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[Effect of the contraction of other muscle groups on muscle strength, latency period and endurance].

The following investigation was undertaken in connection with Sechenov's idea on mutual influence of muscles performing different work. It deals with the influence on test muscle (TM) efficiency of other simultaneously working muscles (SWM). It was shown that tension of SWM or maintenance of complex postures exert a negative influence on the force and latency of the visual-motor reaction and the static effort endurance. The mechanism involved is external inhibition. After its extinction as a result of repeated combinations of both activities the degree of lowering of TM activity grows less and finally its improvement is observed as compared to data obtained in the absence of SWM contractions. It is suggested that when external inhibition is extinguished impulses arising in SWM reinforce and improve according to the law of dominant the functions of nervous centers regulating activities of the TM.

Humans

Muscle strength and power changes during maximal isokinetic training.

This study investigated the effects of short duration, high intensity training on skeletal muscle. The extensors and flexors of the knee were tested and exercised by means of an isokinetic dynamometer. Measurements of peak torque were obtained at velocities ranging from 0 degrees/sec (isometric) to 300 degrees/sec through a distance of 90 degrees. Total work output was measured during repeated knee extensions and flexions for work tasks of 6 sec and 30 sec duration. A 1-min test of repeated maximal contractions was administered to examine muscular fatiguability before and after training. The subjects trained one leg with repeated 6 sec exercise bouts, while the other leg was trained using repeated 30 sec bouts. All training and testing was executed at near maximal force and at a constant velocity (180 degrees/sec). The subjects trained four times per week for a period of seven weeks. The daily work output was equal for the 6 and 30 sec training legs. Results indicate that: (1) isokinetic training programs of 6 and 30 seconds duration can significantly (P less than .05) increase peak muscular torque; (2) training velocity may be an important consideration in improving peak torque; (3) total work output was increased an average of 30% with either training at relatively slow (60 degrees/sec) or fast (180 degrees/sec) velocities; (4) both training programs significantly reduced the fatiguability of the knee extensor muscles.

Adult

Increase of muscle strength from isometric quadriceps exercises at different knee angles.

Isometric quadriceps exercises were performed at two different knee angles, 15 and 60 degrees respectively. The maximal torque was measured in both positions before and after training in 10 healthy females. Both legs were exercised, one at each position. The purpose was to develop practical recommendations for choice of training position. The strength increase was mainly specific according to the angle at which the knee was exercised. It was suggested that isometric exercise would preferably be performed at different knee angles to secure an optimal total strength increase. Isometric exercises improved dynamic strength at a low velocity but not at a high velocity.

Adult

Enzyme activities and muscle strength after "sprint training" in man.

Sprint type strength training was performed 3-4 times a week for 8 weeks by 4 healthy male students (16-18 yrs). The training was carried out on a treadmill at high speed and with high inclination. Muscle biopsies were obtained from vastus lateralis before and after the training period for histochemical classification of slow and fast twitch muscle fibres and for biochemical determination of metabolites and enzyme activities. Muscle fibre type distribution was unchanged, whereas fibre area indicated an increase for both fibre types in 3 subjects after training. The muscle enzyme activities of Mg2+ stimulated ATPase, myokinase and creatine phosphokinase increased 30, 20, and 36 percent, respectively. Muscle concentration of ATP and creatine phosphate (CP) did not change with training. Sargent's jump increased with on average 4 cm (from 47 to 51 cm), maximal voluntary contraction (MVC) with 19 kp (from 165 to 184 kp), and endurance at 50 percent of MVC with 9 s (from 47 to 56 s), respectively. After training all subjects showed a gain in body weight (mean 1.4 kg) and in thigh circumference (mean 1.5 cm) indicating a larger leg muscle volume and consequently also an increase in total ATP and CP.

Actomyosin

Muscle strength and body composition as determinants of blood pressure in young men.

The correlations of blood pressure to various indices of muscularity and fatness were studied in 183 young healthy men (mean age 19.7, SD 2.1 years). Systolic pressure showed significant positive correlations with body fat percentage, isometric strength of trunk extensors, body mass index, lean body mass, strength of leg extensors, heart rate, and the sum of four skinfolds. Diastolic pressure had significant positive correlations with body mass index, lean body mass, body fat percentage, sum of skinfolds, strength of leg extensors, strength of trunk extensors, and age. A stepwise selective multiple regression analysis for systolic pressure resulted in four significantly correlating variables: body fat percentage (p less than 0.001), heart rate (p less than 0.01), lean body mass (p less than 0.05), and strength of trunk extensors per kg body weight (p less than 0.05). For diastolic pressure the analysis resulted in two explaining variables: body mass index (p less than 0.001) and age (p less than 0.05). In a regression equation with 13 variables the strength of trunk flexors was negatively correlated with diastolic pressure. It is concluded that both fatness and muscularity are factors related to blood pressure in young men. The muscularity effect is more clearly associated with trunk and leg extensor strength.

Adipose Tissue

Neural factors versus hypertrophy in the time course of muscle strength gain.

The time course of strength gain with respect to the contributions of neural factors and hypertrophy was studied in seven young males and eight females during the course of an 8 week regimen of isotonic strength training. The results indicated that neural factors accounted for the larger proportion of the initial strength increment and thereafter both neural factors and hypertrophy took part in the further increase in strength, with hypertrophy becoming the dominant factor after the first 3 to 5 weeks. Our data regarding the untrained contralateral arm flexors provide further support for the concept of cross education. It was suggested that the nature of this cross education effect may entirely rest on the neural factors presumably acting at various levels of the nervous system which could result in increasing the maximal level of muscle activation.

Arm

In-plant evaluation of the muscle strength of workers.

The static muscular strength of the back extensors, arm flexors and hand grip were measured on industrial workers (463 men and 139 women) involved in physically demanding jobs. No significant differences in strength were found among workers on different jobs. However, strength differences were evident with respect to age and sex; women were about 60 percent as strong as men, and men below 31 years of age were stronger than men above this age.

Adult

Impact of creatine supplementation alone or combined with exercise on inflammatory and clinical outcomes in chronic musculoskeletal pain treated in the rheumatological field: a systematic review.

Creatine supplementation has demonstrated ergogenic and anabolic effects in healthy and clinical populations. However, its potential therapeutic role in individuals with chronic musculoskeletal pain treated in rheumatological contexts remains unclear. The aim was to evaluate the efficacy and safety of creatine supplementation on pain, physical function/disability, quality of life, muscle strength, skeletal muscle mass, and inflammatory markers in people with chronic musculoskeletal pain usually treated from the rheumatological field. A systematic review was conducted following PRISMA guidelines. Searches were performed in MEDLINE, Web of Science, CINAHL, Scopus, and EMBASE up to July 2026. Eligible studies were randomized or nonrandomized clinical trials that provided creatine supplementation alone or in combination with exercise as a treatment compared to a control or placebo group. Eight studies (n = 189) were included, encompassing fibromyalgia, osteoarthritis, rheumatoid arthritis, and juvenile idiopathic arthritis. Creatine dosages varied from chronic low-dose to loading protocols (20 g/d, 2-5 g/d). Combined creatine plus resistance training may improve strength, skeletal muscle mass, and quality of life beyond exercise alone in osteoarthritis. Trials on fibromyalgia suggest an increase in muscle strength, but inconsistent effects on pain. Rheumatoid arthritis studies suggest gains in skeletal muscle mass and, in pilot studies, reduced disease activity. No major adverse events were reported. In conclusion, creatine supplementation alone may be insufficient to obtain clinical benefits, while combined with resistance exercise it could offer potential benefits for muscle strength, skeletal muscle mass and certain aspects of quality of life in these clinical conditions. However, evidence on pain and inflammation remains limited; Furthermore, the response across different clinical conditions is heterogeneous, highlighting the need for larger, high-quality trials.

Humans

Tumor Signatures of Physical Fitness: Insights from a Preclinical Model.

PURPOSE: Cardiorespiratory fitness (CRF) and muscle strength are associated with cancer risk/mortality in adults. However, there is yet no evidence for pediatric tumors. This study investigated the association of CRF and muscle strength with several tumor-related phenotypes in an aggressive childhood malignancy, high-risk neuroblastoma. METHODS: Twelve mice-bearing orthotopic high-risk neuroblastomas were studied. CRF and muscle strength were assessed using treadmill and grip strength testing, respectively. The following tumor-related outcomes were studied: survival, clinical severity, tumor weight/volume, metastasis, and intratumor immune infiltrates. In addition, tumor samples underwent quantitative proteomic analysis via liquid chromatography-tandem mass spectrometry. Spearman correlations (or logistic regression) were performed between CRF/muscle strength and the abovementioned variables. Proteins that were significantly correlated with CRF or muscle strength were mapped into protein-protein interaction (PPI) networks using the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database. RESULTS: CRF was inversely correlated with clinical severity score ( r = -0.657, P = 0.020). Of 6840 identified tumor proteins, 76 correlated significantly with CRF (19 positively, 57 negatively), whereas 194 correlated with muscle strength (97 positively, 97 negatively). Proteins correlated with CRF were primarily involved in metabolic and structural pathways, including angiotensinogen and elastin. In turn, muscle strength-associated proteins were more abundant and included keratin family proteins (e.g., keratin, type I cytoskeletal 14, and type II cytoskeletal 5), proteins involved in cell adhesion (e.g., desmoglein-1-alpha), and translational regulators (e.g., eukaryotic initiation factor 4A). Network analysis revealed significant enrichment in structural organization and cellular adhesion pathways. CONCLUSIONS: Besides the association of CRF with clinical severity of the tumor, distinct novel tumor proteomic signatures associated with CRF and muscle strength were identified, highlighting potential mechanisms linking physical fitness with childhood cancer biology.

Muscle Strength

Adaptations in skeletal muscle following strength training.

Five men were studied before and after 7 wk of isokinetic strength training to determine its effects on muscle enzyme activities and fiber composition. One of the subject's legs was trained using 10 repeated 6-s maximal work bouts, while the other leg performed repeated 30-s maximal knee extension exercise. The total work accomplished by each leg was constant. Training 4 times/wk achieved similar gains in peak torque for both legs at the training velocity (3.14 rad/s) and at slower speeds. Fatigability of the knee extensor muscles, as measured by a 60-s exercise test, was similar in both legs after training. Biopsy specimens showed significant changes in the % of the muscle area composed of type I and IIa fibers as a result of both strength training programs. In terms of muscle enzymes, only the 30 s exercise program resulted in elevated glycolytic, ATP-CP and mitochondrial activities. Despite these changes, none of the parameters measured were found to be related to the gains in either muscle strength or fatigability during maximal isokinetic contractions.

Adaptation, Physiological

Celery seed extract attenuates sarcopenic obesity and age-related sarcopenia by reducing intramuscular lipid accumulation in mice.

BACKGROUND & AIMS: Sarcopenia is characterized by progressive loss of skeletal muscle mass and function and is increasingly recognized to be influenced by metabolic disturbances associated with aging and obesity. Intramuscular lipid accumulation has emerged as a key pathological feature linking metabolic dysfunction to skeletal muscle deterioration. Celery seed extract (CSE) possesses anti-obesity, anti-inflammatory, and antioxidant properties; however, its potential role in skeletal muscle metabolism has not been well investigated. This study aimed to determine whether CSE attenuates skeletal muscle deterioration associated with obesity and aging through modulation of intramuscular lipid accumulation and related metabolic pathways. METHODS: Diet-induced obese mice and naturally aged mice were used to evaluate the effects of CSE supplementation. Skeletal muscle mass, grip strength, muscle morphology, intramuscular lipid content, mitochondrial metabolic signaling, inflammatory responses, and muscle protein turnover pathways were assessed using biochemical, molecular, and histological analyses. RESULTS: CSE supplementation significantly improved skeletal muscle mass, grip strength, and muscle fiber cross-sectional area in both obese and aged mice. These improvements were accompanied by reduced intramuscular triglyceride and cholesterol accumulation. Mechanistically, CSE improved mitochondrial metabolic signaling by activating the AMPK-PGC-1α pathway and increasing mitochondrial oxidative phosphorylation proteins. In addition, CSE suppressed inflammatory signaling pathways, including MAPK activation and NLRP3 inflammasome signaling, and improved muscle proteostasis by enhancing myogenic regulators while reducing the expression of proteolytic factors such as MuRF1, Atrogin-1, and myostatin. Correlation analyses further indicated that intramuscular lipid accumulation was closely associated with mitochondrial dysfunction, inflammatory activation, and muscle atrophy. CONCLUSIONS: These findings demonstrate that CSE alleviates skeletal muscle deterioration in both obesity- and aging-associated sarcopenia by reducing intramuscular lipid accumulation and improving mitochondrial metabolism, inflammatory responses, and muscle protein turnover. Targeting intramuscular lipid accumulation may therefore represent a promising nutritional strategy for preventing sarcopenia associated with metabolic and aging-related stress.

AMPK–PGC-1α

Effects of Adding Incentive Spirometry to Hospital-Based Cardiovascular Rehabilitation on Pulmonary Complications, Hospital Length of Stay, and Clinical-Functional Recovery After Cardiac Surgery: A Randomized Controlled Trial.

BACKGROUND AND PURPOSE: This study investigated the effects of combining incentive spirometry with cardiac rehabilitation compared with cardiac rehabilitation alone on postoperative pulmonary complications, clinical-functional recovery, and hospital length of stay in patients undergoing cardiac surgery. METHODS: Randomized controlled trial was conducted from May 2019 to October 2023 in two hospitals, including 46 inpatients undergoing cardiac surgery. Participants were assigned to incentive spirometry plus cardiac rehabilitation or cardiac rehabilitation alone. Both interventions were performed twice daily; spirometry used a volume-oriented device, and rehabilitation followed a seven-step protocol (2-4 METs). Outcomes included postoperative pulmonary complications, functional capacity (6-min walk test), handgrip strength, respiratory muscle function, and length of hospital stay. RESULTS: The incentive spirometry associated with cardiac rehabilitation group had a longer extracorporeal circulation time (98 ± 26 min) than the cardiac rehabilitation group (76 ± 1; p = 0.008). Both groups showed a postoperative decline in respiratory muscle strength, and walking distance (MD: -64.37 m; 95% CI: [-24.1; -104.6]; d = 0.71), with no difference in postoperative pulmonary complications and handgrip strength. The incentive spirometry associated with cardiac rehabilitation group did not significantly differ on postoperative hospital stay compared with the cardiac rehabilitation group (MD: -1 day; 95% CI: [-4.71; 2.71]; d = -0.19). CONCLUSIONS: In this study, no additional benefit was observed with the addition of incentive spirometry to cardiac rehabilitation compared with cardiac rehabilitation alone. No significant differences were detected between groups in postoperative pulmonary complications, hospital length of stay, or clinical-functional recovery among individuals undergoing cardiac surgery. TRIAL REGISTRATION: Brazilian Registry of Clinical Trials (REBEC) under the number RBR-8tsjf97.

Aged

Metabolic pathways linked to sarcopenia in the Bushehr Elderly Health Program: kynurenine, nicotinamide, B-vitamins, and sulfur amino acids.

BACKGROUND: Sarcopenia, characterized by the loss of muscle mass and function, is a common condition in the elderly, associated with increased morbidity and mortality. Metabolic pathways, including the kynurenine, nicotinamide, B-vitamins, and sulfur amino acid pathways, may play a significant role in the development and progression of sarcopenia. This study investigates the relationship between metabolic pathways and sarcopenia, aiming to identify potential therapeutic targets. METHOD: Four hundred participants over 60 years were randomly selected from the second stage of the Bushehr Elderly Health Program (BEH). Frozen plasma samples were used to measure metabolomics. We used factor analysis and logistic regression analysis to determine the kynurenine-tryptophan metabolites associated with sarcopenia and its components. RESULT: Study participants included 89 sarcopenic subjects aged 72.92 ± 7.32 years and 307 non-sarcopenic subjects aged 68.12 ± 5.56 years. In full model adjustment, factor 3, which included methionine, tryptophan, 3-hydroxyanthranilic acid, picolinic acid, and xanthurenic acid, was associated with 38.3% lower risk of sarcopenia (OR = 0.617 [95%CI = 0.436–0.875]); Factor 6, which included methylmalonic acid and total homocysteine, was associated with a 33.7% increased risk of sarcopenia (OR = 1.337 [95%CI = 1.031–1.735]); and factor 7, consisting of nicotinamide, were related to a 25.2% lower risk of developing sarcopenia (OR = 0.748 [95%CI = 0.571–0.979]). Additionally, factor 1, which included quinolinic acid, kynurenine, 3-hydroxykynurenine, neopterin, kynurenic acid, anthranilic acid, cystathionine, and total cysteine, was linked to a 49.2% higher risk of low muscle strength, while factors 3 and 7 were associated with approximately a 24% decrease in risk of low muscle strength. Factors 5, consisting of serine and glycine, and factor 7 were related to 43% and 27.7% lower risk of low skeletal muscle index, respectively. While factor 6 was related to a 32.8% higher risk of low skeletal muscle index. Factor 1 was also related to a 32.9% higher risk of low walking speed, while factor 3 was related to a 28.5% lower risk of low walking speed. CONCLUSION: Specific metabolites from the kynurenine, nicotinamide, B-vitamin, and sulfur amino acid pathways are significantly associated with sarcopenia and its key parameters, such as muscle strength, skeletal muscle index, and walking speed. These findings suggest that metabolic profiling could offer valuable insights for early detection and targeted interventions for sarcopenia in elderly populations.

Humans

Therapeutic Exercise Protocol During Hospitalization in Pediatric Oncohematological Patients: Randomized Clinical Trial.

BACKGROUND: Leukemias, lymphomas, and central nervous system tumors are among the most common pediatric cancers and may lead to motor deficits, impaired balance, reduced muscle strength, fatigue, and decreased functional capacity. Early physiotherapy during hospitalization may help prevent inactivity and support functional preservation in this population. OBJECTIVE: To evaluate the effects of a therapeutic exercise program on quality of life, muscle strength, fatigue, and functional capacity in hospitalized pediatric oncohematological patients. METHODS: Thirty participants aged 8-17 years with oncohematological diseases were randomized to an intervention group (IG) or a minimal active physiotherapy comparator group (CG). Assessments included the 6-min walk test, handgrip dynamometry, the PedsQL Multidimensional Fatigue Scale, and the PedsQL Cancer Module at admission and discharge. The IG performed daily 25-min supervised sessions including aerobic, resistance, and breathing exercises with ambulation guidance, whereas the CG received breathing exercises and ambulation guidance. RESULTS: No significant group × time interactions were observed for total fatigue or its domains, overall quality of life or its assessed domains, handgrip strength, or six-minute walk test distance. Time-related changes were observed for some outcomes, but these occurred without evidence of differential change between groups and were not interpreted as effects of the structured exercise protocol. No intervention-related adverse events requiring permanent protocol discontinuation were recorded. CONCLUSION: The structured in-hospital therapeutic exercise protocol could be delivered under close clinical supervision without recorded intervention-related adverse events requiring permanent discontinuation. However, the structured protocol did not demonstrate superiority over the minimal active physiotherapy comparator for fatigue, quality of life, muscle strength, or functional capacity. These findings should be interpreted cautiously because of the small sample size, clinical heterogeneity, variable intervention exposure, and limited intervention-fidelity data. TRIAL REGISTRATION: Brazilian Registry of Clinical Trials (ReBEC), RBR-8sxnfyd.

Humans

Preservation of bulk and strength in muscles affected by neurogenic lesions.

Mechanisms involved in maintaining bulk and strength in partially denervated muscles of patients with neurogenic lesions are discussed. Estimation of muscle fiber hypertrophy by electrophysiological examination is possible, but it depends on the construction of sampling electrodes with precise geometry. The arrangement of muscle fibers of motor units within the muscle is discussed by analogy with the four-color map problem. An experiment to measure the twitch tensions of individual motor units in man is devised; it requires the use of microprocessor control of the stimulus and recurrent measurements of the twitch forces.

Animals

Effects of blood flow restriction training combined with resistance training on lower-limb strength and sport-specific performance in athletes: a systematic review and meta-analysis.

BACKGROUND: In contemporary sports science, athletes and coaches continuously explore strategies to reduce training load and injury risk while increasing muscular strength and sport-specific performance. This meta-analysis evaluated the effects of blood flow restriction training (BFRT) combined with resistance training (RT) on lower-limb muscle strength and sport-specific performance in athletes. METHODS: Relevant randomized controlled trials (RCTs) were systematically searched across major databases (e.g. PubMed, Web of Science, Cochrane, CNKI, Wanfang Data, and Embase) from inception until November 2024. Two independent reviewers carefully assessed the studies. Data analysis was carried out using RevMan 5.4 software, which included heterogeneity testing, meta-analysis, subgroup analysis, and assessment of publication bias. RESULTS: Ten RCTs (181 athletes; 91 in the BFRT and RT group, 90 in the control group) were included. Outcomes determined BFRT combined with RT yielded notable enhancements in lower-limb muscle strength (SMD = 1.09, 95% CI [0.52, 1.66], p&#x2009;<&#x2009;0.05) and muscle hypertrophy (MD = 1.09, 95% CI [0.10, 2.09], p&#x2009;<&#x2009;0.05) compared to control training. However, no significant improvement in sport-specific performance was found (SMD = 0.11, 95% CI [-0.18, 0.40], p&#x2009;=&#x2009;0.46). Substantial heterogeneity was observed for strength outcomes (I2 = 75%), whereas low heterogeneity was observed for sport-specific performance and hypertrophy outcomes (I2 = 0%). No evidence of significant publication bias was detected. CONCLUSION: BFRT combined with RT appears to provide effective augmentation of lower-limb muscle strength and hypertrophy in athletes compared to RT or conventional training alone. It may be prudent to integrate this approach systematically into training cycles to optimize physiological muscle stimulation and training outcomes, despite not directly improving sport-specific performance.

Humans