) utilizing free-weight and machine exercises (traditional) versus functional activities that were overloaded with a weighted vest (functional). Participants were thoroughly familiarized with the exercises and testing prior to beginning the study. Major outcome measures included assessments of functional performance, five-repetition maximum strength, isometric knee extensor force, and quadriceps muscle size. Physical activity and nutrition were monitored. The study results demonstrate that the magnitude of improvement within a given outcome was largely dependent on group assignment, with greater improvements in gait speed and the timed-up-and-go in the functional group, but 2-3× greater five repetition maximum strength improvements for the trap bar deadlift, leg press, and leg extension following traditional resistance training. Both groups showed improvements in isometric knee extensor force and muscle size, suggesting that some aspects of the observed adaptations were generic, rather than specific. Overall, these novel findings suggest that, among older adults, 1) resistance training adaptations exhibit a high degree of task specificity and 2) significant improvements in functional outcomes can be achieved with the use of a weighted vest.

Application SF 36 And EQ 5D To Assess Quality Of Life In Musculo-Skeletal Health Of Elderly Patiens To Determine Intervention: Systematic Review

Background: Elderly Patients which chronic Kidney Diseases on Haemodialysis (HD) experience impaired muscle strength related quality of life (QoL). We analysed HD relationship with physical performance, body composition, and muscle strength; Purpose: To asses QoL in muscle-skeletal health and functional Capacity on elderly Chronic Kidney Diseases maintenance Haemodialysis. Methods: Using systematic literature review with data base EBSCO, ELSIVIER, Pup Med, Science Direct, Walley, start search year 2020-2023, 13 articles Randomize control trial and cross sectional. Groups underwent the following assessments physical QoL using application of the SF-36 questionnaire , and the Euro QoL five item psychologic-questionnaire (EQ-5D) are two of the most popular. Observed 6-minute walk test (6MWT) and handgrip strength, one-repetition maximum of knee flexors and extensors. Result: Main approaches, namely generic and disease-specific instruments, can be applied to measure health-related quality of life, the short form 36 questionnaire (SF-36) and the Euro QoL five item questionnaire (EQ-5D) are two of the most popular. One of the main goals of any interventions to prevent and cure musculoskeletal problems in the ageing population with should be to improve quality of life. Conclusion: To measure health-related quality of life, two basic methods can be used: The EQ-5D and the short form 36 questionnaire. Overview surveys are used to measure the quality of life related to health in individuals suffering from musculoskeletal illnesses. The validation of therapeutic and preventive interventions in this field should be aided by the recent development of specific instruments.

The role of pennation angle and architectural gearing to rate of force development in dynamic and isometric muscle contractions.

Associations between muscle architecture and rate of force development (RFD) have been largely studied during fixed-end (isometric) contractions. Fixed-end contractions may, however, limit muscle shape changes and thus alter the relationship between muscle architecture an RFD. We compared the correlation between muscle architecture and architectural gearing and knee extensor RFD when assessed during dynamic versus fixed-end contractions. Twenty-two recreationally active male runners performed dynamic knee extensions at constant acceleration (2000°s-2) and isometric contractions at a fixed knee joint angle (fixed-end contractions). Torque, RFD, vastus lateralis muscle thickness, and fascicle dynamics were compared during 0-75 and 75-150 ms after contraction onset. Resting fascicle angle was moderately and positively correlated with RFD during fixed-end contractions (r = 0.42 and 0.46 from 0-75 and 75-150 ms, respectively; p < 0.05), while more strongly (p < 0.05) correlated with RFD during dynamic contractions (r = 0.69 and 0.73 at 0-75 and 75-150 ms, respectively; p < 0.05). Resting fascicle angle was (very) strongly correlated with architectural gearing (r = 0.51 and 0.73 at 0-75 ms and 0.50 and 0.70 at 75-150 ms; p < 0.05), with gearing in turn also being moderately to strongly correlated with RFD in both contraction conditions (r = 0.38-0.68). Resting fascicle angle was positively correlated with RFD, with a stronger relationship observed in dynamic than isometric contraction conditions. The stronger relationships observed during dynamic muscle actions likely result from different restrictions on the acute changes in muscle shape and architectural gearing imposed by isometric versus dynamic muscle contractions.

Knee extensor electromyographic activity during different depths of squat exercise in strength training experienced adults: A Systematic Review

B ACKGROUND: Changes in range of motion during partial and deep squats can affect the electrical activity of the knee extensor muscles. There are results’ divergences between studies that evaluated the effects of deep and partial squats on the electrical activity of the knee extensor muscles. AIM: To systematically review the literature on the electromyographic activity of the knee extensor muscles during partial and deep squat exercises in subjects with strength training experience. METHOD: The search included MEDLINE (via Pubmed), Scielo, EMBASE, in addition to a manual search, until June 2023. Cross-sectional observational studies comparing partial squats (up to 90º of knee flexion) and deep squats (maximum knee flexion) that evaluated the electrical activation through surface electromyography in men and women with strength training experience were included. Methodological quality assessment was performed using the adapted Downs and Black tool, as suggested by the Cochrane Collaboration. RESULTS: Of the 636 articles identified, four studies were included. The included studies presented electromyographic values of the two squat variations. No difference was found in the activation of the rectus femoris, vastus medialis and vastus lateralis muscles between partial and deep squats. Regarding methodological quality, one study was classified as having moderate and the other three studies showing high methodological quality. CONCLUSION: The similarity in the knee extensors’ electromyographic activation between partial and deep squat exercises in men and women with strength training experience suggests that both exercises can be used for recruiting these muscles during physical fitness activities.